AGENDA · 2019-06-18 · 6. Committee Members' Reports 7. Future Agenda Items 8. Adjournment...

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ADVISORY COMMITTEE REGULAR MEETINGAGENDA

JUNE 20, 20192:00 PM

MONTEREY COUNTY GOVERNMENT CENTER – NORTH BUILDING, FIRST FLOORCAYENNE CONFERENCE ROOM

1441 SCHILLING PLACE, SALINAS

1. Call to Order

2. Roll Call

3. General Public CommentsMembers of the public may comment on matters within the jurisdiction of the Agency thatare not on the agenda. Public comments generally are limited to two (2) minutes perspeaker; the Chair may further limit the time for public comments depending on theagenda schedule. Comments on agenda items should be held until the items are reached.To be respectful of all speakers and avoid disruption of the meeting, please refrain fromapplauding or jeering speakers.

4. Scheduled Items

4.a Approve May 16, 2019 meeting minutes2019-05-16 AC Minutes.pdf

4.b Consider recommending the Board appoint Bing Seid as the Advisory Committee's South County WellOwner representative, replacing resigning appointee Chris LopezBing Seid Application.pdf

4.c Consider recommending Board approval of release of draft Groundwater Sustainability Plan Chapter 6,Water Budget, for 30 day public comment periodDraft_Chapter_6_180-400.pdfChapter 6 PowerPoint.pdf

5. General Manager's Report1

https://legistarweb-production.s3.amazonaws.com/uploads/attachment/pdf/380819/2019-05-16_AC_Minutes.pdf

https://legistarweb-production.s3.amazonaws.com/uploads/attachment/pdf/380818/Bing_Seid_Application.pdf

https://legistarweb-production.s3.amazonaws.com/uploads/attachment/pdf/381522/Draft_Chapter_6_180-400.pdf

https://legistarweb-production.s3.amazonaws.com/uploads/attachment/pdf/381521/Chapter_6_PowerPoint.pdf

6. Committee Members' Reports

7. Future Agenda Items

8. Adjournment

Accommodation and Agenda PostingDisability-related modification or accommodation, including auxiliary aids or services, may be requested byany person with a disability who requires modification or accommodation in order to participate in themeeting. Requests should be referred to Ann Camel, Clerk of the Board at [email protected] or831-471-7519 as soon as possible, but by no later than 5 p.m. two business days prior to the meeting. Hearing impaired or TTY/TDD text telephone users may contact the Agency by dialing 711 for theCalifornia Relay Service (CRS) or by telephoning any other service providers’ CRS telephone number.

AGENDA POSTING The meeting agenda was posted at the Salinas City Clerk’s Office and City HallRotunda, Monterey County Offices at 1441 Schilling Place, Salinas, CA on 6/14/19.

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UNOFFICIAL MEETING MINUTES

ADVISORY COMMITTEE

MAY 16, 2019

MONTEREY COUNTY OFFICES, 1441 SCHILLING PLACE, SALINAS, CAYENNE ROOM

1. Call to Order

The meeting was called to order at 2:05 p.m.

2. Roll Call

Present:

Alco Water Company - Tom Adcock; Cal Water Service - Greg Williams; Castroville Comm.

Serv. District – Eric Tynan (arrived 2:12 p.m.); Chevron – Dallas Tubbs; CHISPA - Alfred Diaz-

Infante; City of Gonzales - Harold Wolgamott; City of Salinas – Brian Frus; Driscoll Strawberry

Assoc. – Emily Gardner (arrived at 2:12 p.m.); Environmental Caucus – Robin Lee;

Environmental Justice Coalition for Water – Horacio Amezquita (arrived at 2:45 p.m.); Grower-

Shipper Assoc. of Central CA – Jim Bogart (left 3:06 p.m.), Abby Taylor-Silva arrived at 3:06

p.m.; LandWatch – Tom Ward; Marina Coast Water District – Patrick Breen; Monterey County

Farm Bureau - Norm Groot; Monterey County Water Resources Agency – Howard Franklin;

Monterey One Water – Mike McCullough; Salinas River Channel Stream Maint./River Mgmt.

Unit - Donna Meyers; Salinas Valley Water Coalition- Nancy Isakson; Seaside Basin Watermaster

– Alternate Jonathan Lear; Primary Bob Jaques arrived at 2:08 and left at 4:40 p.m.; Well Owners

North County – Robert Burton

Absent:

Monterey County – Lew Bauman; Monterey County Vintners & Growers – Kurt Gollnick; Rural

Well Owner – So. Co – Chris Lopez; Salinas Valley Sustainable Water Group – Dennis Sites

Vacant Seat:

Environmental/Surf Riders

SVBGSA representatives: Gary Petersen, SVBGSA General Manager; Charles McKee, Legal

Counsel; Ann Camel, Clerk

3. General Public Comments

Tom Virsik referred to an article on the Fox Canyon GSA that has SGMA’s first groundwater market. The Nature Conservancy is a partner.

Page 1 of 8 May 16, 2019 3

4. Scheduled Items

4.a. The Committee unanimously approved the April 18, 2019 meeting minutes. (The 4/18/19

minutes were administratively corrected to reflect Jonathan Lear’s attendance as the

Seaside Basin Watermaster’s alternate.)

4.b. Request for Approval from the SVBGSA for Proposed Integrated Regional Water

Management (IRWM) Projects.

Robert Jaques arrived at 2:08 p.m.

Mr. Petersen stated that the Greater Monterey County IRWM Regional Water Management Group

is in the process of selecting projects to put forward for Proposition 1 Round 1 IRWM

Implementation Grant funds. According to Proposition 1 IRWM Program Guidelines and

Proposal Solicitation Package, projects that may affect groundwater must have the support of the

relevant Groundwater Sustainability Agency (GSA).

The following applicants outlined their projects, which are described at the IRWM website at

http://www.greatermontereyirwmp.org/projects/proposed/

Elizabeth Kraft Monterey County Water Resources Agency (WRA) and IRWM Executive

Committee, stated that grant requests totaled $3.4 million. She outlined the WRA’S “Integration and Reoperation of Nacimiento and San Antonio Reservoirs”

Emily Gardner and Eric Tynan arrived 2:13 p.m..

Eric Tynan presented the Castroville Community Services District, “Well No. 6 - Emergency Deep

Aquifer Supply and Tank Project” .

Mike McCullough presented the Monterey One Water/City of Salinas/Central Coast Wetlands

Group’s “Salinas Water Quality and Agricultural Reuse Efficiency Project.”

Paul Robins presented the Monterey County Farm Nutrient Management and Water Quality

Assistance Program on behalf of the Resource Conservation District of Monterey County in

cooperation with the UC Cooperative Extension Crop Advisors and USDA Natural resources

Conservation services.

Donna Meyers presented the Salinas River Management Unit Association, and Resource

Conservation District of Monterey County’s “Salinas River Multi-Benefit Stream Maintenance

and Habitat Stewardship Program”

Committee members Burton, Franklin, Frus, Groot, McCullough, and Meyers abstained due to

conflicts of interest.

By consensus, the Committee recommended that the draft resolution be approved by the SVBGSA

Board of Directors.

Page 2 of 8 May 16, 2019 4

http://www.greatermontereyirwmp.org/projects/proposed/

4.c Consider recommending the Board release draft Chapter 8, Sustainable Management

Criteria for thirty-day public comment period.

Mr. Petersen stated that the Integrated Sustainability Plan is being tabled temporarily. Mr.

Williams stated the slides still include some of the sustainability indicators for all the Valley. Mr.

Williams presented the PowerPoint presentation. The 4% Salinas Valley Basin pumping reduction

for 2030 and 2070 is inclusive of the 7% for the 180/400 ft aquifer. The 2030 and 2070 projections

are from two different models that both consider climate change.

Horacio Amezquita arrived at 2:45 p.m..

Michael McCullough left at 3:05 p.m. Abby Taylor Silva arrived and Jim Bogart left the meeting

at 3:06 p.m..

In response to Robin Lee, Mr. Williams stated the measurable objective is not the same as the

groundwater elevation, because intrusion could be stopped by pumping water out as well as by

raising water levels.

In response to Abby Taylor Silva, Mr. Williams stated he would have to report back on how many

wells would have exceed the minimum threshold in 2015.

In response to Norm Groot, Mr. Williams stated that the not to exceed 15% he proposes for

Undesirable Result can be revisited at least every five years and even before the completion of this

process to determine whether we can attain the objectives with the financing we have. A public

process would be required.

In response to Robert Burton, Mr. Williams stated that the representative period was selected to

include reservoir operations and wet and dry periods, but it could be expanded or contracted. Mr.

Williams does not believe the 1992 minimum threshold was an outlier year in Figure 8-1 as there

were 3 years that reached this level.

In response to Bob Jaques, Mr. Williams will note not to add the same wells below the minimum

threshold every year so to avoid penalizing the same people.

In response to Dallas Tubbs, Mr. Williams will note that the 15% measure for undesirable results

may be too low if the monitoring wells are not representative of the entire basin.

In response to Harold Wolgamott, Mr. Williams will include his comment “by X feet” to the 15%

referenced in Undesirable Results, e.g. 2 feet or 5 feet.

Tom Virsik referenced his written comments. The concentration of exceedances seems to scream

a need for a management area.

Page 3 of 8 May 16, 2019 5

Heather Lukacs stated there should be different management areas for drinking water protections,

e.g. it is not acceptable for 15% to be the undesirable result measure. Mr. Williams stated we will

note the question whether we should have management areas near public water supply wells to

avoid exceedances around those wells.

Mr. Williams stated that significant policy questions include whether we should expand the

existing groundwater pumping reporting requirements and define pumping allowance.

In response to Abby Taylor Silva, Mr. Williams stated that metering cannot be required of de

minimis users.. Regarding 8.6.2.6, Method for Quantitative Measurement of Minimum Threshold,

she asked about a process for collecting data that is not currently reported. Mr. Williams stated

that this is a policy decision in the implementation plan. The reporting system can be expanded,

perhaps through the WRA.

Bob Jaques stated the regulations’ requirement to report for the basin as a whole is not a good idea,

and wondered if the GSA could have minimum objectives and thresholds for each aquifer. Mr.

Williams stated that setting specific pumping amounts for each aquifer would require more

calculations; not doing so could result in other sustainability criteria being violated.

Robin Lee asked about Section 8.6.2.2, Depletion of Interconnected Surface Waters, and what if

we do not like what is going on today. Mr. Williams asked her to hold the question.

Patrick Breen left the meeting at 3:58 p.m.

In response to Tom Ward, Howard Franklin stated there are 47 or 48 deep aquifer wells, and they

are collecting on most of those wells. They are not all in the pressure area.

Bob Jaques stated that the isocontour line could change, and it may be better to say the total area

is the measure. Mr. Williams stated that the regulation say it is a line that we cannot cross. The

map indicates there are not huge fluctuations annually. If we implement certain projects, it could

affect the isocontour. We can expand the isocontour to allow some flexibility. But when

implementing projects, it may harm other indicators.

Howard Franklin stated that the 2018 data does not show the line going backward, and a larger

buffer over that should be allowed.

Harold Wolgamott suggested moving the line further inland, halfway between where it is and

Highway 1.

Abby Taylor Silva asked if the undesirable result could be established year one of projects without

knowing what the data would be. Mr. Williams responded that the DWR is looking for definitive,

quantifiable items. He suggests 2017 as a buffer. When we get to the five-year date of the Plan,

it could be changed at that point.

Heather Lukacs stated, similarly, the 2017 year could be reviewed for change five years from now.

Mr. Williams stated that it is worth defining the minimum threshold that is currently further inland

Page 4 of 8 May 16, 2019 6

than 2017, so he would like more feedback. It will depend on the financing to implement a project

to stop seawater intrusion.

Nancy Isakson agreed with Heather Lukacs that the 2017 year should be retained to ensure that

something is done.

Eric Tynan left the meeting at 4:19 p.m..

Mr. Williams reviewed the groundwater quality slide and skipped the Groundwater Minimum

Thresholds slide 44 because it gets back to we are only using current wells.

Dallas Tubbs would like to think about chain of command and protocols on how to test wells so it

is equivalent and replicated well to well. Mr. Williams stated that we are not collecting samples

but gathering data from others’ samplings.

Mr. Wolgamott noted we should only use reliable data. In response to Mr. Wolgamott, Mr.

Williams stated we would come up with a new list of wells and new minimum thresholds and

objectives with every five-year update. They would not use a well re-drilled in the same spot.

In response to Nancy Isakson, Mr. Williams stated that nitrates were not included because they are

pushed into an ag well and do not negatively impact crop production, so the grower would not

have to abandon the well.

Bob Jaques stated that we should be sampling for constituents of concern. Mr. Williams responded

that under SGMA, we are not sampling but are looking at whether we are causing any harm. The

Regional Board is responsible for cleaning up the basin.

In response to Norm Groot, Mr. Williams stated they are setting additional nitrates exceedances at

zero unless the DWR does not accept their proposal for undesirable results to be defined as “On

average during any one year, no groundwater quality minimum threshold shall be exceeded as a

direct result of projects or management actions taken as part of GSP implementation.”

Horacio Amezquita asked when the GSA will address the problem of increasing nitrate

concentration and well pollution. Mr. Williams responded that the GSA would not take this issue

on if it is unrelated to SGMA. We are looking at projects that would have an impact on water

quality.

Primary member Bob Jaques left the meeting at 4:40 p.m.. Alternate Jeff Lear was present.

Heather Lukacs asked how we are rationalizing missing data because wells are not sampled

regularly. Mr. Williams responded that the mandate is to increase the water supply without

harming water quality using existing data.

Mr. Williams stated that on May 6, 2019, DWR announced they will provide InSAR data that will

show monthly change in ground surface. Dallas Tubbs commented that absolute subsidence is as

important as the rate of change, so the threshold should work in over time. Mr. Williams stated

Page 5 of 8 May 16, 2019 7

that the minimum threshold for subsidence would be a very low rate of subsidence and not zero

subsidence.

Norm Groot left the meeting at 4:50 p.m..

Harold Wolgamott agreed with Mr. Tubbs, and would like a better definition of the minimum

threshold definition of no subsidence that impacts infrastructure.

In response to Emily Gardner’s asking about the reference to infrastructure, Mr. Williams stated

the legislation is written in that way, and there is a decrease in storage in clay where there is no

pumping.

Mr. Williams stated the surface water depletion section includes many policy questions.

Robin Lee asked whether we agree that the impact on our river flows is significant but not

unreasonable. Mr. Williams answered that whether we are having an impact on ecosystems that

are groundwater dependent is a different policy question.

Horacio Amezquita and Jonathan Lear left the meeting at 5 p.m.

Howard Franklin stated that the WRA will be redefining how to provide environmental flows, so

how do we say the MCWRA is successfully achieving environmental flows in the Salinas River.

Mr. Williams responded that the Plan is based on the best data currently available and will be

revisited in three to five years.

Mr. Franklin objects to the text language that they are successfully achieving environmental flows.

Mr. Williams considered modifying the language to reflect that the WRA is operating under the

NOAA previous biological opinion. It is difficult to say we will not meet those environmental

flows if we do not know what they are, but this is a policy issue.

Nancy Isakson questioned whether we can say that the stream depletion rate is not unreasonable.

Mr. Williams stated that the statement is open for discussion. Since the structures operate in a way

that implicitly understands depletion rates, we have already addressed reservoir depletion rates so

it is not unreasonable. However, we could say release less water in Nacimiento and get the same

amount of flow if we had less depletion. Mr. Isakson stated that is not what she is saying, and she

will provide Mr. Williams with some language.

Donna Meyers stated that “successfully achieving” should be changed to “providing water flows”

Charles McKee suggested “successfully provided environmental flows as long as requirements were in place.”

Donna Meyers asked if the lakes are considered in the statement “Limited recreational

opportunities on the Salinas River, therefore groundwater pumping is not unreasonable for

recreational flows,” and whether this is an accurate statement. Mr. Williams stated that DWR is

only concerned with summer and winter flows.

Page 6 of 8 May 16, 2019 8

Robin Lee asked where the environmental community’s concern about habitats is addressed. She

is concerned about wells on smaller tributaries that may be depleting ecosystems.

Mr. Williams stated that we have mapped potentially dependent ecosystems but not known

groundwater dependent ecosystems. This is a policy decision. He has not identified which we want

to protect. Implementation could include a project to hire a biologist to visit sites identified by

aerial photos to assess whether they are groundwater dependent or not. Then the group could make

policy recommendations on importance and establishing policies, but it will take some time. He

requested further feedback as to whether we are having an unreasonable impact and how we

address groundwater dependent ecosystems or should we address, better understand, and protect

them.

Mr. Williams invited Committee members to provide additional input as soon as possible for

inclusion for the Board’s consideration.

Mr. Wolgamott stated that the GSA does not include surface water so, e.g., pumping in Chualar

would not have environmental factors directly affected Mr. Williams stated that this raises the

question of do we think pumping is significant and unreasonable. If you are pumping from the

400 foot aquifer, it would be hard to say cut back to improve stream flows.

Ms. Lee would like a written description of what Mr. Williams needs to develop good decisions

on the ecology. Mr. Williams stated he is understanding that some people would like to see

ecosystems and that we may have overstated the case about no significant and unreasonable

impacts. But on the other hand, there is uncertainty whether we can say that it is unreasonable.

He’s looking for feedback. He can help guide the Committee, but policy ideas are tough because

there is not much data that we can hang our hat on.

Robin Lee stated that we could propose that we get the data. Mr. Williams stated we could map

them or look at shallow groundwater levels that are within 15 feet to 20 feet, and then we can say

we know it is a Groundwater Dependent Ecosystem. Then it becomes a policy decision whether

to maintain it as a viable system and whether to implement projects and plans to protect them. Mr.

Williams summarized the comment as what is the policy as to whether we are having a significant

and unreasonable impact.

Heather Lukacs asked whether the Agency or a standard of law would determine “significant and

unreasonable.” Mr. Williams stated that the law says the Agency decides, but there will be

disagreement regardless of what is decided

Tom Virsik stated that the direction should be to make it simpler and less complex. Mr. Williams

summarized to focus the discussion on pumping impacts on the 180/400 foot aquifer and not on

the entire river.

Upon motion by Committee member Tubbs and second by Committee member Wolgamott, the

Committee voted to recommend release of Chapter 8. AYES: Committee members Adcock,

Williams, Tubbs, Diaz-Infante, Wolgamott, Frus, Gardner, Taylor-Silva, Ward, Franklin, Meyers,

Page 7 of 8 May 16, 2019 9

____________________________________

_____________________________________

and Burton NOES: Directors Isakson and Lee. ABSENT: Committee members Tynan,

Amezquita, Breen, Groot, McCullough, Lear, Bauman, Gollnick, Lopez, Sites

The meeting adjourned at 5:30 p.m.

APPROVED:

Gary Petersen, General Manager

ATTEST:

Ann Camel, Clerk of the Board

Page 8 of 8 May 16, 2019 10

Salinas Valley Basin Groundwater Sustainability Agency

COMMITTEE APPLICATION FORM

Full Name: *Date:

Information provided by the applicant is not regarded as confidential except for the addresses and phone numbers of references and the applicant's personal information including home and work addresses, phone numbers and email address.

PLEASE NOTE THAT APPOINTEES MAY BE REQUIRED BY STATE LAW AND COUNTY CONFLICT OF INTEREST CODE TO FILE FINANCIAL DISCLOSURE STATEMENTS.

•Current Occupation: (within the last twelve (12) months)

___________________________________________________________

*Current License: (Professional or Occupational, date of issue/or expiration including status.

___________________________________________________________ *Education/Experience: (A resume may be attached for this and any other information that would be helpful to the Board in evaluating your application,)

__________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________

11

*Other County Board/Commission/Committee on which you serve/have served:

__________________________________________________________ __________________________________________________________ __________________________________________________________

*Name and occupation of spouse within the last 12 months, if married, for Conflict of Interest Purposes

*References (at least two (2) list names and contact phone numbers) __________________________________________________________ __________________________________________________________ __________________________________________________________

*Please explain your reasons for wishing to serve and, in your opinion, how you feel you can contribute:

__________________________________________________________ __________________________________________________________ __________________________________________________________

12

DRAFT

Chapter 6

180/400-Foot Aquifer Subbasin

Groundwater Sustainability Plan

Prepared for:

SVBGSA

June 2019

13

DRAFT 180/400-Foot Aquifer Subbasin Groundwater Sustainability Plan

June 17, 2019 Page i

Table of Contents

6 WATER BUDGETS ............................................................................................................................. 1

6.1 Overview of Water Budget Development ......................................................................................... 1

6.2 Water Budget Components ............................................................................................................... 2

6.2.1 Surface Water Budget Components .................................................................................. 4

6.2.2 Groundwater Budget Components .................................................................................... 4

6.2.3 Change in Groundwater Storage Components .................................................................. 5

6.3 Surface Water Inflow Data ................................................................................................................. 5

6.3.1 Runoff from Precipitation ................................................................................................... 5

6.3.2 Salinas River Inflow from the Forebay Subbasin ............................................................... 6

6.3.3 Tributary Flows from the Eastside Subbasin ...................................................................... 8

6.3.4 Irrigation and Precipitation Return Flow to Agricultural Drains ........................................... 9

6.4 Surface Water Outflow Data .............................................................................................................. 9

6.4.1 Salinas River Diversion Data ............................................................................................. 9

6.4.2 Salinas River Outflow to Monterey Bay ........................................................................... 10

6.4.3 Other Surface Water Outflows to Monterey Bay .............................................................. 11

6.4.4 Streamflow Percolation .................................................................................................... 11

6.5 Groundwater Inflow Data ................................................................................................................ 12

6.5.1 Streamflow Percolation .................................................................................................... 12

6.5.2 Deep Percolation of Precipitation ..................................................................................... 12

6.5.3 Deep Percolation of Excess Irrigation .............................................................................. 13

6.5.4 Subsurface Inflows from Adjacent Subbasins .................................................................. 13

Table 6-10: .................................................................................................................................................. 14

6.6 Groundwater Outflow Data ............................................................................................................. 14

6.6.1 Groundwater Pumping ..................................................................................................... 14

6.6.2 Riparian Evapotranspiration............................................................................................. 15

6.6.3 Subsurface Outflows to Adjacent Subbasins ................................................................... 16

6.7 Change in Storage Data .................................................................................................................. 16

6.7.1 Groundwater Level Fluctuations ...................................................................................... 16

6.7.2 Seawater Intrusion ........................................................................................................... 17

6.8 Historical and Current Water Budgets ........................................................................................... 17

6.8.1 Surface Water Budget ..................................................................................................... 17

6.8.2 Groundwater Budget ........................................................................................................ 21

6.8.3 Subbasin Water Budget Summary ................................................................................... 24

6.8.4 Sustainable Yield ............................................................................................................. 24

6.9 Uncertainties in Historical and Current Water Budget Calculations ........................................... 26

6.10 Projected Water Budget .................................................................................................................. 28

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June 17, 2019 Page ii

6.10.1 Assumptions Used in Projected Water Budget Development .......................................... 28

6.10.2 Projected Water Budget Overview ................................................................................... 30

6.10.3 Land Surface Water Budget............................................................................................. 30

6.10.4 Groundwater Budget ........................................................................................................ 32

6.10.5 Change in Groundwater Storage ..................................................................................... 36

6.10.6 Projected Sustainable Yield ............................................................................................. 36

6.10.7 Surface Water Budget ..................................................................................................... 37

6.10.8 Uncertainties in Projected Water Budget Simulations ...................................................... 37

6.11 References ....................................................................................................................................... 39

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June 17, 2019 Page iii

Figures

Figure 6-1: Schematic Hydrologic Cycle (from DWR, 2016) .......................................................................... 3

Figure 6-2: USGS Stream Gauge Locations .................................................................................................. 7

Figure 6-3: Historical Surface Water Budget ............................................................................................... 20

Figure 6-4: Historical Groundwater Budget .................................................................................................. 23

Figure 6-5: Annual Average Historical Total Water Budget ......................................................................... 25

Tables

Table 6-1: Runoff from Precipitation .............................................................................................................. 6

Table 6-2: Average Annual Salinas River Flow from the Forebay Subbasin.................................................. 8

Table 6-3: Tributary Inflows from Eastside Subbasins ................................................................................... 8

Table 6-4: Irrigation and Precipitation Return Flow to Agricultural Drains for Historical and Current Water

Budgets ...................................................................................................................................... 9

Table 6-5: Salinas River Direct Diversions for Historical and Current Water Budget ................................... 10

Table 6-6: Salinas River Outflow to Monterey Bay for Historical and Current Water Budgets ..................... 10

Table 6-7: Other Surface Water Outflows to Monterey Bay for Historical and Current Water Budgets ........ 11

Table 6-8: Deep Percolation from Precipitation for Historical and Current Water Budget ............................ 12

Table 6-9: Deep Percolation from Excess Irrigation for Historical and Current Water Budget ..................... 13

Table 6-10: Subsurface Inflow from Adjacent Subbasins in Historical and Current Water Budgets ............. 14

Table 6-11: Historical Annual Groundwater Pumping by Water Use Sector ................................................ 15

Table 6-12: Current Annual Groundwater Pumping by Water Use Sector ................................................... 15

Table 6-13: Riparian Evapotranspiration in Historical and Current Water Budgets ...................................... 16

Table 6-14: Subsurface Outflow to Adjacent Subbasins/Basin in Historical and Current Water Budgets .... 16

Table 6-15: Seawater Intrusion in Historical and Current Water Budgets .................................................... 17

Table 6-16: Summary of Historical Surface Water Budget .......................................................................... 18

Table 6-17: Summary of Current Surface Water Budget ............................................................................. 18

Table 6-18: Summary of Historical Groundwater Budget ............................................................................. 21

Table 6-19: Summary of Current Groundwater Budget ............................................................................... 22

Table 6-20: Estimated Historical Sustainable Yield for the 180/400-Foot Aquifer Subbasin ........................ 24

Table 6-21: Estimated Historical and Current Surface Water Budget Uncertainties .................................... 27

Table 6-22: Water Budget and Estimated Storage in in Historical and Current Groundwater Budgets ........ 27

Table 6-23: Average Land Surface Water Budget Inflows (acre-feet per year)............................................ 31

Table 6-24: Average Land Surface Water Budget Outflows (acre-feet per year). ........................................ 32

Table 6-25: Average Groundwater Inflow Components for Projected Climate Change Conditions (acre-

ft/year) ...................................................................................................................................... 33

Table 6-26: Average Groundwater Outflow Components for Projected Climate Change Conditions (acre-

ft/year) ...................................................................................................................................... 34

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June 17, 2019 Page iv

Table 6-27: Average Annual Groundwater Budget for Projected Climate Change Conditions (acre-ft/year) 35

Table 6-28: Total Groundwater Inflows and Outflows for Projected Groundwater Budgets ......................... 35

Table 6-29: Projected Annual Groundwater Pumping by Water Use Sector ................................................ 35

Table 6-30: Change in Groundwater Storage for Projected Groundwater Budgets ..................................... 36

Table 6-31: Projected Sustainable Yields .................................................................................................... 37

Appendices

Appendix 6–A. Tabulated annual values of components for historical and current water budgets

Appendix 6–B. Tabulated annual values of components for projected water budgets

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DRAFT 180/400-Foot Aquifer Subbasin GSP 1

June 17, 2019

6 WATER BUDGETS

This chapter summarizes the estimated water budgets for the 180/400-Foot Aquifer Subbasin,

including information required by the SGMA Regulations and information that is important for

developing an effective plan to achieve sustainability. In accordance with SGMA Regulations

§354.18, this water budget provides an accounting and assessment of the total annual volume of

surface water and groundwater entering and leaving the Subbasin, including historical, current,

and projected water budget conditions, and the change in the volume of water stored. Water

budgets are reported in graphical and tabular formats, where applicable.

6.1 Overview of Water Budget Development

This chapter starts with an overview of the Subbasin’s surface water and groundwater budget

components, combines the components into the historical and current water budgets, and

concludes with a description of the future, projected water budgets. The historical, current, and

projected water budgets include both a surface water budget and a groundwater budget.

The historical and current water budgets were developed using best available data, best available

science, and the current understanding of the basin’s hydrogeologic conceptual model. The

historical water budget was based on 20 years of historical data covering 1995 to 2014. The

current water budget was based on 3 years of data covering 2015 through 2017. The projected

water budgets were developed using the future conditions simulated in the Salinas Valley

Integrated Hydrologic Model (SVIHM), which includes estimates of projected climate change

and sea level rise. Because the water budgets are developed using different tools, they should not

be directly compared to each other. The historical and future water budgets will be comparable

when the historical SVIHM is made available and the historical, current, and future water

budgets can all be developed with comparable models.

The water budget terms are presented in tables, graphs, and charts in this chapter. More detailed

tables of annual water budget time series are presented in a series of Appendices.

Each water budget is developed for a specific time period. As described in the Hydrogeologic

Conceptual Model and the Subbasin Conditions chapters, the Subbasin is subject to large

climatic variations over multi-year wet and dry cycles that typically cover a decade or more. A

representative water budget should either capture a complete climatic cycle or, for a water

budget that captures only one part of a cycle, the climatic conditions for the period need to be

explicitly recognized.

The twenty-year period of 1995 to 2014 was selected as the period for the historical water budget

because:

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June 17, 2019

• Relatively complete pumping rates from most wells in the Subbasin were available from

MCWRA,

• A relatively complete climatic cycle occurred, and

• The current water supply management system was in place for a significant amount of time.

The current water budget is based on the average of conditions between 2015 and 2017, the last

years for which complete data are available. Because the current water budget represents a

relatively short time period, it cannot be directly compared to the historical water budget. The

historical water budget is designed to reflect average historical conditions. The current water

budget reflects a snapshot in time that is susceptible to short-term climatic conditions.

Uncertainty in the historical and current water budgets reflect the differing levels of certainty

associated with each component of the water budgets. Although the water budgets are

sufficiently constrained to provide a reliable basis for developing the GSP, an important element

of the GSP is the monitoring program (Chapter 7) that will provide valuable data for improving

the water budget during GSP implementation. Therefore, the individual components of the

historical and curent water budgets, as well as the overall water budgets should be viewed as the

best current estimate and subject to revision and update as more information becomes available.

The projected water budgets are based on model simulations using the SVIHM numerical flow

model developed by USGS and using DWR-provided climate change and sea level rise data. The

SVIHM simulation period extends over a 47-year projected future simulation period. The

climatic fluctuations over the 47-year period were generated by using the historical conditions

from October 1967 through December 2014 and modifying them to reflect the DWR-provided

projections for climate change and sea level rise.

6.2 Water Budget Components

The water budget is an inventory of surface water and groundwater inflows into, and outflows

from, the Subbasin. A few components of the water budget can be measured, such as streamflow

at a gauging station or groundwater pumping from a metered well. Other components of the

water budget are estimated, such as recharge from precipitation or unmetered groundwater

pumping.

Figure 6-1 presents the general schematic diagram of the hydrologic cycle that is included in the

water budget BMP (DWR, 2016).

19


June 17, 2019

Figure 6-1: Schematic Hydrologic Cycle (from DWR, 2016)

20


June 17, 2019

The water budgets for the Subbasin are calculated within the following boundaries:

• Lateral boundaries for the water budget are the perimeter of the 180/400-Foot Aquifer

Subbasin as shown in Figure 1-1.

• Bottom of the water budget is the base of the groundwater subbasin as described in

Chapter 4. The water budget is not sensitive to the exact definition of this base elevation

because it is defined as a depth below where there is no significant inflow, outflow, or

change in storage.

• Top of the water budget is above the ground surface, so that surface water is included in

the water budget.

6.2.1 Surface Water Budget Components

Within the boundaries discussed above, the surface water budget inflows include:

• Runoff from precipitation

• Salinas River inflow from the Forebay Subbasin

• Tributary inflows from the Eastside Subbasin

• Irrigation return flow to agricultural drains

The surface water budget outflows include:

• Salinas River direct diversions

• Salinas River outflow to Monterey Bay

• Other outflows to Monterey Bay

• Streamflow percolation

6.2.2 Groundwater Budget Components

Within the boundaries discussed above, the groundwater budget inflows include:

• Streamflow percolation

• Deep percolation of precipitation

• Deep percolation of excess irrigation

• Subsurface inflows from adjacent subbasins

The groundwater budget outflows include:

• Groundwater pumping

• Riparian evapotranspiration

• Subsurface outflows to adjacent subbasins 21


June 17, 2019

6.2.3 Change in Groundwater Storage Components

For the groundwater budget, the difference between inflows and outflows is equal to the change

in storage. Change in groundwater storage has two components in the Subbasin: change in

groundwater elevation and seawater intrusion. Changes in groundwater elevation represent water

gained or lost in the aquifer due to pumping and recharge. Seawater intrusion is included as a

change in storage component because seawater intrusion reduces the amount of usable

groundwater stored in the Subbasin.

6.3 Surface Water Inflow Data

This section quantifies each of the surface water inflow components listed in Section 6.2.1. Data

are only provided for the current and historical water budgets.

6.3.1 Runoff from Precipitation

A relatively small percentage of precipitation runs off the ground surface, collects in drainage

systems and creeks, and ultimately flows into the Salinas River. For the historical and current

water budgets, runoff is estimated from the following relation between precipitation and runoff,

approximated from a published correlation between runoff and precipitation for the Salinas

Valley (Durbin, et al., 1978).

• For years with annual precipitation less than 9 inches/yr., there is no runoff

• For years with annual precipitation of between 9 and 22 inches/yr., the runoff is 14% of

the amount of precipitation greater than 9 inches/yr.

• For years with annual precipitation greater than 22 inches/yr., the runoff is 14% of

amount of precipitation between 9 inches/yr. and 22 inches/yr. plus 100% of precipitation

greater than 22 inches/yr.

Precipitation for the historical and current water budgets is quantified using the monthly

precipitation record from the National Oceanographic and Atmospheric Administration (NOAA)

/ National Weather Service (NWS) Cooperative Observer Program (COOP) precipitation gauge

at the Salinas Airport (COOP Station 047669). The total precipitation is estimated by

multiplying the monthly precipitation rate by the 90,000-acre area of the Subbasin.

Between 1995 and 2014, the average annual precipitation at the Salinas Airport was 13.4 inches.

As shown in Table 6-1, this results in an annual average total precipitation in the Subbasin of

100,400 acre-feet per year. Applying the runoff formula to the annual precipitation rates results

in an average annual runoff of 7,800 AF/yr., equivalent to approximately 8% of precipitation.

22


June 17, 2019

Table 6-1: Runoff from Precipitation

(Title Row)

Average for the Historical

Water Budget

(AF/yr.)

Average for the Current Water

Budget

(AF/yr.)

Precipitation 100,400 67,800

Runoff from Precipitation 7,800 2,000

Runoff as % of Precipitation 8% 3%

6.3.2 Salinas River Inflow from the Forebay Subbasin

The primary surface water inflow to the 180/400-Foot Aquifer Subbasin is the Salinas River.

Annual Salinas River inflow to the Subbasin at the boundary with the Forebay Subbasin was

estimated by using annual flow data from three USGS stream gauges (Figure 6-2) and the

estimated distribution of 2017 river depletion summarized in a 2018 memorandum titled Salinas

River Discharge Measurement Series Results in Context (MCWRA, 2018). As reported by

MCWRA, the Salinas River depletion during September 2017 between Soledad and Gonzales,

near the Subbasin boundary, was 134 cfs. The Salinas River depletion between Gonzales and the

Chualar gauge was 79 cfs. Therefore, approximately 63% of the Salinas River depletion between

Soledad and the Chualar gauge occurred in the Forebay Subbasin, above Gonzales; and 37% of

the Salinas River depletion occurred in 180/400-Foot Aquifer Subbasin, below Gonzales.

Annual flow at the boundary between the 180/400-Foot Aquifer Subbasin and the Forebay

Subbasin is therefore estimated as the annual flow at the Chualar gauge plus 37% of the loss

between Soledad and Chualar. The flow at Soledad is estimated by combining the flows at the

Salinas River Soledad gauge (#11151700) and the Arroyo Seco below Reliz Creek gauge (#

11152050). The average annual flow calculations are shown in Table 6-2.

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June 17, 2019

Figure 6-2: USGS Stream Gauge Locations

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June 17, 2019

Table 6-2: Average Annual Salinas River Flow from the Forebay Subbasin

Flow Component

Average for the Historical Water Budget

(AF/yr.)

Average for the Current Water Budget (AF/yr.)

A Flow at Salinas River Soledad Gauge 272,400 120,800

B Flow at Arroyo Seco below Reliz Creek Gauge 84,600 91,100

C Combined flows, representing the total flow at Soledad (A + B)

357,000 211,900

D Flow at the Chualar Gauge 285,300 135,100

E Depletion between Soledad and Chualar (C – D) 71,700 76,800

F Depletion in 180/400-Foot Aquifer Subbasin (37% of E)

26,600 28,500

G Estimated Flow at Gonzales (D + F) 311,900 163,600

6.3.3 Tributary Flows from the Eastside Subbasin

There are ungauged tributaries to the Salinas River that discharge from the Gabilan and Diablo

Ranges after flowing across the Eastside Subbasin. These tributaries contribute surface water

inflow to the Subbasin downstream of the Chualar gauge. These ephemeral tributaries are dry for

much of the year but can have significant flow during the wet season. The San Lorenzo Creek

gauge (# 11151300, Figure 6-2) is representative of flow from the Gabilan and Diablo Ranges

and was used to estimate surface water inflow from these tributaries. Based on tabulated data

from Durbin (1978) for the areas of watersheds that drain into the Salinas Valley from the east,

the combined catchments of the small tributaries is approximately 96 square miles, or

approximately 40% of the 233 square mile catchment of San Lorenzo Creek. For the Subbasin

surface water budget, it was assumed that half of this surface water inflow percolates into the

Eastside Subbasin and half flows into to the 180/400-Foot Aquifer Subbasin. Therefore,

contribution from these tributaries is estimated to be 20% of the San Lorenzo Creek gauge

annual flow.

The estimated tributary inflows from the Eastside Subbasin for the historical and current water

budgets are shown in Table 6-3.

Table 6-3: Tributary Inflows from Eastside Subbasins


Water Budget (AF/yr.)


Annual average flows at the San Lorenzo Creek gauge

11,600 4,400

Estimated tributary inflows from Eastside Subbasin

2,300 900

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June 17, 2019

6.3.4 Irrigation and Precipitation Return Flow to Agricultural Drains

A portion of precipitation that infiltrates the ground and applied irrigation water is captured by

agricultural drains and is routed to the Blanco Drain and Reclamation Ditch as surface water. A

USGS stream gauge (#11152650, Figure 6-2) on the Reclamation Ditch provides annual drain

flow data from 2003 through 2017. The average annual flows from 2003-2014 were assumed for

years prior to 2003.

In 2014, an estimate of Blanco Drain annual flows was developed as part of the Pure Water

Monterey Draft EIR (Schaaf & Wheeler, 2014). This report estimated the average annual flow

in the Blanco Drain to be 2,600 acre-feet per year.

Table 6-7 Table 6-4 summarizes the average annual values of irrigation and precipitation return

flow to agricultural drains.

Table 6-4: Irrigation and Precipitation Return Flow to Agricultural Drains for Historical and Current Water Budgets



Average for the Current Water Budget

(AF/yr.) Notes

Blanco Drain 2,600 2,600 Schaaf &

Wheeler, 2014)

Reclamation Ditch 7,400 15,400 Reclamation Ditch gauge

Total Irrigation Return Flow

10,000 18,000

6.4 Surface Water Outflow Data

This section quantifies each of the surface water outflow components listed in Section 6.2.1.

Data are only provided for the current and historical water budgets

6.4.1 Salinas River Diversion Data

Direct stream diversions are reported to the SWRCB. The State’s system for annual reporting of

diversions changed from hard copy to a computerized format between 2004 and 2010. Data

reported to the State through the computerized system are available for download from the

Electronic Water Rights Information Management System (eWRIMS) website. Annual surface

water diversions from the Salinas River from 2010 to 2017 were obtained from eWRIMS for use

in the historical and current water budgets. Between 2010 and 2017, 7% of the diversions in the

26


June 17, 2019

Salinas Valley Basin were in the 180/400-Foot Aquifer Subbasin (Appendix 6-A). Diversions in

years prior to 2010 were estimated by developing a linear correlation between annual

precipitation and 2010-2017 annual diversions for the Basin. This correlation was developed by

estimating the Basin diversions for 1995-2009 from correlation to annual precipitation, and then

assigning 7% of the Basin diversions to the Subbasin.

Table 6-5 lists the estimated average direct diversions from the Salinas River for the historical

and current water budgets. Detailed annual time series for the diversions within the Subbasin are

provided in Appendix 6-A.

Table 6-5: Salinas River Direct Diversions for Historical and Current Water Budget


(AF/yr.)


Notes

Salinas River Diversions

9,700 7,900 eWRIMS data 2010-2017 and average assumed for prior years

6.4.2 Salinas River Outflow to Monterey Bay

Salinas River outflow to Monterey Bay was estimated based on annual flow data from the

Salinas River gauge near Spreckels (gauge #11152500, Figure 6-2). Because the gauge is

located approximately 14 miles upstream of the Salinas River lagoon, an adjustment was made to

the gauged data to better estimate the Salinas River flow to Monterey Bay. We assumed that

between Spreckles and the coast there is a river depletion rate of approximately 2 cfs per mile.

This is based on an assumed reduction from the 3.5 cfs per mile river depletion rate observed

upstream of Spreckles (MCWRA, 2018). Assuming this depletion rate is constant over an entire

year, the total annual depletion between the Spreckles gauge and the coast is approximately

20,000 acre-feet/year. Therefore, the assumed outflow to Monterey Bay is 20,000 acre-feet per

year less than the average annual flow at the Spreckels Gauge.

Table 6-6 lists the estimated average Salinas River outflow to Monterey Bay for the historical

and current water budgets.

Table 6-6: Salinas River Outflow to Monterey Bay for Historical and Current Water Budgets


(AF/yr.)


(AF/yr.)

Notes

Salinas River Outflow to

Monterey Bay 240,700 103,400

Spreckels gauge – 20,000 AF/yr.

downstream percolation

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June 17, 2019

6.4.3 Other Surface Water Outflows to Monterey Bay

Outflows to Monterey Bay from the Blanco Drain and the Reclamation Ditch were estimated

based on annual flow at the Reclamation Ditch gauge (USGS gauge # 11152650, Figure 6-2) and

the 2,600 AF/yr. average flow in Blanco Drain estimated as part of the Pure Water Monterey

Draft EIR (Schaaf & Wheeler, 2014), as described in Section 6.3.4.

Table 6-7 summarizes the average annual values of other outflows to Monterey Bay.

Table 6-7: Other Surface Water Outflows to Monterey Bay for Historical and Current Water Budgets




(AF/yr.) Notes

Blanco Drain 2,600 2,600 Schaaf &

Wheeler, 2014)

Reclamation Ditch 7,400 15,400 Reclamation Ditch gauge

Other Outflows to Monterey Bay

10,000 18,000

6.4.4 Streamflow Percolation

The rate of Salinas River percolation into the groundwater was estimated based on the annual

USGS stream gauge data and the MCWRA river depletion analysis summarized in the Salinas

River Discharge Measurement Series Results in Context (MCWRA, 2018). The gauge data and

depletion rates were used to generate estimates of annual Salinas River inflow from the Forebay

Subbasin and annual Salinas River outflow to Monterey Bay. The difference between inflow and

outflow was used to generate a preliminary estimate of annual stream depletion. When the

stream depletion rates were compared to the annual inflow rates, the data suggested the

following three conditions.

• Salinas River Inflow less than 80,000 AF/yr. (110 cfs): Stream depletion was

approximately equal to inflow. During these relatively dry years, the amount of outflow

to Monterey Bay is negligible relative to the water budget.

• Salinas River Inflow between 80,000 AF/yr. (110 cfs) and 300,000 AF/yr. (415 cfs):

Stream depletion estimates are approximately 80,000 AF/yr. for all inflow rates.

• Salinas River Inflow greater than 300,000 AF/yr. (415 cfs): Stream depletion estimates

are highly variable, but the average of all values is approximately 90,000 AF/yr.

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June 17, 2019

Based on the above relationship of Salinas River inflow and depletion, this component of the

water budget was estimated for each year to be equal to the lesser of Salinas River inflow and

80,000 AF/yr. The corresponding annual streamflow percolation results are provided in

Appendix 6-A.

6.5 Groundwater Inflow Data

This section quantifies each of the groundwater inflow components listed in Section 6.2.1. Data

are only provided for the current and historical water budgets. Future groundwater budget data

extracted from the SVIHM are provided in Section 6.10.

6.5.1 Streamflow Percolation

As stated in Section 6.4.4, annual percolation of streamflow into the groundwater is the lesser of

Salinas River inflows to the Subbasin and 80,000 acre-feet per year, as shown in Appendix 6-A.

6.5.2 Deep Percolation of Precipitation

Deep percolation of precipitation is equal to the total precipitation minus runoff, flows to the

agricultural drains, and evapotranspiration. Total average annual precipitation and runoff were

estimated in Section 6.3.1. Flow to agricultural drains was estimated in Section 6.3.4 and is

incorporated into the surface water budget. Evapotranspiration is not directly measured. For the

historical and current water budgets, evapotranspiration is estimated to be 80 % of the

precipitation. Because the estimated flow to agricultural drains is a combination of flow from

precipitation and applied irrigation, it is not explicitly removed from the precipitation

calculation. Rather, it is removed from the total recharge calculations.

Based on these estimates, the estimated deep percolation of precipitation is calculated in Table

6-8

Table 6-8: Deep Percolation from Precipitation for Historical and Current Water Budget


(AF/yr.)


Total precipitation 100,400 67,800

Runoff 7,800 2,000

Evapotranspiration 80,300 54,300

Deep percolation 12,200 11,500

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June 17, 2019

6.5.3 Deep Percolation of Excess Irrigation

Applied irrigation water that is not consumptively used by plants and is not captured as return

flow by agricultural drains percolates below the root zone and becomes an inflow component to

the groundwater budget. The total amount of water applied for irrigation is a sum of the pumping

for irrigation, Salinas River diversions for irrigation, and CSIP deliveries.

• Agricultural pumping is reported annually by MCWRA for the Pressure Management

Area. This value is adjusted proportionally for the area of the Subbasin relative to the

total area of the Pressure Management Area.

• Salinas River diversions in the Subbasin are estimated from eWRIMS data for 2010 to

2017; and the average values for those years are applied to earlier years in the water

budget.

• CSIP deliveries began in 1999 and are reported annually.

Crop consumptive use was estimated using an average irrigation efficiency of 80% for the

Subbasin. This means 80% of applied irrigation is consumed by evapotranspiration and 20%

becomes either return flow to agricultural drains or deep percolation.

Table 6-9 presents the calculated deep percolation of irrigation without accounting for return

flow to agricultural drains.

Table 6-9: Deep Percolation from Excess Irrigation for Historical and Current Water Budget

Average for the Historical Water Budget (AF/yr.)


Total Agricultural Applied Water 108,600 112,300

Crop Consumptive Use 86,900 89,900

Irrigation return Flow 10,000 18,000

Deep Percolation 11,700 4,500

6.5.4 Subsurface Inflows from Adjacent Subbasins

Based on groundwater flow directions and hydraulic gradients at the Subbasin boundaries,

subsurface inflow to the Subbasin from the Forebay Subbasin has been estimated at

approximately 17,000 AF/yr. (Montgomery Watson, 1997; MCWRA, 2006; Brown and

Caldwell, 2015). The boundary with the Monterey Subbasin is subparallel to groundwater flow

direction resulting in a small amount of subsurface flow between the basins. The flow between

basins is estimated as a net inflow of 3,000 AF/yr. from the Monterey Subbasin into the Subbasin

based on quantities reported by Montgomery Watson (1997). The estimated values are assumed

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June 17, 2019

constant for the historical and current water budgets. Groundwater generally flows from the

180/400-Foot Aquifer Subbasin into the Eastside and Langley Subbasins, as well as to Pajaro

Valley. These subsurface outflows are quantified in Section 6.6.3.

The boundary flows will be reassessed when the calibrated historical SVIHM is available. Table

6-10 summarizes the subsurface inflow components for the historical and current water budgets.

Table 6-10: Subsurface Inflow from Adjacent Subbasins in Historical and Current Water Budgets


(AF/yr.)


(AF/yr.) Notes

Inflow from Forebay Subbasin

17,000 17,000 Estimate from Brown and

Caldwell (2015)

Inflow from Monterey Subbasin

3,000 3,000 Estimate from Montgomery

Watson (1997)

Total Inflows 20,000 20,000

6.6 Groundwater Outflow Data

This section quantifies each of the groundwater outflow components listed in Section 6.2.1.

Data are only provided for the current and historical water budgets. Future groundwater budget

data extracted from the SVIHM are provided in Section 6.10.

6.6.1 Groundwater Pumping

Groundwater is pumped from the Subbasin for multiple water use sectors including agricultural,

domestic, and urban. Groundwater pumping is reported annually to MCWRA in accordance with

Monterey County Ordinance 3717. Reliable annual pumping records, categorized as Agricultural

or Urban, are available from MCWRA for 1995-2015. The records provide annual pumping

rates for all years of the historical water budget. For the current water budget, only one year of

data is available (2015) and therefore the average values of the historical budget period were

used for 2016 and 2017. The pumping rates for the current water budget will be improved when

the MCWRA data for 2016 and 2017 are available. The annual pumping amounts reported by

MCWRA for 1995-2015 are tabulated in Appendix 6-A.

Reporting under Ordinance 3717 does not capture rural domestic pumping because wells with a

discharge pipe less than 3 inches in diameter are exempt from reporting. Therefore, rural

domestic pumping was estimated based on the number of DWR permitted domestic wells in the

Subbasin in 2018 and adjusted for 1995 through 2017 based on percent change in Monterey

County population. The calculations assumed that each well was associated with a single parcel,

and that the annual groundwater pumping was 0.39 AF per parcel. This is consistent with A 2014 31


June 17, 2019

study that estimated the annual indoor water use of a new, three-bedroom home occupied by four

people at 46,521 gallons per year (0.14 ac-ft). Combined indoor and outdoor water use was

estimated at 0.39 ac-ft per household.

Table 6-11 and Table 6-12 summarize the average, minimum, and maximum groundwater

pumping rates in the historical and current water budgets. The minimum and maximum of total

pumping are not equal to the sum of the sectors because the timing of pumping sector extremes

are not coincident

Table 6-11: Historical Annual Groundwater Pumping by Water Use Sector

Water Use Sector Average (AF/yr.)

Minimum (AF/yr.)

Maximum (AF/yr.)

Agricultural 89,000 76,200 110,800

Urban 19,000 14,000 27,500

Rural-Domestic 400 300 400

Total Pumping* 108,400 93,100 131,000

Table 6-12: Current Annual Groundwater Pumping by Water Use Sector

Water Use Sector Average (AF/yr.)

Minimum (AF/yr.)

Maximum (AF/yr.)

Agricultural 91,900 89,000 97,700

Urban 17,000 12,900 19,000

Rural-Domestic 400 400 400

Total Pumping 109,300 108,400 111,100

6.6.2 Riparian Evapotranspiration

Due to the seasonal release of water from the Nacimiento and San Antonio reservoirs, the Salinas

River has been transformed from an ephemeral to a perennial stream that supports significant

non-native riparian vegetation. The non-native riparian vegetation represents a significant loss

of water from the basin through evapotranspiration (ET). In particular, Arundo donax is an

invasive reed that has spread throughout California and other states. The ET rate of Arundo

donax is highly variable but is estimated to be approximately 20 AF/yr./acre (Rhode, personal

communication). The California Department of Fish and Wildlife Biogeographic Information

and Observation System GIS database estimates approximately 800 acres of Arundo in the

180/400-Foot Aquifer Subbasin. For the historical and current water budgets, ET by Arundo

donax was assumed to be 16 AF/yr./acre. The riparian ET occurs at the interface between the

surface water and groundwater budgets and could be incorporated into either budget. For the

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June 17, 2019

historical and current water budgets, the riparian ET is included in the groundwater budget.

Table 6-13 presents the constant riparian ET rate used in the historical and current water budgets.

Table 6-13: Riparian Evapotranspiration in Historical and Current Water Budgets

Average Acre-Feet/Year for the Historical Water Budget

Average Acre-Feet/year for the Current Water Budget

Notes

Riparian Evapotranspiration 12,000 12,000 Estimated acreage

and ET rate

6.6.3 Subsurface Outflows to Adjacent Subbasins

Based on groundwater flow directions at the Subbasin boundaries, subsurface outflow from the

Subbasin occurs at the Eastside and Langley Subbasin boundaries. The combined outflow to

these two subbasins has been estimated at approximately 8,000 AF/yr. (Brown and Caldwell,

2015). In addition, at the northern boundary groundwater flows toward the Pajaro Basin. The

rate of subsurface flow from the Subbasin to the Pajaro Basin is estimated at 1,500 AF/yr. based

on modeling analysis reported by USGS (Hanson et al., 2014b). The estimated values are

assumed constant for the historical and current budgets. The boundary flows can be reassessed

when the calibrated historical SVIHM is available. Table 6-14 summarizes the subsurface inflow

components from the historical and current water budgets.

Table 6-14: Subsurface Outflow to Adjacent Subbasins/Basin in Historical and Current Water Budgets


(AF/yr.)


(AF/yr.) Notes

Eastside/Langley Subbasins 8,000 8,000 Brown and Caldwell, 2015

Pajaro Basin 1,500 1,500 USGS, 2014

Total Subsurface Outflow 9,500 9,500

6.7 Change in Storage Data

6.7.1 Groundwater Level Fluctuations

The change in groundwater storage estimated from observed change in water levels is described

in Section 5.3. Conversion of the measured water level changes to estimated groundwater

storage changes requires an estimate of the storage coefficient and area of the Subbasin. The

storage coefficient is dependent on the material properties of the aquifer and the degree to which

33


June 17, 2019

the aquifer is confined by an overlaying aquitard. The storage coefficient in Subbasin has been

estimated to be 0.036 (Brown and Caldwell, 2015).

The average change in storage to groundwater level fluctuations during the historical period is

approximately 2,100 AF/yr. The average change in storage to groundwater level fluctuations

during the current period is approximately 53,200 AF/yr.

6.7.2 Seawater Intrusion

As reported in Section 5.2, seawater intrusion has occurred and is occurring in response to

groundwater pumping in the 180/400-Foot Aquifer Subbasin. The 10,500 AF/yr. estimated rate

of seawater intrusion into the 180/400-Foot Aquifer Subbasin presented in Section 5.2 is used as

a constant value for both the Historical and Current Water Budget (Table 6-15). This estimate

may be improved based on access to the calibrated SVIHM.

Table 6-15: Seawater Intrusion in Historical and Current Water Budgets

Average for the

Historical Water Budget (AF/yr.)


(AF/yr.) Notes

Seawater Intrusion 10,500 10,500 Estimated from previous

studies (Section 5.2)

6.8 Historical and Current Water Budgets

6.8.1 Surface Water Budget

The surface water inflow and outflow components described in Sections 6.3 and 6.4 are

combined to generate annual surface water budgets for the historical and current water budget

periods.

Table 6-16 summarizes the average, minimum, and maximum annual values for each component

of the historical surface water budget. Table 6-17 summarizes the average, minimum, and

maximum annual values for each component of the current surface water budget.

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June 17, 2019

Table 6-16: Summary of Historical Surface Water Budget

Inflow Average (AF/yr.)

Minimum (AF/yr.)

Maximum (AF/yr.)

Surface Water Inflows

Salinas River from Forebay Subbasin 7,800 0 77,800

Tributaries from East Side Subbasin 311,900 5,000 1,154,900

Precipitation Runoff 2,300 0 11,800

Irrigation Return Flow 10,000 5,000 16,400

TOTAL INFLOW 332,000 12,800 1,254,500

Outflow Average (AF/yr.)

Minimum (AF/yr.)

Maximum (AF/yr.)

Surface Water Outflows

Salinas River Diversions 9,700 2,800 22,400

Salinas River Outflow to Ocean 240,700 0 1,250,600

Other Outflows to Monterey Bay 7,400 2,400 13,800

Net Percolation of Streamflow to Groundwater 73,300 5,000 80,000

TOTAL OUTFLOW 331,000 16,100 1,360,300

Table 6-17: Summary of Current Surface Water Budget


Minimum (AF/yr.)

Maximum (AF/yr.)

Surface Water Inflows

Salinas River from Forebay Subbasin 2,000 0 3,900

Tributaries from East Side Subbasin 163,600 3,300 477,600

Precipitation Runoff 900 0 2,600

Irrigation Return Flow 18,000 8,700 30,800

TOTAL INFLOW 184,500 12,000 514,900


Minimum (AF/yr.)

Maximum (AF/yr.)

Surface Water Outflows

Salinas River Diversions 7,900 7,400 8,200

Salinas River Outflow to Ocean 103,400 0 310,100

Other Outflows to Monterey Bay 15,400 6,100 28,200


TOTAL OUTFLOW 157,700 17,600 425,700

The surface water budget components are highly variable. Figure 6-3 illustrates the annual

inflow and outflow components for the historical budget period. The diagram uses stacked bar

35


June 17, 2019

height to illustrate the magnitude of budget components for each year, with inflows shown on the

positive y-axis and outflows on the negative y-axis. The inflow and outflow components for

each year are tabulated in Appendix 6A.

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June 17, 2019

Figure 6-3: Historical Surface Water Budget

37


June 17, 2019

6.8.2 Groundwater Budget

The groundwater inflow and outflow components described in Sections 6.5 and 6.6 are combined

to generate annual groundwater budgets for the historical (1995-2014) and current (2015-2017)

budget periods.

Table 6-18 summarizes the average, minimum, and maximum annual values for each component

of the historical groundwater budget. Table 6-19 summarizes the average, minimum, and

maximum annual values for each component of the current groundwater budget.

Table 6-18: Summary of Historical Groundwater Budget


Minimum (AF/yr.)

Maximum (AF/yr.)


Precipitation Percolation to Groundwater 12,300 -33,500 18,900

Irrigation Percolation to Groundwater 11,700 5,200 18,100

Subsurface Inflows from Adjacent Subbasins 20,000 20,000 20,000

TOTAL INFLOW 117,200 57,800 131,000


Minimum (AF/yr.)

Maximum (AF/yr.)

Pumping - Total Subbasin 108,300 93,200 131,100

Agricultural 89,000 76,300 110,800

Urban 19,000 14,100 27,500

Rural Domestic 400 300 400

Riparian Evapotranspiration 12,000 12,000 12,000

Subsurface Outflows to Adjacent Subbasins/Basin 9,500 9,500 9,500

TOTAL OUTFLOW 129,800 114,700 152,600

Storage Average (AF/yr.)

Minimum (AF/yr.)

Maximum (AF/yr.)

Change in Storage -12,600 -72,300 8,300

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June 17, 2019

Table 6-19: Summary of Current Groundwater Budget


Minimum (AF/yr.)

Maximum (AF/yr.)


Precipitation Percolation to Groundwater 11,600 5,000 6

Irrigation Percolation to Groundwater 4,500 -9,500 15,500


TOTAL INFLOW 67,200 43,800 105,700


Minimum (AF/yr.)

Maximum (AF/yr.)


Agricultural 91,900 89,000 97,700

Urban 17,000 12,900 19,000



Subsurface Outflows to Adjacent Subbasins/Basin 3,200 -9,500 9,500

TOTAL OUTFLOW 124,400 110,900 132,500

Storage Average (AF/yr.)

Minimum (AF/yr.)

Maximum (AF/yr.)

Change in Storage -57,300 -88,700 -5,200

The annual groundwater budget components are variable, although not as variable as the surface

water budget components. Figure 6-4 illustrates the annual inflow and outflow components for

the historical budget period. The diagram uses stacked bar height to illustrate the magnitude of

budget components for each year, with inflows shown on the positive y-axis and outflows on the

negative y-axis. The inflow and outflow components for each year are tabulated in Appendix

6A.

39


June 17, 2019

Figure 6-4: Historical Groundwater Budget

40


June 17, 2019

6.8.3 Subbasin Water Budget Summary

Figure 6-5 provides a diagram illustrating the interrelationship of the surface water and

groundwater budget components. Average rates for these components over the historical water

budget period are included in the diagram.

6.8.4 Sustainable Yield

The sustainable yield of the Subbasin is an estimate of the quantity of groundwater that can be

pumped on a long-term average annual basis without causing a net decrease in storage. The

sustainable yield can be estimated based on the average annual values of the following

components of the historical water budget:

o Total pumping

o Change in groundwater storage, including seawater intrusion

The sustainable yield is computed as:

Sustainable yield = pumping - change in storage

Table 6-20 summarizes the estimated historical sustainable yield for the 180/400-Foot Aquifer

Subbasin. Based on the water budget components, the sustainable yield of the Subbasin is

97,300 AF/yr., which represents a 10% reduction in total pumping relative to the average annual

historical pumping rate. The values in Table 6-20 are estimates only. The sustainable yield

value will be modified and updated as more data are collected and more analyses are performed.

Table 6-20: Estimated Historical Sustainable Yield for the 180/400-Foot Aquifer Subbasin

Average (AF/yr.)

Total Subbasin Pumping 108,300

Change in Storage (Groundwater Levels) 2,100

Seawater Intrusion 10,500

Estimated Historical Sustainable Yield 95,700

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June 17, 2019

Figure 6-5: Annual Average Historical Total Water Budget

42


June 17, 2019

6.9 Uncertainties in Historical and Current Water Budget Calculations

As described in Section 6.1, the level of accuracy and certainty is highly variable between water

budget components. The water budget uncertainty will be reduced over time as the GSP

monitoring programs are implemented and the resulting data are used to check and improve the

budgets.

Although the uncertainty of each component has not been quantified, the net uncertainty in the

overall water budgets can be assessed based on a comparison between calculated and estimated

change in storage. This difference provides a quantitative estimate of how well the water budget

matches observed conditions. Although this measure doesn’t quantify uncertainty in the

components of the budgets, it allows an assessment of whether the net sum of the components is

reasonable.

The estimated annual change in storage for the surface water budget is zero for all years because

there are no significant surface water storage reservoirs within the subbasin. Table 6-21 shows

that the historical surface water budget has an error of 1,000 acre-feet per year, which is a less

than 1% error. By contrast, the current surface water budget has a 26,800 acre-feet per year

error, which is a 17% error.

Table 6-22 compares the groundwater budget change in storage to the calculated groundwater

change in storage for the historical and current time periods. The difference between

groundwater inflows and outflows for the historical groundwater budget is a storage loss of

2,100 acre-feet per year. The calculated change in storage from groundwater levels is a storage

loss of 400 acre-feet per year. The 400 acre-feet per year estimate represents a 1.3% error in the

historical groundwater budget. By contrast, the difference between groundwater inflows and

outflows for the current groundwater budget is a storage loss of 53,200 acre-feet per year and the

calculated change in storage from groundwater levels is a storage loss of 600 acre-feet per year.

The 600 acre-feet per year estimate represents a 40% error in the current groundwater budget.

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June 17, 2019

Table 6-21: Estimated Historical and Current Surface Water Budget Uncertainties

(Title Row) Historical Budget Current Budget

Budget Average Annual Inflow (AF/yr.) 332,000 184,500

Budget Average Annual Outflow (AF/yr.) 331,000 157,700

Budget Average Annual Change in Storage (AF/yr.) 1,000 26,800

Estimated Average Annual Change in Storage (AF/yr.) 0 0

Difference Between Budget and Estimated (AF/yr.) 1,000 26,800

Difference Between Budget and Estimated (% of Outflow) 0.3% 17%

Table 6-22: Water Budget and Estimated Storage in in Historical and Current Groundwater Budgets

(Title Row) Historical Budget Current Budget

Budget Average Annual Inflow (AF/yr.) 117,200 67,100

Budget Average Annual Outflow (AF/yr.) 129,800 130,800

Budget Average Annual Change in Storage (AF/yr.) -12,600 -63,700

Seawater Intrusion (AF/yr.) 10,500 10,500

Budget Average Annual Change in Storage associated

with Water Level Change (AF/yr.) -2,100 -53,200

Estimated Average Annual Change in Storage (AF/yr.)

Based on Water Level Measurements -400 -600

Difference Between Budget and Estimated (AF/yr.) -1,700 -52,600

Difference Between Budget and Estimated (% of Outflow) -1.3% -40%

The comparison of budget and estimated indicate that the historical budgets are well constrained,

with differences of around 1%. In contrast, the current budgets do not show good agreement to

the estimated values. The water budgets as formulated and presented herein appear reasonably

reliable when considered over a period of decades but are highly uncertain for any single year or

short period.

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June 17, 2019

6.10 Projected Water Budget

The projected water budget is extracted from the SVIHM projected hydrologic conditions with

climate change simulations. Two projected water budgets are presented, one incorporating

estimated 2030 climate change projections and one incorporating estimated 2070 climate change

projections. The future water budget simulations do not simulate a 47-year projected future, but

rather simulate 47 likely hydrologic events that may occur in 2030, and 47 likely hydrologic

events that may occur in 2070.

The climate change projections are based on the available climate change data provided by DWR

(DWR 2018). Projected water budgets will be useful for showing that sustainability will be

achieved in the 20-year implementation period and maintained over the 50-year planning and

implementation horizon.

6.10.1 Assumptions Used in Projected Water Budget Development

6.10.1.1 General SVIHM Characteristics

The SVIHM is a numerical groundwater-surface water model that was constructed using the

code MODFLOW-OWHM (Hanson et al., 2014a). This code is a version of the USGS

groundwater flow code MODFLOW that includes a focus on the agricultural supply and demand

system, through the Farm Process. The model grid consists of 976 rows, 272 columns, and 9

layers, covering the Salinas Valley Groundwater Basin from the Monterey-San Luis Obispo

County Line in the south to the Pajaro Basin in the north, including the offshore extent of the

major water supply aquifers. The model includes operations of the San Antonio and Nacimiento

reservoirs that supply the Basin.

6.10.1.2 SVIHM Assumptions and Modifications to Simulate Future Conditions

The assumptions incorporated into the SVIHM for the projected water budget simulations

include:

• Land Use: The land use is assumed to be static, aside from a semi-annual change to

represent crop seasonality. The annual pattern is repeated every year in the model. Land

use reflects the 2014 land use.

• Reservoir Operations: The reservoir operations reflect the current approach to reservoir

management taken by MCWRA.

• Stream Diversions: The SVIHM explicitly simulates only two stream diversions in the

Salinas Valley Basin: Clark Colony and the Salinas River Diversion Facility (SRDF).

The Clark Colony diversion is located along Arroyo Seco, and diverts stream water to an

45


June 17, 2019

agricultural area nearby. The SRDF came online in 2010, and diverts water from the

Salinas River to the Castroville Seawater Intrusion Project (CSIP) area. Clark Colony

diversions are repeated from the historical record to match the water year. SRDF

diversions are made throughout the duration of the Operational SVIHM whenever

reservoir storage and streamflow conditions allow.

• Recycled Water Deliveries: Recycled water has been delivered to the CSIP area since

1998 as irrigation supply. The SVIHM includes recycled water deliveries throughout the

duration of the model.

6.10.1.2.1 Future Projected Climate Assumptions

Several modifications were made to the SVIHM in accordance with recommendations made by

DWR in their Guidance for Climate Change Data Use During Groundwater Sustainability Plan

Development (DWR, 2018). Three types of datasets were modified to account for 2030 and

2070 projected climate change: climate data (precipitation and reference evapotranspiration,

ETo), streamflow, and sea level.

Climate Data

DWR has provided gridded change factors for 2030 and 2070 climate conditions that can be

applied to historical hydrologic data. These change factors are derived from the statewide

gridded datasets for the Variable Infiltration Capacity (VIC) hydrologic model, and are provided

as monthly gridded values that can be multiplied by historical data between 1915 and 2011 to

produce a dataset of climate inputs for each climate change scenario. The change factors were

multiplied by the historical gridded climate data to produce climate inputs that reflect climate

change. Because the change factors are only available through December 2011 and the SVIHM

uses a climate time series through December 2014 conditions, monthly change factors for

January 2012 to December 2014 had to be assumed. Historical data were analyzed from the

Salinas Airport precipitation gauge record to identify years from 1968 to 2011 that were most

similar to conditions in 2012, 2013 and 2014. As a result, projected climate data from 1981,

2002, and 2004 were applied as the climate inputs for 2012, 2013, and 2014, respectively.

The modified gridded monthly climate data for the entire model period were applied as inputs to

the model, which reads precipitation and ETo data on a monthly basis. The gridded climate data

consist of a precipitation and an ETo value for every grid cell in the uppermost active layer of the

model, for every month of the model simulation period.

Streamflow

DWR has also provided monthly change factors for unimpaired streamflow throughout

California. For the Salinas Valley and other areas outside of the Central Valley, these change

46


June 17, 2019

factors are provided as a single time series for each major watershed. Streamflows along the

margins of the Basin were modified by the monthly change factors. As with the climate data, an

assumption had to be made to extend the streamflow change factor time series through December

2014. We assumed that the similarity in rainfall years at the Salinas Airport rainfall gauge could

reasonably be expected to produce similar amounts of streamflow; therefore, the same years

(1981, 2002, and 2004) were repeated to represent the 2012, 2013, and 2014 streamflows.

Sea Level

DWR guidance recommends using a single static value of sea level rise for each of the climate

change scenarios (DWR, 2018). For the 2030 climate change scenario, a sea level rise value of

15 centimeters was used. For the 2070 climate change scenario, a sea level rise value of 45

centimeters was used. The amount of sea level rise was assumed to be static throughout the

duration of each of the climate change scenarios.

6.10.2 Projected Water Budget Overview

Although the physical processes simulated by the SVIHM are similar to the processes discussed

in the historical and current water budget discussion, the SVIHM output provides slightly

different water budget components than those in the historical and current water budgets. The

SVIHM includes various calculations that can produce three types of water budgets:

• Land surface water budget

• Groundwater budget

• Surface water budget

The land surface water budget is not required by the SGMA Regulations, but it does provide

important information that inform how water is managed in the Salinas Valley. Therefore, we

have opted to include information from the land surface budget in this GSP. The land surface

water budget us to further separate out different components related to crop water use and

groundwater recharge.

The surface water budget is not readily available in this type of model, and further work is

necessary to develop it. The surface water budget will be provided when it is available through

the model post-processing analysis.

6.10.3 Land Surface Water Budget

The land surface water budget quantifies flows into and out of the land surface and root zone of

agricultural areas. The components of the land surface water budget are as follows:

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June 17, 2019

• Water budget inflow components into the crop/land surface:

o Precipitation.

o Recycled water deliveries.

o Surface water deliveries.

o Agricultural application of pumped groundwater.

o Evaporation from groundwater. This is effectively a pass-through value with the

evaporation entering the soil column from below and leaving the top of the soil

column.

o Transpiration from groundwater. This is effectively a pass-through value with the

transpiration entering the crop roots from below and leaving the crops into the

atmosphere.

• Water budget outflow components out of the crop/land surface:

o Evaporation of irrigation water.

o Evaporation from precipitation.

o Evaporation from groundwater. This is effectively a pass-through value with the

evaporation entering the soil column from below and leaving the top of the soil

column.

o Transpiration of irrigation water.

o Transpiration from precipitation.

o Transpiration from groundwater. This is effectively a pass-through value with the

transpiration entering the crop roots from below and leaving the crops into the

atmosphere.

o Overland runoff onto surrounding non-agricultural areas.

o Deep percolation.

o Surface water returns: Unused surface water deliveries that are returned to the

stream system.

Land surface water budget inflow and outflow data for the 47-year future simulation period with

2030 climate change assumptions and the 2070 climate change assumptions are detailed in Table

6-23 and Table 6-24, respectively.

Table 6-23: Average Land Surface Water Budget Inflows (acre-feet per year).

Projected Climate Change Timeframe 2030

(AF/yr.) 2070

(AF/yr.)

Precipitation 135,700 141,200

Recycled Water Deliveries 4,400 4,400

Surface Water Deliveries 8,300 8,500

Agricultural Pumping 94,800 99,500

Evaporation from Groundwater 6,500 6,800

Transpiration from Groundwater 29,600 30,800

Total Inflows 279,300 291,200

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June 17, 2019

Table 6-24: Average Land Surface Water Budget Outflows (acre-feet per year).


(AF/yr.) 2070

(AF/yr.)

Evaporation from Irrigation 14,100 14,800

Evaporation from Precipitation 38,700 38,600

Evaporation from Groundwater 6,500 6,800

Transpiration from Irrigation 64,300 67,200

Transpiration from Precipitation 32,500 32,300

Transpiration from Groundwater 29,600 30,800

Overland Runoff 25,200 27,500


Surface Water Returns 500 400

Total Outflows 288,400 300,700

6.10.4 Groundwater Budget

The inflow components of the projected groundwater budget include:

• Stream leakage

• Deep percolation of precipitation and irrigation

• Underflow from the Monterey Subbasin

• Underflow from the Eastside Subbasin

• Underflow from the Langley Subbasin

• Underflow from the Forebay Subbasin

• Underflow from the Pajaro Valley

The simulated average water budget inflow components for each of the 47 years in the future

simulation with 2030 and 2070 climate change projections are quantified in Table 6-25 .

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June 17, 2019

Table 6-25: Average Groundwater Inflow Components for Projected Climate Change Conditions (acre-ft/year)


(AF/yr.) 2070

(AF/yr.)

Stream leakage 71,541 71,706


Seawater Intrusion 3,465 3,852

Underflow from Monterey 10,856 11,461

Underflow from Eastside 9,794 10,360

Underflow from Forebay 5,265 5,305

Underflow from Langley 1,751 1,775

Mountain front recharge 2,610 2,678

Underflow from Pajaro 135 127

The outflow components of the projected groundwater budget include:

• Total groundwater extraction including municipal, agricultural, and rural domestic

pumping

• Flow to agricultural drains

• Stream gains from groundwater

• Underflow to the Monterey Subbasin

• Underflow to the Eastside Subbasin

• Underflow to the Langley Subbasin

• Underflow to the Forebay Subbasin

• Underflow to the Pajaro Valley

• Underflow to Ocean

The simulated water budget inflow components for each of the 47 years in the future simulation

with 2030 and 2070 climate change projections are quantified in Table 6-26..

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June 17, 2019

Table 6-26: Average Groundwater Outflow Components for Projected Climate Change Conditions (acre-ft/year)


(AF/yr.) 2070

(AF/yr.)

Pumping 135,758 141,616

Drain Flows 7,100 8,024

Flow to Streams 1,833 1,921

Groundwater ET 35,127 36,652

Underflow to Ocean 829 693

Underflow to Monterey 5,354 5,253

Underflow to Eastside 16,977 16,606

Underflow to Forebay 308 322

Underflow to Langley 127 131

Underflow to Upland Areas 889 908

Underflow to Pajaro 956 974

6.10.4.1 Groundwater Budget Summary

Net groundwater inflow and outflow data for the 47-year future simulation with 2030 and 2070

climate change assumptions are detailed in Table 6-27. The total groundwater inflows and

outflows, along with the model error, are shown in Table 6-28.

Unlike the historical and current water budgets, these water budgets have acceptably small

budget uncertainty errors.

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June 17, 2019

Table 6-27: Average Annual Groundwater Budget for Projected Climate Change Conditions (acre-ft/year)


(AF/yr.) 2070

(AF/yr.)

Net GW Extraction 115,349 120,644

Net Drain Flow 7,100 8,024

Net Stream Exchange 69,708 69,785

Net Deep Percolation 41,206 45,125

Ocean Outflow 829 693

Net flow from Monterey 5,502 6,208

Net flow to Eastside -7,183 -6,246

Net flow from Forebay 4,957 4,983

Net flow from Langley 1,623 1,644

Net mountain front recharge 1,722 1,770

Net flow to Pajaro -822 -847

Net Storage Change -4,584 -4,653

Table 6-28: Total Groundwater Inflows and Outflows for Projected Groundwater Budgets


(AF/yr.) 2070

(AF/yr.)

Total In 295,665 308,628

Total Out 294,182 307,063

In-Out 1,484 1,566

%Error 0.50% 0.51%

Combining the land surface and groundwater budgets, groundwater pumping by water use sector

can be summarized, as shown in Table 6-29.

Table 6-29: Projected Annual Groundwater Pumping by Water Use Sector

Water Use Sector 2030 Average

2070 Average

Agricultural 94,800 99,500

Urban (total pumping minus agricultural) 20,500 21,100

Rural-Domestic (not simulated in model, considered minimal) 0 0

Total Pumping 115,300 120,600

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June 17, 2019

6.10.5 Change in Groundwater Storage

As with the historical and current groundwater budgets, groundwater storage change consists of

both groundwater level changes and seawater intrusion. The total change in groundwater storage

is shown in

Table 6-30: Change in Groundwater Storage for Projected Groundwater Budgets

2030 (AF/yr.)

2070 (AF/yr.)

Groundwater Level Change 4,600 4,700

Seawater Intrusion 3,500 3,900

Total 8,100 8,600

6.10.6 Projected Sustainable Yield

The projected sustainable yield for 2030 and 2070 can be calculated in a similar way to the

historical sustainable yield calculated in Table 6-20. The projected sustainable yield can be

estimated by summing all of the average groundwater extractions and subtracting the average

seawater intrusion and the average change in storage. The projected sustainable yields are

quantified in Table 6-31. This table estimates that pumping reductions of between 7.0% and

7.1% will be needed to reduce Subbasin pumping to the sustainable yield. It is important to

remember that simply reducing pumping to within the sustainable yield is not proof of

sustainability.

Table 6-31 additionally includes the estimate of historical sustainable yield for comparison

purposes. However, because of the significant differences in the estimated components between

the historical and projected water budgets, the projected sustainable yield should not be directly

compared to the historical sustainable yield. For example, the total pumping used to calculate

the historical sustainable yield is 86,500 AFY, while the pumping used to estimate the projected

sustainable yields varies between 115,300 and 120,600 AFY. Additionally, the values in Table

6-31 are estimates only. The sustainable yield value will be modified and updated as more data

are collected and more analyses are performed.

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June 17, 2019

Table 6-31: Projected Sustainable Yields

2030 Projected Sustainable Yield

2070 Projected Sustainable Yield

Historical Sustainable Yield

Net Pumping 115,300 120,600 108,300

Seawater Intrusion 3,500 3,900 10,500

Change in Storage 4,600 4,700 2,100

Projected Sustainable Yield 107,200 112,000 95,700

% Pumping Reduction 7.0% 7.1% 11.6%

6.10.7 Surface Water Budget

A surface water budget was not available at the time of this writing and will be provided in the

next draft of this Chapter.

6.10.8 Uncertainties in Projected Water Budget Simulations

There is inherent uncertainty involved in projecting water budgets with projected climate change

based on the available scenarios and methods. The recommended 2030 and 2070 central

tendency scenarios that were used to develop the projected water budgets with the SVIHM

provide a dataset that can be interpreted as what might be considered most likely future

conditions; there is an approximately equal likelihood that actual future conditions will be more

stressful or less stressful than those described by the recommended scenarios (DWR, 2018).

Further, as stated in DWR (2018):

“Although it is not possible to predict future hydrology and water use with certainty,

the models, data, and tools provided (by DWR) are considered current best available

science and, when used appropriately should provide GSAs with a reasonable point

of reference for future planning.

All models have limitations in their interpretation of the physical system and the types

of data inputs used and outputs generated, as well as the interpretation of outputs.

The climate models used to generate the climate and hydrologic data for use in water

budget development were recommended by the DWR Climate Change Technical

Advisory Group (CCTAG) for their applicability to California water resources

planning (DWR, 2018).”

Finally, there is also inherent uncertainty in groundwater flow modeling itself, since

mathematical (or numerical) models can only approximate physical systems and have limitations

in how they compute data. As stated by DWR (2018):

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June 17, 2019

“Models are inherently inexact because the mathematical depiction of the physical

system is imperfect, and the understanding of interrelated physical processes

incomplete. However, mathematical (or numerical) models are powerful tools that,

when used carefully, can provide useful insight into the processes of the physical

system.”

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June 17, 2019

6.11 References

Brown and Caldwell, 2015. State of the Salinas River Groundwater Basin: prepared for

Monterey County Resource Management Agency, Salinas, CA

CA Department of Water Resources (DWR). 2018. Guidance for climate change data use during

groundwater sustainability plan development. Available at: https://water.ca.gov/-

/media/DWR-Website/Web-Pages/Programs/Groundwater-Management/Sustainable-

Groundwater-Management/Best-Management-Practices-and-Guidance-

Documents/Files/Climate-Change-Guidance_Final.pdf

Durbin, T.J., G.W. Kapple, J.R. Freckleton, 1978. Two-dimensional and three-dimensional

digital flow models of the Salinas Valley Ground-water Basin, California, U.S. Geological

Survey Water Resources Investigations Report 78-113.

Hanson, R.T., Boyce, S.E., Schmid, Wolfgang, Hughes, J.D., Mehl, S.M., Leake, S.A.,

Maddock, Thomas, III, and Niswonger, R.G., 2014a, One-Water Hydrologic Flow Model

(MODFLOW-OWHM): U.S. Geological Survey Techniques and Methods 6–A51, 120 p.,

https://dx.doi.org/10.3133/tm6A51.

Hanson, R.T., W. Schmid, C.C. Faunt, J. Lear, and B. Lockwood, 2014b. Integrated hydrologic

model of Pajaro Valley, Santa Cruz and Monterey counties, California, Scientific

Investigations Report 2014-5111.

MCWRA, 2006. Monterey County groundwater management plan: prepared by Monterey

County Water Resources Agency

MCWRA, 2018. Salinas River Discharge Measurement Series Results in Context. Technical

Memorandum.

Montgomery Watson, 1997. Final report: Salinas Valley integrated groundwater and surface

model update.

Schaaf & Wheeler, 2014. Blanco drain yield study; prepared for Monterey Peninsula Water

Management District.

56

https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/Groundwater-Management/Sustainable-Groundwater-Management/Best-Management-Practices-and-Guidance-Documents/Files/Climate-Change-Guidance_Final.pdf




SALINAS VALLEY

GROUNDWATER BASIN

ADVISORY COMMITTEE

CHAPTERS 6 REVIEW

Prepared for Salinas Valley Basin Groundwater Sustainability Agency

1

June 20, 2019

57

Water Budget Update2

58

Report Outline

CHAPTER 1. Introduction

CHAPTER 2. Agency Information

CHAPTER 3. Description of Plan Area

CHAPTER 4. Hydrogeologic Conceptual Model

CHAPTER 5. Existing Groundwater Conditions

CHAPTER 6. Water Budgets

CHAPTER 7. Monitoring Networks

CHAPTER 8. Sustainable Management Criteria

CHAPTER 9. Projects and Management Actions

CHAPTER 10. Plan Implementation

CHAPTER 11. Notice and Communications

◼Ch. 11.1 Communications and Engagement Plan

3

59

Talk Outline4

Water budget requirements

Approach/tools for developing water budget

Overall water budget numbers

Not planning on explaining details of water budget components

60

What is a Water Budget?5

An Accounting of all Inflows and Outflows in a Specified Area

61

SGMA Water Budget Requirements

Water budgets must be

prepared for three periods

Historical – at least 10 years of

historical data

Current

Future – represents 50 years of

projected conditions based on

50 years of historical climate

data

6

62

Historical Water Budget7

Purpose: documents how we arrived at the

current status

Purpose: evaluate reliability of surface

water supply deliveries and aquifer

response to water supply and demand.

Time period:1995 to 2014

Issues: Often lacking necessary data in

earlier years

63

Current Water Budget8

Purpose: document current water use

Time period: 2015 to 2017 (last year for

which complete data are available)

Probably the least informative of the three

water budgets

Unfortunately influenced by recent

drought.

Represents a snapshot in time and

therefore has limited utility 64

Future Water Budget9

Purpose: Estimate future baseline conditions

of supply, demand, and aquifer response

to Plan implementation

Time period: 47 years

Use existing land use

Include projected climate change

The most useful of the three water budgets.

This is the water budget used for

developing our plan65

SGMA Water Budget Requirements (continued)

Each water budget period must

have two water budgets

Groundwater budget

Surface water budget

Two different specified areas for

the water budget

10

66

Water Budget Approach11

Future water budget is based on the

SVIHM predictive model

Balances all inputs and outputs

Matches groundwater level changes

Historical water budget is based on

historical data (historical SVIHM not yet

available).

Data gathered from existing sources

Inputs and outputs don’t necessarily match

or balance 67

Water Budget Tools12

The two approaches do not provide the

same water budget components

Example: SVIHM calculates flow in wells

from 180- to 400-foot aquifer. No data

are available for the historical water

budget

We have tried to re-organize the data

so the water budgets are as

comparable as possible.

68

SVIHM13

Models are the preferred approach to developing water budgets.

Models remain the best tool for managing groundwater

Historical SVIHM not yet available from USGS

Potential issues

Does not explicitly simulate all stream diversions

Assumptions about how crops are irrigated

Models can give a false impression of accuracy. They are good tools, but

are only good esitmates.

69

Historical Water Budget14

InflowAverage

(AF/yr.)

Minimum

(AF/yr.)

Maximum

(AF/yr.)


Precipitation Percolation to Groundwater 12,300 -33,500 18,900

Irrigation Percolation to Groundwater 11,700 5,200 18,100


TOTAL INFLOW 117,200 57,800 131,000

OutflowAverage

(AF/yr.)

Minimum

(AF/yr.)

Maximum

(AF/yr.)


Agricultural 89,000 76,300 110,800

Urban 19,000 14,100 27,500



Subsurface Outflows to Adjacent Subbasins/Basin 9,500 9,500 9,500

TOTAL OUTFLOW 129,800 114,700 152,600

StorageAverage

(AF/yr.)

Minimum

(AF/yr.)

Maximum

(AF/yr.)

Change in Storage -12,600 -72,300 8,300

70

Historical Water budget15

71

Historical Sustainable Yield16

Average

(AF/yr.)

Total Subbasin Pumping 108,300

Change in Storage (Groundwater Levels) 2,100

Seawater Intrusion 10,500

Estimated Historical Sustainable Yield 95,700

72

Future Water Budget17

2030 Projected

Sustainable Yield

2070 Projected

Sustainable Yield

Historical

Sustainable Yield

Net Pumping 115,300 120,600 108,300

Seawater Intrusion 3,500 3,900 10,500

Change in Storage 4,600 4,700 2,100

Projected Sustainable Yield 107,200 112,000 95,700

% Pumping Reduction 7.0% 7.1% 11.6%

73

Water Budget Questions18

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AGENDA · 2019-06-18 · 6. Committee Members' Reports 7. Future Agenda Items 8. Adjournment...

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Transcript of AGENDA · 2019-06-18 · 6. Committee Members' Reports 7. Future Agenda Items 8. Adjournment...