Northern Sacramento Valley Conjunctive Water Management

Investigation

Public Workshop

December 8, 2010

The Glenn-Colusa Irrigation District and

The Natural Heritage Institute

12/8/2010 1

Workshop Objective & Process

• Objective– Respond to questions from October 21, 2010

workshop 1

• Process– Organized questions into topics– Describe each topic– Provide response– Engage in discussion

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How Does The Proposed Project Work?

4

Re-operate Surface Reservoirs with Groundwater “Backstop”

• Reservoir re-operation – Additional releases to meet program objectives

(North of Delta water supply and environmental enhancement)– Expect reservoir refill from surplus surface flows– Honor existing CVP and SWP delivery obligations and

operations constraints

• Groundwater operation– Pump groundwater to “repay” reservoirs if storage conditions put

contract deliveries or temperature control at risk– Groundwater used in lieu of surface entitlements that then

remain in storage– Minimize or avoid GW impacts

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10

Spring(no inflow)

Summer(no inflow)

Fall-Winter(inflow)

Spring(no inflow)

8

Project ReservoirOperation

BaselineReservoirOperation

Re-Operation Case 1- Reservoir Refills

Reservoir Full

100

Deliveries = 50

Target Carryover = 50

50

Reservoir Full

100

Reservoir Full

100

FloodRelease = 20

Inflow = 70

100

Inflow = 70

FloodRelease = 10

100 100

Reservoir Full

Target Carryover = 40

Deliveries = 60

40

10Project ReservoirOperation

BaselineReservoirOperation

Re-operation Case 2- Reservoir Does Not Refill

Reservoir Full

100

Reservoir Full

100

Deliveries = 50

Target Carryover = 50

50

Reservoir Partially Full

80

Target Carryover = 40

Deliveries = 40

40

Target Carryover = 40

Deliveries = 60

40

Target Carryover = 40

Deliveries = 30

40

Reservoir Partially Full

70

Spring(no inflow)

Summer(no inflow)

Fall-Winter(inflow)

Spring(no inflow)

Summer(no inflow)

Inflow = 30

Flood Release = 0

70

Inflow = 30

Flood Release = 0

80

GW

Groundwater = 1040

Project Performance SummaryProject Scenario 2 Evaluated with Revised Model Including Biological

Opinions, Forecast-based Operation and Minimum Reservoir Release Criteria

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Performance MetricSac R

(Shasta)Feather R (Oroville)

Total number of years in simulation (1922-2003) 82 82

Number of years no project releases made 62 45

Number of years project releases made 20 37

Average annual (82 years) project release, (TAF)(Roughly 2/3 environmental and 1/3 ag benefits)

Cumulative benefit over 82 years (TAF) =

25

2,050

30

2,460

Maximum year project release (TAF)(Includes environmental and ag)

180 102

Number of years “payback” pumping is needed 4 11

Average annual (82 years) project pumping (TAF)Cumulative pumping over 82 years (TAF) =

2164

9738

Maximum year project pumping (TAF)(Maximums do not occur in same year)

100 100

Average annual (82 years) reservoir refill from surplus flows (TAF) 23 23

Spillage of payback water 0 -2

Questions How Does The Proposed Project Work?

• Can you do just reservoir re-operation without doing the pumping for repayment?

• Where does the water for environmental enhancements and other project benefits come from?

• How does the payback water get used?

• How do the project benefits compare to the frequency and magnitude of payback?

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• How would the reservoir releases be measured?

• How would it be determined that water needs to be repaid…what triggers reservoir payback?

• Which aquifer are we talking about, the deep or shallow?

• Does the study address the total groundwater picture?

Questions, continued

How Does The Proposed Project Work?

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• What are the existing contractual obligations?

• Public wants assurance that there is adequate thought going into monitoring and mitigation.

Questions, continued

How Does The Proposed Project Work?

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Investigation Tools and Data

Overview of Analysis Tools

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Ground WaterModel

Other User Input

EnvironmentalObjectives

System OperationWith

Conjunctive Management

Surface WaterModel

CalSim Results

Surface WaterModel

CalSim Results

SW-GW InteractionTarget River Flows

GW PumpingReservoir Ops

Other Assumptions

13

Groundwater Model Area and Grid Density

Sacramento

Orland Unit

GCID

Butte Basin

Willows

12/8/2010

Chico

14

Groundwater Flow Model• Regional scale with high spatial detail

– 5,950 square miles (3.8 million acres)– 88,922 surface nodes– 7 vertical layers

• Aquifer properties based on analysis of more than 1,000 production wells

• Calibration– Static calibration for year 2000– Water levels from 257 monitoring wells

• Monthly time step, 1982 through 2003

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Surface Water Operations Model • Spreadsheet-based for ease and speed of

operation• Re-operates Shasta and Oroville Reservoirs

relative to a baseline condition depicted by CalSim II outputs (1922 through 2003)

• Driven by additional target deliveries for:– Environmental restoration in Sac and Feather Rivers– Unmet Sac Valley agricultural demands

• Various operational constraints• Uses generalized SW-GW interaction functions

derived from GW model12/8/2010

QuestionsInvestigation Tools and Data

• Why are critical dry years not used in the analysis?

• What is the time-step used to develop the groundwater model? Is the time-step appropriate for capturing localized effects of day to day well operation and aquifer response?

• Were economic impacts beyond just project costs and benefits considered, such as impacts to specific segments of the agricultural community?

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Project Benefits

QuestionsProject Benefits

• What are the project benefits?

• Are there benefits to the groundwater systems and were they considered in the economic analysis?

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Project Benefits• Increased Sac Valley surface water supply

– More local benefit (water supply) from CVP and SWP

– Reduced overall reliance on Sac Valley groundwater, though increased local pumping in certain years

• Improved habitat in Sac and Feather Rivers through – Recovery of salmon populations– Ecosystem sustainability

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Project Impacts

QuestionsProject Impacts

• What are the impacts of groundwater pumping in the valley on foothill aquifers?

• What are the critical recharge months in the upper reaches? In the area in general?

• Project pumping may be a small share of Valley wide pumping but what proportion is it of pumping within the project area?

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22

Typical Sacramento Valley GW Hydrograph (Butte Co.)

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Sacramento Valley Water Uses and Sources by County

Peak Year Project Pumping (100 TAF1) in Relation to Estimated Annual Baseline Pumping

Area

Estimated Baseline

Pumping (TAF)

Project Pumping as % of Area

Baseline

Butte County 411 24%

Glenn and Colusa Counties 635 16%

Butte, Glenn and Colusa Counties

1,046 10%

Northern Sacramento Valley (Butte, Glenn, Colusa, Tehama and Shasta Counties)

1,323 8%

Entire Sacramento Valley(Source: GW model water budgets)

2,500 +/- 4%

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1 Peak year project pumping is 100 TAF in the Butte Basin and in GCID but the two not occur in the same year based on the 1922 through 2003 modeling

QuestionsProject Impacts

• Is the interconnection between streams and underlying aquifers sufficiently defined to predict the effects of even modest changes in groundwater levels (e.g., Butte and Big Chico Creeks)?

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• What is the extent of the impact on domestic (and other wells)? You show 0 to 6 feet, but you also say that near the wells that are pumping payback water it could be 50 or 60 feet? Even a few feet can have a large impact. This needs to be clarified.

Questions, continued

Project Impacts

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Comparison of Drawdown from Modeling and Averaged for Impact Analysis

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Potential Impact Zones:Worst Case, New Wells

Regional Aquifer Drawdown in Aug 1990 , Scenario 1, New Well Field

Figure 11-15, p.11-16 from Modeling Report, Feb 2010

Next Steps

• Draft and Final Investigation Report

• Additional public meetings

• Phase 2

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