Enhanced Canal Recharge

Feasibility Report

Yolo County Flood Control and Water Conservation District

Woodland, California USA

December 2012

This report is part of an AB303 grant funded project from the Local Groundwater Assistance program of the California Department of Water Resources. This report is a combined report including both Enhanced Canal Recharge and Gravel Pit Recharge tasks. Cooperation and access to the Capay Mining Facility was kindly provided by Granite Construction, Inc.

34274 State Highway 16, Woodland, CA 95695 530-662-0265 www.ycfcwcd.org

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Table of Contents

Introduction ............................................................................................................................. 1

Background Information: Inflatable Dam on Cache Creek at Capay ............................ 3

Map of soil infiltration rates by canal reach ...................................................................... 3

Canal Infiltration Rates in Ponded Sections (Percolation Tests) .................................... 4

Percolation Tests: Field Data Acquisition Methods ...................................................... 7

Percolation Tests: Results ................................................................................................ 8

Potential for Increased Groundwater Storage ................................................................... 9

Promising Canal Stretches for Recharge ......................................................................... 11

Wintertime Canal Recharge Feasibility: Administrative Costs and Other Factors .... 11

Gravel Pit Recharge ............................................................................................................. 12

Aggregate Industry Partnerships ....................................................................................... 13

Infiltration Rate Estimates from Canal Flow Measurement: Data Acquisition ...... 13

Infiltration Rate Estimates from Canal Flow Measurement: Results ...................... 14

Gravel Pit Water Level and nearby Groundwater Levels: Data Acquisition ............ 15

Gravel Pit Water Level and nearby Groundwater Levels: Results ............................ 20

Conclusions ........................................................................................................................... 22

Recommended Action Plan ............................................................................................... 22

Introduction

During the original construction of the District’s canal system in 1914, it was known

that some canal reaches were very “leak prone” and that other areas lost less to

groundwater. At the time, a few of the leaky canal stretches were lined with

concrete, but 95% of the canals were left as dirt lined. Presumably, only a portion of

the canal was lined to save money, as lining canals is very expensive. However,

today it is the policy of the District to leave the canals unlined, to promote

groundwater recharge during the irrigation season (summer).

“Losses from this system, as seepage and evaporation, vary from year to

year, but have ranged from 15 to 65 percent from 1970 to 1996... The

greatest part of the losses is the result of seepage and percolation along the

canals and laterals. It is important to note, however, that the major part of

these losses are recoverable from the groundwater basin. Over the years,

various parties have suggested that the District should concrete-line its water

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delivery system to minimize seepage losses. From the standpoint of

managing the water supply available from the Cache Creek system, lining

the District's water delivery system is not deemed to be a prudent water

management measure.” (YCFCWCD Water Management Plan 2000

http://archive.org/details/watermanagementp00borcrich)

In between winter storms, the canals are dry. If during these dry times in winter,

water could be diverted from Cache Creek into the canals, increased recharge could

be realized.

For this study, infiltration of canal recharge water was measured or summarized

using the following methods:

1. Delivery amount by volume minus sales and spills. The difference is gain

to groundwater.

2. Instantaneous flow rate measurement upstream and downstream of two

points. The difference is gain to groundwater.

3. Percolation tests. Water was ponded in more than 6,600 linear feet of

canal. The rate of drop in water level can be converted to a volumetric

infiltration rate.

All three methods compared well showing similar results (as explained in the

section on Percolation Test Results).

A map was also made showing SURRGO Soil Survey infiltration rates on all reaches

of the canal system. Historical recharge rates and measurements were also

summarized and compared to current findings. Infiltration measurements in

sections of canal were scaled up to the entire canal system. (Of note, there exists

infiltration data from 1914 in the District Archives.)

In addition to groundwater recharge from the bottom of unlined canals, winter

water can be applied to land areas, such as gravel pits, to promote recharge.

Delivering winter water for groundwater recharge to a nearby gravel pit near the

town of Capay, CA, was planned. However, this task was modified. Instead of

delivering water to the gravel pit, losses from a stretch of canal near the pit were

very closely measured. The losses from the canal entered the pit through an

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underground path. Water levels in the canal, the pond in the pit, and nearby

monitoring wells were measured. The responsiveness of the pond to water losses in

the canal was analyzed. The gravel pit near Capay was unexpectedly found to have

a low infiltration rate, as explained in the Gravel Pit Results section.

Background Information: Inflatable Dam on Cache Creek at

Capay

In 1994, a 500 foot long inflatable bladder was installed on the top of Capay Dam.

This dam raises the water level 5 feet during the irrigation season. Previously,

wooden boards had to be installed at the beginning of each summer, taking 9

workers two days to accomplish. The process was repeated to remove the boards

each fall. Today, the bladder can be raised or lowered in 20 minutes at the touch of

a button. The bladder can also be operated remotely during storms and safely

observed w/ video camera surveillance.

The bladder was installed for safety reasons, but the District also wanted to have

the ability to inflate the dam in winter or early spring, when water is still flowing in

the Creek. Inflating the bladder in the winter allows the diversion of water in to the

canals for recharge purposes. This operation of the dam could facilitate

implementing the District's proposed groundwater recharge / recovery projects in

the canal system.

Map of soil infiltration rates by canal reach

Soil map data from Soil Survey Geographic (SSURGO) Database from the NRCS,

showing infiltration rate of the upper horizon layer of soil, was overlaid on the canal

system. SSURGO data presents a high and low infiltration rate for each soil horizon

and the low infiltration rate was used for the map. The lowest rate should be the

limiting rate for overall infiltration rate and therefore this low rate was used. A new

map, titled Soil Permeability, was created showing the infiltration rate along all

sections of the canal. The Soil Permeability map is attached.

SSURGO: Natural Resources Conservation Service, United States Department of

Agriculture. Soil Survey Geographic (SSURGO). Available online at

http://soildatamart.nrcs.usda.gov. Accessed June 2010.

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Table 1. below shows a summary of canal lengths by infiltration rate as shown in

the attached Soil Permeability map. The majority of the canals have an infiltration

rate of 0.57 in/hr or less, while only 4 percent of the canals have an infiltration rate

of 1.98 in/hr or higher.

Table 1. Summary of canal length by infiltration rate as presented in

the attached Soil Permeability Map.

Infiltration Rate Canal Length Percent Infiltration

in/hr ksat Miles Length Category

0 0.0 0.08% Low

0.06 45.3 27% Low

0.2 51.2 31% Low

0.57 64.5 39% Med

1.98 2.6 2% High

5.95 3.1 2% High

total 166.9 total miles

The Soil Permeability map was used to plan and identify good areas for

measurement of ponded infiltration rate: high, medium, and low flow rates. The

map can also be used to identify promising sections of canal for future recharge

projects. Areas of higher recharge, in red and orange, are more promising than

green areas, with lower infiltration rates. Short sections of red canal areas near the

Capay Dam historically have been lined with concrete and are not available for

recharge activities today.

The map was also used to scale up the pond tests on each canal section (low, med,

high) to the infiltration rate of the entire District. The percent of high, medium, and

low infiltration rate areas was calculated from the map, and the results of the high,

medium, and low pond test were used to multiply up to the entire District canal

system. The results are presented in the Canal Infiltration section.

Canal Infiltration Rates in Ponded Sections (Percolation Tests)

At the end of the 2010 irrigation a large construction repair project necessitated

ending the irrigation season early, Sept 15, 2010. Usually the season ends as

irrigation demand tapers off, but with the quick drawdown in the canals, we were

able to “pond up” sections of the canal and block all inflow and outflow to these

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sections. With our SCADA flow monitoring system, the drop in water level was

automatically measured and logged by the data collection system. In this way,

static pond infiltration rates were measured on more the 6,600 feet of canal.

Twenty-two canal sites were evaluated for possible inclusion in the ponding tests

(Table 2). Fourteen sites were eliminated right away, as they were located in

sloughs, did not have a downstream check to pond water, or were concrete lined

and were likely to have a very low infiltration rate. The remaining 8 sites were

considered in depth. One major concern was the ability to stop all incoming water

into the ponding area during the test. This meant that any remaining water draining

out of the canal system, and any drain water from nearby fields, had to be diverted

out of the ponding area. Only 4 sites were able to be configured this way; West

Adams @ Granite, the Chapman Reservoir Inlet, the Yolo Central Spill, and the

Winters Canal @ the Fredericks Flume. The Fredericks Flume site was tested, but no

data was collected. The steepness of the canal and the position of the water level

sensor was too far upstream of the check, so no water was beneath the sensor

during the test and no measurements could be made.

The remaining three sites were successfully measured during the pond test. These

sites are listed in bold in Table 2.

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Table 2. Twenty two canal sites were evaluated for the end of season percolation test. The three sites highlighted in bold

were selected.

Canal Monitoring Site Operational? Site Notes

Possible

Infiltration

site

Upstream

Check

Downstream

Check Measured?

Clover Spill X earthen lined x CLV 0543 CLV 0601 No

PLP Spill #1 x earthen lined x PLP 0965 PLP 1013 No

PLP @ Gayle Check broken earthen lined x PLP 0534 PLP 0593 No

West Adams Canal @ Granite x earthen lined x WEA 0170 WEA 0240 Sept. 18, 2010

Alder Canal @ Gordon Slough Heading x earthen lined x WEA 0970 ALD 0009 No

Winters Canal @ Fredricks x earthen lined x WIN 1119 WIN 1313 attempted

Chapman Inlet x earthen lined x WIN 1536 WIN 1603 Sept. 14-15, 2010

Yolo Central Spill x earthen lined x YOC 0970 YOC 1008 Sept. 28-29, 2010

Alder Drop x concrete lined

Chapman Outlet x concrete lined

Cottonwood Spill x in slough

Fairfield Ditch Heading no sensors earthen lined

Gordon Slough Heading x in slough

Hungry Hollow Spill x in slough

PLP Spill #2 x concrete lined

Salisbury Spill x in slough

University Spill x concrete lined

West Adams Canal Heading x concrete lined

Willow Slough @ 98 x in slough

Willow Slough Bypass x in slough

Winters Canal Heading x concrete lined

Yolo Central Heading x no d/s check

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Percolation Tests: Field Data Acquisition Methods

Water depth in the canals is measured constantly with a network of telemeterized

non-contact ultrasonic sensors. These data are logged on a server at District HQ

running the ClearSCADA database. A duplicate “hot standby” server is

simultaneously running at a remote location to ensure no lost data. The main use of

this system is to monitor canal flows and to manage irrigation deliveries. For the

pond infiltration test, this system was used to monitor dropping water levels in

sections of ponded canal. Canals were visually monitored periodically during the

test to check for leaks or water entering to ensure that changes in water level were

due to losses to groundwater only (evaporation over the few hours of the test were

estimated and found to be very small and were ignored).

Hydrographs showing the water level were printed out and the slope of the line

during the ponding test was measured and converted to infiltration in inches/hour.

Table 3 shows the date and duration of the ponding test for each location.

Table 3. Dates and time of ponding tests in three sections of canal during

September 2011

Canal section name Date of Pond Test Length of time used for level

drop measurement (hours)

WEA @ Granite 9-18-2010 8

WIN Chapman inlet 9-14-2010 12

YOC Spill 9-29-2010 15

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After the canals dried out, the canal cross section dimensions were measured with

a tag line stretched across the canal and a measuring tape was used to measure

canal depth at each station along the tag line. The beginning and end of each

ponded canal section was measured and a minimum of 5 intermediate cross

sections were used to model the geometry and volume of the canal. Figure 1 shows

how the top one inch of water surface in the canal can be modeled as long thin

slab, or volume, of water. The upstream depth of water eventually reaches zero, as

the canal drops over its length while the water surface stays level (Figure 1).

Figure 1. The top surface of the ponded canal water was modeled as a one inch

thick rectangular volume of water (blue line).

Percolation Tests: Results

Table 4 shows the results of the percolation test in inches/hour. The results are

compared to SSURGO database values. The infiltration rates are also converted to

losses in CFS/mile and acre feet/day mile. These loss data can be used to “scale

up” and estimate losses for the entire District canal system (Table 4).

Ponded canal versus full flow infiltration rate is presented in Figure 1. The water

surface during the pond test was level, while the canal floor drops along its length

(Figure 1.) Therefore, the dimension of the modeled “thin slab of water” is a

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different size at the ponded water surface, versus a full flowing canal. The

difference in these dimension are reflected in “ponded” versus “full flow” volumes in

Table 4.

Table 4. Results of ponding tests in three sections of canal during September 2010 Canal

section

name

Length

of

section

(ft)

Average

width full

flow (ft)

Volume of

top one

inch

ponded (cf)

Volume

of top

one inch

full flow

(cf)

Ksat

inches/hr

Measured

Ksat

inches/hr

SSURGO

cfs/

mile

acre

feet

/

day

mile

WEA @

Granite

1,440 30.6 3,336 3,675 0.50 .32 - 20 1.87 3.7

WIN

Chapman

inlet

3,552 18.66 5,523 5,523 0.29 .12 - 1.2 0.66 1.3

YOC Spill 1,640 12 1,367 1,640 0.25 .12 - .50 0.31 0.62

Note: Ksat from SSURGO does not match the Soil Infiltration map exactly because the map used low

values from the uppermost soil horizon, where depth is variable depending on location, and this

table uses the low value for the top 20 cm of the soil profile, regardless of the depth to the first

horizon.

Potential for Increased Groundwater Storage

The farms and cities within the District depend on the groundwater recharge that

occurs because of the unlined canals. The amount of recharge has been quantified

over the years and is presented Figure 2. The additional amount of recharge

available from winter water diversion (Table 5) into the canals will be compared to

the current amount of recharge that occurs.

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Figure 2. YCFCWCD Annual losses to recharge. These losses are calculated as the

total releases from storage, minus the sales. The result is losses and the total is

assumed to be losses to groundwater, although small amount of evaporation and

spill occur. In 1977 and 1990 there were no deliveries of irrigation water and hence zero losses.

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

year

rech

arg

e w

ate

r (a

f)

The water lost from the canal system is mostly recoverable from the groundwater.

Figure 2 shows the amount lost to range from ~18,000 af in 2009 to a maximum of

~64,000 af in 1989 and on average 38,264 af of water is lost. Other data, for

example, Table 3 of the 2000 Water Management Plan

(http://www.archive.org/download/watermanagementp00borcrich/watermanage

mentp00borcrich.pdf), show that on average 28,500 af are lost to recharge each

year from the District’s system.

Table 5. Recharge estimates using pond test infiltration data

Category Canal

length

(mi)

af/day

mile

af/

day days af

Large Main Canal Winters Canal 16.05 1.3 21 212 4,423

Medium Main Canal West Adams Canal 10.55 3.7 39 212 8,275

Small Lateral Canal Laterals (using YOC Spill as average loss rate) 140.3 0.62 87 212 18,441

Total 166.9 31,140

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In Table 5, estimates of losses from the pond infiltration tests were multiplied by

total length of the canal and an assumed 212 day season. Two hundred and twelve

days is the average season length between 1981 and 2009 (with minimum length

of 171 and maximum of 280 days). This analysis of pond infiltration data shows

that 31,140 af would be lost in an average length season. This amount is in

between the two estimates of losses from sales data discussed above (Figure 2).

Promising Canal Stretches for Recharge

There are two main canals in the District’s system: the Winters Canal, which diverts

water south of Cache Creek at Capay, and the West Adams which diverts waters on

the north and opposite side of the Creek. All other canals in the system branch off

of one of these two main canals (the Soil Permeability map, attached, shows the

canal system).

Any winter time diversions into the canal system will, by design, pass first into the

Winters or West Adams Canals.

The volume of recharge water depends on both the infiltration rate and the size of

the canal. Two stretches of canal can have a similar infiltration rate, for example

canal sections ‘WIN Chapman inlet’ and “YOC Spill’ from Table 3, but very different

recharge rates due to differences in overall size of the canal.

In most stretches of canal, the infiltration rate is relatively low. But because there

are so many miles of canal (166.9) the total infiltration rate for the system can be

significant. In other words, there are no particularly promising sections of canal,

most of the system must be used to achieve significant amounts of recharge.

Wintertime Canal Recharge Feasibility: Administrative Costs

and Other Factors

The main factor limiting wintertime recharge is that the canal system has dual

modes: summer-mode and winter-mode. During summer-mode the canals are full

for irrigation deliveries. During winter-mode the canals are empty to accept storm

runoff. Changing the canal configuration from summer-mode (irrigation) to winter-

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mode typically requires a crew of 10 people to work one week. If a storm comes in

the winter and the canal system is in summer-mode (full of water for recharge), the

canals could overtop and flooding and damage could result.

For wintertime recharge the canals must be in summer-mode. However, since

storms cannot be predicted more than a few days in advance, when storms are

predicted, there is not enough time to switch from summer to winter mode.

Therefore the canals must remain in the wintertime configuration for the duration of

the winter season and recharge water cannot be introduced into the canals.

It is possible to install a system of automated gates, which would allow the canals

to switch from winter to summer mode in minutes, instead of days, allowing

wintertime recharge to occur. Although these gates could preserve the ability of the

canals to carry flood flows at a moments notice, it would take many years to plan,

finance, and install this system.

Even with an automated gate system, the system must be managed in such a way

to monitor for approaching storms, protect against localized flooding, and protect

the headgates and diversion works at Capay from flood damage. There will be an

incremental increase in administrative costs for these activities. Additionally, the

financing of a capital improvement program to install automated gates will incur

additional administrative overhead.

Gravel Pit Recharge

The use of existing gravel pits for active groundwater recharge has been discussed

for many years in Yolo County (YCFCWCD Water Management Plan 2000). Active

recharge allows the opportunity to increase groundwater storage and optimize

conjunctive use of both surface and groundwater resources. Optimized conjunctive

use can provide more water for all uses, without creating new surface water

reservoirs.

In 2006, the Yolo County Flood Control and Water Conservation District (the District)

completed a Countywide groundwater simulation model, which specifically looked

at using gravel pits in a groundwater recharge and recovery scenario.

For this current grant project, we planned to deliver water to the pit at Capay for

active recharge. However, no wintertime deliveries of water were made. Certain

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aspects of the District’s irrigation system made it difficult or impossible to deliver

the water during winter. Infrastructure improvements of more than $25,000 were

needed to deliver the water, but were not part of the original budget. Additionally,

the road to the canal heading is dirt and not passable at times during wet winter

weather and the control gates could not be reached. After the end of the study, the

District installed remote control on these gates, but this feature was not available at

the time for the gravel pit test.

The gravel pit at the Granite Capay Facility is a 10 acre excavation in the ground, left

over from extraction of aggregate resources (gravel) (see Map 1).

Aggregate Industry Partnerships

Both aggregate mining and the District (or predecessor water companies) have a

long history in Yolo County, starting with the first white settlements in the 1850’s.

The aggregate industry along Cache Creek has been mining for high quality

aggregate resources since the late 1800’s. (Irrigation diversions started in 1856 at

the Moore Dam, with a water right currently held by the District.) Historically, gravel

mining was generally in the main Creek channel itself, but off-stream mining is

documented starting around 1981.

For the current study, Granite Construction kindly agreed to provide access to their

mining facility near Capay, CA, the pond, monitoring wells, and other monitoring

data in exchange for a copy of this report, when completed.

Infiltration Rate near the Gravel Pit from Canal Flow

Measurement: Field Data Acquisition

During normal canal operations, losses to groundwater must be taken into account.

For example, if a canal has sales for a particular day of 75 cfs, 100 cfs of water

must be delivered to the canal heading, to account for losses. By carefully

measuring flows upstream and downstream of a particular point along the canal,

losses can be quantified.

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From April 30, 2012 to June 17, 2010, canal flows were manually measured daily

at 6 locations in the West Adams Canal system near the Granite Capay aggregate

mining facility (Figure 3). The weir stick overpour method was used

(http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/). The flows after June 17,

2010 became too high for use of the weir stick method and those measurements

were stopped. Two sites, the uppermost WEA0170 and the lowermost WEA0240

were equipped with continuous flow measurement sensors and telemetry allowing

real-time collection of flow data at these two sites (Figure 4). Figure 4 is a screen

shot from the District’s Real-time SCADA system. For each day shown in Figure 4, a

single value for daily average difference in flow was estimated and used to make

the hydrograph shown in Figure 5. Figure 5 shows the losses in cfs between the two

sites.

Infiltration Rate Estimates from Canal Flow Measurement:

Results

Shown in Figure 3 are the acre feet of water lost per day in the West Adams canal,

during the early irrigation season, from late April until mid May of 2010.

Approximately 20 acre feet were lost per day along that 1.81 mile section of canal

(WEA0170 to WEA0351CK), or 5.5 cfs per mile.

Figures 4 and 5 shows the losses from the canal nearby the Granite gravel mining

facility, between the WEA0170 and the WEA0240, a distance of 0.7 miles. The

water that was leaving the canal due to infiltration was moving into the ground and

percolating to the groundwater surface, “filling the profile” and raising the

groundwater. The daily average losses from the data in Figure 5 are 9.4 cfs, or 13.4

cfs/mile.

The difference in losses to groundwater between Figures 3 and 5 do not match

because the measurements involved different sections of canal.

15

Gravel Pit Water Level and nearby Groundwater Levels: Field

Data Acquisition

The monitoring wells surrounding the pit were surveyed during installation by

Granite Construction Inc an unknown number of years ago and this well casing

elevation data was supplied to District. For this current study, a GPS Total Station

survey instrument, with sub centimeter accuracy, was used to tie the canal water

and pond water levels in with the monitoring well casing elevations. A U-10 Hobo

waterlevel data logger was deployed in each of the wells and the pond, while the

previously constructed SCADA station at WEA0240 measured the water levels in

the canal. Water level monitoring locations are summarized in Table 6 and shown

on Map 1.

Table 6. recharge amounts using current infiltration data

Location name Reference Elevation

ft msl (NGV27)

UTM

10 S

Easting

UTM

Northing Notes

MW1 204.02 582888.54 4285410.24 Monitoring Well #1 (MW1)

MW2 198.29 583698.40 4285985.65 Monitoring Well #2 (MW2)

MW3 194.22 583963.88 4285390.20 Monitoring Well #3 (MW3)

Pond 1A Pond surface variable

-- --

Pond size and surface elevation is variable, for location please see Map #1

WEA0240CK 201.715 583033.94 4285899.23 West Adams Canal 0240 Check

16

Figure 3. Daily flow at 6 locations on the West Adams Canal near the Granite Capay facility. The difference in flow between

the uppermost location (WEA0170) and the most downstream location (WEA0351CK) is converted to af/day.

0

20

40

60

80

100

120

140

160

180

4/30

/201

0

5/1/

2010

5/2/

2010

5/3/

2010

5/4/

2010

5/5/

2010

5/6/

2010

5/7/

2010

5/8/

2010

5/9/

2010

5/10

/201

0

5/11

/201

0

5/12

/201

0

5/13

/201

0

5/14

/201

0

5/15

/201

0

5/16

/201

0

5/17

/201

0

Date

cfs

(o

r a

f/d

ay

)

WEA0170

WEA0180CK

WEA0240

WEA0267CK

WEA0315CK

WEA0351CK

af/day lost

17

Figure 4. Screenshot showing upstream and downstream flows at two locations. The difference in flow between the green

(upstream) and blue (downstream) lines is loss to groundwater.

18

Figure 5. Losses to groundwater as measured by difference in flow between two SCADA stations. Manual overpours from

STORM are measurements taken with the weir stick method.

Losses between WEA170 and 240

0

2

4

6

8

10

12

14

16

5/11

/2010

5/18

/2010

5/25

/2010

6/1/

2010

6/8/

2010

6/15

/2010

6/22

/2010

6/29

/2010

7/6/

2010

7/13

/2010

Date

cfs

SCADA

manual overpours from STORM

19

20

Gravel Pit Water Level and nearby Groundwater Levels: Results

Figure 6 shows the response of groundwater level and the pond surface level to rain

and irrigation water present in the canal. The water level in the pond rose 10 feet

when irrigation water was placed in the canal at the beginning of May, 2010 (Figure

6.) The closest monitoring well to the canal (MW2) rose more than 30 feet. At the

end of the irrigation season in September 2010, the groundwater level in MW2

immediately dropped, while the pond dropped very slowly.

The phase 1A pond at the Granite Capay Facility is 10 acres in size. A rise of 10 feet

in water level is 100 acrefeet (af). One hundred af is a very small amount of water

for the District which delivers over 180,000 af per year. Although the pond looks

like a surface water reservoir, it would be very small if so and not much use to the

District if it only held 100 af. It is better to think of the pond as a very large diameter

well. The water level in the pond reflects the water level in the surrounding aquifer.

The water levels for the pond in Figure 6 show that during irrigation season, the

pond is intermediate between the canal and MW2, up gradient, and MW3, down

gradient. It is apparent that the pond is filling with water from the canal.

During the non-irrigation season, the pond water level stays higher than the

surrounding aquifer, as shown in the monitoring wells. If there was a good hydraulic

connection between the bottom of the pond and the surrounding aquifer, the pond

should quickly drain. This does not appear to happen.

The pond is used at the Granite facility to dispose of ‘fines’ from the gravel washing

process. Perhaps the bottom of pond is clogging up with silt. The sides of the pit,

above the pond high water level, may not be clogged with silt and high groundwater

from the surrounding aquifer can drain into the pond, filling it. However, when the

surrounding groundwater levels drop below the level of the pond, the pond drains

very slowly. For the 24 days after the end of irrigation season, when no water was

present in the canal, the pond level dropped only 6.2 inches, a rate of 0.01 inches

per hour. This rate is more than 10 times smaller than any infiltration rate

measured in the canals (Table 4). Of note, the water level is MW1 was still high after

the end of irrigation season and water could be coming from up gradient to keep

the pond high, perhaps lowering the measured infiltration rate.

21

Figure 6. Water levels (NGV27) at the Granite Capay Facility during 2010. Rain also shown in vertical bars.

begin

irrig.

end

irrig.

22

Gravel Pit Conclusions

It appears that using the gravel pit pond as a recharge basin would not be very

effective, as it drains slowly in its current configuration. If the pond were filled with

water, it would remain relatively static and not recharge the aquifer. These are

preliminary results. Perhaps if the pond was filled with water above its current level

and no fines were added, infiltration rates could be increased. However, the current

plan for this particular pond is to eventually fill it completely with fines from the

washing process, and reclaim the land. The canal bottoms in the District’s system

appear to have much higher infiltration rates. The canals and other opportunities in

the area for active recharge basin development should be explored.

Recommended Action Plan

The Granite Capay facility pond has a low capability as a recharge facility and likely

should not be used for an active recharge program, however other gravel mining

facilities may be appropriate. The District’s canal system should be the focus of

future active recharge systems. This is due to higher infiltration rates in the canals

versus the gravel pit and the large size overall of the District system. Other gravel

pits in the Cache Creek system may be more appropriate for active groundwater

recharge.

Although not discussed earlier, but mentioned here, the gravel pits along the Cache

Creek system involve large amounts of administrative overhead due to coordination

of mining operations and safety, unusual wintertime water delivery systems, and

important environmental concerns. In contrast, the District’s existing canal system

is already designed to accept water, is efficient with no pumps, and may be ideal for

wintertime recharge. Over the next decades, the District should continue upgrading

its canal infrastructure with automated gates for wintertime recharge operations.

WEST ADAMS CANAL

HUNGRY HOLLOW CANAL

YOLO CENTRAL CANAL

MOO RE CANAL

COTTONWOOD CANAL

WILLOW CANAL

WALNUT CANAL

WIN

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SOF 0568L

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SOF 0519L

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MAP 0242L

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MAP 0140LMAP 0109R

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MAP 0055L

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ROG 0021R

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ROS 0099L

ROS 0086L

ROS 0069L

ROS 0040R

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WIL 1844R

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WIL 1735LWIL 1725L

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LegendKSAT in inches per hour

0"

0.06"

0.2"

0.5"

1.9"

5.9"

Sloughs

District Canal or Slough

District Pipeline

Private