A CONCEPTUAL SALT BUDGET FOR CHARACTERISTIC WATER

0 downloads 0 Views 136KB Size Report
drainage water discharged to the San Joaquin River (from 57 TAF in 1990 to .... application of the Integrated Groundwater and Surface Water Model (IGSM)2.
A CONCEPTUAL SALT BUDGET FOR CHARACTERISTIC WATER DISTRICTS IN THE WESTERN SAN JOAQUIN VALLEY, CALIFORNIA Tracy Brumbaugh1 Clinton Williams1 Manucher Alemi1 Nigel Quinn2 ABSTRACT When considering salinity management in the San Joaquin Valley there is a tendency to take a broad approach and assume that all water districts have similar hydrologic characteristics, employ the same suite of technologies to address the soil management to sustain crop productivity, and maintain water quality. However, this article shows that water districts with different characteristics face different salt management challenges within the Valley. The three water districts chosen in this study are Westlands Water District, Panoche Water District, and West Stanislaus Irrigation District. They each have different histories, differ in the source of their irrigation water supply and differ in the physical and institutional constraints on their drainage return flows. These factors can have an impact on salt budget within each district. Approximate values of salt budget components for the three irrigation districts are presented. INTRODUCTION The westside of the San Joaquin Valley includes the San Joaquin River Basin and the Tulare Lake Basin with 2.4 million acres of mostly irrigated agricultural land. Historical drainage discharged to the San Joaquin River was about 55 thousand acre-feet (TAF) per year from an estimated 50 000 acres of land with installed subsurface drain. The Tulare Lake basin at the southern end of the Valley has no natural drainage outlet and annually discharges 15 TAF of drainage water to evaporation ponds. In areas without installed subsurface drains and no or inadequate natural drainage, salts accumulate in the groundwater aquifer and the water table may rise over time. Farmers and water districts within the Valley have adopted various irrigation improvements and drainage reduction measures to manage salts and trace elements in response to regulatory requirements to protect environmental 1

Engineer-Water Resources, Associate Land and Water Use Analyst, and Supervising Land and Water Use Analyst, respectively; Data Services and Program Development Branch, Office of Water Use Efficiency, Department of Water Resources, 1416 Ninth Street, Sacramento, California 95814. 2 Group Leader, Hydroecological Engineering and Decision Support, Earth Science Division, Berkeley National Laboratory, Berkeley, CA 94720.

resources. These actions have resulted in significant reduction in the volume of drainage water discharged to the San Joaquin River (from 57 TAF in 1990 to about 30 TAF in 2000). Acreage of and discharge rates to evaporation ponds have also been reduced, since selenium induced teratogenesis in wildfowl embryos was found. For example, the evaporation pond acreage reduced from about 6 000 acres in 1990 to about 4 000 acres in 2000. The irrigation and drainage management measures and some fallowing have been the primary mechanisms for water conservation and reduction of contaminant loads to water bodies in the region. These measures coupled with separation and safe disposition of salts from the root zone or groundwater aquifer could result in sustainable soil and water quality. Drainage reduction and separation of salts from drainage help maintain agricultural productivity and water quality, and have the benefit of creating new sources of water supply. BACKGROUND One of the principal subsurface geological features of the San Joaquin Valley is the Corcoran clay formation. Formed as a lakebed about 600 000 years ago, this clay layer ranges in thickness from 20 to 200 feet and underlies most of the westside of the Valley. The Corcoran clay divides the groundwater system into two major aquifers – a confined aquifer below and a semi-confined aquifer above. The Diablo Range to the west is comprised of complex, uplifted sediments, which are composed predominantly of sandstones and shales of marine origin. These sandstones and shales contain salts, as well as trace elements such as selenium. With decreasing elevation from the west to east, soil textures become finer. These fine textured soils are characterized by low permeability and increased concentrations of water-soluble solids, primarily salts and trace elements. Furthermore, there are discontinuous clay lenses at different depths within the semi-confined aquifer, resulting in localized shallow groundwater. Three water districts are addressed in this paper, chosen for their distinct applied water and drainage characteristics. For example, West Stanislaus Irrigation District (WSID) can release drainage water to the San Joaquin River, Panoche Water District (PWD) has limited access to release drainage water to the San Joaquin River, and Westlands Water District (WWD) has no means for drainage water removal. Additionally, the districts differ in the quality of their irrigation water supply. WSID receives medium-quality water from a combination of Central Valley Project (CVP) and San Joaquin River water, PWD receives high-quality water from CVP water, and WWD receives some high-quality CVP water as well as lower-quality groundwater (depending on the availability of CVP water). Panoche Water District PWD is located in the northern part of the Valley. Soils in the PWD can be characterized as very deep, nearly level to gently sloping, and moderately to poorly drained soils that are drained to some extent on low alluvial fans. PWD

began receiving its first water from the San Joaquin River in 1947 under interim contracts. In August 1949, contract negotiations began with United States Bureau of Reclamation (USBR) for the CVP water, and a long-term contract was established in 1955. Currently PWD has a contract for the delivery of 99 TAF of water per year. PWD receives a yearly average of nine inches of precipitation, most of which falls during the months of November through March. Reference evapotranspiration measured in PWD averages 55 inches per year. PWD’s service area is approximately 38 000 acres. Actual irrigated land is approximately 36 000 acres. The five major irrigation methods in PWD (in order by highest to lowest acreage, in 1997) are (1) sprinkler (hand move) and graded (surface ¼ mile: siphon tube); (2) graded (surface ¼ mile: siphon tube); (3) trickle (surface and subsurface); (4) graded (surface ¼ mile: gated pipe); and (5) sprinklers (hand move). Historically, drainage water discharged from the PWD service area flowed through the wildlife refuges and then into the San Joaquin River. As a result of environmental limitations, it became necessary to remove the drainage water from the wildlife areas. Therefore, in 1996 the drainage water (from PWD and other districts in the area) was rerouted through a newly constructed channel that bypasses the refuges. The water now travels through the bypass, and portions of the San Luis Drain and is then discharged to the River. Due to selenium load limitations imposed by the Central Valley Regional Water Quality Control Board, a large portion of the subsurface drainage water (about 4.5 TAF annually) collected by PWD is blended back into the delivery system at several different locations. Additionally, as of 1997, PWD does not allow tailwater (surface drainage water) into its drainage or distribution system. The water is to be retained on farm by the individual water users where it is pumped back into the farmer’s delivery system and redelivered to the field. This promotes more efficient water use and reduces the volume of drainage water conveyed to PWD’s drainage works. West Stanislaus Irrigation District WSID is located in the northern part of the Valley. WSID was formed in 1920 and began diverting water from the River in 1929. Diversions increased from 12 TAF to a maximum of 113 TAF in 1984. After construction of the Friant Dam in 1942, the quantity of water available to WSID users decreased, and the quality of water became increasingly saline. WSID signed a contract with USBR in 1953 to receive 20 TAF of water from the CVP, which was increased to 50 TAF in 1976. WSID receives a yearly average of ten inches of precipitation, most of which falls during the months of November through March. Temperatures range from an

average monthly low of 17F in winter months, to a high of 111F in summer months. Reference evapotranspiration is 57.0 inches/year. WSID total acreage and irrigable area is 24 500 and 21 500 acres, respectively. White Lake Mutual Water Company also irrigates approximately 5 000 acres under an agreement. The soils are moderately to well drained, and permeability is low to medium. The majority of agricultural acreage is used to produce almonds, apricots, dry beans, green beans, melons, peas, walnuts, wheat, and can tomatoes. The five major irrigation methods (in order by highest to lowest acreage) are furrow (gated pipe), border (gated pipe), sprinkler, and micro/drip. Drainage water flows back into the River, either directly into natural channels or onto riparian land adjacent to the River. Westlands Water District WWD is located in the southern half of the Valley. It is approximately 15 miles wide and 70 miles long. Formed in 1952, it included approximately 376 000 acres. WWD later merged with its western neighbor to form the current 604 000acre district with an irrigable acreage of 567 800 acres. In 1968, USBR created a 40-year contract with WWD, providing 900 TAF of CVP water per year. Then in 1986, a new agreement added an additional 250 TAF of water per year1. WWD receives a yearly average of seven inches of precipitation, most of which falls during the months of December through March. The mean annual temperature is 62F. Reference evapotranspiration is 58 inches/year. Approximately 60 different crops are grown in WWD. In 2000, cotton, tomatoes, wheat, and almonds comprised almost 64% of the 564 200 cropped acres. WWD crops are irrigated using groundwater and CVP water. In the 1990’s, approximately 40% of all crop acreage was irrigated by surface irrigation systems (furrow and/or border irrigation), approximately 20% was irrigated by pressurized systems (sprinklers and/or drip irrigation), and approximately 40% was irrigated by a combination of surface and pressurized systems. Currently, there is no outlet for drainage water. Some farms reuse subsurface drainage water. Some lands are fallowed annually due to inadequate water supplies and drainage-related problems. Shallow groundwater levels are typically highest in April after preirrigation and lowest following the cropping season in October after crops have extracted a portion of the shallow groundwater. FLOW AND SALT MODELING Numeric models have been developed to understand and predict groundwater levels and flow on the West Side of the San Joaquin Valley. These models 1

Water Management Plan, 1999.

provide a tool by which the effects of future changes in water use and management might affect groundwater levels. However, current models don’t integrate water salinity data with flow to determine components of a salt budget for the west side of the Valley. In 1990, the United States Geological Survey created a three-dimensional groundwater flow model that was calibrated for a portion of the Valley1. This model was used to evaluate alternative management approaches over a 50-year period. The model evaluated groundwater responses to: land retirement; reduced recharge; increased groundwater pumping; and simultaneous reductions in recharge and increases in groundwater pumping. Results from the model showed that land retirement was an effective management tool on a local scale but not on a regional scale and that management of the semiconfined aquifer as a salt sink could be maintained from 40 to 275 years. This model represented one of the first comprehensive, calibrated attempt to characterize the hydrology of the Valley. Following the Belitz and Phillips model, the USBR completed the Central Valley Groundwater and Surface Water Model (CVGSM). CVGSM is a specific application of the Integrated Groundwater and Surface Water Model (IGSM)2. The CVGSM model simulates water inflow and outflow using various specific parameters including crop type, soil type, rainfall, applied irrigation water, potential ET, and irrigation efficiency. Additionally, stream-flow, stream-aquifer interactions, and unsaturated flow are also simulated. However, the model does not consider salt transport or loading. Presently CVGSM is being updated and improved as the WESTSIM model and will include a land use module. However, neither CVGSM nor WESTSIM have been calibrated for large-scale use. WESTSIM is capable of incorporating a salt budget module, but this is not in the current plans. Further development is needed to include salt budgets for future management planning. A number of other hydrologic models have been developed for use in the Valley but none of them have been sufficiently calibrated or include a salt budget module to allow for salt transport characterization. Most models suffer from a general lack of measured data that is needed for rigorous calibration. Various attempts at modeling salt budgets in the Valley have been attempted. In 1990 a course salt budget estimate was published by SJVDP3. These values were obtained using a mass balance approach4 from published and estimated data. The salt budgets obtained were derived from data collected from 1980 to1985 and will be referred to as the 1985 estimates. These values represent a rough estimate of salt in the Valley and were never validated with measured observations.

1

Belitz and Phillips, 1992. Montgomery Watson, 1993. 3 Technical Information Record by Swain and Associates, 1990. 4 CH2M Hill, 1988. 2

WATER AND SALT BUDGETS The principal components of water flow and salts (dissolved solids) into and out of the planning subareas (water and salt budget) in the Valley were estimated and reported in the San Joaquin Valley Drainage Program Technical Information Record mentioned above. The system is comprised of two subsystems: The rootzone subsystem, which includes all surface water and subsurface water to the free water table, and the semi-confined aquifer system which includes all subsurface water below the free water table to the Corcoran clay. Because shallow groundwater is the focus of drainage problems, the base of the semi-confined aquifer was chosen as the lower boundary for salt budget calculations. The water and salt budgets reported in the 1990 Technical Information Record were developed using the Department of Water Resources' Hydrologic and Economic Model database, the U.S. Geological Survey’s Regional Aquifer System Analysis model database, and USBR and local water district data. The average annual salt budget for each of the three districts was taken from the 1985 estimates and is shown in Figures 1, 2 and 3. Using 1990-1999 water supply and drainage discharge data (flow and quality) from the three districts, the net annual salt gain or loss (Figure 4) was calculated for the three districts (the gain/loss calculation doesn’t include other salt inflow and outflow such as salt dissolution, lateral inflow or leakage through Corcoran clay and lateral outflow). PWD receives water from groundwater and CVP; WSID receives water from the San Joaquin River and CVP; and WWD receives water from the CVP and groundwater with no drainage discharges out of the district. Both WSID and PWD discharge drainage water to the River. RESULTS AND DISCUSSION Panoche Water District The 1985 estimate surface water inflow was 132 TAF (including 87 TAF from surface deliveries and 35 TAF from precipitation), including a salt inflow of 43 000 tons (see Figure 1); 12 TAF from groundwater, and 700 acre-feet from aquifer inflow, including a salt inflow of 19 000 tons (with 18 000 tons due to salt dissolution), for a total of 145 TAF of water and 75 000 tons of salt. Surface water outflow was 16 TAF, which removed 12 000 tons of salt; consumptive use was 101 TAF, which removed no salt; and semiconfined aquifer outflow was 29 TAF

Title: Water salt 1.2. Creator: Adobe Illustrator(R) 9.0 Preview: This EPS picture was not saved with a preview included in it. Comment: This EPS picture will print to a PostScript printer, but not to other types of printers.

Title: Westlands 3. Creator: Adobe Illustrator(R) 9.0 Preview: This EPS picture was not saved with a preview included in it. Comment: This EPS picture will print to a PostScript printer, but not to other types of printers.

(including 4 TAF through subsurface drainage discharges and 11 TAF through Corcoran clay), which removed 56 000 tons of salt (31 000 tons through drainage discharges and 16 000 tons by leakage through the Corcoran clay to the confined aquifer), for a total outflow of 146 TAF of water and 68 000 tons of salt . The 1985 estimate of net salt accumulation was 7 000 tons. The major source of salt is applied water and salt dissolution. The major salt outflow is leakage through the Corcoran clay layer and drainage discharge. PWD had a discharge to the San Joaquin River during 1990 to 1996, but beginning in 1997 it was reduced through district-wide recycling of the drainage water to comply with selenium load limits imposed by the waste discharge requirements. During 1990-1999 the net annual salt loss (salt from surface water delivery plus salt from groundwater delivery less salt outflow due to drainage discharges) ranged from 40 000 to 100 000 tons per year (Figure 4). However, after PWD started recycling its drainage water and reduced its drainage volume in 1996, the salt loss from the district declined to 35 000 tons in 1999. During the period from 1990 to 1999, approximately 600 000 tons of salt were removed from PWD.

-30

Net Annual Change Cumulative Change

-50

-200

-60 -300 -70 -80

-400

Panoche

-90

-500

-100

-600

50

180

WSID Net Change

160

40

140

30

120 20 100 10

80

0

West Stanislaus

Cumulative Salt Change (Thousand Tons)

Net Annual Salt Change (Thousand Tons)

WSID Cumulative Change

60

-10

40

1600

10000

WWD Net Change WWD Cumulative Change

1400

8000

1200 6000 1000

Westlands

4000

800 2000

600 400

0 1990

1992

1994 Year

1996

1998

Figure 4. 1990 to 1999 District Salt Gain/Loss

Cumulative Salt Change (Thousand Tons)

Net Annual Salt Change (Thousand Tons)

-100

Cumulative Salt Change (Thousand Tons)

Net Annual Salt Change (Thousand Tons)

-40

0

PWD also provided water flow and quality data1 from 1985 which was used for rough validation of the 1985 estimates. According to measured data, salt inflow to PWD was 29,000 tons (compared to 43,000 tons from the 1985 estimate) and 50,000 tons of salt was removed (compared to 31,000 tons from the 1985 estimate). In both cases these measured values resulted in a larger net removal of salt from PWD than the 1985 estimate. This confirms that better salt budget models are needed if they are to be used as a management tool in the San Joaquin Valley. West Stanislaus Irrigation District The 1985 estimate of surface water inflow was 70 TAF (including 32 TAF from canal water deliveries, 8 TAF from precipitation, and 18 TAF from San Joaquin River), including a salt inflow of 29 000 tons (see Figure 2); groundwater inflow was 3 TAF, including a salt inflow of 3 800 tons (with 3 600 tons from salt dissolution); and aquifer inflow was 100 acre-feet, including a salt Inflow of 3 800 tons, for a total of 73 TAF of water and 37 000 tons for salt. The surface water outflow was 10 TAF, which removed 4 500 tons of salt; consumptive use was 44 TAF, which removed no salt; and semiconfined aquifer outflow was 19 TAF, which removed 33 000 tons of salt, for a total outflow of 73 TAF of water and 38 000 tons of salt. The 1985 estimate shows a net loss of 1 000 tons of salt from the district. During 1990-1999, Figure 4 shows that the net annual salt load ranged from a maximum gain of 50 000 tons in 1990 to a loss of 4 500 tons in 1998 (from surface water delivery plus salt from groundwater delivery less salt outflow due to drainage discharges). Additionally, during the period from 1990 to 1999, WSID accumulated approximately 180 000 tons of salt. Westlands Water District The 1985 estimate of surface water inflow was 1 809 TAF (including 1 407 TAF from surface deliveries and 378 TAF from precipitation), including a salt inflow of 633 000 tons (see Figure 3); 170 TAF from groundwater, including a salt inflow of 220 000 tons; and 14 TAF from aquifer inflow, including a salt inflow of 844 000 tons (with 780 000 tons due to salt dissolution and 53 000 tons from stream inflows), for a total of 1 993 TAF . Surface water outflow was 4 TAF, which removed 2 000 tons of salt; consumptive use was 1 472 TAF, which removed no salt; and semiconfined aquifer outflow was 336 TAF, which removed 522 000 tons of salt (including 236 TAF of water leaking through Corcoran clay, removing 323 000 tons of salt) for a total of 1 812 TAF of water flowing out of the system. The 1985 estimate of net salt accumulation was 1 175 000 tons or 1.5

1

Personal communication with Chris Linneman, Summers Engineering.

tons per acre. The major source of salt is applied water and salt dissolution. The major salt outflow is leakage through Corcoran clay. During 1990-1999 the net annual salt gained (salt from surface water delivery plus salt from groundwater delivery with no salt outflow) ranged from 1.5 million tons to about 440 000 tons per year (Figure 4). The 1990-99 estimates assume no drainage water and no other sources and sinks for salts. During the period from 1990 to 1999, WWD accumulated approximately 8 million tons of salt. CONCLUSIONS The 1985 estimate for the PWD shows a negligible rate of salt accumulation. During 1990-1999 there was a loss of salt from the district, but it declined as a result of drainage water recycling (Figure 4). The 1985 estimate shows that WSID was in a state of hydrologic balance with surface and semi-confined aquifer inflows mostly balanced by outflow. A small net loss of salt of less than 0.1 tons/acre-yr was estimated. The 1990-1999 estimate shows that the district is gaining salt at a small rate. Approximate salt gain/loss results from the 1985 estimate and during the period from 1990 to 1999 show that WWD continued to gain salt from irrigation water sources. The 1990-99 salt calculation is an approximation of salt gain and loss. A precise calculation of salt budget components requires salinity and flow data, and a salinity model which incorporates flow and salt transport within the complex groundwater system of the Valley. Specific data relating to water quality and flow for the various components of the conceptual salt budget model are necessary for calibration and validation of any future comprehensive salinity flow model. Evaluating root zone salinity is critical in determining management practices and maintaining agricultural productivity. REFERENCES Westlands Subarea Report. Westlands Water District. October 1998. Water Conservation Plan. Westlands Water District. 1992. Panoche cropping pattern spreadsheet. (Personal communication, Chris Linneman, 2002). www.westlandswater.org Technical Information Record. San Joaquin Valley Drainage Program. September 1990. Panoche Water District: 1999 Water Conservation Plan (5 Year Update). Panoche Water District. October 2000.

Water Management Plan, 1999. Westlands Water District. September 1999. Water Conservation Plan. West Stanislaus Irrigation District. March 1994. Financial Statement and Annual Report: 2000. West Stanislaus Irrigation District. December 2000. Simulation of Water-Table Response to Management Alternatives, Central Part of the Western San Joaquin Valley, California. U.S. Geological Survey WaterResources Investigations Report 91-4193. Belitz, K. and S.P. Phillips. 1992. Documentation and User’s Manual for the Integrated Groundwater and Surface Water Model. Montgomery Watson. December 1993. San Joaquin Valley Hydrologic and Salt Load Budgets.CH2M Hill. October 1988.