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Conceptual diagram showing
groundwater flow in the
Owens Valley (Danskin, 1998);
click to enlarge.

by Bob Harrington, Hydrologist
May, 2006 

Groundwater conditions in 2005 improved due to ample recharge and restricted pumping. On August 8, 2005, Judge Lee Cooper ruled in Inyo County Superior Court that LADWP was in violation of certain court orders regarding implementation of mitigation projects associated with the Long-Term Water Agreement (LTWA) and Memorandum of Understanding. Among the sanctions imposed on LADWP by Judge Cooper were a limitation on pumping to not greater than 57,412 acre-feet per runoff year and a requirement that 16,294 acre-feet of water be spread per runoff year in the Laws area for groundwater recharge until the Court lifts the sanctions. The sanctions will be in place until LADWP establishes 40 cfs flows in the Lower Owens River. LADWP's Operations Plan for the 2005-2006 runoff year (April 2005 through March 2006) originally called for 90,000 acre-feet of pumping, however the sanctions imposed by the Superior Court forced a reduction in pumping to the court-ordered limit of 57,412 acre-feet. LADWP produced a modified Operations Plan on September 28, 2005 that reduced their planned pumping to 57,412 acre-feet. At the end of the 2005-2006 runoff year, LADWP reported that they pumped 56,765 acre-feet, and spread 24,237 acre-feet of water in Laws, of which 17,102 acre-feet was pursuant to the court order.

Runoff from the 2004-2005 winter snowpack was above normal, forecasted to be 128% of normal for the Owens Valley. The depth-to-water measurements in Table 1 show that the combination of enhanced recharge due to high runoff, court-ordered recharge in Laws, and relatively low pumping as ordered by the Court resulted in a rise in water table elevation throughout the Owens Valley. The twenty-eight wells listed in Table 1 are 'indicator wells,' a small subset of LADWP's monitoring wells that have proven useful for predicting changes in the water table due to groundwater extraction and recharge. In all wellfields, water levels increased from April 2005 to April 2006; however, in all wellfields except Bairs-Georges and Laws, water levels are below the levels of the mid-1980's baseline vegetation mapping period. Noteworthy are the large increases in water table elevation in Laws due to the large amount of water spreading.

Water tables should continue to rise in 2006-2007. Forecasted runoff for the Owens Valley runoff year 2006 is 135% of normal runoff for the Owens Valley, and LADWP remains subject to the court sanctions that limited pumping during 2005-2006. In accord with the court sanctions, LADWP's Operations Plan for the 2006-2007 runoff year specifies 57,412 acre-feet of pumping and 16,294 acre-feet of water spreading in Laws. Table 2 provides LADWP's planned pumping for each wellfield. LADWP plans to have 40 cfs flowing in the Lower Owens River sometime in early-2007, which would result in the sanctions being lifted. In the event that the sanctions are lifted, LADWP may elect to modify the Operations Plan according to section V.D of the LTWA, which could result in higher pumping that currently indicated in the Operations Plan. Nonetheless, the Court-ordered restrictions on pumping and requirements for water spreading will remain in place for most of the 2006 runoff year, which should result in a general increase in water table elevations, similar to that which occurred in the 2005 runoff year.

Table 1. Depth to water (DTW) at indicator wells, April 3, 2006. All data are in feet. Baseline is the average of 1985, 1986, 1987 April water levels (as available). Negative change from April '05 indicates a declining water table; negative deviation from baseline indicates the water table is below baseline. 

Table 2. LADWP planned pumping for runoff-year 2006.

When LADWP inventoried Owens Valley vegetation from 1984 through 1987, water tables were generally high throughout the valley because of a series of wet years (1982-86) and relatively low groundwater pumping. The vegetation mapped during 1984 through 1987, which became the baseline for management under the Inyo/Los Angeles Water Agreement (LTWA), reflected the high water table prevalent at that time. Following the inventory, during the first three years of a six-year drought, LADWP pumped large amounts of groundwater: approximately 210,000 acre-feet (1987), 200,000 acre-feet (1988), and 155,000 acre-feet (1989). In response to the stress of groundwater pumping, water tables declined in most wellfields to substantially below the plant root zones, and as a result, native groundwater-dependent vegetation declined. 

In 1990, in recognition of the decline in water tables and vegetation, the Inyo/Los Angeles Standing Committee adopted the "Drought Recovery Policy," which requires that groundwater pumping be managed in a conservative manner to allow substantial recovery of water tables, soil moisture, and vegetation. Since then, LADWP's pumping has been lower than the pumping of the late-1980's. In response to both lower pumping and several high runoff years, water tables rose during the 1990's. 

Figures 1a-c illustrate the regional water table decline from baseline to 1991 due to pumping and drought, subsequent recovery to a peak in 1999, and a subsequent decline. Red areas indicate areas of groundwater dependent vegetation where the water table is below baseline; green areas are areas above baseline. The water table change maps shown in Figures 1a-c were produced by interpolating measurements made during April of each year in several hundred LADWP shallow groundwater monitoring wells. April measurements are used because there are more data for April than any other month, and usually (though not exclusively) April is the annual maximum water level at locations where seasonal cycles in evapotranspiration mediate water levels. Although the methods used to produce these maps leave some uncertainty in the water table depth at any particular location, they provide a useful regional picture of how the water table has varied since the mid-1980's. This information is used by the Water Department to relate changes in groundwater levels to changes groundwater dependent vegetation conditions. Figure 1a shows the difference between depth to water during the baseline period (1985-1987) and depth to water in 1991. Figure 1a represents the most depressed water levels since the baseline mapping period, and extensive areas below baseline due to drought and pumping are evident. Figure 1b shows the difference between baseline water levels and April 1999 levels. Figure 1b represents the highest water levels since the baseline mapping period. Figure 1c shows the difference between baseline levels and April 2005. Figure 1c represents recent water table conditions relative to baseline water levels. LADWP production wells are generally arrayed along the western edge of the valley floor (indicted in Figures 1a-c as black dots), because situating wells on the west edge of the valley places them upslope of the LA Aqueduct in favorable aquifer material.

Figure 1a. Baseline to 1991	Figure 1b. Baseline to 1999	Figure 1c. Baseline to 2005
Figure 1a-c. Depth to water deviation from baseline water levels (feet) in areas of groundwater dependent vegetation. Red indicates areas where the water table is below baseline. Figure 1a represents the deepest water tables during the drought of 1987-1991; 1b shows the how the water table recovered during the mid to late 1990's, but remained below baseline in some areas; Figure 1c shows how the water table has declined since its high point in 1b.

Areas of greatest water table decline in Figure 1a coincide with the locations of highest groundwater extraction along the western edge of the valley floor. In Figure 1b, the areas that remain the most below baseline are also near areas where the greatest amount of pumping has occurred. Comparison of Figures 1a and 1b shows that some areas recovered during the 1990's in response to high recharge and pumping managed under the Drought Recovery Policy; however, areas near centers of pumping remain below baseline levels. Since 1999, low recharge due to low runoff and a steady increase in pumping resulted in declining water levels until 2004; high runoff during 2005 resulted in some recovery, however many areas still remain below baseline (Figure 1c). 

In the Laws area, north of Bishop, the water table responds dramatically to pumping and recharge from the McNally canals (e.g., well T492 in Figure 2). Water tables declined to over forty feet below baseline between the mid-1980's and 1991 (Figure 1a). However, in 1999, several monitoring wells in the area were at baseline or above (Figure 1b). These high water table levels were the result of reduced pumping and recharge induced by LADWP's operation of the McNally canals and water spreading in the Laws area during the summer of 1998, resulting in the water table rising over 10 feet in some wells. Water levels in the Laws area declined since 1999 in response to pumping and low recharge. Water was again diverted from the Owens River into the McNally canals in 2005-2006, which provided much needed recharge in the Laws area and produced the rise in the water table apparent in well T492. 

Pumping on the Bishop Cone and recharge from the extensive network of surface water conveyances balance to stable water levels in west Bishop (e.g. well T387 in Figure 3). Water tables in the area between Bishop and Big Pine are relatively stable due to the absence of pumping stress (e.g. T479 in Figure 2). 

Figure 2. Water level hydrographs from a well in Laws (T492) and Bishop (T387). Water levels in Laws vary due to pumping and intermittent recharge from surface water spreading; water levels in Bishop are maintained relatively constant by the buffering effect of the network of surface water conveyances in the Bishop area.

The Big Pine wellfield has historically been subject to high levels of groundwater pumping by LADWP for the Fish Springs Fish Hatchery. Water table hydrographs near Big Pine show a typical pattern of a mid-1980's maximum, rapid decline in the late-1980's, gradual recovery to a level below the maximum level, a gradual decline since the late 1990's, and recovery during 2005 and 2006 (well T425 in Figure 3). 

The Taboose-Aberdeen wellfield has undergone intermittent stress when wells have been operated during droughts. Some of LADWP's highest capacity wells are located on the alluvial fan in the western part of this wellfield; when operated at full capacity these wells cause drawdown beneath phreatophytic vegetation on the valley floor. Water table hydrographs in this wellfield reflect large pumping induced fluctuations (e.g., well T421 in Figure 3). 

The Thibaut-Sawmill wellfield is subject to a constant pumping stress due to the Blackrock Fish Hatchery, plus additional stress from pumping for the LA Aqueduct. The water table in this wellfield shows large pumping-induced fluctuations where it is not buffered by surface water conveyances such as the LA Aqueduct and Blackrock Ditch. 

The Independence-Oak wellfield is subject to sustained pumping due to a large number of wells that are exempt from the on-off provisions of the LTWA. As a result, the water table in the Independence area is depressed below baseline.

Pumping in the Independence-Oak wellfield also impacts the northern portion of the Symmes-Shepherd wellfield. The amount of water pumped from the Symmes-Shepherd wellfield has varied greatly. After nearly a decade of relatively modest pumping, pumping in this wellfield increased in 2003, resulting in a pumping-induced decline in the water table. A recent pumping induced decline and subsequent recovery was observed in well T401 due to the operation of well W075 (Figure 4). Following the cessation of pumping from W075 in April 2005, T401 has partially recovered.

The Bairs-Georges wellfield has a small pumping capacity, and has been pumped little in the past fifteen years, resulting in water levels fluctuating around their baseline levels (e.g., well T398 in Figure 4). 

Pumping in the Lone Pine wellfield has primarily been for town supply, Diaz Lake, and an irrigation enhancement/mitigation project east of town. LADWP has constructed a new production well west of the town of Lone Pine on Lone Pine Creek to supply the LA Aqueduct. LADWP and the County are currently developing a process and plan for testing this well and implementing management to protect groundwater dependent natural resources and non-LADWP wells.