Groundwater Conditions

Groundwater conditions in 2006 improved due to ample recharge from high runoff and water spreading, and restricted pumping due to court-ordered limits on LADWP’s 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 limitations on pumping to no 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. In December 2006, LADWP began releases from the LA Aqueduct intake into the Lower Owens River, but sanctions limiting pumping remain in place until the court decrees that all requirements have been met. LADWP’s Operations Plan for the 2006-2007 runoff year (April 2006 through March 2007) called for pumping to the court-ordered limit of 57,412 acre-feet. At the end of the 2006-2007 runoff-year, LADWP reported it pumped 58,630 acre-feet, and spread 17,565 acre-feet of water in Laws pursuant to the court order. In their May 5 2007 report to the Court, LADWP explained that 1,999 af were pumped to avert freezing of the LA Aqueduct from December 2006 through February 2007, thus, excluding freeze protection, their pumping for runoff-year 2006 was 56,636 af and below the Court’s limitation of 57,412 af. The court order recognizes pumping for emergencies such as freeze protection, however proper notification of the emergency was not given to the Court and parties, and LADWP’s exceedence of the court-ordered limit of 57,412 af is currently under discussion.

Runoff during the 2006-2007 runoff-year was above normal, forecasted to be 126% 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 and relatively low pumping as ordered by the Court resulted in a general rise in water tables throughout the Owens Valley. The thirty-four 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. Water levels increased in most indicator wells from April 2006 to April 2007; however, except in the Bairs-George and Laws wellfields, water levels generally remain below the levels of the mid-1980’s baseline vegetation mapping period. Of the thirty-four wells in Table 1, nine were above baseline in April 2007.

Water tables will decline in 2007-2008. Forecasted runoff for the Owens Valley runoff-year 2007 is 58% of normal runoff for the Owens Valley, so recharge will be less than during 2005 and 2006. Inyo County and LADWP have entered into a three-year interim management plan (IMP) which provides for specific sole-source uses in the Owens Valley and curtailing export pumping if it will cause groundwater levels to decline below their April 2007 levels. In anticipation of the end of the court sanctions, LADWP submitted a draft Operations Plan that calls for 61,950 af of pumping during runoff-year 2007 (Table 2), reflecting the intent of the IMP. The Operations Plan for runoff-year 2007 has not been finalized, and currently, the Court-ordered restrictions on pumping and requirements for water spreading remain in place. The pumping figures in Table 2 may be modified in the final Operations Plan.

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 vegetation 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 and 1b illustrate the decline of the water table from baseline to 1992 due to pumping and drought and subsequent recovery.  Red areas indicate areas where the water table is below baseline; green areas are areas above baseline.  LADWP production wells are generally arrayed along the western edge of the valley floor (indicted in figures 1a and 1b as blue circles), because this location situates the wells upslope of the LA Aqueduct in areas of high groundwater transmissivity.  Figures 1a and 1b were developed by interpolating depth to water measurements from several hundred shallow groundwater monitoring wells throughout the Owens Valley. These maps showing how depth to water has changed over time in areas of groundwater dependent vegetation are used by the Water Department to relate changes in groundwater levels to changes in vegetation conditions.  Figure 1a shows the difference between depth to water during the baseline period (1985-1987) and depth to water in areas of groundwater-dependent vegetation in 1992, the last of six consecutive dry years. Figure 1a represents the most depressed water levels since the baseline mapping period – Figure 1a shows extensive areas below baseline due to drought and pumping. Figure 1b shows the difference between baseline water levels and April 2006 levels.

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.

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 1992 (Figure 1a). However, as of April 2007, all indicator wells in Laws were above baseline (Figure 1b). These high water table levels were primarily the result of recharge induced by LADWP's diversion of water into the McNally canals and water spreading operations.

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 2). 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).

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 runoff-years 2005 and 2006 (e.g., 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 in 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 area 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).

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.

Groundwater levels have risen during the past two years, but in 2007 they are expected to decline due to low recharge.  The forecasted runoff for April 2007 through March 2008 is 58% of normal (four years have been drier since 1935, the driest of which was 1961, at 51% of normal).  Although high runoff and court-limited pumping allowed the water table to recover during the past two years, only the Laws and Bairs-Georges wellfields have indicator wells at or above baseline.  In an analysis conducted by LADWP for the 2007 Operations Plan, given the pumping shown in Table 2, it was predicted that wellfield average water levels in a subset of indicator wells would decline between 0.3 and 4.1 ft (Taboose-Aberdeen and Laws respectively), except for the Symmes-Shepherd wellfield, where water levels were predicted to rise 0.2 ft.