Methods
During summer 1999, ICWD's vegetation research assistants ran 1,457 transects in 90 vegetation parcels. The parcels visited were from south of Lone Pine to north of Bishop and were located in both wellfield areas (within the range of influence of LADWP groundwater pumps) and in areas not affected by pumping (control areas). ICWD's program of annually inventorying a subset of LADWP vegetation parcels began in 1991. The purpose of the program is to assess the current year's conditions and compare them with the Inyo/Los Angeles Water Agreement's "baseline" conditions as defined by LADWP's 1984-87 vegetation map.

The 1999 vegetation data were analyzed in conjunction with an ICWD-derived depth-to-water table (DTW) model prepared using the spring season water level data. The DTW estimates yielded by the model allow us to identify which Owens Valley areas experienced water table recovery to the level where it had been during the baseline years, 1985-1987 for hydrology. The average April DTW during the baseline years was used as the target for water table recovery. After reviewing all the data for 1998 (which followed a wet year on the valley floor) and 1999 (which followed a dry year) it appeared that, when the modeled water table for a given parcel reached average baseline depth or rose above that depth, there was a high probability that the cover of perennial species within the parcel reached or exceeded the measured baseline perennial cover amount. However, when water tables failed to rise to baseline, full perennial recovery rarely occurred.

Vegetation Parcel Categories
Of the 90 parcels monitored during 1999, 32 of them were determined to be controls (not directly or measurably affected by pumping). The remaining 58 were believed to have been affected by pumping since the baseline vegetation mapping period. Using water table and vegetation data, it was concluded that 30 of these parcels had yet to experience both water table and perennial vegetation recovery to baseline levels. Because of this, it was recommended that groundwater pumping within the area of these parcels continue to be subject to the provisions of the Drought Recovery Policy (DRP). The DRP calls for pumping to be managed in an environmentally conservative manner until there has been substantial recovery in soil moisture and water table conditions in areas of groundwater dependent vegetation that have been affected by pumping. The 30 DRP parcels occurred in all but the Lone Pine wellfield.

Twenty-two parcels had experienced water table and perennial cover levels equal to or exceeding baseline conditions. Thus, these parcels were determined to be free from the DRP (DRPfree). For these, it was recommended that management proceed according to conservative management guidelines being discussed by Inyo County and Los Angeles. These parcels occurred in all but the Bairs-Georges wellfield.

For six parcels, located in the Taboose- Aberdeen, Laws, and Independence wellfields, a determination regarding status according to the Drought Recovery Policy could not be made due to limits in available information, such as water table depth.

Results
Each year, I calculate the percent change in perennial cover relative to baseline. The calculated values are then averaged for the Control, DRP, and DRPfree parcel groups. Results for 1999 were used to update a graph of vegetation change maintained since 1991 (see Figure 3). I also look at the average percent cover of species by life form. A comparison of the percent cover of grasses, shrubs, weeds, and "others" (generally forbs) between baseline and 1999 is presented in Figure 4. General trends measured in the 1999 vegetation data were as follows:

Control Areas: Perennial cover exceeded baseline levels, despite low 1999 precipitation (Figure 3). The higher cover was the result of increases in grasses and/or shrubs, but neither species growth form showed universally higher cover in 1999 than baseline (Figure 4).

Parcels Still Subject to the DRP: Perennial cover was significantly below baseline levels (Figure 3). The low cover was primarily the result of significantly lower grass cover in 1999 compared with baseline (Figure 4).

Parcels Free from the DRP: Like the control parcels, perennial cover exceeded baseline (Figure 3). Increased shrub cover relative to baseline appears to have significantly contributed to the higher perennial cover than measured during the baseline period (Figure 4).

Vegetation Conditions by Wellfield
Below, water table trends and vegetation conditions are presented for each of the nine Owens Valley wellfields. The various wellfields are roughly defined, usually by the creeks that feed them (see Figure 1, "Owens Valley Wellfields"). They also vary in size and in the number and capacity of pumps within them. Previous studies have indicated that the effective rooting depth of Owens Valley groundwater dependent shrubs is 4 meters; therefore, in the following discussion, I note when water tables averaged below 4 meters. (Owens Valley grasses, however, typically root to about 2 meters.) The following discussion proceeds up the valley from south to north. The number following the wellfield name is the total acre-feet (AF) of water pumped from that wellfield during 1984-1998. (also see Figure 1).

Lone Pine (25,229 AF): Beginning in 1987, water tables dropped below baseline levels in this relatively small wellfield, apparently due to pumping and/or drought. Although they declined, average water tables did not drop beneath 4 meters for the four parcels that we monitor in the Lone Pine area. Water tables began to rise in 1993 and have been in the baseline range since about 1996. It appeared that pumping only affected one of the four parcels. Perennial cover in the affected parcel has generally increased since the end of the drought, and in 1999 it equaled baseline conditions. This parcel was categorized as DRPfree.

Bairs-Georges (17,826 AF): Pumping reached an all-time high in 1987, but since 1990 pumping has been greatly reduced. Pumping and the drought led to water tables falling below 4 meters in the one large parcel containing groundwater dependent Nevada saltbush scrub that we monitor in this wellfield. By 1991, perennial cover in this parcel was less than two-tenths of what it had been during baseline. However, when pumping was decreased in 1990, water tables began to climb. Although the water table rose above the baseline average in 1996 and has remained above baseline since then, recovery of perennial species has been slow. Perennial cover peaked in 1998 at about seven-tenths of baseline, but declined again in 1999 to less than half of baseline; therefore, in 1999 it was still categorized as DRP.

Figure 3.Changes in perennial plant cover relative to baseline for parcels monitored 1991-99. Control parcels are those presumed to have not been affected by pumping since 1985. There were 32 parcels in this group in 1999. Cover for the Control group has significantly exceeded baseline cover since 1995 (statistical significance is indicated by asterisks). Parcels in the DRP group are those in which either water tables or perennial plant cover or both have failed to recover to baseline levels. There were 30 parcels in this group in 1999. Average perennial cover for the DRP group has been significantly below baseline in all but the wettest years (1995 and 1998). Beginning in 1996, some parcels began to show water table and perennial cover improvement, so the DRPfree group was created for parcels in which both water tables and cover returned to or exceeded baseline. In 1999, there were 22 parcels in this group, and their perennial cover averaged significantly above baseline in 1998 and 1999. (Click on figure to enlarge).

Independence (145,303 AF): Pumping in this wellfield peaked in 1987 and has been reduced somewhat since then. Pumping occurs in this wellfield to supply the Independence Springfield Enhancement/Mitigation and other irrigation projects near Independence. We monitor five wellfield parcels near Independence. The two located closest to town, one to the north of town and one to the east, are still considered DRP. Neither parcel has experienced water table recovery to the baseline level. Perennial cover in both parcels exceeded baseline in the wet year, 1998, but cover declined in both parcels in 1999, with cover in the northern parcel falling below baseline levels. Baseline perennial cover recorded for the eastern parcel was unusually low and original field data cannot be located; therefore, it is hoped that the aerial photo study will help better describe baseline conditions for this particular parcel and a few others like it (see "Aerial Photo Study"). Two of the DRPfree parcels are located near Fort Independence, and although the area is hydrologically complex, they appear to have experienced both water table and perennial recovery to baseline level. The other DRPfree parcel straddles the aqueduct east of town, and it has also shown water table and perennial cover levels comparable to baseline.

Thibaut-Sawmill (253,293 AF): Approximately 13,000 AF per year are routinely pumped from this wellfield to supply the Blackrock Fish Hatchery. Each year during 1987-89, over 20,000 AF were pumped. The constant pumping seems to have lowered the water tables to the east of the Los Angeles Aqueduct (east of the pumps), but water tables beneath the two eastern parcels that we monitor were never below 4 meters. Perennial cover in these parcels typically hovers near baseline level or exceeds it. In the remainder of this wellfield, four meadow parcels are monitored. The water table had dropped well below baseline in three of these by 1989, and has not shown obvious recovery since then. 1999 perennial cover in these three DRP parcels was below baseline. The other parcel is categorized as DRPfree because its perennial cover never declined significantly below baseline, in recent years its cover has exceeded baseline and, although its water table showed decline since 1986, it never fell below 3 meters. (The water table in the latter parcel is probably buffered by ditches that flow through and around it.)

Figure 4.  Average percent cover by life form (grass, other, shrub, weed) in parcels monitored in 1999 as compared with LADWP baseline conditions (1984-87). Statistically significant changes in 1999, denoted by asterisks, consisted of either a decrease in grass cover relative to baseline in DRP parcels or an increase in shrub cover in the DRPfree parcels. (Click on figure to enlarge).

Taboose-Aberdeen (212,562 AF): This wellfield experienced high amounts of pumping in the early 1970s, then a high amount again (>40,000 AF) in both 1986 and 1987. In each year since 1990, pumping has been below 10,000 AF. In recent years, the bulk of pumping has been shifted from the pumps located west of Highway 395 to one large pump (Well 349) located in the northern part of the wellfield near Charlie's Butte. Water tables were lowered throughout this region by the drought and pumping. In the southernmost part of this wellfield, water tables reached baseline levels in 1998 in the three parcels that we monitor. All showed perennial cover above baseline in 1998 (the wet year) and were therefore categorized as DRPfree, but in 1999, perennial cover in one of the parcels dropped significantly below baseline. Throughout the central part of this wellfield, water tables have been rising, but have reached baseline level in only one of the four parcels monitored. That parcel was the only parcel with 1999 perennial cover equal to baseline (therefore categorized as DRPfree), the other three had perennial cover below baseline and remained categorized as DRP. In the northern part of the wellfield, vegetation monitoring efforts were increased in 1999, but not hydrological monitoring. This area is hydrologically complex, and there are not enough monitoring wells to sufficiently monitor the effects of Well 349. In 1999, data showed perennial cover approximately equal to baseline in three parcels and below baseline in two.

Big Pine (436,415 AF): Largely because of pumping to supply the Fish Springs Fish Hatchery, annual pumping in this wellfield has hovered around 25,000 AF. In 1987, pumping was almost 50,000 AF, and it remained high through 1989. We monitor four parcels south and east of town. All four were categorized as DRP because they showed water table declines below baseline and below 4 meters, and none experienced water table or perennial cover increases to baseline level as of 1999. Faring somewhat better are the two parcels we monitor north of town. One showed water table and perennial cover recovery to baseline by 1997 and no adverse trends have been observed since that time. It has been categorized as DRPfree. The other has been on the verge of water table and perennial cover recovery, but as of 1999 was still categorized as DRP.

Bishop (141,743 AF): Since 1987, pumping has averaged about 10,000 AF per year. Because of the many irrigated parcels in the Bishop area, there are only a limited number of parcels in the wellfield that were dominated by native groundwater dependent species. Some lowering of the water table occurred in areas southeast of town since 1987, but they were gradual. In 1999, the two southeastern groundwater dependent shrub-dominated parcels that we monitor had water tables very close to baseline, but in both perennial cover was below baseline level. Two meadow parcels monitored northeast of town showed water table declines during the 1987-92 drought. In one parcel the water table has recovered to baseline, in the other it is below baseline but still well within the grass root zone. 1999 perennial cover in both parcels exceeded baseline; therefore both were categorized as DRPfree.

Laws (237,078 AF): High amounts of pumping (35,000-40,000 AF) occurred in 1987-89, moderate amounts (9,000-18,000 AF) occurred in 1990-96, and relatively small amounts (<3,000 AF) occurred in 1997-99. Water tables dropped, usually below 4 meters, in all but one of the 15 parcels monitored in this wellfield; therefore, that one parcel, which is located adjacent to the Owens River south of the town of Laws, is classified as a Control. Although water tables were still depressed under most of these parcels in April 1998, by spring 1999, water tables rose abruptly, causing a return to baseline levels under 11 of the 14 parcels. The rise in water table was most likely due to a combination of 1998 surface spreading from the McNally canals, which was part of an effort to recharge the Laws aquifer with Owens River water, reduced pumping amounts, and, to a lesser extent, high natural recharge. Perennial cover in six parcels reached baseline in 1999 even though it was a dry year in terms of precipitation. Cover in the other eight parcels did not return to baseline levels in 1999; they are, therefore, still categorized as DRP. It is unknown how long water tables will remain at baseline levels in the Laws wellfield in the absence of flows through the McNally canals.

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