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Vegetation information for Dispute Resolution
regarding operation of the McNally canals

prepared by
Sara J. Manning, Ph.D., Vegetation Scientist

October 11, 2000

 

The following memo/report addresses these items concerning vegetation conditions in Laws: (1) Description of where vegetation has decreased or changed from baseline due to pumping/operation of McNally canals; (2) Significance of decrease or change in vegetation; and (3) Linkage of vegetation decrease or change to change in water table depth.

The Inyo/Los Angeles Water Agreement mandates the Inyo County Water Department (ICWD) and Los Angeles Dept. of Water and Power (DWP) to manage groundwater pumping and surface water to avoid significant adverse changes in vegetation. Baseline vegetation conditions, against which subsequent changes are compared, were agreed to be the conditions mapped by DWP during a 1984 - 1987 vegetation inventory.

In 1991, a vegetation monitoring program outlined in the Green Book (Box I.C.1.a.ii.) commenced. The objective was to annually inventory a subset of DWP=s mid 1980s vegetation parcels. Vegetation conditions measured each year, particularly changes in total cover, changes in cover of perennial species, and changes in plant life form have been compared with conditions documented during the mid 1980s. Inventory methods and results are described below.

The vegetation monitoring data have documented significant declines in groundwater dependent vegetation in areas affected by water table drawdown due to groundwater pumping (wellfield areas). In contrast, control areas, where effects of groundwater pumping do not extend and where surface water management practices have not been altered, have shown no significant decline in groundwater dependent vegetation from 1991 through 1999. These results are presented in Figure 1. Two types of wellfield parcels have been identified: (1) DRP which are parcels still subject to management restrictions imposed by the Drought Recovery Policy because water levels and/or perennial vegetation cover have not recovered to average baseline levels, and (2) DRPfree which are parcels where the water table and perennial cover had returned to baseline level. These results are presented and discussed in annual reports produced by ICWD (Manning 1991; 1992; 1994; 1997; 1998; 1999; 2000a; 2000b; Inyo County Water Dept. staff 1999).

 

Figure 1. Average change in cover relative to baseline for parcels monitored 1991-1999. Parcels are grouped as control (not affected by pumping or changes in surface water management practices) and wellfield, which include the two categories: DRP (unrecovered wellfield parcels) and DRPfree (wellfield parcels exhibiting recovery of water table and perennial cover). Asterisks denote statistically significant changes from baseline (p < 0.05) using the t-test.

 

Several vegetation parcels in the Laws wellfield have been included in ICWD=s annual inventory program. Only one Laws parcel has been categorized as control.

Methods

Vegetation Data Collection

Every year since 1991, ICWD has run line point transects in selected vegetation parcels to assess annual vegetation conditions. Transects were run June through August. The protocol for running each transect has been fundamentally the same since 1991. Transect locations and orientations were randomly located within the parcel, a temporary 50m transect tape was stretched, and the top layer of live plant material was recorded at 0.5m intervals beginning at 0.5m and ending at 50m. Improvements to the 1991 protocol that have been incorporated over the years include the generation of random transect starting points using an ESRI Avenues script in ArcView and the use of Trimble GPS devices to record actual field locations of transects.

The subset of DWP vegetation parcels that has been selected by ICWD and DWP for monitoring includes a representative range of phreatophytic meadow and scrub assemblages in the Owens Valley. It is impossible for ICWD=s limited staff to monitor all the parcels; therefore, a list of candidate parcels was generated. Few changes have been made to the list since 1992, and there are 134 parcels currently on the list. Candidate parcels were selected based on the following criteria: parcel contained a permanent monitoring site; parcel was categorized as management type B or C or was classified as a community type in which phreatophytes were dominant; DWP baseline transect data existed for parcel; parcel was relatively small thus more likely to be a homogeneous plant assemblage; parcel location allowed us to sample a wide geographic area; and parcel was free from known major confounding factors such as regular irrigation or land surface alterations. Each year, the parcels were prioritized in roughly the same manner. All parcels identified as containing a permanent monitoring site have been inventoried each year. For the other parcels, an attempt has been made to annually collect data from parcels that met the above criteria. Parcels on the list that are typically given low priority include: (1) Rabbitbrush Scrub parcels that we have since learned to be abandoned agricultural fields that were recolonized by a rabbitbrush subspecies that may or may not be phreatophytic (these tend to be clustered in the Poleta Canyon area); (2) any Type A parcel which does not include a permanent monitoring site; and (3) parcels in which human activities have altered significant portions of the parcel. In some wet years, it has been impossible to run transects in some parcels due to flooding (these have included both wellfield and control parcels), but these parcels typically remain high priorities in subsequent years. A few new parcels have been added to the list in recent years in an attempt to address changes in groundwater pumping practices.

Eighteen of all the parcels monitored by ICWD using the line-point technique occur in the Laws wellfield. The parcels and key attributes are listed in Table 1 and locations are mapped in Figure 2. The Laws wellfield area contains approximately 146 parcels spanning about 10,343 acres. The 18 Laws parcels cover about 7% of the total wellfield, or 719 acres (Table 2). Large portions of the wellfield are covered by non-phreatophytic shrublands, abandoned cultivated lands that have never revegetated, and irrigated lands and other managed areas (Type E). Of the 3,737 acres of groundwater dependent meadow and shrublands, ICWD monitors nearly 20% (Table 2).

Depth to Water Table Estimates

An estimate of annual April depth to water (DTW) beneath each inventoried vegetation parcel was produced using kriging (Harrington and Howard 2000). In ArcView, annual DTW grid coverages were developed from spring (typically April) test well readings taken each year since 1985. Values in all grid cells within or intersecting the parcel boundaries were averaged to derive an estimate of DTW beneath the parcel. The parcel average DTW for each year is presented in Table 3.

For management purposes, the parcel DTW from April of 1985-1987 was averaged and set as the baseline DTW (Harrington and Howard 2000; Inyo County Water Dept. Staff 1999). This DTW approximately represents water table conditions at the time of the DWP baseline vegetation mapping, carried out 1984-1987. Baseline DTW has been used as a target to quantify the physical conditions under which perennial vegetation within a parcel has increased (see for example: Inyo County Water Dept. Staff 1999; Manning 1999; Manning 2000a; and Manning 2000b).

Table 1. Laws vegetation parcels that have been monitored by ICWD since 1991. Baseline plant community, total live cover, and dominant species (species accounting for > 30% of the live cover) are listed. Not all parcels have been inventoried in all years.

 

Table 2. Number of parcels, acreages, and percentages of the Laws wellfield by vegetation type, and a comparison of the 18 monitored parcels.

Veg Type	Description	Laws Wellfield			ICWD Monitored
		# parcels	acres	% of wf	# parcels	acres	% of type
A	abandoned agriculture	17	916	8.9	0	0	0
A	non-phreatophytic shrublands	20	3,578	34.6	0	0	0
A	phreatophytic shrublands	17	1,073	10.4	3	74	6.9
B	phreatophytic shrublands	7	307	3.0	1	35	11.4
A	alkali meadow	11	383	3.7	1	21	5.5
C	alkali meadow	36	1,765	17.1	9	380	21.5
C	shrubby alkali meadow	4	209	2.0	4	209	100.0
D	riparian forest	1	60	0.6	0	0	0
E	irrigated agriculture	20	1,497	14.5	0	0	0
E	intermittent ponds	5	75	0.7	0	0	0
E	rush/sedge meadow	8	480	4.6	0	0	0
	TOTAL	146	10,343		18	719	7.0

 

Precipitation Data

Total pre-growing season precipitation, October 1 through April 30, was summarized using data from the Bishop Airport (approximately four miles south of Laws) and from the two ICWD rain gauges located in the Laws wellfield. ICWD rain gauge 1 is located at permanent monitoring site L1 in the monitored parcel LAW063. Rain gauge 2 is located in the field immediately west of the Laws Railroad Museum.

Data Analysis

Perennial cover change was analyzed statistically to examine whether vegetation in Laws had changed significantly relative to baseline conditions as mapped by DWP in the mid 1980s. DWP baseline data were compared with ICWD line point transect data for each year in which transects were run in a given Laws parcel. The software program Statistica was used to perform t tests to test for the difference between DWP baseline perennial cover and perennial cover in a subsequent year. A one-tailed test was used to detect a difference not only in amount of change but also in direction (positive or negative) (Sokal and Rohlf 1987). A change was determined to be significant if the probability (p) that the means were different due to chance alone was < 0.05. Data for parcel LAW085, the parcel that contains the Laws 2 permanent monitoring site, were not analyzed statistically because original DWP baseline transect data are not available.

For years in which concurrent data existed, linear regression was performed to determine the degree to which perennial cover was correlated with DTW and pre-growing season precipitation. Significance (p < 0.05) of the correlation coefficients was determined using Statistica.

 

Table 3. Averaged DTW (in meters) beneath Laws parcels. These values were derived by averaging grid cells within or intersecting the boundary of the parcel. Kriging was based on test well data collected in April each year (see Harrington and Howard 2000).

 

 

 

 

 

 

 

 

 

 

 

Results

Precipitation

Pre-growing season precipitation for the October 1 through April 30 of the year noted are summarized for the Bishop Airport in Figure 3. The first full water year of ICWD rain gauge monitoring was 1992-1993. Pre-growing season precipitation data for the two Laws rain gauges and the same season=s data for the Bishop airport appear in Figure 4.

At the Bishop Airport, eight of the 19 seasons shown had precipitation amounts equal to or greater than the long term average (1982, 1983, 1986, 1988, 1993, 1995, 1996, and 1998) (Figure 3). Precipitation in Laws was typically slightly less than at Bishop Airport, with gauge 1 typically showing the least amount of precipitation (Figure 4). In 1993 and 1998, precipitation at the airport was greater than in Laws. In 1997, Laws precipitation exceeded that of the airport.

 

Figure 3. Total pre-growing season precipitation, in inches, for 1982 through 2000 as measured at the Bishop Airport. Data from NCDC (1982-2000). The long-term average for the airport is 4.25 in.

 

Figure 4. Comparison of pre-growing season precipitation totals for Bishop Airport, Laws rain gauge 1 and Laws rain gauge 2. Data are presented in Table 4.

Table 4. Pre-growing season (October 1 through April 30) precipitation in inches for Bishop Airport and Laws rain gauges 1 and 2.

GAUGE	1993	1994	1995	1996	1997	1998	1999	2000
Bishop	7.59	2.23	6.36	4.53	2.90	7.57	2.14	2.04
Laws RG1	5.92	2.18	6.10	3.99	3.85	4.55	1.19	0.95
Laws RG2	6.21	2.20	6.64	4.22	4.02	5.48	1.77	1.46

 

Statistical Analysis of Vegetation Change

Many Laws parcels showed perennial cover significantly lower than baseline in most years (Table 5).

Parcel LAW122, which has been classified as a control site because it appears to have been minimally affected by groundwater pumping and surface water operations in Laws (Manning 1999), showed perennial cover significantly less than baseline in 1994 when its cover was 43% as compared with baseline cover of 59.6%. LAW122 showed perennial cover equal to or significantly greater than baseline in all other years it was monitored.

All other parcels had had the water table beneath them lowered due to pumping and/or changes in surface water operations (Inyo County Water Dept. Staff 1999; Manning 1999). Of these, three parcels (LAW107, LAW110, and LAW120) occasionally showed perennial cover significantly greater than baseline in or after 1998. The rest of the parcels monitored showed perennial cover either indistinguishable from or significantly less than baseline.

 

Table 5. Average perennial cover in all Laws parcels monitored by Inyo County Water Dept. (INY) from 1991 through 2000. Baseline perennial cover is listed under DWP. t tests were performed and significant differences from baseline are denoted with an asterisk. Results that are significantly lower than baseline are shaded; results that are significantly greater than baseline appear in bold.

% COVER, PERENNIALS ONLY
Parcel	DWP	INY91	INY92	INY93	INY94	INY95	INY96	INY97	INY98	INY99	INY00
LAW030	23.08	12.00*						16.25*	21.16	27.25	32.07
LAW040	14.67		9.17*				11.75	9.25	16.75	13.83	9.43
LAW052	27.83	4.16*						4.91*	7.75*	8.83*	4.50*
LAW062	21.44		1.50*			3.00*	5.50*	9.71*	11.21*	18.07	13.50*
LAW063	11.50	4.54*	2.44*	5.31*	5.50*	7.92	8.75	11.37	6.31*	15.13	9.88
LAW065	9.67		1.75*	4.08*	3.58*	7.58	6.00	5.28*	5.07*	7.92	7.00
LAW076	6.50		2.80*								9.79
LAW078	51.71		7.50*					20.21*	24.57*	44.50	55.41
LAW082	16.50	5.50*						2.58*	5.83*	4.33*	5.14*
LAW085 #	30.64	5.11	5.79	17.92	5.50	18.75	13.79	9.78	10.87	12.50	19.00
LAW104	9.00		5.58*
LAW107	46.86		22.08*	13.08*	18.08*	26.25*	24.66*	34.83	38.00	62.25*	61.71*
LAW109	18.50	3.54*
LAW110	35.17	11.33*	10.89*	20.64*	29.14		40.88	38.81		59.41*	63.71*
LAW112	20.33		16.33			14.50*	20.33	13.83*	20.50	13.67*	11.57*
LAW120	25.92	14.18*	12.58*	19.17*	11.58*	29.08	28.83	29.50	41.66*	33.17	41.29*
LAW122	59.56		58.92	58.08	43.00*	57.58	68.25*	64.33	65.58	88.25*	56.29
LAW137	20.42		8.63*			15.25	12.43*	16.00	18.36	21.86	16.50

# = DWP baseline data not available, so statistical analyses not performed.

 

Description of Water Table and Vegetation Conditions for 2000 Monitored Parcels

Graphs of water table and perennial cover conditions were produced for each parcel in which line point transects were run in 2000. Trends in each parcel are discussed below. In the corresponding graphs, the 2m and 4m depths are distinguished. These depths correspond to the management rooting depths of the phreatophytic native grasses and phreatophytic shrubs, respectively. Drops below 4m could be viewed as changes in which the water table falls below the root zone of phreatophytes. The following parcel by parcel description first discusses the parcel that appears to mimic a control parcel (LAW122), and the rest of the parcels are discussed in numerical order.

LAW122 (Figure 5): This parcel parallels the Owens River south of the Laws Museum area. The water table beneath this parcel showed a relatively minor decline during the drought. From 1985 through 1989, then from 1995 - 2000 the water table averaged above 4m. Although the parcel is located within the potential effects of pumping from wells in the Laws wellfield, it appears that those effects may be buffered in this parcel due to its proximity to the river. Vegetation cover was high during the baseline period (60%). In all years but 1994, perennial cover was indistinguishable from or significantly greater than baseline. In 1994, when average water table depth had been below 4m for five years, perennial cover dropped to 43%, a significant decline from baseline.

LAW030 (Figure 6): Water from Coldwater Creek has flowed into this parcel in recent years. Therefore, at least in portions of the parcel, conditions have been wetter than indicated by the DTW information, which continue to show the water table below baseline (6.74m). Perennial cover had been significantly below baseline in 1991 and 1997, but since 1998 it has not been significantly different from baseline. A portion of this parcel is being considered for permanent irrigation (Type E status) by DWP.

LAW040 (Figure 7): DTW beneath this parcel was about 4m in 1985, but in all years since then, it has been below 4m. After water spreading in 1998, the water table briefly rose above the 1985-1987 baseline average depth (5.94m). Between 1999 and 2000, the water table dropped 2m. Perennial cover in this parcel typically averages below baseline, but has not been statistically significantly lower since 1996. In wet years, this parcel has high cover of the introduced weeds: Salsola tragus (tumbleweed) and Bassia hyssopifolia (bassia).

LAW052 (Figure 8): From 1988 to 1998, the water table was below the 1985-1987 baseline average depth of 2.92m and also below 4m. In 1999, the water table briefly reached the baseline average depth, but by 2000, it had dropped over 2m and thus fell below 4m. Perennial cover has been significantly below baseline in all years this parcel has been monitored, including 1999 and 2000. Grass cover has dropped substantially and tumbleweed is dominant in wet years.

LAW062 (Figure 9): From 1988 to 1998, the water table was below baseline average (3.92m) and below 4m. In 1999, the water table briefly returned to baseline level, but from 1999 to 2000, it dropped about 2m, thus again falling below 4m. Perennial cover in all monitored years except 1999 but including 2000 was significantly below baseline. This parcel is prone to dense outbreaks of tumbleweed and bassia.

LAW063 (Figure 10): From 1988 to 1998, the water table was below baseline average (4.06m). This parcel borders the Lower McNally Canal and is thus subirrigated when the canal is run. From 1991 through 1994 and in 1998, perennial cover in this parcel was significantly lower than baseline. In other years (1995-1997 and 1999-2000) perennial cover was not significantly different from baseline. Between April 1998 and April 1999 the water table rose to baseline water table level due to water in the McNally canals. Correlated with this rise and despite low precipitation in 1999, perennial cover increased from significantly less than baseline to statistically indistinguishable from baseline. Both the water table and the average perennial cover dropped from 1999 to 2000, but the drop in cover was not statistically significant. The parcel is prone to weeds, especially bassia.

LAW065 (Figure 11): After averaging below baseline (3.14m) and below 4m since 1988, the water table rose abruptly to 3.91m in response to water in the McNally canals between 1998 and 1999 and thus approached but did not meet the baseline level. Perennial cover was significantly below baseline 1992-1994 and 1997-1998. In all other years (1995-1996 and 1999-2000) it was statistically indistinguishable from baseline. The parcel is prone to weeds in wet years.

LAW076 (Figure 12): This parcel was inventoried by ICWD in 1992 and 2000 only. It was mapped by DWP as a Type A parcel composed of Greasewood Scrub. Because greasewood is a phreatophyte, ICWD opted to monitor the parcel in 2000 despite its Type A status. The water table under this parcel had shown a decline below baseline average (2.73m) and below 4m from 1988-1998. Perennial cover, when monitored in 1992, was significantly less than baseline. The water table returned to 2.8m by spring 1999, then dropped 1.2m to 4m by April 2000. Perennial cover in 2000 was statistically indistinguishable from baseline level cover.

LAW078 (Figure 13): The water table was below baseline (2.28m) and below 4m from 1988 to 1998, then reached baseline by spring 1999. In 1992, 1997, and 1998 perennial cover was significantly below baseline. However, corresponding with the increase in water table to baseline, and in spite of 1999 being a dry year, perennial cover increased and was not significantly different from baseline in 1999. The water table dropped about 1m to 3.4m from 1999 to 2000, but this drop did not fall below 4m and appeared to not affect perennial cover. Bassia proliferates in this parcel in wet years.

LAW082 (Figure 14): The water table beneath this parcel was below baseline (3.95m) and below 4m from 1988 to 1998. Perennial cover was significantly below baseline in all years this parcel was monitored (1991, 1997-2000). Although the water table rose above baseline between April 1998 and spring 1999, perennial cover remained significantly below baseline in 1999. Between 1999 and 2000, the water table dropped below 4m and 2000 perennial cover was also significantly less than baseline. Despite being mapped by DWP as a rabbitbrush meadow, grass cover as recorded with transects has been extremely low. Tumbleweeds proliferate in wet years.

LAW085 (Figure 15): The water table beneath this parcel was below baseline (4.21m) from 1988 to 1998. In 1999, the water table rose to 3.71m, then it declined to 4.36m in 2000. Perennial cover was below baseline in all years this parcel was monitored (1991 through 2000). Because original transect data for this parcel do not exist, statistics were not used to analyze the perennial cover decreases.

LAW107 (Figure 16): Baseline average DTW for this parcel was 2m, but the water table was at or below 4m from 1988 through 1995. From 1996 through 2000, the water table was above 4m, and in spring 1999, it exceeded baseline average. Perennial cover was significantly lower than baseline 1992-1996, was indistinguishable from baseline in 1997 and 1998, and exceeded baseline in 1999 and 2000, after the water table reached baseline average depth in 1999. By April 2000, the water table had dropped 0.65m to 2.47m, but 2000 perennial cover continued to exceed baseline. Thus, perennial cover exceeded baseline for two consecutive years in which precipitation was below normal, but in which the water table had returned to approximately baseline and not dropped below 4m. High cover of bassia had been recorded in this parcel in wet years.

LAW110 (Figure 17): The DTW data for this parcel show the water table dropped below 4m and remained below 4m until 1996. In spring 1999, the water table approached but did not quite reach the baseline average depth (2.8m); however, in both 1999 and 2000, it remained above 4m. Perennial cover was significantly below baseline 1991-1993. In 1994, 1996, and 1997, it was statistically indistinguishable from baseline. In 1999 and 2000, it was significantly greater than baseline, despite both years having below average precipitation. Transects were not run in this parcel in either 1995 or 1998 due to flooded conditions. Bassia proliferates in wet years.

LAW112 (Figure 18): The water table under this parcel was below baseline (3.8m) and 4m from 1988 through 1998. In 1999, it exceeded 4m, but not its baseline level. Perennial cover was statistically indistinguishable from baseline in 1992, 1996, and 1998. But, in 1995, 1997, 1999 and 2000, it was significantly below baseline. (Note: ICWD has reviewed the older transect data and found that in 1996 field assistants were actually out of the parcel, and well to the west it, according to GPS positions for six transects. These six transects have been removed from the calculation of perennial cover and the perennial cover shown for 1996 is calculated from the other six transects that were within the parcel boundary.)

LAW120 (Figure 19): According to the DTW data, the water table has been below baseline average (4.17m) since 1988 (through 2000). Because the baseline DTW was below 4m, the water table has not been above 4m in April of any year since 1987. Perennial cover was significantly below baseline from 1991-1994, not significantly different from baseline during 1995-1997 and in 1999, and significantly greater than baseline in 1998 and 2000. There is evidence there has been intermittent water spreading in this parcel (S. Manning, pers. obs. in early June 1998), so cover changes in this parcel may have been affected by this practice. Besides addition of supplementary surface water, the capillary fringe above the water table has been shown to be very thick at the permanent monitoring site (L3) located in this parcel, so plants may have adequate access to water despite the water table being below 4m. Capillarity (or spreading) may account for the 2000 perennial cover being significantly greater than baseline despite the low water table and below average precipitation. This parcel should be the subject of further investigation of past water spreading practices.

LAW137 (Figure 20): The baseline DTW beneath this parcel was below 4m, and DTW data as of April 2000 do not show that the water table has risen to baseline. Perennial cover was less than baseline in 1992 and 1996 and statistically indistinguishable from baseline in all other years (1995, 1997-2000).

To summarize, Laws vegetation parcels can be separated into three categories:

(1) those under which the water table left the root zone in the late 1980s and showed no evidence (based on DTW and 2000 perennial cover conditions) of re-entering it as of April 2000: LAW030, LAW040, LAW052, LAW082, LAW085, LAW112;

(2) those under which the water table left the root zone in the late 1980s and showed evidence that it may have barely re-entered it as of April 2000: LAW062, LAW065, LAW137; and

(3) those under which the water table left the root zone in the late 1980s but returned to the root zone prior to 2000 as evidenced by 2000 DTW and vegetation response: LAW063, LAW076, LAW078, LAW107, LAW110, LAW120, LAW122.

Correlation Between Change in Water Table Depth and Change in Perennial Cover

Map Analysis. Maps showing the DTW according to the kriging results were generated for 1987 (baseline year for Laws), 1992 (an example of a year with low water tables), 1999 (the year in which water tables rose abruptly due to water spreading from the McNally canals, and 2000 (one year following the water spreading). Corresponding to the DTW maps, Laws area maps showing the vegetation parcels inventoried in 1992, 1999, and 2000 and the relation of perennial cover to baseline in each parcel in each year were also generated.

The maps show the following:

Figure 21. DEPTH TO WATER IN 1987. During 1987 (and for two years prior to 1987, but map not shown), water tables were within plant root zones beneath most of the parcels later inventoried by ICWD. Water tables beneath the high cover alkali meadow parcels (LAW078, LAW107, LAW110, LAW122) were well within the grass root zone, and at least portions of all parcels except LAW030 and LAW040 showed water table levels within the shrub root zone.

Figure 22a. DEPTH TO WATER IN 1992. Water tables declined in 1988 and remained low for the next several years. This kriged ArcView grid showing water table depth in 1992 is presented as an example. The water level beneath all parcels had shown a decline and all but parts of LAW110 and LAW122 had declined beneath 4.7m.

Figure 22b. 1992 PERENNIAL COVER RELATIVE TO BASELINE. Corresponding to the decline in water levels, perennial cover in 10 of the 12 parcels inventoried in 1992 showed a significant decline from baseline levels, as indicated by the red color.

Figure 23a. DEPTH TO WATER IN 1999. Water levels as of spring 1999 reached their highest levels since 1987. The rise in water table is associated with supplying the McNally canals with Owens River water beginning in late spring of 1998 and spreading the water out of the canals during the summer and fall of 1998. By spring 1999, water table levels averaged equal to or above the 1985-1987 baseline average DTW for 9 of the 15 parcels monitored in 1999.

Figure 23b. 1999 PERENNIAL COVER RELATIVE TO BASELINE. Despite very low total precipitation prior to the 1999 growing season, perennial cover in several Laws parcels showed an increase equal to or greater than baseline (shown in yellow and green). This increase in cover occurred in conjunction with an abrupt increase in water table beneath all the monitored parcels from 1998 to 1999 (see Figure 21a). By summer 1999, only four parcels remained significantly below baseline cover levels.

Figure 24a. DEPTH TO WATER 2000. Relative to 1999 (Figure 21a), water tables had dropped throughout the Laws wellfield area by April 2000. This drop is associated with the absence of recharge vi