Inyo County Water Department monitors vegetation conditions on the floor of the Owens Valley each year to evaluate compliance with the Long-Term Water Agreement (LTWA). The primary goal of this monitoring is to detect changes in vegetation characteristics (i.e. live cover, species composition) from characteristics documented during the baseline vegetation mapping period (see Green Book, technical appendix to the LTWA). Baseline refers to a valley-wide survey (1984-1987) of vegetation live cover and species composition on over 2,000 LA-owned vegetation parcels in Owens Valley CA. The Agreement describes maintaining the irrigation to lands that were irrigated in the 1981/82 runoff year, and maintaining the vegetation characteristics of groundwater dependent vegetation communities in parcels recorded during baseline (1984-1987). The degree of groundwater-dependence for each parcel’s plant community was characterized for water management purposes and is central to the vegetation management goals and compliance monitoring. Five vegetation management types were classified based on parcel scale evapotranspiration estimates derived from species-level leaf porometer measurements scaled up to the parcel with baseline vegetation cover and composition data. Parcels in which ET exeeded annual precipitation were classified as irrigated lands (type E), riparian/marsh (type D) or groundwater dependent meadow or shrubland (Types C and B respectively). Parcels in which ET was equivalent to annual precipitation were classified as Type A:
- Irrigated lands in 1981/1982 runoff year(Type E)
- Riparian/marsh (Type D)
- Groundwater-dependent grassland/meadow (Type C)
- Groundwater-dependent shrubland (Type B)
- Precipitation-dependent plant communities (Type A).
Transition of any parcel to a groundwater and vegetation condition that precedes it alphabetically, or moving down the above list from 1-5 was articulated to be undesirable and contrary to the goals of the Agreement. Loss of water conveyance through a site or groundwater drawdown are causes of declines in soil water content, limiting actual evapotranspiration and net primary productivity. The depth to the water table constrains the spatial distribution of groundwater-dependent ecosystems (GDEs) in Owens Valley and is thus central to vegetation management under the LTWA.
Line point program
The line-point-intercept method (50-m transects) is used to provide estimates of live vegetation cover in parcels potentially influenced by groundwater extraction and these data are used to statistically compare cover and composition to baseline data each year. This reinventory method was adopted by the Inyo-LA technical group for compliance monitoring and has been ongoing since 1991.
Vegetation Compliance Map – based on field sampling
The Welch-Satterwaite t-test and weighted ANOVA with weights equal to the inverse of the variance are used to test differences in vegetation cover at the 0.05 level. This test is the first of the annual analysis for each monitored parcel. If the parcel is out of compliance due to declines in apparent cover, remote sensing is also evaluated to corroborate the apparent change. Spectral indices such as the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), normalized difference water index (NDWI) can be used for change detection of plant cover. Additionally spectral mixture analysis of Landsat TM satellite data provides fractional vegetation cover estimates (see remote sensing section).
Above – Color scheme represents 2014 compliance for perennial vegetation within parcels intersecting the zone-of-influence of pumping wells. Red parcels are those significantly below baseline, Yellow parcels are those where no significant change from baseline was declared. Green parcels are those above baseline. The attributes in the pop-out window, activated by clicking on individual parcels, are defined as: W_C (W = wellfield,C = control); Plant_Comm (Holland type vegetation communities); Acres; PCL (parcel code); compliance 2014 (1 = below baseline, 2 = no change, 3 = above baseline).
Reinventoried vegetation parcels below baseline
Parcels failing vegetation compliance in terms of perennial cover for several years in a row are shown below. Total perennial cover is displayed and its components are partitioned into perennial shrub, perennial grass and perennial non-gramminoid herbaceous cover.
Laws 35 (LAW035)
Laws 43 (LAW043)
Laws 52 (LAW052)
Laws 62 (LAW062)
Laws 65 (LAW065)
Laws 78 (LAW078)
Laws 82 (LAW082)
Big Pine Wellfield
Big Pine 162 (BGP162)
Blackrock 21 (BLK021)
Contact Zach Nelson with questions about this web page, vegetation monitoring/analyses and data requests.