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. '::-A ;' . . 00247 'f IMPACTS ON VEGETATION FROM GROUNDWATER PUMPING, 2001 Evaluation SAN LUIS VALLEY PROJECT, CLOSED BASIN DIVISION EXECUTIVE SUMMARY AgI'o Engineering, Inc. (Agro) has evaluated and monitored vegetation changes in the San Luis Valley Project, Closed Basin Division (Project) encompassing a time period from before Project pumping began (1984-85) until the present. This evaluation has utilized a combination of two approaches; ground sampling and remote sensing. Ground sampling of both biomass and vegetative cover at key locations has been essential in identifying and assigning values to the changes that are seen on the micro- scale at specific locations. While transect monitoring provides a quantitative record of these changes, photographic monitoring provides a qualitative, visual record of these changes. Ground sampling also makes it possible to quantify the changes that are observed on the macro-scale for the entire project area using remote sensing techniques and verifies the causes for change that are detected using remote sensing techniques. Remote sensing has utilized LANDSAT satellite data to compute vegetation indices and semi-quantitatively monitor vegetation changes (both biomass and percent cover) over the wider project area. Precipitation for 2001 was approximately 11 inches. This was the year with the most precipitation ever studied and was considerably higher than 1984 (6% inches), 1985 (9 inches) and 2000 (4 inches). In 2001, the runoff was 96% of normal due to a snow pack that was 99% of average. The runoff in 2001 peaked in May rather than June. The higher precipitation and runoff resulted in more exposed water area than in 2000. In 2001, water covered a total of 2,515 acres, representing more than twice the acreage of water present in 2000. This water level was not as high as might have been expected from the abnormally high precipitation and average runoff, but indicates that a large amount of the available water supply went to replenish the low antecedent soil moisture left after a vei'Y di'Y year in 2000 and was also utilized by the vegetation within the project. Most of the water within the pmject ai'ea in 2001 was shallow and palusti'ine. Vegetation within the Pmject area is largely driven by precipitation. The higher than normal precipitation in 2001 was reflected in the vegetation. The mean project NDVI was up 24% from the Pre-project baseline. Of the seven areas where NDVI decreases from the baseline have been previously documented, Areas D, E and G are visible in 2001. Most of these declines are a function of irrigation management on neighboring ranches, The areas where pumping may be affecting vegetation still include Area A and Area E. In 2001, Area A showed very little area with a decrease in vegetation and the majority of the area was positively effected by the higher than normal precipitation. Area E shows a small area of decrease in vegetation in the upper portion of Stage 4. Most of the effected area along the streams is related to irrigation management on the