Common Misconceptions about Pumping and Vegetation
- In dry years water tables naturally decline — it can’t be blamed on groundwater pumping
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While it seems intuitive that water tables would decline in dry years, long term data and hydrological models suggest something different. According to Danskin (1998) water tables on the valley floor historically were relatively stable because the presence of numerous springs and seeps acted as a buffer which minimized water table fluctuations. Consider a bathtub. The water table (i.e. water in the tub) goes only as high as the walls of the tub. When the bathtub is full and more water is added, the water table doesn’t get any higher — the excess flows over the side. Similarly, when the water is turned off, the water table doesn’t immediately get lower — the water simply stops flowing over the side. The flow over the side is analogous to the flow of springs and seeps. In dry years, flows of springs and seeps were impacted before water tables were. In the 23 year period from 1936-1959 when DWP didn't pump, hydrographs show little water table fluctuation, and what fluctuation occurred was not correlated with runoff (i.e. dry years).
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On the other hand, now that high volumes of water have been pumped continuously since 1970, the bathtub is no longer full. Runoff and pumping are now both correlated with water tables.In the presence of high pumping, water tables are impacted by dry years, but this is actually a pumping impact, not a “natural” occurrence i.e. this did not occur before there was massive pumping in Owens Valley. See the graphs of valleywide pumping and runoff for an example showing data from a test well near Independence.
