[env-trinity] Important report on groundwater-surfacewater interaction in the Central Valley.

[Felice Pace]

The Nature Conservancy has released an important *report on
groundwater-surfacewater interaction* in the Central Valley.



Summary:


Groundwater is intimately connected to surface water, which has profound
implications for sustainable water resource management. California has
historically overlooked this important interaction and as a consequence,
decisions about groundwater extractions have generally failed to address
the resulting impacts to aquatic ecosystems such as rivers, wetlands and
springs. This has contributed to a loss of approximately 95 percent of the
historical wetlands and river habitat in California’s Central Valley.



In February 2016, the Conservancy published a study that uses an integrated
hydrologic model to reconstruct the historical impacts of groundwater use
on groundwater levels and stream flow conditions in California’s Central
Valley. The results illustrate how rivers and streams that historically
gained surface flows from groundwater now lose surface flows to
groundwater. As a consequence, Central Valley rivers are now losing almost
1.5 billion gallons of water each day – that is enough water to supply 2.5
times the water needs for Los Angeles—than they did in the 1920s.  In
addition, groundwater aquifers contain 6.5 trillion gallons less water now
than they did at the start of the study period.



Groundwater sustainability agencies across the state will soon be required
to manage groundwater resources to avoid causing undesirable results to
groundwater levels and interconnected groundwater and surface water. These
groundwater levels and areas of interconnection support
groundwater-dependent ecosystems (GDEs). Therefore, an important first step
in sustainable groundwater management is to understand how groundwater
pumping impacts surface water and GDEs, both of which include streams.

A summary report and the full technical document are available here:


http://scienceforconservation.org/downloads/groundwater_and_stream_interaction
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