Hydrologic data used to develop summer (July 1 to September 30) meadow ground water balances were collected in 2012 and 2013. These were both exceptionally dry years that followed an unusually wet year in 2011. Records maintained by the DWR (California Data Exchange) indicate that total annual precipitation was roughly 65 to 90% of long-term averages in the Sierra Nevada during 2012 and 2013. May snowpack measurements ranged from 220% of long-term averages in 2011to 7% in 2013 (Table 6). Snowmelt is usually a major source of water in the Sierra Nevada, so the very low snowpacks in 2012 and 2013 indicate very limited water supply during those years. Groundwater balance results are therefore representative of two successive drought years, and may not represent meadow conditions during wetter years. Meadow groundwater balances for this project were developed based on hydrologic field data provided by the University of California Merced, including data collected by the Department of Water Resources, Balance Hydrologics, the U.S. Geological Survey, and the USDA Forest Service, Lake Tahoe Basin Management Unit (Table 7). Monitoring equipment (Table 8) was installed in summers of 2011 and 2012. Methods Conceptually, groundwater balances can be expressed as: ∑(GWI – GWO)= ∑(QO – QI) + ∑(ET – RF) - ∆SA (1) where: GWI is groundwater flowing into the meadow from surrounding bedrock aquifers; GWO is groundwater flowing out of the meadow into streams, downstream alluvial aquifers, or surrounding bedrock aquifers; ∑(GWI - GWo) is the seasonal sum of the difference between inflowing and outflowing groundwater ; ∑(QO – QI) is total volume of water represented by the difference between inflows and outflows during the monitoring period, as determined by periodic streamflow measurements and stage records; ∑(ET – RF) is the total volume of water represented by the difference between evapotranspiration and rainfall during the monitoring period; and ∆SA is the decrease in groundwater stored in meadow alluvium during the monitoring period (values will be negative for increases in storage) Groundwater balances were determined by measuring inflows and outflows of surface water, precipitation, changes in groundwater levels, and the specific yields of meadow aquifers. By convention, flows into the meadow aquifers were considered positive and
Hydrologic data used to develop summer (July 1 to September 30) meadow ground water balances were collected in 2012 and 2013. These were both exceptionally dry years that followed an unusually wet year in 2011. Records maintained by the DWR (California Data Exchange) indicate that total annual precipitation was roughly 65 to 90% of long-term averages in the Sierra Nevada during 2012 and 2013. May snowpack measurements ranged from 220% of long-term averages in 2011to 7% in 2013 (Table 6). Snowmelt is usually a major source of water in the Sierra Nevada, so the very low snowpacks in 2012 and 2013 indicate very limited water supply during those years. Groundwater balance results are therefore representative of two successive drought years, and may not represent meadow conditions during wetter years. Meadow groundwater balances for this project were developed based on hydrologic field data provided by the University of California Merced, including data collected by the Department of Water Resources, Balance Hydrologics, the U.S. Geological Survey, and the USDA Forest Service, Lake Tahoe Basin Management Unit (Table 7). Monitoring equipment (Table 8) was installed in summers of 2011 and 2012. Methods Conceptually, groundwater balances can be expressed as: ∑(GWI – GWO)= ∑(QO – QI) + ∑(ET – RF) - ∆SA (1) where: GWI is groundwater flowing into the meadow from surrounding bedrock aquifers; GWO is groundwater flowing out of the meadow into streams, downstream alluvial aquifers, or surrounding bedrock aquifers; ∑(GWI - GWo) is the seasonal sum of the difference between inflowing and outflowing groundwater ; ∑(QO – QI) is total volume of water represented by the difference between inflows and outflows during the monitoring period, as determined by periodic streamflow measurements and stage records; ∑(ET – RF) is the total volume of water represented by the difference between evapotranspiration and rainfall during the monitoring period; and ∆SA is the decrease in groundwater stored in meadow alluvium during the monitoring period (values will be negative for increases in storage) Groundwater balances were determined by measuring inflows and outflows of surface water, precipitation, changes in groundwater levels, and the specific yields of meadow aquifers. By convention, flows into the meadow aquifers were considered positive and
54_Meadow_GW_Final_report_June_2015.docx