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
Table 2: Erosion depths measured in meadows on NFS lands in the Sierra Nevada, Mean erosion depth range (m) Number of meadows Percentage of total Average area (ha) Average depth (m) 0.0 32 29 7.1 0.0 0.0 to 0.6 47 42 10.0 0.4 >0.6 32 29 16.7 1.1 Table 3: Summary of meadow hydrologic regimens from previous studies Reference Study Area Meadow condition Date of water table rise Period with water table @ land surface Period of overbank flow Period of no surface flow Annual water table drop (m) Wood, 1975 Yuba River, 2,225 m Unincised September April-June to late October 0.6 to 1.2 Hammersmark and others, 2008 Bear Creek, 1,010 m Restored Mid-July to late November 1.5 to 3.5 Loheide and Gorelick, 2007 Alkalai Flat, Last Chance watershed, 1,680 to 2,350 m Restored October April April None 1.5 Loheide and Gorelick, 2007 Big Flat, Last Chance watershed, 1,680 to 2,350 m Restored April April None 1.5 Loheide and Gorelick, 2007 Doyle Crossing Meadow, Last Chance watershed, 1,680 to 2,350 m tributary; nearby meadow incised 2 m October- November April None 1.4 Loheide and Gorelick, 2007 Coyote Flat, Last Chance watershed, 1,680 to 2,350 m 3-5 m February None None None 1.8 Hammersmark and others, 2008 Bear Creek, 1,010 m 2 m November None (2005) Late December (2006) None Mid-July to late November 1.0 to 2.0
Table 4: Previous studies of streamflow changes following restoration of Sierra Nevada meadows Reference Study area Bedrock geology Average annual precipitation (mm) Type of analysis Type of comparison Changes to streamflow following restoration/erosion Hammersmark and others, 2009 Bear Creek, Lassen County basalt 508 Model Before and after restoration Slight decrease in baseflow duration and volume within meadow, increase in baseflow volume downstream of meadow Ohara and others, 2013 Last Chance Creek, Plumas County granodiorite, pyroclastic flows,underlain by lacustrine clay 428 Model Before and after restoration Increased baseflow volumes Tague and others, 2008 Trout Creek, Lake Tahoe Basin Granodiorite and glacial deposits 500 to 1,000 streamflow data Before and after restoration Decreased winter flows, increased flows in spring and early summer Essaid and Hill, 2014 Sagehen Creek, Sierra County Pyroclastic flows, glacial deposits 850 Model Before and after erosion Decreased spring flows, increased late summer flows. Table 5: Physical characteristics of meadows monitored for summer groundwater balances, 2012 Meadow National Forest Condition Bedrock geology Watershed area (km2) Meadow area (ha) Average elevation (m) M14 Sierra Partially eroded Glaciated granite 1.7 5.1 2,342 M20 Sierra Partially eroded Glaciated granite 0.5 1.4 2,662 Round Stanislaus Eroded Glaciated granite 2.6 2 1,991 Wolfin Stanislaus Partially eroded Weathered granite 0.2 3 1,554 Faust Stanislaus Restored Metamorphic 0.4 2 1,646
Meadow Groundwater levels Specific yields Streamflow Precipitation M14 PSW USGS PSW PSW M20 PSW USGS PSW PSW Round UCM USGS UCM DWR Wolfin UCM USGS UCM DWR Faust Cabin UCM USGS UCM DWR Trout Creek UCM USGS USGS DWR Middle Perazzo BHI USGS BHI DWR Lower Perazzo BHI USGS BHI DWR Thompson DWR USGS DWR DWR Big Flat UCM USGS UCM DWR Table 8: Hydrologic monitoring installations for meadow groundwater balances Meadow Number of piezometers Depth range of piezometers (m below land surface) Number of wells Depth range of wells (m below land surface) Streamflow monitoring stations M14 13 0.9 to 1.4 0 n/a 1 M20 14 1.0 to 1.3 0 n/a 1 Round 2 1.9 to 2.7 7 2.3 to 4.0 2 Wolfin 4 1.8 to 2.9 10 0.8 to 3.1 1 Faust Cabin 2 1.7 to 2.7 7 2.5 to 3.3 1
Lower Perazzo 1,200 2,256 3,456 16,531 Eroded Thompson 1,500 488 1,988 0 Eroded Big Flat 4,350 616 4,966 0 Restored July 1 to September 30, 2013 Meadow Meadow storage change Groundwater inflow from bedrock Groundwater discharge to stream Meadow condition M14 820 1,848 2,668 3,207 Partially eroded M20 -120 704 584 3,108 Partially eroded Round 3,300 220 3,520 3,425 Eroded Wolfin 780 2,952 3,732 0 Partially eroded Faust Cabin 1,340 1,000 2,340 0 Restored Trout Creek 60 2,588 2,648 26,103 Restored Middle Perazzo -120 6,720 6,600 7,752 Restored Lower Perazzo 560 3,476 4,036 4,855 Eroded Thompson 990 680 1,670 0 Eroded Big Flat 4,020 10,480 14,500 0 Restored
Table 13: Maximum, minimum, and average groundwater levels in meters below land surface in meadows monitored for groundwater balances July 1 to September 30, 2012 Meadow Maximum Minimum Average Meadow condition M14 1.09 0.48 0.83 Partially eroded M20 0.64 0.55 0.6 Partially eroded Round 1.94 1.16 1.62 Eroded Wolfin 1.24 0.70 1.06 Partially eroded Faust Cabin 1.84 1.00 1.37 Restored Trout Creek 0.72 0.40 0.67 Restored Middle Perazzo 0.52 0.34 0.46 Restored Lower Perazzo 1.57 1.01 1.28 Eroded Thompson 1.71 1.22 1.53 Eroded Big Flat 2.40 1.00 1.81 Restored July 1 to September 30, 2013 Meadow Maximum Minimum Average Meadow condition M14 1.23 0.83 1.10 Partially eroded M20 0.58 0.49 0.52 Partially eroded
Round 2.10 1.18 1.76 Eroded Wolfin 1.81 1.14 1.58 Partially eroded Faust Cabin 1.98 1.28 1.69 Restored Trout Creek 0.83 0.48 0.69 Restored Middle Perazzo 0.89 0.53 0.65 Restored Lower Perazzo 1.44 1.17 1.37 Eroded Thompson 1.71 1.38 1.60 Eroded Big Flat 1.89 0.83 1.44 Restored Table 14: Vertical hydraulic gradients observated in paired wells and piezometers in water-balance meadows [positive gradients are vertically upward] July 1 to September 30, 2012 Meadow Well/Piezometer pair Maximum gradient Minimum gradient Average gradient Meadow condition Round P1/W2 0.65 -0.27 0.24 Eroded Round P2/W2 0.33 -0.08 0.10 Eroded Round P2/P1 -0.01 -0.05 -0.03 Eroded Wolfin P2/W4 0.07 0.01 0.03 Partially eroded Trout Creek W4/P3 0.03 -0.02 0.00 Restored Trout Creek W4/P4 0.02 0.00 0.00 Restored Trout Creek P3/P4 0.04 0.00 0.02 Restored Lower Perazzo W1/P1 -0.02 -0.04 -0.03 Eroded
Lower Perazzo W1/P2 0.24 0.02 0.14 Eroded Lower Perazzo P1/P2 0.21 0.05 0.11 Eroded Thompson TC-5/TVP6 0.00 -0.08 -0.03 Eroded Thompson TV-W1/TVP2 0.50 0.03 0.32 Eroded Big Flat P1/P2 0.17 0.01 0.13 Restored July 1 to September 30, 2013 Meadow Well/Piezometer pair Maximum gradient Minimum gradient Average gradient Meadow condition Round P1/W2 0.61 -0.39 0.18 Eroded Round P2/W2 0.31 -0.11 0.07 Eroded Round P2/P1 0.00 -0.05 -0.03 Eroded Wolfin P1/W4 -0.16 -1.00 -0.32 Partially eroded Wolfin P2/W4 -0.05 -0.42 -0.24 Partially eroded Wolfin P2/P1 0.05 -0.01 0.01 Partially eroded Trout Creek W4/P4 0.01 -0.02 0.00 Restored Trout Creek P3/P4 Restored Trout Creek W0/P2 0.01 -0.04 -0.01 Restored Lower Perazzo W1/P1 -0.03 -0.05 -0.04 Eroded Lower Perazzo W1/P2 0.17 0.02 0.08 Eroded Lower Perazzo P1/P2 0.11 0.07 0.09 Eroded Thompson TC-5/TVP6 0.01 -0.06 -0.03 Eroded Thompson TV-W1/TVP2 1.39 0.77 1.28 Eroded Big Flat W2/P2 0.31 0.11 0.24 Restored
Table 15: Surface inundation of water-balance meadows, October 1, 2012 to May 31, 2013 Meadow Percent of meadow area inundated Average number of days of inundation Average inundation depth, m Meadow condition Round 60 60 0.06 Eroded Wolfin 67 62 0.05 Partially eroded Faust Cabin 0 0 0 Restored Trout Creek 50 16 0.04 Restored Middle Perazzo 33 27 0.20 Restored Lower Perazzo 75 9 0.09 Eroded Thompson 25 37 0.15 Eroded Big Flat 100 4 0.04 Restored