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Created Ponds as Indicators of Restored Sierra Nevada Meadow Hydrology
AuthorMcMahon, Adam Michael
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Stream degradation has led to extensive restoration of wet-meadow systems in the Sierra Nevada. Pond-and-plug restoration reconnects the stream with its historic floodplain and dams eroded gullies, which then fill with water, creating a series of ponds. Elevated groundwater tables and stream flooding return natural function and wet-meadow vegetation. Little research has examined the impacts of these anthropogenic ponds on the hydrology of meadows, and ponds may represent a potential loss in the water budget via evaporation. In addition, ponds provide an opportunity to study proposed hydrologic models of groundwater flow in meadows. Meadows may act as a "sponge, valve, or drain" by absorbing and then releasing groundwater through the season, by recharging the meadow with groundwater through springs, or by allowing percolation of groundwater to deep aquifers. We measured groundwater and pond surface elevations and ponds' areas along with above and below meadow stream flow through a summer following a winter with 30% less snowpack than average. While total meadow pond evaporation was significant, it accounted for less than 10% of total meadow ET. Individual pond evaporation accounted for 40-70% of measured pond declines with the remaining decline attributed to seepage to meadow groundwater, as no surface outflow occurred in selected study ponds. Pond and piezometer decline were highly correlated, with R-squared values generally > 0.9. Spatial and temporal variations in pond elevations indicate possible areas with and without groundwater inflow into meadows. Groundwater storage, inflow, and outflow was evident, but most meadows exhibit heterogeneity in groundwater flow. Prior to historic incision, some meadows may have had only seasonal outflow. The periods and amounts of augmented base flow from restored meadows vary among project areas.