This memo summarizes groundwater monitoring data at Van Norden meadow from 2014- 2017. Measured monitoring well depths were converted to groundwater elevations where possible to determine groundwater elevations through space and time in the meadow. Changes in depth to groundwater were plotted at each well, and groundwater elevations were plotted relative to topographic elevations at select well transects. Groundwater elevations were interpolated across the meadow to create groundwater elevation and depth to groundwater maps from June to September, 2015–2017. Any inconsistencies or errors in water depth measurements were identified and removed from the plots where possible. In particular, conversions of depth measurements to elevation were found to be problematic in some areas due to well replacements, potential settling of wells over time, and potential errors in recording of data. Some recommendations for future well monitoring efforts are provided to help reduce potential errors.

Groundwater elevations appear to be most strongly related to climate conditions (wet versus dry years) and the influence of localized water sources to the meadow. Dominant water sources include Castle Creek, South Yuba River and springs and seeps along the southwestern and northeastern edges of the meadow. The draining of the lake in October 24 2015 may have influenced groundwater elevations in the lowermost portion of the meadow in late summer 2016, but elevations in the majority of the meadow in 2016 were similar to those observed in 2015, despite continued drought and low precipitation levels. The highest groundwater elevations were observed in 2017 when wet climate and high snowpack kept the meadow saturated into July.

Additional research on the water sources to the meadow is needed, but based on the groundwater elevation maps, water inputs to the meadow from the tributaries (Castle Creek and South Yuba River) and the groundwater seeps along the southwestern edge and northeastern corner of the meadow serve to sustain the observed groundwater elevations through the summer. Water surface elevations resulting from the fixed base-level of the dam appear to influence groundwater elevations only in the lowermost portion of the meadow (transects G-I).