Elucidating the effects of dam restoration on hydrologic patterns in streams and tributaries

Abstract:

Dam restoration or removal can result in a hydrogeological regime change, as the draining and refilling of reservoirs influences the regional water table position We evaluate how the refilling of Lake Perez, central Pennsylvania, influences surface water-groundwater interactions in the lakebed, within a stream that runs through the lakebed, and in a tributary upstream of the lake.

Lake Perez was drained in 2008 to address structural stability problems at the dam. Following restoration in the spring of 2014, the reservoir was partially refilled and drained. To quantify the controls of dam restoration on hydrologic patterns in the watershed, stream discharge and temperature were continuously monitored above and below the lake since September 2013. Groundwater levels and temperature were also monitored at two sites (total of 19 wells) within the lakebed and one site upstream of the reservoir (total of 8 wells). Results from streambed tracer tests are also available to help quantify lakebed exchange characteristics.

Data collected prior to and during these filling and drainage events provide insight into shallow surface flow and short-term drainage dynamics of a small watershed influenced by damming. Pre-dam restoration groundwater level data from Shavers Creek suggest the potential for groundwater discharge to the stream, while geochemical evidence indicates that low permeability legacy sediments impeded groundwater-stream water interactions. We demonstrate how the initial stages of refilling the lake have altered groundwater-surface water interactions within the lakebed and in local upstream tributaries.