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Groundwater study underway in Upper Delaware

A scientist in a kayak tows an electromagnetic-induction tool that measures changes in the sediment beneath the river within several meters of the riverbed. A seepage meter designed to measure the amount of water flowing across the riverbed is visible in the foreground.

September 4, 2012

UPPER DELAWARE RIVER — An effort to better understand the magnitude and significance of groundwater discharge (GWD) to the hydrology and ecology of the upper reaches of the Delaware River is underway.

United States Geological Survey (USGS) staff have been conducting research this summer to evaluate the influence of groundwater influx on fisheries and aquatic resources at three locations on the Upper Delaware River. USGS provides support to federal, state and local public entities for better management of natural resources based on unbiased scientific data, according to USGS research hydrologist Donald Rosenberry.

The study focuses on three river reaches near Frisbie Island, Hankins, NY and Callicoon, NY. Geophysical methods are being used to map the riverbed to determine areas where it is likely that groundwater is discharging to the surface.

The GWD to surface water exchange is an active component of stream ecosystems that influences whole-system processes that may play an essential role in supporting aquatic life, providing habitat stability and mitigating some effects of land use on water quality.

Identifying and protecting such areas could help to conserve aquatic populations. It has been hypothesized that groundwater influx or upwelling may be related to species presence and abundance. The study will help to determine the influence of groundwater on habitat during low-flow warm-water conditions.

Several variables have been measured at each location, such as bed sediment temperature, which helps determine thermal conditions in the substrate during warm-water periods. Fiber optic cables were deployed at each reach. A laser pulse sent down the cable allows measurement of the temperature along every meter increment, allowing for two-dimensional rendering of the distribution of GWD.

“Groundwater provides a constant cold temperature year-round, so it offers a thermal refuge for fish and other animals when the river gets warm,” said Rosenberry. “What we’re doing is looking at the spatial distribution of the groundwater discharge and then actually trying to quantify the discharge.

Just how much water is flowing into the river? And how much does that vary over time? Does it decrease in late summer, or is it a really large reservoir that’s fairly constant? What drives the research is the ecological impact. Anyone who’s interested in the fishery here would benefit from these results.”