A Multiscale Approach for Monitoring Groundwater Discharge to Headwater Streams by the U.S. Geological Survey Next Generation Water Observing System Program in the Neversink Reservoir Watershed, New York
Summary
Groundwater that drains to surface water via seeps and springs is generally referred to as “discharge.” Groundwater discharge is a primary component of stream base flow, or streamflow that occurs between storms, periods of snowmelt runoff, and periods of quick soil drainage. Streams that gain groundwater as they flow are common across glaciated regions such as the Delaware River Basin, and the hydrogeologic mechanisms that control exchanges of surface and groundwater are complex (Figure 1). Because of this complexity, groundwater discharge rates are rarely evenly distributed throughout stream networks, which may instead be dominated by locations of preferential discharge along riparian wetlands, streambanks, and the streambed (Briggs [...]
Summary
Groundwater that drains to surface water via seeps and springs is generally referred to as “discharge.” Groundwater discharge is a primary component of stream base flow, or streamflow that occurs between storms, periods of snowmelt runoff, and periods of quick soil drainage. Streams that gain groundwater as they flow are common across glaciated regions such as the Delaware River Basin, and the hydrogeologic mechanisms that control exchanges of surface and groundwater are complex (Figure 1). Because of this complexity, groundwater discharge rates are rarely evenly distributed throughout stream networks, which may instead be dominated by locations of preferential discharge along riparian wetlands, streambanks, and the streambed (Briggs and Hare, 2018). Streams may also lose flow to groundwater across parts of the network, causing patches of disconnection among stream channels at low flow. Stream and river ecosystems depend on preferential groundwater discharge to support summer low flows, control water temperature, and maintain water quality (Miller and others, 2016). Furthermore, groundwater discharge promotes stream channel flow connectivity during dry times, allowing fish and other organisms to move freely in search of food, shelter from predation, and thermal refuge. Groundwater discharge is a crucial component in many model-based forecasts of future water quality and habitat viability along headwater streams. However, U.S. Geological Survey (USGS) streamgage density is generally low in mountain headwater stream networks, and traditional streamflow measurements may not sufficiently capture groundwater discharge characteristics that are needed to improve predictions. By collecting new and varied types of data related to groundwater discharge at scales from streambank to watershed, the Next Generation Water Observing System (NGWOS) program (https://www.usgs.gov/mission-areas/water-resources/science/next-generation-water-observing-system-ngwos) supports model calibration, water resource-related predictions, and management decisions.
Multiscale Groundwater Monitoring in the Neversink Reservoir Watershed: The USGS is incorporating new and diverse types of groundwater discharge-related data into the development, calibration, and validation of predictive models (Barclay and others, 2022). These data include tracers of groundwater age and relative depths of groundwater flow paths that contribute to streamflow. Groundwater age, or transit time, reflects the varied flow paths that determine the water quality and persistence of stream base flow. In the Neversink Reservoir Watershed, a subbasin in the headwaters of the Delaware River Basin in the Catskill Mountains of New York State, groundwater discharge with a range of transit times includes both shallow and deep groundwater sources. Those varied depth flowpath sources may shift in dominance over the seasons and from wet to drought years (Burns and others, 1998). Shallow groundwater is sensitive to land use and climatic changes, including urban development, whereas deeper groundwater is typically more resilient, providing a buffer against stressors to sensitive stream ecosystems (Hare and others, 2021). Shallow groundwater also warms over summer months, and that heat is transferred to headwater streams via discharge (Figure 1), with negative potential effects on cold water habitat and thermal refuge for fish. Starting in 2019, the USGS, through its NGWOS program, developed a multiscale methods and technology testbed approach to monitoring groundwater discharge processes in the Neversink Reservoir watershed. As groundwater discharge dynamics are complex because of geographic differences in groundwater recharge (precipitation minus runoff, quickflow, and evapotranspiration), topography, and geology, the monitoring of discharge processes necessitates an innovative approach that includes emerging water tracing methods and enhanced local geologic mapping.
Chemical patterns and thermal regimes in headwaters, unlike many higher order streams, can show substantial spatial variability. Groundwater gains and losses exert a spatially discontinuous influence on streams that reflects, in part, the preferential nature of groundwater discharge as controlled by recharge, topography, and geology. Such variability in discharge patterns presents a challenge for USGS monitoring and interpretation. New thermal infrared field surveying techniques combined with localized point measurements allow discrete discharge locations such as streambank springs to be assessed in detail, but extrapolation of such measurements to the larger catchment can be difficult. Conversely, streamflow based methods of physically or chemically distinguishing base flow from rapid runoff in high-order streams can be applied to broad catchment areas, but spatial detail is lost.
As a first step in 2019, NGWOS updated and (or) activated streamgage sites at six locations in the headwater subbasin with sensors for water temperature and electrical conductivity, in addition to establishing two sites for intensive monitoring of groundwater discharge at existing streamgages along the West Branch Neversink River and mainstem Neversink River. These two sites were complemented at the watershed scale by establishing 51 multiyear water and air temperature monitoring stations across headwater streams with a range of sizes and elevations. Geophysical and drone data were also collected at the stream monitoring sites and paired with emerging analytical methods to refine the mapping of near-surface geology across the subbasin. This multiscale and multiparameter approach represents a transferable example of groundwater discharge monitoring to support the improvement of water quality, temperature, flow permanence, and habitat forecasts in headwater stream systems. Data for this project are publicly released through the Science Base pages linked here and through the National Water Information System database (U.S. Geological Survey, 2022), depending on data type.
Figure 1. This conceptual diagram of the system of surface and groundwater flow in the Neversink Reservoir watershed shows warmer shallow groundwater flow paths contributing to streams through surficial sediments in summer, while discharge of cooler, deeper bedrock groundwater reaches streams directly from bedrock discharges and indirectly from hillslope flow paths (modified from USGS Fact Sheet 2022-3077).
References Cited:
1. Barclay, J.R., Briggs, M.A., Moore, E.M., Starn, J.J., Hanson, A.E.H., and Helton, A.M., 2022, Where groundwater seeps—Evaluating modeled groundwater discharge patterns with thermal infrared surveys at the river-network scale: Advances in Water Resources, v. 160, article 104108, 14 p., accessed May 2022 at https://doi.org/10.1016/j.advwatres.2021.104108.
2. Briggs, M.A., and Hare, D.K., 2018, Explicit consideration of preferential groundwater discharges as surface water ecosystem control points: Hydrological Processes, v. 32, no. 15, p. 2435–2440, accessed April 2022 at https://doi.org/10.1002/hyp.13178.
3. Burns, D.A., Murdoch, P.S., Lawrence, G.B., and Michel, R.L., 1998, Effect of groundwater springs on NO3− concentrations during summer in Catskill Mountain streams: Water Resources Research, v. 34, no. 8, p. 1987–1996.
4. Eddy-Miller, C.A., Constantz, J., Wheeler, J.D., Caldwell, R.R., and Barlow, J.R.B., 2012, Demonstrating usefulness of real-time monitoring at streambank wells coupled with active streamgages— Pilot studies in Wyoming, Montana, and Mississippi: U.S. Geological Survey Fact Sheet 2012–3054, 6 p.
5. Hare, D.K., Helton, A.M., Johnson, Z.C., Lane, J.W., and Briggs, M.A., 2021, Continental-scale analysis of shallow and deep groundwater contributions to streams: Nature Communications, v. 12, article 1450, 10 p., accessed April 2022 at https://doi.org/10.1038/s41467-021-21651-0.
6. Miller, M.P., Buto, S.G., Susong, D.D., and Rumsey, C.A., 2016, The importance of base flow in sustaining surface water flowing the Upper Colorado River Basin: Water Resources Research, v. 52, no. 5, p. 3547–3562, accessed April 2022 at https://doi.org/10.1002/2015WR017963.
7. U.S. Geological Survey, 2022, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed [8/15/2022], at http://dx.doi.org/10.5066/F7P55KJN
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Briggs, M.A., Gazoorian, C.L., Doctor, D.H., and Burns, D.A., 2022, A multiscale approach for monitoring groundwater discharge to headwater streams by the U.S. Geological Survey Next Generation Water Observing System Program—An example from the Neversink Reservoir watershed, New York: U.S. Geological Survey Fact Sheet 2022–3077, 6 p., https://doi.org/10.3133/fs20223077.