Combined use of thermal methods and seepage meters to efficiently locate, quantify, and monitor focused groundwater discharge to a sand‐bed stream

Abstract

Quantifying flow of groundwater through streambeds often is difficult due to the complexity of aquifer‐scale heterogeneity combined with local‐scale hyporheic exchange. We used fiber‐optic distributed temperature sensing (FO‐DTS), seepage meters, and vertical temperature profiling to locate, quantify, and monitor areas of focused groundwater discharge in a geomorphically simple sand‐bed stream. This combined approach allowed us to rapidly focus efforts at locations where prodigious amounts of groundwater discharged to the Quashnet River on Cape Cod, Massachusetts, northeastern USA. FO‐DTS detected numerous anomalously cold reaches one to several m long that persisted over two summers. Seepage meters positioned upstream, within, and downstream of 7 anomalously cold reaches indicated that rapid groundwater discharge occurred precisely where the bed was cold; median upward seepage was nearly 5 times faster than seepage measured in streambed areas not identified as cold. Vertical temperature profilers deployed next to 8 seepage meters provided diurnal‐signal‐based seepage estimates that compared remarkably well with seepage‐meter values. Regression slope and R2 values both were near 1 for seepage ranging from 0.05 to 3.0 m d−1. Temperature‐based seepage model accuracy was improved with thermal diffusivity determined locally from diurnal signals. Similar calculations provided values for streambed sediment scour and deposition at subdaily resolution. Seepage was strongly heterogeneous even along a sand‐bed river that flows over a relatively uniform sand and fine‐gravel aquifer. FO‐DTS was an efficient method for detecting areas of rapid groundwater discharge, even in a strongly gaining river, that can then be quantified over time with inexpensive streambed thermal methods.

Influence of groundwater on distribution of dwarf wedgemussels (<i>Alasmidonta heterodon</i>) in the upper reaches of the Delaware River, northeastern USA

“…Because shallow hyporheic flow paths in coarse-grained sediments are primarily horizontal and temperature-profile methods assume primarily vertical flow, it should not be surprising that data might be difficult to interpret. Other studies in finer sandbed streams have obtained conclusive and consistent results using these methods (Rosenberry et al, 2016;Hatch et al, 2010). Excluding the questionable temperature-based data in Table 2, when all other location-specific data are aggregated over an entire M or N reach, the conclusion is consistent; greater groundwater discharge occurs at M than at N reaches.…”

Direct Observations of Hydrologic Exchange Occurring With Less‐Mobile Porosity and the Development of Anoxic Microzones in Sandy Lakebed Sediments

“…The pore‐scale numerical simulations of Liu and Kitanidis () illustrated a need to conduct experiments regarding less‐mobile parameters over a range of flow velocities. Accordingly, our experiments include controlled lakebed injections over a range of downward flux conditions similar to those observed in nearby flow‐through kettle lakes and sand‐and‐gravel‐bed rivers (Rosenberry et al, , ). Preliminary experimentation at Snake Pond in June 2016 using a DDPA at a fixed injection flux indicated that the experimental shoreline sediments have an average hydraulic conductivity of 10 m/day.…”

Thermal detection of discrete riparian inflow points (DRIPs) during contrasting hydrological events

“…DRIPs can influence stream temperature, nutrient availability, and redox conditions in headwater systems (Crawford et al, 2017;Lowry, Walker, Hunt, & Anderson, 2007) and act as biogeochemical hotspots or control points that have a disproportionally large impact on stream water quality (Bernhardt et al, 2017;McClain et al, 2003). DRIPs are important for shaping stream ecosystems and thus progress has been made on detecting their locations along stream networks using topographic and thermal approaches (Kuglerová et al, 2014;Leach, Lidberg, Kuglerová, Ågren, & Laudon, 2017;Rosenberry, Briggs, Delin, & Hare, 2016). Nevertheless, the seasonal dynamics of DRIPs have not been fully comprehended.…”