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

Water Resources Research
By: , and 

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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.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Combined use of thermal methods and seepage meters to efficiently locate, quantify, and monitor focused groundwater discharge to a sand-bed stream
Series title Water Resources Research
DOI 10.1002/2016WR018808
Volume 52
Issue 6
Year Published 2016
Language English
Publisher AGU
Contributing office(s) National Research Program - Central Branch, Toxic Substances Hydrology Program
Description 18 p.
First page 4486
Last page 4503
Country United States
State Massachusetts