Application of Distributed Temperature Sensing for coupled mapping of sedimentation processes and spatio‐temporal variability of groundwater discharge in soft‐bedded streams

Abstract

The delineation of groundwater discharge areas based on Distributed Temperature Sensing (DTS) data of the streambed can be difficult in soft‐bedded streams where sedimentation and scouring processes constantly change the position of the fibre optic cable relative to the streambed. Deposition‐induced temperature anomalies resemble the signal of groundwater discharge while scouring will cause the cable to float in the water column and measure stream water temperatures. DTS applied in a looped layout with nine fibre optic cable rows in a 70 × 5 m section of a soft‐bedded stream made it possible to detect variability in streambed temperatures between October 2011 and January 2012. Detailed monthly streambed elevation surveys were carried out to monitor the position of the fibre optic cable relative to the streambed and to quantify the effect of sedimentation processes on streambed temperatures. Based on the simultaneous interpretation of streambed temperature and elevation data, a method is proposed to delineate potential high‐groundwater discharge areas and identify deposition‐induced temperature anomalies in soft‐bedded streams. Potential high‐discharge sites were detected using as metrics the daily minimum, maximum and mean streambed temperatures as well as the daily amplitude and standard deviation of temperatures. The identified potential high‐discharge areas were mostly located near the channel banks, also showing temporal variability because of the scouring and redistribution of streambed sediments, leading to the relocation of pool‐riffle sequences. This study also shows that sediment deposits of 0.1 m thickness already resulted in an increase in daily minimum streambed temperatures and decrease in daily amplitude and standard deviation. Scouring sites showed lower daily minimum streambed temperatures and higher daily amplitude and standard deviation compared with areas without sedimentation and scouring. As a limitation of the approach, groundwater discharge occurring at depositional and scouring areas cannot be identified by the metrics applied. Copyright © 2015 John Wiley & Sons, Ltd.

Air/water/sediment temperature contrasts in small streams to identify groundwater seepage locations

“…In contrast with the Lagrangian method, where the temperature is measured at single location in time, Fiber Optic Distributed Temperature Sensing (FO‐DTS) technology measures the temperature continuously with a spatial resolution down to 0.5 m for distances up to the kilometer scale depending on the cable length (Hare et al, ; Lowry et al, ; Selker et al, ). However, similar spatial limitations as for the Lagrangian framework apply for FO‐DTS (Briggs et al, ; Lowry et al, ; Sebok et al, ). Together with another method, thermal imagery (Loheide & Gorelick, ), FO‐DTS can cover larger stream distances.…”

“…Although the method covers large streambed areas, there are limitations related to both the temporal and spatial scales; the measurements are snapshots in time and depend on the location of the dragged sensor. Because groundwater seepage can be very localized, a seepage location may potentially be missed (Hare et al, ; Sebok et al, , ). In contrast with the Lagrangian method, where the temperature is measured at single location in time, Fiber Optic Distributed Temperature Sensing (FO‐DTS) technology measures the temperature continuously with a spatial resolution down to 0.5 m for distances up to the kilometer scale depending on the cable length (Hare et al, ; Lowry et al, ; Selker et al, ).…”

Fiber‐Optic Sensing for Environmental Applications: Where We Have Come From and What Is Possible

“…Fiber-optic distributed temperature sensing (DTS or FO-DTS) is the most widely used fiber-optic sensing method for environmental applications (especially hydrologic applications; Bense et al, 2016;Briggs et al, 2012;Schneider et al, 2011;Sebok et al, 2015). Although FO-DTS (Hartog & Gamble, 1991).…”

Subsurface nitrate reduction under wetlands takes place in narrow superficial zones

“…Several monitoring campaigns were performed after the sampling of the cores in order to compose their respective hydrogeological models and to acquire information about the groundwater chemistry. [29][30][31] Brynemade wetland at the Odense river Basin (Denmark) (55º13'12''N, 10º17'35''E; WGS84) was restored in 2003 and was used to document seasonal changes in flow dynamics and nitrate/pesticide degradation performance in a re-established wetland-river system. The restoration included re-raising the riverbed and re-meandering the river to the position it had prior to the 1958 channelization.…”

“…Unlike the Brynemade site, the Evi site is never flooded. Groundwater flow is strongly dependent on precipitations and no reverse flow from streambed to aquifer was observed, [30,31]. The main climate parameters were an annual mean temperature of 8.4ºC and an annual accumulated precipitation of 860 mm (Years: 2001 to 2010, grid 20x20 km for temperature and 10x10 km for precipitation), [32].…”