Spatially variable stage‐driven groundwater‐surface water interaction inferred from time‐frequency analysis of distributed temperature sensing data

Abstract

[1] Characterization of groundwater-surface water exchange is essential for improving understanding of contaminant transport between aquifers and rivers. Fiber-optic distributed temperature sensing (FODTS) provides rich spatiotemporal datasets for quantitative and qualitative analysis of groundwatersurface water exchange. We demonstrate how time-frequency analysis of FODTS and synchronous river stage time series from the Columbia River adjacent to the Hanford 300-Area, Richland, Washington, provides spatial information on the strength of stage-driven exchange of uranium contaminated groundwater in response to subsurface heterogeneity. Although used in previous studies, the stage-temperature correlation coefficient proved an unreliable indicator of the stage-driven forcing on groundwater discharge in the presence of other factors influencing river water temperature. In contrast, S-transform analysis of the stage and FODTS data definitively identifies the spatial distribution of discharge zones and provided information on the dominant forcing periods (≥2 d) of the complex dam operations driving stage fluctuations and hence groundwater-surface water exchange at the 300-Area. Citation: Mwakanyamale, K., L. Slater, F. DayLewis, M. Elwaseif, and C. Johnson (2012), Spatially variable stage-driven groundwater-surface water interaction inferred from time-frequency analysis of distributed temperature sensing data, Geophys. Res. Lett., 39, L06401,

Upscaling lacustrine groundwater discharge rates by fiber-optic distributed temperature sensing

“…In contrast to the aforementioned methodologies, FO-DTS is useful for spatially detailed measurements at larger scales, and therefore has the potential to provide temperature information for tracing LGD with high spatial resolution at scales exceeding previous detailed investigations of local flow. FO-DTS has successfully been applied for qualitative identification of complex of groundwater upwelling patterns in streams [Slater et al, 2010;Mwakanyamale et al, 2012], wetlands [Lowry et al, 2007], and coastal zones [Henderson et al, 2009]. Hence, spatially detailed FO-DTS observations may provide an adequate measure to upscale detailed point observations or provide an efficient screening tool for identifying locations for detailed analyses of groundwater upwelling.…”

Statistical mapping of zones of focused groundwater/surface-water exchange using fiber-optic distributed temperature sensing

“…Strong amplitudes (! 0.4) at longer periods (2-16 d) found in the stage power spectrum are also apparent in FO-DTS power spectra in locations of enhanced GWSWE [Mwakanyamale et al, 2012]. The 2-to 4-d periods are interpreted as the original high-amplitude periods driving river stage fluctuations, with periods at multiples of these assumed to be harmonics.…”

“…Mwakanyamale et al [2012] demonstrated how SA, in this case based on an S-transform, better discriminated zones of focused GWSWE, relative to temperature anomalies alone. GWSWE was found to have a distinct spectral signature in FO-DTS data and to coincide with locations along the river where the Hanford-Ringold contact is predicted to be locally deeper (i.e., thicker Hanford Formation) in electrical images [Slater et al, 2010;Mwakanyamale et al, 2012]. Dam releases govern the power spectrum of the stage time series, and this spectral signature is imprinted on the streambed temperature spectra where enhanced GWSWE occurs.…”

“…[10] We used time-frequency analysis (the S-transform) in previous work [Mwakanyamale et al, 2012] examining the FO-DTS time series. Alternatives to the S-transform include wavelets [e.g., Henderson et al, 2009] and empirical orthogonal functions (EOF) [e.g., Ghil et al, 2002].…”

“…By providing measurements with high spatial ($0.5-2 m) and temporal ($10-60 s) resolution along cables several kilometers in length, FO-DTS has led to insights into local-scale hydrological processes that were previously impossible to resolve with traditional temperaturemonitoring instruments. There is burgeoning interest in FO-DTS for studies of GWSWE, as evident in recent work [e.g., Selker et al, 2006;Henderson et al, 2009;Slater et al, 2010;Mwakanyamale et al, 2012;Briggs et al, 2012]. The utility of FO-DTS for studies of GWSWE derives from the temperature contrast between groundwater and surface water.…”