Estimation of Sediment Hydraulic Conductivity in River Reaches and its Potential Use to Evaluate Streambed Clogging

Abstract

Streambed substrates have pervasive effects on stream biodiversity and biogeochemistry. The excessive input of fine sediments in streams and the subsequent alteration of the physical characteristics of streambed substrates are considered today as a major environmental issue. The estimation of streambed hydraulic conductivity (K) may be simpler than other estimations of reach-scale physical characteristics and could serve to quantify the alterations of streambeds across stream networks. In this study, we examined between-reach and within-reach variability and temporal changes of streambed K across 101 stream reaches in France, including nine reaches previously judged as clogged and nine as references (unclogged). We also examined the relationships between K and some environmental variables such as vertical hydraulic gradient, streambed grain size, flow velocity or distance to the bank. We demonstrated that 15 measurements of streambed K per reach could be used to compare streams among each other and over time. Clogged reaches displayed much lower K than reference reaches, and more generally, reach-averaged K and the number of non-null K values per reach allowed discriminating reaches among each other without observer bias. K was higher in upwelling compared with downwelling areas, probably because of fine sediment uplifting. With the low cost in terms of equipment (<€100 per unit) and time (2-4 h per site), reach-scale streambed K estimates are promising for studying the alterations of streambed substrates across stream monitoring networks such as clogging, but also for understanding large-scale drivers of these alterations, or for upscaling recent developments in hyporheic ecology at the reach scale.

Benthic and hyporheic macroinvertebrate distribution within the heads and tails of riffles during baseflow conditions

“…The fine sediment content of hyporheic substrates (subsurface sediments) was found to be significantly greater at the riffle heads in this study, reflecting the widely reported characteristics of vertical hydraulic exchange (VHE). Downwelling water is typically associated with the transport of sediment into the river bed at the head of riffles, whilst upwelling water, often at the riffle tail, has the potential to flush fine sediments from interstitial spaces (Huettel et al, 1996;Ren & Packman, 2007;Datry et al, 2015). A number of other studies have also reported greater quantities of fines in the riffle head associated with downwelling water and flows during high discharge events Dole-Olivier & Marmonier, 1992;DoleOlivier et al, 1997;Saenger et al, 2005).…”

“…This pattern of fine sediment deposition (typically sand-and silt-sized fractions of B2 mm; Wentworth, 1922;Jones et al, 2012) directly influences the structure and composition of invertebrate communities (Brunke & Gonser, 1999) but also the nature of vertical hydrological exchange (Leek et al, 2009;Hartwig & Borchardt, 2015;Datry et al, 2015). Consequently, the dynamic pattern of vertical hydraulic exchange exerts a strong influence on physical and chemical conditions such as temperature, oxygen concentrations and the residence time of water (Olsen & Townsend, 2003;Krause et al, 2011b).…”

Variability of Darcian Flux in the Hyporheic Zone at a Natural Channel Bend

“…The results suggested that neither K v nor lnK v was normally distributed at the 95% confidence level, except for lnK v in January 2016 (N = 31, p = 0.000 for K v in July 2015; N = 31, p = 0.002 for lnK v in July 2015; N = 30, p = 0.000 for K v in January 2016; N = 30, p = 0.318 for lnK v in January 2016). Previous research showed that streambed hydraulic conductivity was not normally distributed across 101 reaches or that K v had a lognormal distribution [30,31]. During the two test periods, the high values of K v were observed in the center of the channel and (Figure 3a,b).…”

“…Previous research showed that streambed hydraulic conductivity was not normally distributed across 101 reaches or that Kv had a lognormal distribution [30,31]. During the two test periods, the high values of Kv were observed in the center of the channel and (Figures 3a,b).…”

Variability of Darcian Flux in the Hyporheic Zone at a Natural Channel Bend

“…The results suggested that neither Kv nor lnKv was normally distributed at the 95% confidence level, except for lnKv in January 2016 (N = 31, p = 0.000 for Kv in July 2015; N = 31, p = 0.002 for lnKv in July 2015; N = 30, p = 0.000 for Kv in January 2016; N = 30, p = 0.318 for lnKv in January 2016). Previous research showed that streambed hydraulic conductivity was not normally distributed across 101 reaches or that Kv had a lognormal distribution [30,31]. During the two test periods, the high values of Kv were observed in the center of the channel and (Figures 3a,b).…”