Data from Rickel et al. (2021), Seasonal shifts in surface water-groundwater connections from electrical resistivity in a ferricrete-impacted stream

These data are described in Rickel, A., Hoagland, B., Navarre-Sitchler, A. and Singha, K. (2021). Seasonal shifts in surface water-groundwater connections from electrical resistivity in a ferricrete-impacted stream. Geophysics, v. 86, no. 5, 13 p. 10.1190/GEO-2020-0599.1.

The efficacy of the hyporheic zone (HZ) — where surface water and groundwater mix — for processing nutrients or uptake of metals is dependent on streambed hydraulic conductivity and stream discharge, among other characteristics. Here, we explore electrical resistivity tomography (ERT) of hyporheic exchange in Cement Creek near Silverton, Colorado, which is affected by ferricrete precipitation. To quantify flows through the HZ, we conducted four-hour salt injection tracer tests and collected time-lapse ERT of the streambed and banks of Cement Creek at high and low flow. We installed piezometers to conduct slug tests, which suggested a low permeability zone at 44-cm depth likely comprised of ferricrete that cemented cobbles together. Based on the ERT, the tracer released into the stream was constrained within the shallow streambed with little subsurface flow through the banks. Tracer was detected in the HZ for a longer time at high flow compared to low flow, suggesting that more flow paths were available to connect the stream to the HZ. Tracer was confined above the ferricrete layer during both the high- and low-flow tests. Mass transfer and storage area parameters were calculated from combined analysis of apparent bulk conductivity derived from ERT and numerical modeling of the tracer breakthrough curves. The hyporheic storage area estimated at low discharge (0.1 m2) was smaller than at high discharge (0.4 m2) and residence times were 2.7 h at low discharge and 4.1 h at high discharge. During high discharge, in-stream breakthrough curves displayed slower breakthrough and longer tails, which was consistent with the time-lapse electrical inversions and One-dimensional Transport with Inflow and Storage (OTIS) modeling. Our findings indicate that ferricrete reduces the hydraulic conductivity of the streambed and limits the areal extent of the HZ, which may lower the potential for pollutant attenuation from the metal-rich waters of Cement Creek.

本数据集相关研究由Rickel A、Hoagland B、Navarre-Sitchler A与Singha K于2021年发表，题为《受铁质结核（ferricrete）影响的溪流中基于电阻率成像解析地表水-地下水联系的季节变化》，刊载于《Geophysics》第86卷第5期，共13页，DOI为10.1190/GEO-2020-0599.1。

潜流带（hyporheic zone, HZ）即地表水与地下水的混合区域，其对营养物质的转化或金属的吸收效能，受河床水力传导度、溪流流量等多重因素影响。本研究以科罗拉多州锡尔弗顿附近受铁质结核沉淀影响的塞门特溪为研究对象，探索其潜流交换的电阻率层析成像（electrical resistivity tomography, ERT）特征。

为量化潜流带内的水流过程，我们开展了4小时的盐注入示踪试验，并在高、低流量工况下，对塞门特溪的河床及岸坡开展了时移电阻率层析成像监测。我们安装测压管开展瞬态试验（slug test），结果显示，在44厘米深度处存在一处低渗透带，该区域大概率为胶结砾石的铁质结核层。

基于电阻率层析成像数据，注入溪流的示踪剂被限制在浅河床范围内，岸坡下方几乎无地下水流活动。相较于低流量工况，高流量工况下示踪剂在潜流带中的检出时长更长，表明此时存在更多连接溪流与潜流带的水流路径。在高、低流量试验中，示踪剂均被约束在铁质结核层上方。

通过联合分析电阻率层析成像得到的视体电导率，以及示踪剂突破曲线的数值模拟结果，我们计算得到质量传递与储集面积参数。低流量工况下估算的潜流带储集面积（0.1 m²）小于高流量工况下的0.4 m²；停留时间在低流量时为2.7小时，高流量时为4.1小时。高流量工况下，溪流内的示踪剂突破曲线呈现出更缓慢的突破过程与更长的拖尾现象，这与时移电阻率反演结果以及带流入与存储的一维输运模型（One-dimensional Transport with Inflow and Storage, OTIS）的模拟结果一致。

本研究结果表明，铁质结核会降低河床的水力传导度，限制潜流带的平面分布范围，这可能会削弱塞门特溪富金属水体的污染物衰减潜力。