Bedrock infiltration and mountain block recharge accounting using chloride mass balance

Abstract

Abstract:Mountain front catchment net groundwater recharge (NR) represents the upper end of mountain block recharge (MBR) groundwater flow paths. Using environmental chloride in precipitation, streamflow and groundwater, we apply chloride mass balance (CMB) to estimate NR at multiple catchment scales within the 27 km 2 Dry Creek Experimental Watershed (DCEW) on the Boise Front, southwestern Idaho. The estimate for average annual precipitation partitioning to NR is approximately 14% for DCEW. In contrast, as much as 44% of annual precipitation routes to NR in ephemeral headwater catchments. NR in headwater catchments is likely routed to downgradient springs, baseflow, and MBR, while downgradient streamflow losses contribute further to MBR. A key assumption in the CMB approach is that the change in stored chloride during the study period is zero. We found that this assumption is violated in some individual years, but that a 5-year integration period is sufficient.

Tracing groundwater recharge sources in a mountain–plain transitional area using stable isotopes and hydrochemistry

“…Groundwater recharge in mountain-plain transitional areas can generally be divided into direct recharge of local precipitation and mountain-front recharge. Mountain-front recharge is subdivided into surface and subsurface components, with the former representing seepage from surface water bodies (e.g., river seepage) and the latter consisting of mountain block recharge, which is the subsurface water flow from the mountain block to an adjacent basin (Manning and Solomon, 2005;Aishlin and McNamara, 2011).…”

On the optimal design of experiments for conceptual and predictive discrimination of hydrologic system models

“…However, the measurement error can be quantified given the assumed error on the data inputs required for a chloride mass balance calculation-namely, the annual precipitation and basin yield, and mean chloride concentration in precipitation, runoff, and groundwater. We adopt conservative error estimates of 20% on precipitation and basin yield, and 5% on chloride concentration, as was done by Aishlin and McNamara [2011]. Treating these error levels as 95% confidence intervals, the variance on the recharge flux is equal to approximately 0.005 m d -1 .…”

Seismic Refraction and Electrical Resistivity Tests for Fracture Induced Anisotropy in a Mountain Watershed

“…These studies have either modeled how much water goes to bedrock infiltration (Kormos et al, 2015), used a chloride mass balance approach (Aishlin and McNamara, 2011), or used satellite imagery to delineate fractures (Acker, 2008). So far, no study has been carried to better understand the characteristics of fractured bedrock at depth and at varying azimuths.…”

“…So far, no study has been carried to better understand the characteristics of fractured bedrock at depth and at varying azimuths. Aishlin and McNamara (2011) estimated that as much as 44% of annual precipitation goes to bedrock infiltration at the within the DCEW, goes to bedrock infiltration.…”

“…The conceptual hydrologic model for the DCEW accounts for soil-bedrock water flow directed towards stream channels and infiltration of precipitation through sandy soil to bedrock (Aishlin and McNamara, 2011). However, in reality, the system is more complex because fractures in crystalline rocks (Illman, 2006) create highly variable hydraulic properties (Acker, 2008).…”