A numerical investigation of bedrock groundwater recharge and exfiltration on soil mantled hillslopes. Issue 15 (9th June 2020)

• Record Type: Journal Article
• Authors: Gardner, W. Payton; Jensco, Kelsey; H. Hoylman, Zachary; Livesay, Robert; P. Maneta, Marco
• Is Part Of: Hydrological processes. Volume 34:Issue 15(2020)
• Page Start: 3311
• Page End: 3330
• Publication Date: 2020-06-09
• Subjects: aquifer recharge -- mountain block aquifer -- soil moisture -- streamflow generation -- watershed storage; Hydrology -- Periodicals; Hydrology -- Research -- Periodicals; Hydrologic models -- Periodicals; Hydrological forecasting -- Periodicals; 631.432
• DOI: 10.1002/hyp.13799
• Languages: English
• ISSNs: 0885-6087

Abstract

Abstract: Here we use Richards Equation models of variably saturated soil and bedrock groundwater flow to investigate first‐order patterns of the coupling between soil and bedrock flow systems. We utilize a Monte Carlo sensitivity analysis to identify important hillslope parameters controlling bedrock recharge and then model the transient response of bedrock and soil flow to seasonal precipitation. Our results suggest that hillslopes can be divided into three conceptual zones of groundwater interaction, (a) the zone of lateral unsaturated soil moisture accumulation (upper portion of hillslope), (b) the zone of soil saturation and bedrock recharge (middle of hillslope) and (c) the zone of saturated‐soil lateral flow and bedrock groundwater exfiltration (bottom of hillslope). Zones of groundwater interaction expand upslope during periods of precipitation and drain downslope during dry periods. The amount of water partitioned to the bedrock groundwater system a can be predicted by the ratio of bedrock to soil saturated hydraulic conductivity across a variety of hillslope configurations. Our modelled processes are qualitatively consistent with observations of shallow subsurface saturation and groundwater fluctuation on hillslopes studied in our two experimental watersheds and support a conceptual model of tightly coupled shallow and deep subsurface circulation where groundwater recharge and discharge continuously stores and releases water from longer residence time storage. Abstract : Richards equation models of soil and deep bedrock circulation indicate that the hillslope can be broken into conceptual zones of interaction: (a) the upslope zone of soil lateral flow and soil moisture accumulation, (b) the zone of vertical soil leakage and bedrock recharge and (c) the zone groundwater exfiltration and soil saturated flow. The extent of zones and the partitioning of water between soil and deep bedrock flow is a function of the contrast in soil and bedrock hydraulic properties. These zones are present throughout the year but move up the slope during times precipitation and down slope during periods of no precipitation.