Effect of bedrock permeability on subsurface stormflow and the water balance of a trenched hillslope at the Panola Mountain Research Watershed, Georgia, USA

Abstract

Abstract:The effect of bedrock permeability on subsurface stormflow initiation and the hillslope water balance is poorly understood. Previous hillslope hydrological studies at the Panola Mountain Research Watershed (PMRW), Georgia, USA, have assumed that the bedrock underlying the trenched hillslope is effectively impermeable. This paper presents a series of sprinkling experiments where we test the bedrock impermeability hypothesis at the PMRW. Specifically, we quantify the bedrock permeability effects on hillslope subsurface stormflow generation and the hillslope water balance at the PMRW. Five sprinkling experiments were performed by applying 882-1676 mm of rainfall over a ¾5Ð5 m ð 12 m area on the lower hillslope during ¾8 days. In addition to water input and output captured at the trench, we measured transpiration in 14 trees on the slope to close the water balance. Of the 193 mm day 1 applied during the later part of the sprinkling experiments when soil moisture changes were small, <14 mm day 1 was collected at the trench and <4 mm day 1 was transpired by the trees, with residual bedrock leakage of >175 mm day 1 (91%). Bedrock moisture was measured at three locations downslope of the water collection system in the trench. Bedrock moisture responded quickly to precipitation in early spring. Peak tracer breakthrough in response to natural precipitation in the bedrock downslope from the trench was delayed only 2 days relative to peak tracer arrival in subsurface stormflow at the trench. Leakage to bedrock influences subsurface stormflow at the storm time-scale and also the water balance of the hillslope. This has important implications for the age and geochemistry of the water and thus how one models this hillslope and watershed.

Subsurface lateral flow from hillslope and its contribution to nitrate loading in streams through an agricultural catchment during subtropical rainstorm events

“…This can be improved by monitoring soil water potential. Single trench flow measurement often gives more direct evidences of generation of subsurface flow than soil water monitoring, but the results often need careful interpretation as they may be affected by the characteristics of trenched cross-section and the saturated flow around the trenches (Tromp-van Meerveld et al, 2007) as well as by the representativeness of the trenched hillslopes and their connection to riparian zones within catchment (van Verseveld et al, 2009). Moreover, most of the trenched hillslope experiments often lack detailed hydro-biogeochemical data that are needed for flow separation and further understanding of the hydrological processes at different scale (e.g.…”

Response of a fractured bedrock aquifer to recharge from heavy rainfall events

“…Previous studies have modeled infiltration to fractured bedrock with success (Haught, 2010;Salve et al, 2008;Katsuyama et al, 2005;Tromp-van Meerveld, 2007). Haught (2010) measured cumulative infiltration at three bedrock outcrops in a watershed in British Columbia and fit the observed data to three infiltration models: the Horton (1940), Philip (1957), and Green and Ampt (1911) models.…”

Effect of the spatial distribution of physical aquifer properties on modelled water table depth and stream discharge in a headwater catchment

“…We used the physically-based hillslope model Hill-vi (Weiler and McDonnell, 2004;Weiler and McDonnell, 2006;Tromp-van Meerveld and Weiler, 2008;Anderson et al, 2009a,b) for runoff generation by simulating water fluxes in the saturated and unsaturated zone of the hillslope. The model is based on the concept that two compartments define the saturated and unsaturated zone for each hillslope grid cell, based on topography and soil depth.…”

“…In these models and most other hillslope models, soil and aquifer properties were assumed to be laterally homogeneous, whereas many field observations show lateral variations in soil depth, porosity and conductivity. These variations are local (Tromp van Meerveld et al, 2007) or linked to topography with respect to soil (Curmi et al, 1998) or weathered materials (Dewandel et al, 2003(Dewandel et al, , 2006. Few modelling studies have investigated the effect of these lateral variations.…”

“…Saulnier et al (1997) showed that variation in soil depth with topography does not really affect discharge. In contrast, local variation of soil depth can have a major effect on flow connectivity and thus discharge, as demonstrated by field observations and modelling approaches (Tromp van Meerveld and Weiler, 2008). Lateral variation in transmissivity was modelled using a Topmodel approach and calibrated with field observations (Lamb et al, 1997;Seibert et al, 1997).…”