Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge

Hydrology and Earth System Sciences
By: , and 



Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is developed and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that the loamy sand topsoil wets up via macropore flow and subsequent redistribution of moisture into the soil matrix. Recharge does not occur until near-positive pressures are achieved at the top of the sandy glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in the macropore system due to seasonal ploughing of the topsoil, and a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Although the wetting process in the topsoil is complex, a SMBM is shown to be effective in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table and a water table rise during the summer period while flow gradients in the unsaturated profile were upward suggest that preferential flow is also occurring within the outwash deposits below the topsoil. A variation of the source-responsive model proposed by Nimmo (2010) is shown to reproduce the observed water table dynamics well in the lower outwash horizon when linked to a SMBM that quantifies the potential recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils and provide a useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation.
Publication type Article
Publication Subtype Journal Article
Title Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge
Series title Hydrology and Earth System Sciences
DOI 10.5194/hessd-9-8455-2012
Volume 9
Year Published 2012
Language English
Publisher European Geosciences Union
Contributing office(s) National Research Program - Western Branch
Description 38 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Hydrology and Earth System Sciences
First page 8455
Last page 8492
Country United Kingdom
County Shropshire County
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