Relative performance of a soil moisture accounting model in estimating return flow

Abstract

The current practice of estimating return flow (also known as ground water recharge) from irrigation and rainfall is mostly based on soil moisture accounting (SMA) models and involves many restrictive assumptions. Prominent among them is the existence of a threshold moisture content termed ‘field capacity’, which must be quantified as a flow parameter to be compatible with its hydraulic implication in the SMA models. This paper presents (i) a method for quantifying field capacity as a flow parameter, and (ii) assessment of a proposed SMA model for estimation of return flow, in comparison with an earlier distributed model based on a finite difference solution of the Richards' equation, for studying the possibility of replacement of the more elaborate distributed model by the easy to adopt SMA model. The method for quantifying field capacity as a flow parameter is more suitable for coarse soils. The assumptions implicit in the SMA model result in estimated daily rates of return flow which are not acceptable although seasonal totals are reasonably acceptable.