Factors affecting the flow of aflaj in Oman: A modelling study

Shallow sloping drainage tunnels dug into the hillsides to intercept water tables are an important source of water supply in many semi-arid countries. This paper deals with the modelling of such drainage tunnels, with particular reference to the aflaj (singular falaj) of Oman; factors affecting their flow, their response to recharge and their imposition on the surrounding aquifer are investigated. The equations governing groundwater flow in unconfined aquifers are modified to realistically reproduce the observed flow response. In this way the effect of falaj flow can be incorporated into the strategy for the management of scarce water resources. The modelling results show that the falaj flow follows an exponential recession and its rate is related to aquifer geometry and parameters. The results have been used to estimate the contributing length of aflaj under various hydrological conditions and to indicate the most likely recharge mechanism for a falaj situated in wadi gravels. Furthermore, the close resemblance between the predicted falaj flow and field flow measurements, from Oman, is a measure of the model's applicability.