Discharge Variations of a Falaj with Arbitrary Shape in a Wadi Aquifer: Case of Al-Aswad Falaj, Oman

Abstract

A falaj (plural aflaj) (also called qanat) is a unique type of near-horizontal well that extracts groundwater by gravity. Wadi aquifers, usually bounded by lateral no-flow boundaries, are a vital source of water supply in many arid and semiarid regions. Many aflaj residing in these aquifers do not usually follow a straight line. Therefore, in response to this knowledge gap, this work aims to develop a semianalytical model capable of predicting the discharge of a falaj of an arbitrary shape in a strip-shaped Wadi aquifer. The model is obtained by Laplace and Fourier transformations along with the image well method to simulate lateral no-flow boundaries and the principle of superposition to simulate the falaj shape. The effects of the width of the Wadi aquifer and the location of the falaj on the variability of the falaj discharge are explored. The scaled sensitivity of falaj discharge to hydraulic parameters of the aquifer is investigated and compared to that of the infinite extent aquifer. The lateral no-flow boundary reduces the scaled sensitivity of the discharge of falaj to hydraulic parameters of the aquifer by an order of magnitude in our case. The developed model is coupled to a parameter estimation code and applied to the discharge data of the arbitrary shape branched Al-Aswad falaj constructed in the strip-shaped Wadi Mayh aquifer, Oman. The results show that the coupled simulation-parameter estimation model estimates the hydraulic parameters of the Wadi Mayh aquifer satisfactorily. It is also found that the model of the infinite extent aquifer estimates the hydraulic conductivity of the Wadi Mayh aquifer by a third of its expected value. Therefore, the lateral no-flow boundaries of the Wadi aquifer should not be neglected in the analytical modeling of the falaj discharge. The main novelties of this work over previous ones are considering the strip shaped Wadi aquifer and applying the model to a real-world discharge data of a falaj.