Identification of the hydrological model of a runoff-sourced falaj using empirical methods

ABSTRACT This study examines a historical ghaili falaj named Falaj Al-Sahamah, fed by the runoffs of the Halfeen valley in Izki, Ad-Dakhiliyah governorate. This falaj consists of a subterranean gently sloped tunnel dotted with a row of access wells, the first and deepest of which is sunk at the center of the valley. This research aims to suggest a hydrological model for Falaj Al-Sahamah. To this end, the most crucial step is to estimate the falaj's flowrate using the Manning equation. The dimensions of six undamaged spots along the canal were measured. Our analysis puts an estimate of 48 L/s on the falaj's discharge, pouring into the tank downstream, when the falaj was active. On the opposite side of the tank, two interconnected outlet points are visible, one of which lies at the top and the other at the bottom of the tank. Using Torricelli's law, it transpired that the flowrates of these points depend on the height of water inside the tank, fluctuating between a maximum of 67 and a minimum of 0 L/s. It means that the outflow is greater than the inflow, leaving no water in the tank unless the inflow is more than 67 L/s. This research is key to uncovering agricultural, historical, economic, and social aspects in future studies of the falaj system.