Estimation of Surface Infiltration and Subsurface Percolation Rates for Namman Basin

Abstract

This study investigates infiltration and percolation processes in Namman basin, south east of Makkah city, in the western region of Saudi Arabia. Double ring method was used to estimate infiltration rates in 18 sites in Namman basin and its major tributaries. Variations of soil moisture content values with time and vertical water percolation rates were estimated using the Neutron Probe instrument installed at the intersection of main stream of Namman basin and one of its major tributaries. The results of the study indicated that infiltration rates are very high in the main channels of Namman basin and its tributaries. The mean value of infiltration rate was about 2 cm/min, while mean values of initial and final infiltration rates were 3.7 and 1.6 cm/min, respectively. The neutron probe experiment showed that maximum measured soil moisture value was about 24%. Value of moisture content of soil at various soil depths has increased by about 20% within 10 min from the beginning of the experiment. A linear empirical relationship between wetting front arrival time and soil depth was found and used to predict wetting front arrival time to various soil depths. The relation also suggests that wetting front needs about 2 h to reach depths up to 25 m provided that ponding head does exist on the soil surface. The results of the study can be utilized for various hydrological investigations of Namman basin such as water budget, rainfall losses, groundwater recharge and runoff estimations.