EFFECTS OF INFILTRATION VARIABILITY ON MODELED TRANSMISSION LOSSES IN EPHEMERAL CHANNELS

The ability to accurately quantify transmission losses and other hydrologic measurements within a watershed is essential to the evaluation of water resources. This necessity for accurate measurements is generally amplified when determining these resources in arid and semi-arid environments such as the Middle East & North Africa region where the escalating population; along with increased water usage has stressed the region’s water resources in excess of its annual renewable supplies. An assessment of water resources through the construction of hydrologic models, enhanced in-situ gauging capabilities, and remote sensing-based datasets have been utilized to better understand the current and future resources required to sustain this region.

The Wadi Feiran Basin (1,851 km²) located in southern Sinai Peninsula, Egypt is composed of an interconnecting series of relatively homogenous wadi channels. In order to evaluate the spatial variations in infiltration within the basin, a combination of field-based double ring infiltrometer tests (DRI) and hydrologic measurements collected from near surface (10-200cm depth) vertically installed temperature probe arrays (TPA). In addition, globally derived satellite-based meteorological datasets (precipitation, temperature, wind speed, relative humidity, and solar radiation) were used along with empirical infiltration assessments (EIA). The data collected was used to characterize the variability in infiltration rates within the basin and estimate the effect on modeled transmission losses.

Field derived TPA data (avg. 21.4cm/hr), DRI tests (avg. 12.5cm/hr), and EIA (>12.7 cm/hr, calculated using wadi soil characteristics: >90% sands & gravel) show relatively high infiltration rates within the major wadi system of the basin. The various methods and rates were integrated into the Soil & Water Assessment Tool (SWAT) model to determine first-order transmission losses and potential effects of different field-based estimates within the basin. Initial comparison between base model (BM) results and the enhanced integrated model (EIM) shows a 7% decrease in modeled transmission losses (BM: 15.2x10⁶m³, EIM: 10.3x10⁶m³) and an estimated 12.4% increase in surface runoff (BM: 16.8x10⁶m³, EIM: 25.4x10⁶m³) with respect to total rainfall (70.4x10⁶m³).