Abstract
The proper planning of storage structures, waterways, irrigation schemes, water harvesting, erosion control structures, and groundwater development strategies requires accurate estimation of surface runoff. However, hydrologists in Saudi Arabia face serious challenges, specifically due to the rare availability of surface runoff data. In this study, the soil conservation service-curve number (SCS-CN) method integrated with geographic information system (GIS) and remote sensing (RS) was utilized to estimate the surface runoff in Wadi-Uranah basin, in the western region of Saudi Arabia. Different thematic maps such as slope, hydrologic soil group (HSG), land use/land cover (LULC), and daily rainfall have been created in GIS environment and processed to generate the curve number (CN) and surface runoff maps. Based on the soil classification results, the study area was categorized into two HSGs (B and C). The dominant HSG was group C, representing about 98.8% of the total area. The LULC analysis showed four main land use types in the study region: urban, rocks, barren soil, and agricultural areas. Furthermore, the finding results showed that CN values for the normal conditions (CNII) ranged between 74 and 93 in agricultural and both urban and rock areas, respectively. The CNII values were further corrected using slope data to derive slope-adjusted CNII. Moreover, the rainfall-runoff results showed an increase in the daily runoff of the study region with a minimum of 15 mm to a maximum of 74 mm. Another interesting result was rainfall-runoff linear regression analysis that showed a good correlation of 0.98. Additionally, the peak runoff hydrograph flows for 10-, 50-, and 100-year return periods obtained from the SCS-based dimensionless unit hydrograph were 828, 1353, and 1603 m3/s, respectively. Therefore, this study highlights that the SCS-CN method integrated with RS and GIS deserves further attention for estimating runoff of ungauged basins for better basins management and conservation purposes.
Highlights
Watershed runoff plays an important role in designing hydraulic structures, controlling soil erosion, and assessing the water yield potential of the watershed [1,2]
In the absence of runoff measurements, estimated direct runoff has shown accurate results via soil conservation service-curve number (SCS-CN), a model developed by hydrologists at the Department of Agriculture of the United States [4,5,6]
III, which is highly recommended for the hydrological analysis [42]
Summary
Watershed runoff plays an important role in designing hydraulic structures, controlling soil erosion, and assessing the water yield potential of the watershed [1,2]. The provision of accurate information about runoff is barely available due to the high installation and maintenance costs of the hydrologic gauging stations. Reliable information on watershed runoff must be continuously developed to facilitate the creation and management of watershed programs [3]. In the absence of runoff measurements, estimated direct runoff has shown accurate results via soil conservation service-curve number (SCS-CN), a model developed by hydrologists at the Department of Agriculture of the United States [4,5,6]. The SCS-CN model combines the parameters of the watershed with the climatic factors in a single entity called the curve number (CN). Liu and Li [11] computed the runoff over a watershed in the Loess Plateau of China with the SCS-CN method, and stated that the SCS-CN is an effective and successful method for estimating runoff. Topno et al [12]
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