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The morphometric parameters of the main Wadi Al-Burdi basin and its third order sub-basins were computed (Figures 9(a)9(c) and Table 1) with emphasis on its implication for hydrologic processes. The wadis dissecting the mountain ranges to the east are characterized by complex and interlocking patterns reflecting the morphotectonic evolution of these drainage basins, where the paleo-channels flow in different directions from the contemporaneous flow pathways (Figures 4(a)–4(f)). The textural dissection of Wadi Al-Burdi was considered to be low as drainage density and stream frequency are low, since the study area is covered with highly resistant hard basement rocks, making it susceptible to flooding (Figures 2 and 4(a)–4(f)). The main basin of Wadi Al-Burdi has an area of 36.7 km2, and a mean basin elevation of 166.6 masl. It has a moderate relief with an average slope percent of 10.6. Its shape is relatively elongated with a length of 20.3 km. It has a shape factor of 3.1 (Table 1). The basin sinuosity factor is 1.98, which suggests tectonics as the major factor influencing the basin's development, which is well correlated with the geologic structures (Figures 2 and 4). The lag time, time of concentration, and time to peak of the third order sub-basins of Wadi Al-Burdi were computed before and after urbanization (2010 and 2015). They were estimated for the main basin to be 161 min, 165 min, and 251 min for the 2010 land-use map, and 149 min, 150 min, and 235 min for the 2015 land-use map, respectively (Table 5). This reflects that the size, slope, shape, surface roughness, and land-use of the contributing basin have a direct influence on runoff.
Table 5

Estimated morphometric and storm time parameters of the third order sub-basin and the main basin

  Area (A) km2Watershed length (L) kmWatershed slope (%)Average overland slopeLag time (Tl) min.Time of concentration (Tc) min.Time to peak (Tp) min.
2010 Sub-basin No. 1 15.02 11.10 15.38 0.037 82 85 170 
Sub-basin No. 2 4.07 4.24 10.07 0.033 47 42 143 
Sub-basin No. 3 3.43 3.68 11.66 0.045 39 34 125 
Sub-basin No. 4 2.81 3.53 4.36 0.017 62 47 149 
Sub-basin No. 5 0.97 1.71 5.39 0.033 31 21 117 
Main basin 36.70 20.28 10.49 0.022 161 165 251 
2015 Sub-basin No. 1 15.02 11.10 15.38 0.037 77 78 157 
Sub-basin No. 2 4.07 4.24 10.07 0.033 44 38 123 
Sub-basin No. 3 3.43 3.68 11.66 0.045 36 31 115 
Sub-basin No. 4 2.81 3.53 4.36 0.017 57 43 136 
Sub-basin No. 5 0.97 1.71 5.39 0.033 29 19 108 
Main basin 36.70 20.28 10.49 0.022 149 150 235 
  Area (A) km2Watershed length (L) kmWatershed slope (%)Average overland slopeLag time (Tl) min.Time of concentration (Tc) min.Time to peak (Tp) min.
2010 Sub-basin No. 1 15.02 11.10 15.38 0.037 82 85 170 
Sub-basin No. 2 4.07 4.24 10.07 0.033 47 42 143 
Sub-basin No. 3 3.43 3.68 11.66 0.045 39 34 125 
Sub-basin No. 4 2.81 3.53 4.36 0.017 62 47 149 
Sub-basin No. 5 0.97 1.71 5.39 0.033 31 21 117 
Main basin 36.70 20.28 10.49 0.022 161 165 251 
2015 Sub-basin No. 1 15.02 11.10 15.38 0.037 77 78 157 
Sub-basin No. 2 4.07 4.24 10.07 0.033 44 38 123 
Sub-basin No. 3 3.43 3.68 11.66 0.045 36 31 115 
Sub-basin No. 4 2.81 3.53 4.36 0.017 57 43 136 
Sub-basin No. 5 0.97 1.71 5.39 0.033 29 19 108 
Main basin 36.70 20.28 10.49 0.022 149 150 235 
Figure 9

Wadi Al-Burdi, Jazan area: (a) the selected third order sub-basins for the hydrologic modeling; (b) sub-Basin flow distances; (c) basin model.

Figure 9

Wadi Al-Burdi, Jazan area: (a) the selected third order sub-basins for the hydrologic modeling; (b) sub-Basin flow distances; (c) basin model.

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