Morphological-hydrological relationships and the geomorphological instantaneous unit hydrograph of Makkah Al-Mukarramah watersheds

The present study focused on developing the predominant relationships between morphological and morphological-hydrological parameters of watersheds in the Makkah Al-Mukarramah region, Kingdom of Saudi Arabia (KSA). These relationships are essential for flood mitigation studies in the region. The relationships developed in this study are averaged over 43 watersheds (varying in size from 42.2 to 6081.4 km2) to provide a theoretical basis for regional morphological and hydrological analyses. In addition, the similarity of the hydrologic response of these watersheds is studied via the theory of geomorphological instantaneous unit hydrograph (GIUH). The results show that there is a relatively high similarity among the 43 basins (the average similarity parameter is 0.61, and the values vary from 0.57 to 0.68 at 95% confidence). Comparisons of the peaking factor between the Soil Conservation Service (SCS) and the Arid-Zone, Ari-Zo, (Albishi et al., Arabian Journal of Geosciences 10:1–13, 2017) models show that the common SCS model underestimates the peak discharge. The time of concentration is overpredicted by the Kirpich (Civil Engineering 10:362, 1940) equation (up to 17 times) compared to the Ari-Zo model. The GIUH and SCS models overestimate the time to peak when compared with the Ari-Zo model. These results are crucial for flood estimation and mitigation in the region. © 2021, Saudi Society for Geosciences.