Abstract
This study aims to evaluate and identify potential floods in coastal areas with simple slopes of the Al-Lith valley basin, and to identify urban areas exposed to flooding with flood water in the coastal city of Al-Lith during the period between 1988-2019 as a model for the coastal city of Saudi Arabia, and designing strategies to mitigate the effects of floods and the establishment of a Department of Urban Planning Flood Risk. These are very important things for political and planning decision-makers, as the city suffers from repeated exposure to the risk of floods as a result of its occurrence directly below the Al-Lith valley basin. In order to reach these goals, the (Light Detection and Ranging, Lidar) data was analyzed to build and develop a two-dimensional model of the depth, speed and spread of water using a hydraulic model (Hydrologic Engineering Center-River Analysis System, HEC-RAS) to calculate the risk matrix of floods. Changes in Earth's use of the city of Al-Lith were monitored by analyzing consecutive satellite visualizations made by the American satellite Landsat in the years 1988, 2000, 2013, and 2019. The hydrological model (Hydrologic Engineering Center-Hydrologic Modelling System, HEC-HMS) was applied in calculating the floods hydrograph curve for the Al-Lith Valley basin during different return periods, and estimating the calculation of the amounts of flood water and flow rates depending on the (SCS Unit Hydrograph) method.