This paper presents the derivation of the intensity-duration-frequency (IDF) curves for the Kingdom of Saudi Arabia. Such curves were obtained based on rainfall events measured in 28 meteorological stations distributed throughout the Kingdom. For 20-28 years period, 2027 rainfall storms of durations ranging from 10 min to 24 hours were collected and analyzed. Both Institute of Hydrology model (IH-Flood) and Excel-sheet program are used for developing IDF equations for every station. The method of least squares was used to get relationships for the parameters of the IDF formulas. The calculated goodness of fit shows strong correlations range between 0.99 and 0.98 for one of the parameters, and between 0.92 and 0.74 for the other parameters and thence indicating robust IDF formulas for practical use. Regionalization of the IDF parameters for the 13 distinct regions of the Kingdom has been developed. In addition, an average of IDF parameters is made over the Kingdom as a whole to be used in regions of no rainfall records. The resulting IDF curves are usually used for flood estimation in urban/rural watersheds. Using the resulting IDF curves is highly recommended for rigorous, efficient and safe design of hydraulic structures and flood protection works.

Wastewater Lake, known as Almisk Lake, has been the dumping site of Jeddah's sewage for the last ten years. The lake was created as a stopgap measure to deal with the increasing amounts of wastewater in the growing city. It is located along wadi Bani Malek; the biggest wadi in east Jeddah (302 km 2 ). The lake covers an area of 2.88km 2 at a site 130 m above the mean sea level. A non-engineered earthen dike was built to prevent the wastewater polluted by toxic industrial wastes from flowing back to the city. About 40,000 m 3 of wastewater are transported to the lake every day and expanding significantly. Water levels are continuously rising. With winter rainfall, dangerous environmental consequences from wadi Bani Malek floods arise. Residents in the east of the Jeddah highway are in fear over the dam collapsing. Fears of Sewage Lake could overflow and flood Jeddah city are growing strongly. The purpose of the present paper is to simulate the floods of wadi Bani Malek at the lake site for various return periods to evaluate the threats on the lake, to develop conceptual model to evaluate the impacts on the subsurface flow to Jeddah city. Hydrological conditions for the study area were sought. The Watershed Modeling System (WMS) and Hydrological Modeling System (HEC-HMS) models were used. Water budget components' for the lake were calculated. Proposed measures to alleviate the threats of the lake have been recommended. Results of the paper will promote ongoing solutions for sewage disposal in the city of Jeddah.

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Egypt is an arid country with scarce and limited renewable water resources. Water availability is one of the main problems facing the water resources planning, development and management. A reliable source of surface water is limited and groundwater, which is a vital resource, is used to meet the water demand for agricultural purposes. Due to the limitation of the available areas for agriculture, a government policy started to reclaim the highly elevated desert fringes in many locations in Upper Egypt such as Wadi Al Assiuti, West El Fashn Project, West Samalut Project, West Tahta Project, East Luxor reclamation area, and West Esna Project. However, different operation and traditional management practices for meeting water requirements in these areas using unlined surface water canals and traditional flooding irrigation system lead to water logging in the low lying lands causing soil salinization and water logging problems. Previous studies recommended optimal integration of groundwater with surface water in a conjunctive use system to mitigate this problem. However, there was no detailed analysis and optimization approach to analyze the economic and reliability benefits from different conjunctive use alternatives. In the present study economic assessment of potential and feasible conjunctive use alternatives and planning were explored for Wadi Al Assiuti Area. Quasi 3-D numerical model was developed using TRIWACO Package and GIS based comprehensive database to simulate the steady and transient flow in saturated and unsaturated zones. The calibrated model was used to assess the appropriate scenarios for applying the conjunctive use and assessing these scenarios. An economic-engineering network flow optimization approach was used to analyze the economic and the reliability benefits Sustainable Development via Optimal Integration of Surface and Groundwater… 20 from different conjunctive use alternatives. It was found that integrated management under flexible water allocation can generate sustainable development through minimizing the problem of water salinization and the cost of water pumping and consequently economic benefits to the Wadi. The GIS based model was proved to be an efficient tool for formulating integrated and sustainable management plan. The Quaternary alluvial aquifer system considered as a promising aquifer. About 48,000 m 3 /day can be abstracted from two well fields to supply the required water for future development.Monitoring system is required to assess the deep aquifers within the study area.