INTEGRATION OF GIS AND HEC-RAS IN FLOODS MODELING OF THE OUERGHA RIVER, NORTHERN MOROCCO

European Scientific Journal, Jan 2015

In recent years, hydrological hazards continue to worsen due to climate changes affecting the whole world. In Morocco, after a long period of severe drought that has ravaged the country since the eighties, the last years were exceptionally rainy. Records have been exceeded in terms of rainfall and flooding that affected many parts of the country. The Ouergha River, contributing with 50% of total water yield of the Sebou basin which is one of the most important watersheds in Northern Morocco, broke all records in 2009/2010 providing an exceptional amount of water of 7,4 109 m3. In this study, one-dimensional hydraulic modeling with HEC-RAS®, allowed to calculate the water flow profiles for some flood events that occurred downstream of Al Wahda dam. The exploitation of obtained results led to establish flood extension maps for each calculated profile, which made it possible to evaluate the management of the dam by the Sebou hydraulic Basin Agency. This type of results acquired from the hydraulic simulation and geographic information system, can significantly contribute in flood management interventions against overflows that persist despite the existence of a large dam (Al Wahda), because of extreme climatic and hydrologic events observed in recent years.

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INTEGRATION OF GIS AND HEC-RAS IN FLOODS MODELING OF THE OUERGHA RIVER, NORTHERN MOROCCO

European Scientific Journal January 2015 edition vol.11 INTEGRATION OF GIS AND HEC-RAS IN FLOODS MODELING OF THE OUERGHA RIVER, NORTHERN MOROCCO Midaoui Abdelbasset 0 Dr. Lahrach Abderrahim 0 Chaouni Abdel_Ali 0 Bourak Abdellah 0 Dr. Benaabidate Lahcen 0 Laboratory of Georesources 0 Environment 0 Faculty of Sciences 0 Technology 0 University Sidi Mohamd Ben Abdellah 0 Morocco Boukharas Laila 0 0 Environment Department , Agadir Idawtanane Prefecture, Ministry of Interior In recent years, hydrological hazards continue to worsen due to climate changes affecting the whole world. In Morocco, after a long period of severe drought that has ravaged the country since the eighties, the last years were exceptionally rainy. Records have been exceeded in terms of rainfall and flooding that affected many parts of the country. The Ouergha River, contributing with 50% of total water yield of the Sebou basin which is one of the most important watersheds in Northern Morocco, broke all records in 2009/2010 providing an exceptional amount of water of 7,4 109 m3. In this study, one-dimensional hydraulic modeling with HEC-RAS, allowed to calculate the water flow profiles for some flood events that occurred downstream of Al Wahda dam. The exploitation of obtained results led to establish flood extension maps for each calculated profile, which made it possible to evaluate the management of the dam by the Sebou hydraulic Basin Agency. This type of results acquired from the hydraulic simulation and geographic information system, can significantly contribute in flood management interventions against overflows that persist despite the existence of a large dam (Al Wahda), because of extreme climatic and hydrologic events observed in recent years. Ouergha River; Modeling; Hec-Ras; GIS - Introduction After a long period of severe droughts that ravaged Morocco since the eighties, important values of rainfall and flow rates have been observed during the last past years. Many floods affected a large part of the country. The Ouergha River broke all records in 2009/2010 season, by providing exceptional amount of water: 7.4x109 m3, almost four times the annual average of this River (ABHS, 2006). This study aims to understand the hydraulic behavior of the Ouergha River regarding the management of Al Wahda dam. The studied section is located downstream to the Ouergha watershed, from the dam towards the confluence with the Sebou River. The flow is mainly conditioned by the dam releases. Problem and objectives The Ouergha sub-catchment contributes by 50% to the total annual average intakes of Sebou basin. Figure (2) shows the importance of hydrological processes at the Ouergha and its tributaries. Furthermore, recent years have recorded unusual hydrological phenomena, following the exceptional meteorological disturbances. The season 2009/2010 was one the important records over 72 years (1939 - 2010) regarding the intake and flow of the Ouergha River, which was the main cause of floods, occurred downstream in the Gharb Plain. From December 19, 2009 to January15, 2010, the Ouergha basin upstream to Al Wahda dam experienced three major floods with hourly peaks ranging from 4000 m /s to 6030 m3/s, which can be considered as a 3 complex flood with a total volume of 3x109m3. The maximum outflow of the dam has reached 2000 m3/s, with 67% as peak-flow reduction rate, while restraint exceeded the normal rating to 104% fill. To better understand the sequence of events that occurred during the flood of September 2009 to January 2010, in the studied area, a hydraulic model was built with the aim of simulating the flow. Then, results were used in mapping flooded areas, which also allowed assessing the role of Al Wahda dam in the peak-flow reduction. Building the hydraulic model Device and tools used Beavers (1994) performed some of the first work connecting the hydraulic modeling and GIS. This work was based on the same approach using HecRas (Hydrologic Engineering Center River Analysis System) which gives good predictions results as well as two-dimensional models (Horritt and Bates, 2002) and the ArcGis. The Connection between the two programs is provided by the HEC-GEORAS extension dedicated to run on ArcGis (Cameron, 2011). The whole (Figure 3) constitutes therefore a coherent computing tool that allows primarily to prepare the geometric data (preprocessing) then, to make the necessary calculations (simulation) and finally, to exploit the results (post-processing). The following products were used, as background to extract the elevation data and to digitize geometric entities: * GDEM ASTER (ASTER: Advanced Space borne Thermal Emission and Reflection Radiometer, GDEM: Global Digital Elevation Model), developed jointly by the Ministry of Economy, Trade and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA). This is a high resolution Digital Elevation Model (30 meters) geo-referenced in WGS84 coo (...truncated)


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Midaoui Abdelbasset, Lahrach Abderrahim, Chaouni Abdel Ali, Bourak Abdellah, Benaabidate Lahcen, Boukharas Laila. INTEGRATION OF GIS AND HEC-RAS IN FLOODS MODELING OF THE OUERGHA RIVER, NORTHERN MOROCCO, European Scientific Journal, 2015, 2,