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
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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
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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)