HYDRAULIC MODELLING USING HEC-RAS AND GIS, APPLICATION TO OUED INAOUEN (TAZA, NORTHERN MOROCCO) H. Tabyaoui a , F. El Hammichi a , M. A. Er-Rguiouag b , A. Lahrach b a Sidi Mohamed Ben Abdellah University, Polydisciplinary Faculty of Taza, B.P. 1223, Taza-Gare, Taza 35000, Morocco - labrisques@yahoo.fr, f_elhammichi@yahoo.fr b Sidi Mohamed Ben Abdellah University, Faculty of Sciences and Technique, Fez, B.P. 2202 – Route d’Imouzzer, Fez, Morocco Intended Topic or session: C.4 KEY WORDS: Hydraulic modeling, river basin planning, GIS, Oued Inaouene, Morocco. ABSTRACT: This paper discusses a GIS approach for floodplain mapping to aid in the design of the drainage facilities. The approach establishes a connection between the one-dimensional HEC-RAS hydraulic model and GIS software, allowing for improved three-dimensional visualization and analysis of floodplain data. It also permits GIS to function as an effective planning tool by making hydraulic data easily transferable to floodplain management, flood insurance rate determination, economic impact analysis, and flood warning systems. The methodology is applied to a reach of Oued Inaouene, located in the west of the city of Taza (Northern Morocco). The research was conducted in the Hydraulic Basin Agency of Sebou, in order to help improve their hydraulic design capabilities. 1. INTRODUCTION Since antiquity, hydraulic schemes created by man have the objective not only to use the vital functions of water but also to protect humans against its destructive forces. These last years, climate change and the resulting services required by society challenge the cadastral surveyor to increase skills in unfamiliar areas. Some topics covering the wide field of hydraulic schemes are developed. Research activities will include new subjects like: river training works and flood protection measures, water supply systems, water resources management and natural hazards in catchments areas, safety of dams and storage schemes as well as environmental aspects in relation with river restoration and definition of minimum discharge and finally financial and contractual questions of hydraulic schemes. Today, computer models play a pivotal role in these analyses by aiding in the determination of water surface profiles associated with different flow conditions. Many works tried to connect the information describing the water profiles with their physical locations on the land surface (Beavers, 1994; Tate et al., 2002). From many hydrologic software, HEC-RAS (Hydrologic Engeneering Center – River Analysis System) is a good choice for 1D food plain modelling (USAC, 1997). The model is fully available from the web and copes with a variety of problems as rainfall-runoff modelling, river and civil works hydraulics, and the mapping of hydraulic hazard. Its ArcGIS application companion HEC-GeoRAS makes it easier to gather physical data required by the model from a high resolution DEM (USAC, 2009). The extension allows users to create an HEC- RAS import file containing geometric data from an existing digital terrain model and complementary data sets. Results exported from HEC-RAS may also be processed. The study was carried in the reach of Oued Inaouen, located in the west of the City of Taza in northern Morocco. Analysis shows that the computed program HEC-RAS contains a calculation module adequate to short time flooding events, which is typical of Mediterranean climate. 2. STUDY AREA The Oued Inaouene basin is a 3322 Km² square basin situated between the Middle-Atlas mountain in the south and the Rif Chain in the north. The Oued Inaouen river flows along an east- west direction (figure 1 & 2). The Oued Inaouen basin is characterized by impervious marly substratum more or less reinforced limestone and sandstone beds covering 60% of the total area of the basin. These soft rock formations are continuously subjected to strong mechanical erosion, unlike the carbonate formations that outcrop in the South and affected by major karsts dissolution. The Oued Inaouen basin has a Mediterranean climate with oceanic influence. Examination of series of annual rainfall shows an average annual rainfall of 600 mm and a clear interannual irregularity. Rainfall inputs to the model cover the period from 1970 to 2007 collected by 16 stations situated in and around the basin. Climate series are composed of real weather data and disruptions due to changes in measurement conditions. The correction of these artificial discontinuities is made by the cumulative method. The double-mass curve is used to adjust inconsistent precipitation data by comparing date for a single station (Oued Amlil station as a reference) with that of a pattern composed of the data from several other stations in the area. The graph of the cumulative data of one variable versus the cumulative data of a related variable is a straight line so long as the relation between the variables is a fixed ratio (figure 3).