243 2 nd International Conference on Managing Rivers in the 21 st Century: Solutions Towards Sustainable River Basins Modeling Floodplain Inundation by Integration of Hydrological With Hydraulic Model, Case Study: Muda River, Kedah RABIE ALI HUSSEIN, Ph.D student, River Engineering and Urban Drainage Research Centre (REDAC), Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia. Email: rabie.red06@student.usm.my AMINUDDIN AB. GHANI, Deputy Director, REDAC, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia. Email: redac02@eng.usm.my NOR AZAZI ZAKARIA, Director, REDAC, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia. Email: redac01@eng.usm.my MOHD. SANUSI S. AHMAD, Lecturer, Lecturer, School Of Civil Engineering, University Science Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia. Email: cesanusi@eng.usm.my ZORKEFLEE ABU HASAN, Senior Lecturer, River Engineering and Urban Drainage Research Centre (REDAC), Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Penang, Malaysia. Email: redac04@eng.usm.my ABSTRACT River flood is recurrent natural phenomena in tropics and sub tropical climate. Among all kinds of natural hazards of the world flood is probably most wide spread, frequent and destructive. In recent years, remote sensing and GIS has become the key tool for flood modeling. This paper will discuss the modeling of floodplain by integrated hydrological with hydraulic model. The hydrologic model will determine the runoff that occurs following a particular rainfall event. The primary output from the hydrologic model is hydrographs at varying locations along the waterways to describe the quantity, rate and timing of stream flow that results from rainfall events. These hydrographs then become a key input into the hydraulic model. The hydraulic model simulates the movement of flood waters through waterway reaches and calculates flood levels and flow patterns. Furthermore, 2D simulation will apply to simulate and analysis of river flows with complex topography and to predicting river bed and bank erosion. The model should be capable of simulating transition between subcritical and supercritical flow in or near hydraulic structures, flow near channel confluence, and sudden river morphological changes such as channel expansion and contraction. Keywords: floodplain; hydrological with hydraulic model; Radar; erosion. 1 Introduction Flooding is ranked the most destructive disaster in the world, caused extensive damages in the world over the past years resulting in human losses and extensive economic damages. (Environment Agency, 2001) Floods are regular natural disasters in Malaysia which happen nearly every year, most floods that occur are a natural result of cyclical monsoons during the local tropical wet season that are characterized by heavy and regular rainfall from roughly October to March. (Ho, 2002). Malaysia covers an area of 330,000 km² comprises two regions, namely Peninsular Malaysia and the States of Sarawak and Sabah, The average annual rainfall is estimated at 2420 mm for Peninsular Malaysia, 2630 mm for Sabah and 3830 mm for Sarawak. The total annual surface water resources are estimated at 566 billion m³ with 147, 113 and 306 billion m³ for Peninsular Malaysia, Sabah and Sarawak respectively. The topography of Peninsular Malaysia is characterized by central mountains which slope steeply to the relatively flatter undulating coastal plains on the eastern and western sides with ground elevations of up to 2000 m above mean sea level. Similar terrain exists in Sabah and Sarawak. More than 150 rivers existed in the country; the rivers path is short with steep gradients in the upper stretches and flat with meandering stretches in the lower reaches. It has been estimated that some 29,000 km² or 9% of the total land area are flood prone, affecting more than 15% of the total population. (Keizrul, 2003) The objectives of the present study include the following: (1) to develop a hydrological model for the rivers of the Muda Basin (Figure 1) that is capable of accurately simulating spatially distributed flow patterns within ephemeral rivers that are characterized by exceptionally complex channel systems, highly variable flow regimes. (2) develop a computer model of the Muda River System within the study area to define the nature and extent of the flood hazard;(3) model the effects of existing developments and existing flood mitigation measures to determine their impact on flooding.