Integrated Triangular Irregular Network (ITIN) Model for Flood Risk Analysis Case Study: Pari River, Ipoh, Malaysia Shanker Kumar SINNAKAUDAN, Aminuddin AB GHANI, CHANG Chun Kiat, Mohd. Sanusi S. AHMAD & Nor Azazi ZAKARIA River Engineering and Urban Drainage Research Center (REDAC), Engineering Campus, University Science Malaysia, 14300 Nibong Tebal, Penang, MALAYSIA Email: redac04@eng.usm.my Tel: +604 – 5937788 ext 5465 Fax: + 604 – 5941036 Abstract Accurate river channel and flood plain representation plays vital part in flood risk analysis (Sinnakaudan; 2001 b ). Terrain models such as TINs and DEMs are normally used to represent floodplains. But unfortunately finding a terrain model with a high density of stream channel elevation points that are sufficient for hydraulic modeling is not a easy task. However for years engineers and researchers have developed a high-resolution cross-section data for hydraulic modeling from field surveys, photogrametries and topographic maps. This research presented here introduces the procedures for creating integrated multiresolution TIN (ITIN) models for high-resolution flood plain representation for flood risk analysis. The high-resolution river channel geometric data stored in HEC-6 hydraulic model and low-resolution flood plain data in the form of DEM created in ArcView GIS 3.2a were integrated by resolving the coordinate incompatibility in the both system. An integration procedure (ArcView extention) namely AVHEC6.avx has been developed between HEC-6 Hydraulic Model and ArcView GIS 3.2a to visualize model outputs in a more presentable manner through 3D capabilities of GIS. Keywords: ITIN; DEM; GIS; HEC-6; Flood Risk. Introduction Triangulated Irregular Network model or TIN is a finite set of points which are stored with their elevation. The model is a piecewise linear model that in 3 Dimensional space can be visualize as a simply connected set of triangles [3; 18]. The heirarchical or multiresolutional TIN model allows a mixture of different detail levels in parts of the terrain, which are very much suitable for flood plain analysis [18; 13; 17]. The idea of creating a multiresolution TIN is rather old, and detailed literature reviews can be found in the forms of graphics, GIS, algorithme foundation, and others areas [8; 9; 10]. However the usage of TINs in flood plain analysis is gaining much attention recently due to dramatic increase in the capability of desktop-based Geographic Information System (GIS) to perform more sophisticated tasks in spatial data management [1; 13; 17; 15] Terrain representation with high accuracy would be the most important task in visualizing areas inundated by floods. Constructiong a continuous floodplain terrain model with a high density of stream channel elevation points sufficient for hydraulic modeling are cost intensive and generally not available. However for years, engineers and researchers have developed a high- resolution cross-section data for hydraulic modeling from field surveys, photogrametries and topographic maps [2; 19, 16; 13; 12]. The problem is that these high-resolution data used to simulate the hydraulic models such as HEC-6 and FLUVIAL-12 are often stored in hydraulic coordinate systems (referenced by the location of the river stations and elevations- Sta, Elv) and incompatible with GIS coordinate structure (referenced by east (x-coordinate), north (y-coordinate) and elevation (z-coordinate) [17; 13]. Currently, there are no available methods with which to integrate HEC-6 hydraulic model output data with ArcView GIS. The study presented herein utilizes the simulated results from HEC-6 hydraulic model and ArcView GIS 3.2 (with Spatial Analyst and 3D Analyst extensions) [4;5;6;7] to offer an approach to resolve this deficiency by using the hydraulic and hydrological data from Pari River catchment in Ipoh, Perak, Malaysia (Fig. 1). The Methodology The HEC-6 model was simulated using 2 sets of geometric data as shown in Table I. The first set of data contains only the information for river channel and flood plain within the bund (Fig.2a). The second set of data is extended to 200 meter to the left and right side of the bund (Fig.2b). The sample cross-section output for each data was shown in Fig. 3 and Fig. 4. An ArcView GIS extension namely AVHEC-6.avx was written in an Avenue Script language and Dialog Designer with a series of ‘point and