The effect of riverine terrain spatial resolution on flood modeling and mapping

Abstract

Spatial resolution of river and riverine area is an important aspect of hydraulic flood modeling that affects the accuracy of flood extent. This study compares the accuracy of Digital Elevation Models (DEMs) produced from three methods of land surveying measurements and their effect on the results of river flow modeling and mapping of floodplain. Four data sets have been used for the creation of the DEMs: Light Detection and Ranging (LiDAR) point cloud data (raw data and processed), classic land surveying and digitization of elevation contours from 1:5000 scale topographic maps. LiDAR offers advantages over traditional methods for representing a terrain. Optech ILRIS-3D (Intelligent Laser Ranging and Imaging System) is a land based LiDAR system and has been used in this study. Separating LiDAR points into ground and non-ground is the most critical and difficult step for DEM generation from LiDAR data. In this study, geomorphologic filters, GIS operations and expert knowledge have been applied to produce the bare earth DEM. The HEC-GeoRAS and HEC-RAS software have been used as pre- and post-processing tools to prepare model inputs, simulate of river flow, and delineate flood inundation maps. The methodology has been applied in the suburban part of Xerias river at Volos-Greece, where typical hydrologic and hydraulic methods for ungauged watersheds have been used for flood modeling and inundation mapping. The results show that flood inundation area is significantly affected by the accuracy of DEM spatial resolution and could have significant impact on the delineation and mapping of flood hazard areas.