ACCURACY OF DEM-BASED TOPOGRAPHIC DATA IN FLOOD INUNDATION MODELLING: A CASE OF WAMI RIVER, TANZANIA
Abstract
Ihe objective of this Biper is to evaluate and further convnent on the accuracy of the DEW- based topographic data us input in flood mchdelling. Recent studies have indicated that hydraulic of the modified sections based on high resolution are geometrically and hydraulically similar to the measured ones, In the study hydraulic modelling intended to guide a developnent project whereby a protection embankment is contemplated. Therefore, accuracy in terns of positioning/alignment of natural features such as river banks and heights/elevarions was imperative m arrain. In order m achieve these, accuracy of various topographic data sources were qualitatively and/or quantitatively before and after hydraulic modelling, As the river reach is ungauged the hydraulic and with field available iLfonnation and professional judgement. Bused on error analysis, i' was found that uncalibrated 90m resolution SIRM DEM-based topographic data are biased ie., 80% of the error mass is negative. The error increases with elevation The final input to the hydraulic model was a composite/hyhrid DEM derived after merging geometric dara from four representative field-measured cross sections, a 2-m interval contour map covering part of the river valley, and calibrated Wm resolution DEM. Although, calibration improves rhe data, it does nor remove completely the inherent bias. Funher ro DEM calibratiom it was rherefore recommended to include an elevation uncertainty value of -0.5 m, as derivedfrom topographic analysis, into simulated water surface profiles elevations. The hydraulic model satisfactorily simulated flfh'd inundation extent after considering the elevation uncertainty. In order to improve rhe findings further studies should use adequate measured crass sections and DEM of higher resolutions
Recommended Citation
Ndomba, P. (2014). ACCURACY OF DEM-BASED TOPOGRAPHIC DATA IN FLOOD INUNDATION MODELLING: A CASE OF WAMI RIVER, TANZANIA. Tanzania Journal of Engineering and Technology (TJET), 35(1), 15-35. https://doi.org/https://doi.org/10.52339/tjet.v35i1.466
Publisher Name
University of Dar es Salaam