DEM elaboration in urban areas – methods in collecting and processing topographic data

Abstract

The city of Rio Grande is currently undergoing accelerated urban expansion driven by the dynamic economy of the maritime industry. The  consolidation of settlements associated with this rapid urban expansion has resulted in inefficient rainwater runoff, with occurrence of constantly flooding areas. The mainly flat morphology of the terrain (D z<1 m) combined with a lack of infrastructure has contributed to a critical urban drainage scenario at the Cassino Beach area. This work aimed at describing a method for collecting and processing topographical data, focusing on flooding-susceptible areas in Cassino. 191 elevation points were collected using a Geodesic GPS (Leica Geosystems), based on a regular grid; data was orthorectified using a geoid model. The collected elevation points were interpolated using two methods: Kriging and IDW. Comparison of the two DEMs with 30 control points showed mean altimetry
error of 0.227m and 0.218m for IDW and Kriging, respectively. Despite this difference, Kriging interpolation showed smoothed values and underestimated the absolute maximum, whereas IDW interpolation accentuated the absolute maximum, but with values close to the control points. Due to convergence and preservation of elevation variability, necessary for a correct large-scale hydrological model, the IDW DEM is recommended for hydro-geomorphological analyses at the study area.