Analysis of the accuracy in producing flood risks models by GIS, LiDAR and HEC-RAS approaches.

Abstract

Changes in the hydrological patterns have been related to the climate change and anthropogenic activities in the last decades. Floods occur when the water carried per unit time exceeds the river channel capacity and the riverbanks are overpassed. The River Tay (Perth, Scotland) was chosen for this study due to its long history of well documented flood events. However, due to its wide variability in its hydrological factors, the study area was limited to the river section between the junction of the rivers Tummel and Tay, and Dunkeld village, in the Pitnacree Reach. The results obtained from HEC-RAS approach were the most accurate and realistic. The averaged bankfull depth, hydraulic radius, flow velocities and critical shear stress for mean flow discharges were 1.6 metres, 1.5 metres, 0.87 m3/s, and 0.0085, respectively. The maximum depth value was 3.03 metres of height. The averaged bankfull depth, hydraulic radius, flow velocity and critical shear stress for QMED discharges are 3.1 metres, 3.01 metres, 1.5 m3/s, and 0.0121, respectively; the maximum bankfull depth had 5.9 metres of height. The results analysis concluded that changes in the hydraulic parameters of the river channel have significant impacts in its morphology and geometry, affecting directly to the flood risks models and flood extent maps. In addition, it was also concluded that HEC-RAS approach produced accurate flood risks and flood extent maps for the reach under study, therefore, they could be used to improve land management plans to mitigate flood impacts in this riverine area full of agriculture embankments.