Investigating Causes of Highway Crossing (Bridges and Culverts) Outlet Erosion in Selected Structures of Mekelle to Adigrat Highway - Tigray, Ethiopia

Abstract

Roads are backbones for one’s country economy and play great role in public’s mobility. To make these well function proper drainage systems must have; and these drainages are major causes for land degradation and gully formation. This investigation was conducted in selected road crossings; Agulae river bridge and Kehen and Betehaweriat culverts of Mekelle to Adigrat highways using hydrologic and hydraulic analysis. Hydrologic and hydraulic analysis was conducted with the help of HEC RAS 4.1.0 for bridge and HY 8 hydraulic analysis software’s for culvert. Agulae river bridge has scouring problem up to 13.00 m, 13.96 m left and 18.97 m, 20.04 m right for 50 and 100 years peak flood; and overtopping 0.24 m for 50 years. Kehen and Betehaweriat culverts have high outlet velocity 6.456 m/s and 5.241 m/s and high Froude number, 3.4 and 2.92 respectively. Remedial measures were reviewed based on the hydraulic analysis result computed. Based on hydraulic analysis results; the recommend energy dissipaters are 1.204 m thickness stone riprap for bridge; and USBR type IV basin for culverts.