Investigating the Effects of River Channel Meander on Bridge Hydraulics

Meanders in a river channel can result in significant changes in river hydraulics, and in time, the river could transform into an entirely different river from what it was originally. River Mayogwa in Jalingo, Taraba State is one of such rivers that have undergone remarkable change of course over the years. This paper was aimed at investigating the effect of a sinuous meander at the upstream reach of the bridge on flow characteristics at the inlet and outlet of the bridge. A ground survey of the river channel and flood plain was first undertaken. Digital elevation model (DEM) of the area was then created in Geographic Information System (GIS) using the survey data as input. The 50-year and 100-year discharges at the bridge point were determined using the Hydrological Engineering Corps Hydraulic Modelling System (HEC-HMS). The digital elevation model and the river discharge at the bridge were used as input in the Hydrological Engineering Corps River Analysis System (HEC-RAS) to simulate flow along the present river channel. Afterwards, the river was trained to straighten out the meander, and the flow hydraulics through this new (alternative) course was simulated again in HEC-RAS to study the effect of the new river course on the river hydraulics. The 50-year and 100-year discharges were obtained as 82.02 m3/s and 177.6 m3/s. Results showed that siltation on the downstream face due to the meander resulted in flow area reduction of 72.7% and 65% for the 50 years flood and 100-year flood respectively. The bridge was able to pass the 50-year flood without overtopping, but was overtopped by the 100-year flood, passing only 61% of the discharge. The alternative course will allow 94.5% of the 100-year flood to pass under the with a corresponding water surface elevation attenuation of 1.41 m downstream and 0.96 m upstream of the bridge. The river meander at the bridge section has severely impaired the flow of water through the bridge. The results obtained indicate that the bridge would be overtopped in the vent of the 100-year flood.