Scour Evaluation for the Nile River Bends on Rosetta Branch

Abstract

The objectives of this research were to analyze and evaluate the effect of releasing flow discharges on river meandering in addition to estimating the local scour at 13 bridge piers distributed on 3 bridges located on Rosetta branch. The meandering length was 3.5 Km (from km 145.00 to km 148.50) D.S of El-Roda Gauge at Kafr El-Zayat City. Several sorts of data were collected including site maps, velocity measurements, bed samples, hydrographic survey data, water levels and discharges at several years and seasons, as well as visual inspection photos to be used in the current study. The configurations in bed level, the thalwege line, and the scour holes were determined by comparing the surveyed entire reach at years 1982, 1998, 2003 and 2006. Study area was simulated four times by 2-D mathematical model “SMS” using a survey reach at years 1982, 1998, 2003 and 2006. This was done to estimate the velocities and the water levels for different discharges at the entire reach. The flow was used as upstream boundary condition and the water level was used as downstream boundary condition. The model was calibrated and verified using the field measured velocities. Two proposed alternatives were suggested and numerically simulated separately. The first alternative, the outer bends were filled with layers of filter and riprap to level -5.00 m MSL. The second alternative included filling the scour regions to level -5.0 m MSL in additional to dredging the inner sides of the bends where sedimentation regions were located to level -3.00 m MSL. The two alternatives were numerically tested under maximum and emergence flows. The results analysis proved that flow conditions were enhanced and improved under the second alternative when compared to the first one. Based on the results, layers of filter and riprap were designed to fill the scour holes.