الفهرس 
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Abstract
The objectives of this research are to analyze and evaluate the effect of releasing flow discharges on river meandering and the scour at the bridge piers. This part of river meandering includes 13 piers distributed on 3 bridges. The meandering reach is located on Rosetta branch. It is consisting of two successive bends of length of 9.0 Km from km 145.00 to km 154.00 D.S of El-Roda Gauge at Kfer El-Zayat City. This reach is selected to conduct the current investigation. 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. The developing of bed level, thalwege line and scour holes were determined by comparing the surveyed entire reach of years 1982, 1998, 2003 and 2006. Study area was simulated four times by 2D mathematical model “SMS” using a survey reach of years 1982, 1998, 2003 and 2006. This was done to estimate the velocities and the water levels at different discharges on 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 measured velocity data. The model was run for sixteen times at different flow conditions (minimum, average, maximum and emergency). The resulted velocities of these runs were compared. The obtained results showed the local scour in bridge piers. The empirical equations used to predict the general scour, contraction scour and bend scour of the whole reach and around bridge piers.Two proposed alternatives were suggested and simulated separately by the SMS model. In the first alternative, the outer bends were filled with layers of filter and riprap up to level -5.00 m MSL. In additional to alternative 1, the inner sides of the bends were dredged to level -3.00 m MSL as second alternative. The model was run for the two alternatives at maximum and emergence flows with its corresponding water levels. The results illustrated that the second alternative improved the flow conditions better than the first one. Based on the results, layers of filter and riprap were designed to fill the scour holes.The empirical equations were used to predict the long term degradation and bend scour of the bed morphological changes along the entire reach of the Rosetta Branch. 2-D model was used to scour at the bridge piers in the study area was predicted using 2-D (SMS) model considering two scenarios of high river discharges. The results showed that in case of discharges released were maximum (69.90, 220.00m.m3/day), the total scour evaluated at the 3 bridges were, (11.65, 16.93m) for bridge No.1, (9.08, 13.35m) for bridge No.2 and (9.11, 14.07m) for bridge No.3. The expected extend of the scour holes around the main piers of the Bridges were also predicted. It is recommended to follow up the dimension of the scour holes every year or after occurring high floods.