A Study on the Assessment of Bridge Pier Shape to Minimize Local Scour

Local Government Engineering Department (LGED) intends to construct a bridge over the river Shitalakhya on Kapasia (Lalon Bazar) to Bashgram GC via Panli GC via Horinaraynpur GC via Kushalibaha Hat road in the Kapasia Upazila of Gazipur District. The horizontal lay out of the bridge in UTM projection system at Left Bank (Dhandia Bottola Bazar) is 24°04'26.83"N & 90°37'52.64"E and at Right Bank (Raniganj Bazar) is 24°04'32.26"N & 90°38'03.54"E. Estimated Standard High Water Level is 7.520 mPWD, minimum vertical navigational clearance as per BIWTA is 7.620m and calculated deck height is 2.950m. Thus clear height of the bridge is 15.140 mPWD and crest of the deck level of the bridge at mid point is 18.090 mPWD. The pier scour depth has been calculated as per Manual on hydrologic and hydraulic design of bridges prepared jointly by Bangladesh University of Engineering and Technology (BUET) and Institute of Water Modeling (IWM) in 2008. Seven (7) methods as Breusers [1965], Laursen [1963], Neill [1987], Jain and Fischer [1980], Chitale [1988], Melville [1997] and Richardson & Davis [1995] have been applied for pier scour depth calculation among which Jain and Fischer [1980] method shows the highest scour depth. The present study shows the scour depth for different methods with different effective pier width for non-uniform pier instead of uniform pier.