Rupayan Saha

Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Civil and Environmental Engineering

Committee Chair

Seung Ho Hong

Committee Co-Chair

Omar I Abdul-Aziz

Committee Member

Leslie C Hopkinson


Recently, United States faced catastrophic flooding in West Virginia, Texas, Louisiana, Oklahoma, and Arkansas, and the flooding resulted in several bridge failures. Among them, Bridge scour is one of the main causes of many bridge failures, and leads to financial losses as well as loss of life. Since 1960, a lot of scour research has been completed and several estimation methods were already in the hand of hydraulic engineers. However, scouring is still a challenging topic. Currently, the issues of scour are once again rising because the occurrence of extreme weather events are expected to increase in frequency. Furthermore, current practice of scour estimation shows over-prediction and sometimes, under-prediction. One possible reason is adding separate estimates of contraction and local scour when in fact these processes occur simultaneously. Another possible reason is that current scour equations are based on experiments using free-surface flow in idealized-rectangular flumes even though extreme flood event can cause bridge overtopping flow in combination with submerged orifice flow and the resulting scouring depth is site-specific. In this study, experiments were carried out by professor Hong at the hydraulics laboratory in the School of Civil and Environmental Engineering at the Georgia Institute of Technology in a compound shape channel using 1:60 bridge model of the Towaliga River Bridge at Macon, Georgia including river bathymetry in different flow conditions (free, submerged orifice and overtopping flow). Finding a solution regarding maximum scour depth calculation in clear water scour condition using required analysis of experimental results is contributed by myself. Based on the findings from laboratory experiments coupled with widely used empirical scour estimation methods, such as Colorado State University (CSU) pier scour equation, Melville-Sheppard equation and Ambient pier scour method, a comprehensive way of predicting maximum scour depth is suggested which overcomes problem regarding separate estimation of different scour depths. During the analysis, the effect of flow contraction on local scour was evaluated, and the result confirmed the necessity of single scour depth prediction method rather than separate estimation of different scour depths. In addition, an area-average contraction scour depth prediction method using ambient bed elevation around the local scour was also suggested and analyzed by measured flow contraction ratio. Also, the effect of vertical flow contraction and the effect of existence of a pier bent (located close to the abutment) on the maximum scour depth was investigated. The results show that in pressure flow, a combination of lateral and vertical contraction boosted the maximum scour depth. Results from the existence of the pier bent show that the location of maximum scour depth is unbiased on the presence of the pier bent but the amount of maximum scour depth is relatively higher due to the discharge redistribution when the pier bent is absence rather than its presence.