HYDRAULIC PERFORMANCE OF BRIDGES EXCAVATIONS AT BRIDGES by B.E. Colson and K.V. Wilson, Hydrologists Conducted by UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY for Mississippi State Highway Department in cooperation with Federal Highway Administration U.S. Department of Transportation September 1973 TABLE OF CONTENTS Abstract Introduction Background     Definition of symbols Site description Field data Analysis of data Conclusions References TABLES 1. Floodflow data, Big Black River near Canton, Miss. (relief opening 2) 2. Floodflow data, Big Black River near Canton, Miss. (relief opening 1) 3. Floodflow data, Big Black River near Canton, Miss. (relief opening 3) 4. Floodflow data, Big Black River near Canton, Miss. (relief opening 4) 5. Floodflow data, Big Black River near Canton, Miss. (relief opening 5) ABSTRACT Excavation increaseS the hydraulic capacity of bridges where the minimum flow area occurs under the bridge. Excavation under bridges as a means of increasing the hydraulic capacity was studied by observing the fall and discharge through five bridge openings across a singlw flood plain. Three of the bridges had total get-a-way areas larger than the areas under the briges before excavation and increased in hydraulic capacity were indicated. A fourth bridge had a get-a-way sub-area larger than the excavated areas near the abutments and an increase in hydraulic capacity was also indicated. One bridge had a restricted area just downstream which acted as the control area and no increase in hydraulic capacity was indicated. Data from one bridge indicated that the maximum effective area is equal to the minimum area measured along the upstream or downstream perimeter of the excavation. After excavation, velocities were less uniform and were greater near the bottom than at the surface. The usable data in this report are limited to a single excavation for each bridge. Therefore, optimum excavation geometry for bridges will require further study. LizardTech's Djvu plug-in is needed to view these reports. CLICK HERE TO VIEW THE ENTIRE REPORT For questions or comments, contact K. Van Wilson.