Harmonizing Dam Rehabilitation with Floodplain Management

Abstract

The Yellow River Watershed Structure No. 15 (Y-15) is a project that has been ongoing for Gwinnett County since the year 1999 with sometimes insurmountable political, technical, and financial hurdles. Residents did not support the project and application of the design criteria resulted in massive and costly spillway improvements to bring the structure into compliance with the high hazard design criteria. In mid 2004 Golder Associates Inc. was contracted by Gwinnett County for the design of the conceptual solution proposed by previous consultants. Golder’s evaluation of the conceptual design identified several modifications could be made to the preliminary design parameters. During preliminary design, the proposed spillway was significantly modified such that the size of the chute was reduced by 30% (over 200 linear feet) and the proposed ogee weir was replaced by a broad-crested weir. These changes were possible by modifying the spillway crest to permit additional flow during more frequent storm events, but the existing mapped 100 year floodplain remains unchanged. Golder’s proposed reduction in the size of the spillway structure aided in the final acceptance of the project by local residents.