CSS were engaged as subconsultants by The Balmoral Group USA, to complete the hydrologic and hydraulic analysis for the proposed upgrade of the Fannie Road Bridge crossing of Big Escambia Creek in Escambia County, Florida.
Peak discharges were estimated using regional regression analysis and were verified through application of flood frequency analysis techniques based on Bulletin 17B of the Interagency Advisory Committee on Water Data (1982). Inputs to the regression analysis were extracted from a CatchmentSIM project of the Big Escambia Creek catchment that was developed using LiDAR information. The Big Escambia Creek catchment was determined to occupy a total area of 878 km2.
Flood behaviour along Big Escambia Creek was defined using a two-dimensional hydraulic model that was developed using the RMA-2 software. The RMA-2 model was used to simulate flood behaviour for ‘existing’ conditions as well as ‘proposed’ conditions for 2 different bridge replacement options. Difference mapping was prepared showing the spatial distribution of increases and decreases in peak flood level and flow velocity.
The velocity estimates generated by the RMA-2 model were used in conjunction with detailed geotechnical information to prepare contraction and pier scour estimates. The scour estimates were used to assist in the design of the bridge piers