Iowa Bridge Backwater Software Users Manual Version 1.0 TR-476, September 2003

(2003) Iowa Bridge Backwater Software Users Manual Version 1.0 TR-476, September 2003. Transportation, Department of

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Abstract

This manual describes how to use the Iowa Bridge Backwater software. It also documents the methods and equations used for the calculations. The main body describes how to use the software and the appendices cover technical aspects. The Bridge Backwater software performs 4 main tasks: Design Discharge Estimation Stream Rating Curves Floodway Encroachment Bridge Backwater Design discharge estimation: Design discharges are estimated by 2 methods, both from USGS reports for flood frequency in Iowa (Lara, 1987, Eash, 2001). Stream Rating Curves: Stage versus discharge relationships for streams are estimated using the Manning Equation and assuming uniform flow. This is a user friendly replacement for the PC VAL program previously used in Iowa. Floodway: Floodway encroachments can be computed, using the methods and assumptions of the Iowa Department of Natural Resources, Water Resources Division. Bridge Backwater: The estimation of backwater from bridges is a major portion of the software. The methods used by the Iowa Department of Transportation (IDOT) and Iowa Department of Natural Resources (IDNR) for Bridge Backwater Estimation are used. These methods are based on methodology from Hydraulic Design Series 1 (HDS-1), Hydraulics of Bridge Waterways, Federal Highway Administration (FHWA), 1970. Hydraulic Design Series 1 will be referenced throughout the manual, as HDS-1.