K-4 - Professional Services Agreement - Highway 6 Reconstruction - MSA

o USGS flood frequency regression equations for Iowa. o Gauging station including, as applicable, a Log-Pearson Type III distribution or transferring gaged discharges from other locations. o Evaluation of design flows for structures along the same watercourses, if available. • Hydraulic Design o No existing floodplain models exist for any of the locations to be analyzed. For this design, MSA will construct an existing conditions HEC-RAS model which will be used to evaluate up to three (3) alternative replacement culverts. Alternatives will be evaluated according to their ability to pass 100-yr flow rates with no (0.00-ft) increase in flood elevations upstream of the highway accounting for possible effects related to raising of the roadway profile. • Report Documentation o MSA will prepare a short technical memorandum with supporting figures documenting the findings of the study. It is anticipated that this memorandum will be no longer than two (2) pages, not including figures. Limited Detail Designs. MSA will complete limited detail hydraulic design for one (1) culvert located approximately 0.3 miles west of the intersection of Hwy 6 and Park Rd. Hydraulic sizing will be completed for the culvert according to the following tasks: • Design Flow Estimates o Delineate watersheds. The drainage area tributary to the culvert will be delineated using GIS tools and topographic mapping available from online sources. o Develop runoff coefficients. Runoff coefficients including curve numbers and times-of-concentration values will be developed for each culvert’s watershed. Land uses will be assigned using GIS tools and input data including parcel mapping, tax assessment information (if available/appropriate), aerial photographs, and NRCS soil maps. Curve numbers will be assigned according to land use types and underlying hydrologic soil groups. Times-of-concentration values will be calculated using land use classifications assigned in the previous step and topographic mapping available from online sources. o Peak flow rates for design events will be determined using the computer model HydroCAD. • Hydraulic Design of Culverts o The required size of the culvert will be determined using a spreadsheet tool designed by MSA that utilizes Manning’s equation to estimate barrel-control hydraulic capacity and the orifice equation to estimate inlet-control capacity. • Report Documentation o MSA will prepare a brief technical memorandum describing methods and design results.