FLOOD02774 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I II II I II I I I I I I The cost estimates shown in table 2 do not include the costs for bridge improvements that would be required in order to achieve the specified levels of protection. Further analyses would be required to size the necessary bridge structures and estimate their costs, Real estate acquisition for right-of-way and easements costs were not estimated for this study, Floodplain Issues The effects of the proposed facilities on the existing conditions flood boundaries were evaluated using non-detailed methods and engineering judgment. In summary, the flooding problems at Pipestone are a result of bridge constrictions and inadequate ditch capacities, The channel constriction where Main Ditch flows through the Highway 75, Highway 23, and Burlington Railroad bridges causes severe backwater effects during large flood events. The existing bridges at 9th Avenue NE and at Hiawatha A venue also cause flows to backup during large flood events, Inadequate ditch capacity is another factor that creates flooding problems within the City. In general, construction of the Main Ditch channel improvements, new diversion channel, and culvert crossing downstream of 9th Street NE would help to reduce the 100-year and 500-year floodplain limits in that area. However, construction of the proposed levees upstream of 9th Street NE would not necessarily improve, and may actually worsen, the flooding problems along that reach if the appropriate bridge modifications are not made. Backed up flows behind the bridges would tend to overtop or go around the levees causing flood damage within the levee- protected areas. The flooding problems could then be exacerbated by levee failure or by ponded water within the interior drainage areas that would drain more slowly than for existing conditions. A thorough hydraulic analysis would be required prior to final design of the levee improvements. Acquisition of Commercial and Residential Structures Conceptual evaluations for acquisition of commercial and residential structures within the 100- year floodplain in Pipestone were performed as part of this study, Preliminary cost estimates for the acquisitions were also prepared and are presented in table 3. Data and analyses from the previous Section 205 Reconnaissance Study were used as the basis for the evaluations and cost estimates for this study, Land use data for both residential and commercial structures were previously collected for Pipestone within and just outside of the Main Ditch 500-year flood plain limits. Data compiled for each structure included the estimated ground elevation, the estimated first floor height above the ground, the type of structure, and the structure's market value. Market values were estimated for each building (or group of buildings) based on the assessed values (1994) obtained from the 12