Agenda - Council - 01/27/2009 - Laserfiche WebLink

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2 discharges and the effective hydrology. The revised hydrologic analysis resulted in a base flood discharge of approximately 580 cfs for the project reach. The effective HEC -2 hydraulic model was imported into the HEC -RAS model using the effective discharges to create a duplicate effective model. The duplicate effective BFEs matched the effective BFEs in the FIS report within 0.1 foot. For comparison purposes, the revised discharges were inserted into the duplicate effective model to replace the effective discharges. Our review revealed that, as a result of the decreasing discharges, the BFEs will decrease in all locations. The maximum decrease in BFE, 1.1 feet, occurred approximately 1,600 feet upstream of the Ermine Boulevard Northwest Culvert. The existing conditions (corrected effective) model was created by incorporating updated topographic information into the duplicate effective model (with revised discharges). Our review of the corrected effective model revealed that the BFEs both increased and decreased compared to the BFEs in the duplicate effective model (with revised discharges). The maximum increase in BFE, 0.5 foot, occurred approximately 1,500 feet upstream of the Ermine Boulevard Northwest Culvert. The maximum decrease in BFE, 0.7 foot, occurred just downstream of the Ermine Boulevard Northwest Culvert. The proposed conditions model was created by replacing the existing 72 inch culvert at Ermine Boulevard Northwest with the proposed single 14 -feet span by 6 -feet rise culvert. Our review of the proposed conditions model revealed that the BFEs both increased and decreased compared to the BFEs in the corrected effective model. The maximum increase in BFE, 0.01 foot, occurred approximately 60 feet downstream of the Ermine Boulevard Northwest culvert. The maximum decrease in BFE, 0.7 foot,occurred approximately 70 feet upstream of the Ermine Boulevard Northwest Culvert. As a result of the revised hydrologic analysis, the updated topographic information, and the proposed project, the BFEs will decrease compared to the duplicate effective (with effective discharges) BFEs. The maximum decrease in BFE, 1.1 feet, occurred just downstream of the Ermine Boulevard Northwest Culvert. As a result of the revised hydrologic analysis, the updated topographic information, and the proposed project, the BFEs will decrease compared to the duplicate effective (with revised discharges) BFEs. The maximum decrease in BFE, 0.7 foot, occurred just downstream of the Ermine Boulevard Northwest culvert. As a result of the revised hydrologic analysis, the updated topographic information, and the proposed project, the width of the SFHA will increase in some areas and decrease in other areas compared to the effective SFHA width along Trott Brook. The maximum increase in SFHA width, approximately 360 feet, will occur just downstream of Ermine Boulevard Northwest. The maximum decrease in SFHA width, approximately 400 feet, will occur approximately 100 feet upstream of the Ermine Boulevard Northwest Culvert. As a result of the revised hydrologic analysis, the updated topographic information, and the proposed project, the floodway width will increase in some areas and decrease in other areas compared to the effective floodway width along Trott Brook. The maximum increase in floodway width, approximately 360 feet, will occur just downstream of Ermine Boulevard Northwest. The maximum decrease in floodway width, approximately 100 feet, will occur approximately 600 feet upstream of the Ermine Boulevard Northwest Culvert. Upon completion of the project, your community may submit the data listed below and request that we make a final determination on revising the effective FIRM, FBFM, and FIS report.