Lower Byersville Creek Flood-Risk Mapping Update - City of ...

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City of PeterboroughLower Byersville Creek Flood-Risk Mapping UpdateRESULTS OF ANALYSISFigure 3.1Rainfall of July 14-15, 2004 over Byersville Creek Watershed3-2087-09-01/R_3-04108226_Byersville Creek Mapping Update 3-208/11/10
City of PeterboroughLower Byersville Creek Flood-Risk Mapping UpdateRESULTS OF ANALYSIS3.1.3 Flows Computed By PCSWMM ModelAppendix C provides a detailed presentation of peak flows computed by thePCSWMM EXTRAN model for the lower Byersville Creek watershed.The peak flows computed by the EXTRAN model for a numerous set of conduitsrepresenting the various flow paths within the area, was resolved into a simplified setof peak flows to be applied in the steady-state HEC-RAS model.Detailed model output tables presented in Appendix D show the flow values appliedwithin the HEC-RAS model.3.1.4 Mapping of Surface Flooding Using HEC-RASFigure 3.2 presents the mapping of estimated surface flooding for the July 14-15,2004, as determined from the water surface elevation computed by the HEC-RASmodel using peak flows from the PCSWMM2005 model.The mapping of the surface flooding areas has been carried out using the DEMsupplied by the City. The general procedure for mapping out the surface floodingareas is as follows:• Water surface elevations computed by HEC-RAS at each cross-section (sectionlocations are shown on the map figure) are considered to be the water surfaceelevation along the full width of the cross-section.• Between each cross-section, the water surface is assumed to be an inclined, flatplane. GIS software tools are used to map out where this plane intersects theground surface defined by the DEM. This intersection is the edge of the surfaceflooding area.• The results are reviewed and adjustments are made in locations where the initialmapping does not appear reasonable when considering topographic contouringand considering whether surface flow from the main path of flow could inactuality spread laterally to all locations indicated on the initial mapping.The PCSWMM EXTRAN surface/overland flowrates presented in Appendix C, andthe resulting mapping of surface flooding as shown on Figure 3.2 demonstrate whatcan be considered as acceptable model performance. The directions and depths ofsurface flow, and the mapping of surface flooding areas appears to be a reasonablyaccurate reflection of what is known to have actually taken place during the 2004event.It should be noted that this favourable result did in part depend on relying on roughestimates of the breadth and depth of the washouts of the former CNR embankmentas reported by local residents, and an assumption that there was 60% blockage of theErskine Avenue storm inlet.3-2087-09-01/R_3-04108226_Byersville Creek Mapping Update 3-308/11/10
Page 1 and 2: EXCELLENCE INENVIRONMENTALCONSULTIN
Page 3 and 4: City of PeterboroughLower Byersvill
Page 17: City of PeterboroughLower Byersvill
Page 25 and 26: WEBBER AVRALPHSON CRWENTWORTH ST1+0
Page 33 and 34: APPENDIX A: PHOTOS PROVIDED TO XCG
Page 43 and 44: February 9, 2010Dear Resident,XCG C
Page 45 and 46: MOUNTAIN ASH RDBARNES CRROBERT RDER
Page 47 and 48: ResponseNo.XCG file 3‐2087‐09
Page 49 and 50: XCG file 3-2087-09-01 APPENDIX B Pa
Page 53 and 54: C.2.1 Subcatchment Refinements:Refi
Page 55 and 56: FIGURE C-2: SCHEMATIC OF MODIFIED P
Page 57 and 58: For the Regional Storm, the event r
Page 59 and 60: Photo date May 28, 2007Photo date M
Page 61 and 62: WEBBER AVRYE STMOUNTAIN ASH RDROBER
Page 65 and 66: FIGURE D-3 Examiner Ditch West Spil
Page 67 and 68: TABLE D-3HEC-RAS RESULTS for EVENT
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TABLE D-5HEC-RAS RESULTS for EVENT
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TABLE D-7HEC-RAS RESULTS for REGION
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TABLE D-9HEC-RAS RESULTS for REGION
Page 75 and 76:
TABLE D-11HEC-RAS RESULTS for REGIO
Page 77 and 78:
TABLE D-13HEC-RAS RESULTS for REGIO
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Lower Byersville Creek Flood-Risk Mapping Update - City of ...

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