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• ` : <br /> Public Works Memoraodum <br /> NO. 2010-19 <br /> DATE: Apri123, 2010 <br /> TO: Honorable Mayor McElroy and City C ncil <br /> FROM: Ryan P. McCrady, City Manager � <br /> Richard G. Marley, P.E., Director of Public Works �C-a.Z ��( G� <br /> SUBJECT: Agreement with Hanson Professional Services, Inc. for Lake Decatur <br /> Dam Hydraulic Study <br /> SUMMARY RECOMMENDATION: <br /> It is recommended that the City Council approve the attached resolution authorizing an <br /> agreement with Hanson Professional Services, Inc., (Hanson)to conduct the Lake Decatur <br /> Dam Hydraulic Study for a fee not to exceed $70,100. <br /> PRIOR COUNCIL ACTION: <br /> Appendix A provides a summary of the prior Council action. <br /> BACKGROUND: <br /> The Sangamon River channel located immediately downstream of the dam has experienced <br /> scour due to outlet flow from the spillway and gated outlet works. As part of the Illinois <br /> Department of Natural Resources' (IDNR) Join Application for Permit review, they <br /> suggested that the City continue to observe and maintain the channel bottom to prevent <br /> additional scour. A large scour hole was noted in preliminary inspections of the stream bed. <br /> Scour damage has the potential to undermine the integrity of the dam. <br /> The Lake Decatur Dam Repair project, City Project 2009-02, is scheduled to begin in early <br /> May. The work will require the downstream side of the dam to be dewatered, which will be <br /> an excellent time to perform a thorough inspection of erosion and scour damage in the <br /> streambed. Once complete, Hanson will perform a hydraulic analysis of the existing dam to <br /> model the existing condition; evaluate the predicted scour below the dam; and recommend <br /> countermeasures. <br /> POTENTIAL OBJECTION: There are no known objections to this resolution. <br /> INPUT FROM OTHER SOURCES: Department of Water Management, Hanson <br /> Professional Services, Inc., and Illinois Department ofNatural Resources <br /> STAFF REFERENCE: Richard Marley, Director of Public Works, Keith Alexander, <br /> Director of Water Management, Matthew Newell, City Engineer and Curtis Cassidy, Civil <br /> Page � 1 <br />