Phase A - Alternatives Analysis Report - Urban Drainage and Flood ...

PHASE A – ALTERNATIVES ANALYSIS REPORTMajor Drainageway Planning Update for Hidden Lake-Bates LakeAlternative AnalysisThe general approach taken for the alternatives development was to minimize the extent of planned facilitiesto only those deemed necessary. Arterial road crossing improvements were designed for the 100-year eventand other facilities such as reconstructed channels and pipes were designed to convey the remainder of the100-year event that could not be contained within the road cross-section without flooding structures.Regional detention facilities were designed for full spectrum detention, which controls releases for all stormevents (minor and major) up to the 100-year storm. A detailed list of the alternatives considered and thecosts associated with them is presented in Section 5.• Alternative 1: No Drainageway Improvements – Maintain Existing ConfigurationThis alternative will maintain the existing channel, pipes, and crossing structures without considering anytype of improvements to increase conveyance or improve flood prone areas. It does consider generalroutine, restorative and rehabilitation maintenance of the existing channel and facilities.• Alternative 2: Regional DetentionThis alternative will either construct a regional detention facility to help attenuate peak flows or modifyexisting detention facilities to bring them up to District standards and draft an agreement between theprivate owner, the local sponsor, and the District for a flowage and maintenance easement on the facility.• Alternative 3: Improved ConveyanceThis alternative replaces undersized storm drain pipes, boxes, channels, and culvert crossings with ones thatwill convey enough runoff to minimize flooding damages in a 100-year storm event. This alternative alsoincludes constructing new channels, pipes, boxes, and culvert crossings where previously no improvementsexisted.Table ES-2 – Summary of Costs for Recommended PlanStructural Improvements $2,110,545Traffic Control $157,133Utility Relocations $133,076Land Acquisition $123,585Engineering, CM, & Contingencies $738,691Operation and Maintenance $97,000Total $3,360,030AcknowledgementsThis report was prepared with cooperation from local officials as well as the Urban Drainage and FloodControl District. In particular, we would like to acknowledge the assistance received from the District, theCity of Arvada, the City of Westminster, and Adams County.Participant NameKen MacKenzieShea ThomasBesharah NajjarKelly HargadinGeorgia SimpsonJohn BurkeTable ES-3 – Project Participants and StakeholdersOrganizationUrban Drainage & Flood Control DistrictUrban Drainage & Flood Control DistrictAdams CountyAdams CountyCity of ArvadaCity of Westminster• Alternative 4: Water QualityThis alternative improves the stormwater quality with in the study area. This will be accomplished byconstructing stormwater quality detention facilities either in the bottom of existing detention facilities,constructing new stormwater quality detention facilities, or directly connecting open channels to perviousareas allowing runoff to be filtered by vegetation and the soil before it reaches water bodies or groundwateraquifers.• Alternative 5: Combination of AlternativesThis alternative utilizes a combination of the alternatives presented above to provide the best overall plan toprovide a means of improving stormwater conveyance, reducing flooding, and improving stormwaterquality for the reaches identified in the Hidden Lake – Bates Lake project area.Recommended PlanThe recommended plan of improvements for the Hidden Lake – Bates lake study area is Alternative 5,which presents a plan that combines the most cost effective structural and non structural improvements.These alternatives have the lowest overall project cost and provide the level of protection identified by theproject team and sponsors.The cost summary for the recommended plan is provided in Table ES-2. The Recommended Plan ispresented in Figures 7-1 though 7-6.ES-2