2004-11-23 CC Packet - Laserfiche WebLink

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:Flood Mitigation The model results for the 2-year and l00-year storms for both existing and proposed oonditions, as well as with the 100-year storm for projected future 1and1.1Se are shown on Figures 8 through 10. These figures illuStrate that a moderate drop in maximum water levels (~ng from approximately 0-2 feet) along the corridor is expected under.proposed oonditions, relative to existing conditions, for the 2-year and l00-year storm events. MaiDteDance The overall approach with the stable stream. design is to create a self mS\inttim1\8 system. However, it is expected for the first three to five years that minor repairs and maintenance will be required while the stream. settles into equilibrium oondition. This option will still require active beaver management 8nd dam removal in order to tnaitttain the desired drainage. Future Stonnwater ConveyaDce The proposed channel desigrl will provide the needed capacity for future needs based on the City of Hugo's land use plan. If the hydrology of the watershed changes significantly due to a change in the city's la>>duse plan, then the stream will need to be adjusted to establish a new equilibrium. However, this is an unlikely scenario due to the small portion of the watershed that is currently forecasted to experience more intensive urban development, specifically in the very southwestern portion of the watershed. The major change would be from agricultural (pasture with some row crop) to estate residential. Also, development will be subject to RCWD and Hugo regulation of peak and volume oontrols. From a hydrologic pe1spective, this does not imply a large change in I'UIlOft: and the channel as designed wiU accommodate these future flows for the 20-year planning horizon. Bioloak Condition The meandered channel will be approximately 300A.longer than the straight channel and will be connected with its floodplain. This will lead to improved flow regimes downstream and improved habitat for the biota by creating structural features such as pools and riftles (Karr, 2002). Downstream Water Quality This design will increase the interaction of the in-stream flow with the floodplain and will allow settling, storage, and recycling of in-stream nutrients in channel and on the floodplain. Additionally, the meandered channel will have more benthic, or stream bottom, surface area, which will improve in-stream water quality. Dissolved nutrients are primarily removed by sorption, or attachment, onto bottom sediments or through uptake by microbial oommllnities on the stream. bottom (Mulholland et aI., 1985), and in-stream. processes are important determinants of stream. water nutrient ooncentlations (Mulholland and Hill, 1997). A greater surface area provides more substrate for microbial oommunities in addition to more attacbment sites, and phosphorus retention has been related to stream bottom area (Doyle et aI., 2003)." ONCLUSI CWD engiDeeriq- stUdies show that no....... diteh... (option 1) to the profiled cause of nutrients to pour downstream. Mblor maintenailce (option 4) Is Dloreofthe saDIe. Th eander (opdon 2) Is aD unknown aDd Is likely unstable. A lot bas been learned since th 9OO's about wetlands, drainage, aadwater quality. The engineers aDd. the U ofM rofessor. . SandJVel'l)'t reporttbat option 3, Stable StreaDl<RelaabDifation, otTerstbe dvantages in.~water quality, minimal. m..infentlDee, fl8Odadtigatiollt I'Dl water conveyance, biologie condition, and surprisingly, overaD coSt. EeonolDie penaIt!. or wonening water quality are severe aDd option 3 bas the best dumce ofiDl . w . 3 e Attached are a few other diagrams provided in the engineering reports. Thank: you for listening!