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Precedent for the raising of structures exists in Georgetown as at least one homeowner has already used this approach to eliminate flooding problems. The home which was raised is located on Rose Street at South Clear Creek. . No modification of existing channels required No Corps 404 permit required No impacts to channel aesthetics No environmental impacts to creeks . Flood insurance costs eliminated for building owners available storage capacity. Four of the five reservoirs are owned and used by Public Service Company for power generation. Together, these four facilities account for 94 percent of the total available storage capacity of 4,368 ac-ft. This is a substantial amount of storage, but the use of these reservoirs in power generation means that Public Service Company has little flexibility in their operation. Because of this, essentially no existing storage capacity is available' for use in flood control. In 1995, Public Service Company worked closely with the Town to manage its releases to mitigate flood flows as much as possible. Despite these efforts, flooding in the Town still occurred. Construction of new or expanded storage was deemed impractical because of the high cost of spillway construction and lengthy environmental permitting process. Pros and cons associated with the raising of structures in the floodplain are presefite'd below. Pros The pros and cons of the upstream storage concept are summarized below. Pros Cons · No aesthetic impacts to Town or existing channels · No inconvenience to Town residents during construction . High cost Total Georgetown cost - $2.1 Million Cost for average residential structure - $35,000 . Homeowner resistance due to perceived aesthetic impacts . Homeowner displacement during construction . Alteration of historic buildings Cons 5.2.2 Upstream Storage . Existing storage unavailable 1995 = lO-yr event (Qpeak = 960 cfs) 1,600 ac-ft storage required to protect against 1995 event . High cost for new or expanded storage (PMF spillway) . Long/costly environmental permitting process · The Town does not own or control operation of the major existing upstream storage facilities Under the upstream storage concept, storage facilities upstream of Georgetown in the South Clear Creek watershed would be utilized to reduce peak flood discharges on South Clear Creek. Both existing storage facilities and potential new facilities were given consideration. A significant problem with this approach is that peak flood events in Georgetown have historically been the result of spring snowmelt. Snowmelt runoff hydrographs are very broad, lasting weeks or months, and because of their long time frame contain very large volumes of water. Providing enough storage capacity to reduce peak flood flows from snowmelt events is rarely feasible for small communities given typical economic and space constraints. 5.2.3 Channel Dredging Five existing reservoirs are located in the lower portion of the South Clear Creek watershed upstream of Georgetown. Table 5-2 provides the name of each reservoir, its owner, use and total Under the channel dredging concept, the capacity of Clear Creek and South Clear Creek would be increased by dredging of the channel invert. According to long-time town residents, in the years before current environmental regulations took effect, it was standard practice to periodically remove accumulated bed material from Clear Creek and South Clear Creek in order to maintain capacity. Following the flood of 1995, a 404 Permit was obtained from the Corps of Engineers which allowed for dredging but limited the material which could be removed to a minimum size of 2 ft. This restriction greatly limited the potential effectiveness of dredging operations. In order for dredging to be an effective part of an overall flood mitigation plan, a permit without such size restrictions would have to be obtained. Additionally, long term effectiveness of any dredging operation will require either that the process be repeated periodically or that incoming sediment be trapped upstream of the dredged reaches in debris basins. Field investigations indicate that there is little or no room available for a debris basin on South Clear Creek. Finally, dredging to significant depths (>1.5 ft) will likely undermine some existing sections of channel bank protection and cribbing. These sections will have to be reconstructed thus adding to the cost of this concept. It is noted that although the Town owns and maintains the two creeks themselves, the banks and associated cribbing are owned by the indi vidual property owners. For purposes of an example storage computation, flow data for the 1995 spring snowmelt event was obtained for the USGS streamgage for Clear Creek at Lawson (Gage No. 06716500). Peak snowmelt flows at this gage in 1995 had a computed recurrence interval of approximately 10 years and caused substantial flooding in the Town of Georgetown. Using the flow data for Clear Creek at Lawson, a snowmelt hydrograph was developed for South Clear Creek. From this hydrograph, the storage capacity required to keep South Clear Creek flows below the limiting capacity of 275 cfs throughout the entire event was computed. The estimated storage required was approximately 1,600 ac-ft. 5-3 5-4