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A summary of the pros and cons of the channel dredging concept is presented below. The pros and cons of the floodwallllevee concept and conceptual level cost estimates are presented below. Pros . No modificatio~ of homes or historic structures required No requirement that bridges be raised Structures remoVed from floodplain (elimination of flood insurance requirement) Pros . . . Levees on lower Clear Creek could be incorporated into trail system . If constructed to FEMA height criteria, structures would be officially removed from floodplain (flood insurance no longer required) Cons Cons . Environmental permitting required (Corps 404 permit) . Environmental impacts to creeks (reduction in fish habitat) . Aesthetic impacts to creeks . Limitations on long term effectiveness Lack of space for debris basin Dredging must be repeated periodically . May have to replace existing cribbing . Approval required by State and National Historic and Preservation Offices . No reduction and possible worsening of basement flooding (resulting from higher water levels in channel) . Severe aesthetic impacts . Approval required by State and National Historical Preservation Offices . Difficult to implement due to lack of public land or right-of-way along creeks. Extensive coordination/cooperation with landowners required. . Environmental permitting required (Corps 404 Permit) . High cost (floodwallsllevees + raise bridges) South Clear Creek I 0- Year Protection = $1.5 Million South Clear Creek 100- Year Protection = $1.9 Million (52.0 Million FEMA) 5.2.4 Channel Floodwall/Levee System Under the floodwallllevee system concept, channel capacity through Town would be increased through the construction of concrete floodwalls or earthen levees (where space permits). Because of the proximity of existing homes and businesses to the creek banks, floodwalls would be necessary along most reaches with levees being feasible only along portions of Clear Creek downstream of the 11th Street Bridge. In order to provide loo-year protection, floodwall heights would range from approximately I to 3 feet. In order to meet FEMA criteria for removal of structures from the floodplain (and eliminate flood insurance requirements for these structures) an additional 3 feet of freeboard would be required, resulting in flood walls ranging in height from 4 to 6 feet. Floodwalls and levees meeting this height criterion would have severe aesthetic impacts. The cost of constructing floodwalls along the two creeks is anticipated to be quite high mostly due to the need for dewatering during construction. All channel banks and existing cribbing are owned by the individual property owners, so most floodwalls would have to be constructed on private property. Finally, in addition to the construction of flood walls and levees, a number of brid"es which cross South Clear Creek would have to be raised. " Clear Creek I 0- Year Protection = Clear Creek I 00- Year Protection = $1.0 Million $1.4 Million (51.6 Million FEMA) 5.2.5 Permanent Bypass Conveyance In flood events of the recent past, flooding has been confined to South Clear Creek with the main Clear Creek channel providing adequate capacity. In order to protect downstream areas, the Town's flood fighting strategy involves partially breaching the South Clear Creek channel bank at Griffith Street between 8th and 9th Streets. Breakout flows are directed north on Griffith Street using sandbags, then west at Park Street and finally northwest into Clear Creek. Flooding along this stretch of South Clear Creek could be eliminated by providing additional conveyance structures to supplement the existing channel capacity. The additional conveyance could conceivably be provided in at least three different ways: . Street Con 'levance. Streets along the flow path (Griffith, Park etc.) could be paved and given an inverted crown or curb and gutter to provide conveyance. This is probably not practical for a number of reasons: I) the inverted crown or curb and gutter would harbor treacherous ice for a majority of the winter; 2) pavement is difficult and expensive to maintain in the harsh winter climate of the mountains and the Town may lack sufficient tax base to shoulder the added maintenance costs; 3) paving and/or curb and gutter would change the existing rural character of the affected neighborhoods. 5-5 5-6