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culvert in Reach L-II, damages are very low and consist primarily of minor erosion and debris removal and cleanup. Erosion control.structures should be installed in this reach and routine maintenance should be done to eliminate debris accumulation especially at structures. As recommended in the previous Master Plan, signs should be posted in the East Tincup Village Campground warning of the flood potential in this area. The existing channel in Reach L-IO is clogged with debris from past flooding and from adjacent property owners. This channel should be cleaned out and re-opened to eliminate potential problems. In addition, erosion control structures should be c:onstructed to stabilize the channel in portions of the reach where velocities exceed 6-feet per second. Subsequent routine maintenance should be done to keep the channel open and free from debris. Plan Implementation In addition to the individual components of the recommended alternative plan, the phasing of implementation of the alternatives is important. Because this is a Master Plan, components of the system are related and must be implemented only after appropriate consideration of the relative impacts and benefits. The following is a listing of the components of the recomtnended alternative plan in the suggested order of implementation: 8 Between the outlet of the Zeta Street culvert and the confluence with Apex Gulch, damages are minor and consist primarily of minor erosion and debris cleanup and removal. Erosion control check structures should be constructed to stabilize the channel. Regular routine maintenance should be done to remove debris accumulation and keep the ('.Mnne' open. 9. The two reaches with the highest damages historically are the downstream-most reaches L-I and L-2. These reaches contain low-density, high-value residential properties with a history of flooding problems. With the recent construction of the enlarged culvert at 20th Avenue, most of the damages in reach L-I have been eliminated. Therefore, the initial phase of implementation is to enlarge the culvert under Y oungfield Street to a lOO-year capacity structure. This improvement and the recently completed improvements at 20th Avenue will provide a clear flow path between the upper basin and Maple Grove Reservoir thereby reducing the damages which have historically been caused by water ponding behind these structures. 1 10. Construction of the detention basin near the upper portion of Denver West is the next phase in the recommended alternative plan. This detention basin will help to control nuisance flooding in the downstream reach caused by the more frequent flood events. The reach with the next highest damage potential is Reach L-5 downstream of South Golden Road. Construction of the IO-year channel in this reach will provide a safe conveyance for the more frequent floods and will eliminate a large portion of the average annual damages in this reach. In addition, this will be the downstream-most portion of the recommended lO-year system in the next upstream reach. 2. Selected toe of bank erosion protection between Y oungfield Street and 20th Avenue should be constructed. These improvements should protect against channel deterioration in this reach. 11 The final phase ofimplemeotation of the recommended alternative plan is to construct erosion control check structures on the steep lower portion of Apex Gulch. While velocities in this reach are high enough to cause erosion damage, the channel is Dirly stable and shows signs of only minor past erosion problems. This option, and others which eliminate minor or maintenance level damages only, should be done only after other areas of higher damage have been dealt with. 12 Reach L-6, in its existing condition, experiences wide spread flooding problems and has numerous undersized &cilities. The IO-year channel option with the enlarged culverts at Orion Street, Orchard Street, and 10th Avenue should be constructed as a system. In addition, the structure under South Golden Road should be enlarged to a IOO-year capacity structure. If the improvements in this reach must be phased, the structures at road crossings should be done first starting with Orion Street. Next, the structures at 10th, Orchard, and South Golden Road should be enlarged. The final step would be constructing the enlarged channel between the structures. 3. Attention shifts from the mainstem of Upper Lena Gulch to the Pleasant View tributary for the next phase of the Plan. The lOO-year channel in Reach P-3 on Pleasant View should be constructed. This will give full protection to this entire tributary through the IOO-year flood. The existing lOO-year channel currently protects the lower reaches from damages. This lOO-year channel will contain the flow in this upper reach which presently flows overland and will eliminate a significant portion of the average annual damages. 4. The Mountain Side Mobile Estates trailer park has the potential for damages in a large flood event. This implementation phase is to enlarge the existing culvert crossing at the trailer park entrance and the undersized channel from the outlet of the 6th Avenue culvert downstream to the end of the trailer park to provide capacity for the IO-year flow. While some residual damages will still be expected, they are primarily from large flood events greater than the 50-year flood. 5 Damages to property on Apex Gulch are relatively small and occur primarily to the Heritage Square development. The culvert at the upper driveway should be replaced with a lO-year capacity culvert to eliminate the overflows and flow splits which cause flooding of Heritage Square and the adjacent undeveloped property. Amoco Gas Station driveway 6. 7. 34 of the Zeta Street and the outlet the of the culvert under outlet Between the