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XIl-5 At the present time, the owners of the land adjacent to the South Platte River in this reach on the southeast or right side are proposing to increase the depth and width of the channel and fill their property to an elevation above the 100-year flood elevation. This approach would not require the reconstruction of the 15th Street Dam, but it would require the placement of a large amount of fill in the floodplain. The dam would be modified to incorporate a boat chute which would increase the flow capacity of this structure. Further analysis may show that in addition to adding a boat chute to the Burlington Dam, the dam itself may need to be replaced with an inflatable dam which could be collapsed in times of flood. ously with a 100-year flood on the South Platte River, the Cherry Creek channel would not have adequate capacity for the additional flow from the South Pl atte. Reach 6 - Cherry Creek to Franklin. The limited structural improvements alternative in this reach would involve planting vegetation along 7,000 feet of bank to provide erosion protection. The channel between Frankl in and 1-70 would be deepened and made more efficient to carry 100-year flows at a lower elevation. The key structural improvement in this reach is the rais- ing of the Franklin Street Bridge which is overtopped by the 100-year flood, and the reconstruction of the adjacent railroad bridge. The railroad bridge is constructed on wooden piers about 1.5 feet wide and 16 feet apart. These two bridges cause a major obstruction to flow which causes extensive over- bank flooding on the left (west) bank upstream to Interstate 70. These bridges are also an obstruction to boating since even under normal river conditions there is barely enough clearance to allow passage of a raft or a kayak. The limited structural improvements alternative would not necessarily be implemented immediately, but over a number of years. Therefore, it should be used in combination with floodplain management to insure that new struc- tures in the floodplain will not be constructed in the 100-year floodplain and to insure that existing structures that are replaced or improved will be floodproofed or elevated. The limited structural improvements alternative is a combination alternative by definition since it includes lined channels, natural waterways, struc- tural improvements and floodplain management. Reach 7 - Franklin to Sand Creek. The limited structural improvements alternative for this reach would include approximately 5,000 feet of bank riprap stabilization to protect against erosion, and the reconstruction or relocation of 60-inch water line located immediately upstream of the York Street Bridge. There is a 7 foot high dam at this utility crossing to pro- tect it against erosion. The dam would be removed after the water line was lowered. Land Acquistion or Floodplain Relocation This approach to flood damage reduction involves the relocation of struc- tures and facilities from the floodplain in order to prevent damage and danger to the occupants. It is normally most applicable when the area is subject to frequent damaging floods. This approach can also be used to pre- vent development in currently undeveloped floodplains by the acquisition of floodplain properties by local governments. Generally, this approach can be justified in areas where the value of the proposed land use is greater than the value of the existing land use, in other words, it can not normally be justified based on the reduction of damages alone. This alternative was not considered for any of the reaches in this study because of the generally high land values and because the record of flooding does not indicate fre- quent damaging floods. The undeveloped land in the central Platte Valley area is of such high value that it may not be feasible to purchase it in order to prevent development. The Franklin Street Bridge and the railroad crossing in the previous reach are in close proximity to the Burlington Dam. These three structures act together in determining 100-year flood water surface elevations. Therefore, a combination of improvements would be needed to provide the desired results. The Burlington diversion dam is a major obstruction to boating.