Design Engineering Report: Avon Exhibit 1

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Precast Structure Stabilitv Stability analyses were conducted to evaluate the pre-cast structures that would be placed at Bob Jr. and Bob Sr. These pre-cast structures were evaluated for drag forces against potential sliding and overturning of the structure. Maximum velocities (and resulting forces) were utilized, which occur at Bob Jr. at 1,400 cfs and at Bob Sr. at 5,430 cfs under the 100-year flood scenario. The drag forces were then compared to the frictional resistance to develop a FOS to prevent sliding. A FOS was then calculated for both pre- cast structures. Similar to the analysis of the particle "critical size," a FOS of 1.0 indicates that the pre-cast structure may slide; a FOS greater than 1.0 indicates a stable design. At Bob Jr. FOS sliding = 5.5, and at Bob Sr., FOS sliding = 4.9. The drag forces were then summed with the overturning moments about the toe of the structure to determine the resultant force and develop a FOS for overturning. At Bob Jr. FOS overturning = 6.3, at Bob Sr. FOS overturning = 5.7. Again, these analyses indicate that the pre-cast structures are of more than sufficient size to avoid sliding or overturning in a 100-year flood situation. In all of the above stability analyses conservative assumptions and values were utilized. The structures were analyzed independently for a number of different mobilization scenarios. The conclusion is that all structures are designed to be stable under the 100- year flow scenario and during the maximum potential mobility flow less than the 100- year event. The potential for scour is considered minimal and all structure designs include substantial keying into the bed of the channel. XI. Summary The proposed design, stream reach and recreational experiences sought are very appropriate for this RICD application. Our opinion is based on the fact that the recreational experiences sought, which includes three distinct levels of freestyle kayaking, the 350 feet long reach between the three whitewater course structures, and the depth and width of the course are all reasonable. A USGS gage is available for administration of the RICD and all federal and state statutory requirements will be met. The flows requested for appropriation are the minimum for each structure as shown in hydraulic analyses. The design would not increase the Base Flood Elevations and the design has an adequate factor of safety to be considered stable under the 100-year flood scenario. The proposed project is expected to have insignificant temporary environmental impacts associated with construction and no long-term environmental impacts. XII. References Andre, B& Czenkusch, A. 2005. Personal Communications, Managers, Colorado Division of Wildlife. Site Visit, October 13, 2005. 970-947-2924. CWCB, 2003. Recreational In-channel Diversion ("RICD ") Policy Regarding Technical Criteria. Colorado Water Conservation Board, November 21, 2003. 10of11