a. A permit from the State Engineer is required before commencing construction of any dam or reservoir involving the storage or impoundment of water in Wyoming. Maps or plans must be submitted with the application for a permit to construct such a dam. See Section 1(c) of Chapter VI 11, page 55, for special conditions applicable to maps for applications for certain stock reservoirs, fishing preserve reservoirs, and floodwater detention reservoirs; additional details are provided in Chapter VI of this Manual.
b. Special requirements for plans of dams include: - (1) A profile of the damsite along center line, and a maximum cross-section of the proposed dam.
- (2) The outlet works and spillway in detail. The spillway cross-section must be shown. A computation of capacity and all necessary data used must be included.
- (3) The scale used on any part of the map or plans should be sufficiently large to reflect all important details. Reservoir contour maps snail normally be drawn to a scale of 1" = 400' or larger. When the maximum length or width of the reservoir basin is more than 2 miles, the scale of the reservoir contour map may be reduced to not less than 1" = 1000' providing that all necessary detail is clearly shown. Profiles shall be drawn to a longitudinal scale of 1" 200' or larger. Cross-section plans shall be on a scale of not less than 1" 20'. Detailed plans including plans of outlet works and other structures, shall be on a scale of not less than 1" = 4'. Important dimensions must be shown on all plans of structures.
- (4) For earth dams, the slope must not be less than 3 to 1 for the front or water side and 2 to 1 for the back side unless conditions justify steeper slopes. In this case, engineering data must be submitted in support of steeper slopes than these maximums. Special conditions may require flatter slopes. The width on top shall be at least 1/5 of the height plus 4 feet, and in no case less than 3 feet for dams 10 feet or more in height. A minimum freeboard (from the top of the dam to the bottom of the spillway) of 5 feet is ordinarily required on all earth dams. This minimum may be reduced, but only when specifically requested and prior approval is granted by the State Engineer. Justification for reducing the freeboard requirement below 5 feet must be submitted along with the application and should include information on the conditions, size and characteristics of the drainage area above the reservoir, the location of buildings, roads and other structures downstream from the dam, the effect of wave action on the face of the dam at maximum water level, and any other information concerning the conditions at the -Jam site.
- (5) For reservoirs with a dam height greater than 20 feet or reservoirs with a storage capacity greater than 50 acre-feet or reservoirs located in an area where extensive property damage or loss of life Eight result from over-topping or failure of the dam, the spillway shall have sufficient capacity to pass the flood flow for a projected 100 year storm. The design of the spillway shall he such that a minimum of 11/2 feet of freeboard, between the top of the dam and the maximum water level in the spillway, is maintained, If the design indicates erosive velocities in the spillway channel, a protective lining shall be added or redesign of the Spillway shall be marie. The State Engineer may require additional freeboard and/or spillway capacity if, in his judgment, it is necessary.
- (6) The State Engineer may require detailed construction plans and specifications for structures, along with computations governing the design thereof.
- (7) A capacity table showing the capacity of the proposed reservoir must be shown on the reservoir filing map. See sample map on page 65.