BOARD01548

• Board Meeting Date: 1/25/2005
• Description: Proposed Revisions to the Rules and Regulations for Dam Safety and Dam Construction
• Board Meetings - Doc Type: Memo

and structures located in the flooded section. References to all computer programs, data
sources and related documents used in the evaluation shall be included; and

5.4.3 Supporting documentation and tabulation of assumed parameters, including Mannings
"n" values for the stream channel and the floodplain shall be included.

5.5 Hydrology Report - A hydrology report is required that presents the inflow design flood for
determining the required spillway capacity. The hydrology report shall be in a form acceptable to
the State Engineer and shall include, but not be limited to the following:

5.5.1 A topographical map delineating the drainage area tributary to the dam, with the
drainage area size labeled in square miles; the location of the proposed dam by quarter
section, section, township, range, and principle meridian; the bearing and distance from
Station 0+00 on the dam to a section comer, or, the location of Station 0+00 on the dam
determined by GPS, NAD83 datum, provided as UTM coordinates; the name of the natural
watercourse on which the dam is located or indicate the dam is off-stream, and name of the
primary watercourse which the dam is tributary, or name of the drainage basin in which the
dam is located; and the elevation of the dam crest;

5.5.2 A description of all basin response factors, including the topography, geology, and
vegetative cover of the tributary drainage area;

5.5.3 A summary of all hydrologic parameters for the method used, the inflow design flood
hydrograph, volume of the flood, and hazard classification of the dam;

5.5.4 A spillway discharge rating table (in cubic feet per second) for each foot of elevation
above the spillway crest up to the crest of the dam, including the equations used for
determining the discharge rate; and

5.5.5. A table showing the reservoir area (in acres) and storage capacity (in acre-feet) for
each foot of elevation from the invert of the outlet to the crest of the dam, and indicating the
amount of dead storage (in acre-feet), elevation of the invert of the outlet, elevation(s) ofthe
spillway crest(s), and elevation of the dam crest. All elevations shall be based on USGS
datum, referenced to the invert of the outlet;

5.5.6 The inflow design flood (IDF) requirements for determining the spillway capacity are
summarized in the following table. The PMP values are normally determined from the
appropriate Hydrometeorological Report (HMR) (HMR 49 for west of the continental
divide HMR 52 for the eastern plains and HMR 55A for the Front Range). The 100-year,
50-year, and 25-year events are normally determined from the National Weather Service
NOAA Atlas #2 "Precipitation-Frequency Atlas of the Western United States" Volume I1I-
Colorado, U.S. Department ofCommetce, NOAA, National Weather Service, Silver
Springs, Maryland, 1973. Floods ofIesser magnitude may be acceptable for good cause
shown. Spillways designed in accordance with these Rules will not be required to be

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