FLOOD04325

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Rules and Regulations for Dam Safety and Dam Construction
• Date: 9/30/1988
• Prepared For: State of Colorado
• Prepared By: State of Colorado DNR
• Floodplain - Doc Type: Educational/Technical/Reference Information

STATE OF COLORADO

DIVISION OF WATER RESOURCES
OFFICE OF STATE ENGINEER

SPECIFICATIONS TO GOVERN THE CONSTRUCTION OF A LIVESTOCK WATER TANK

Preparation of Foundation for Dam-All vegetable matter of every description, including roots to a depth of two
feet, shall be removed from the entire area upon which the dam will rest, together with boggy or unstable materials
and deposited outside the toes of the dam. The banks of the stream channel shall be dressed to a slope of about 1%:1.
A bonding trench, with sloping sides and a bottom width of not less than 5 feet and depth of 4 feet, shall then be
excavated beneath the center line of the dam the full length thereof, which trench shall be refilled with the most imper-
vious materials available. The foundation of the dam shall then be lightly plowed lengthwise of the dam, to provide
proper contact between the foundation and the dam embankment.

Placing of Dam Embankment-The materials shall be placed in the bonding trench and in the embankment of the
dam in layers not exceeding 6 inches in thickness, after which each layer shall be thoroughly compacted by a heavily
loaded disc cultivator, a corrugated or sheep's foot roller, the treads of a caterpillar or trucks, or by livestock used in the
construction. During the construction period, the top of the embankment shall be maintained as a horizontal plane the
full width and length thereof, and no side dumping of materials shall be permitted. The materials shall at all times
contain sufficient moisture to provide proper compaction. Puddling of material with water shall not be permitted.
No frozen material or large clods or stones shall be incorporated in the dam. The upstream face of the dam shall be
constructed with a slope not steeper than 2%:1, and the ~Qwnstream face on a slope not_steeper than 2:1. The crest or
top of the finished dam shall be not less than 8 feet in width.

The upstream two-thirds of the dam shall be constructed of the most impervious materials, such as clay loam, or a
mixture of clay and sand, and the downstream one-third of more pervious material, such as sand or gravel. The up-
stream face of the dam shall be adequately protected against wave action by stone riprap, or other suitable materials
when required.

Outle~hould the state engineer so require, there shall be located beneath the dam an outlet pipe not less than 8
inches in diameter, equipped with a control valve attached to the upstream end of the pipe, together with suitable
mechanism for operating the valve. Such outlet pipe shall be provided with cutoff collars. The pipe shall be placed in a
trench bottomed in stable formation, and shall be completely surrounded with well compacted impervious materials.

SpiJIway-For the protection of the dam, an adequate spillway shall be constructed around one or both ends of the
dam, of sufficient width to provide a capacity to carry the entire discharge from the drainage basin above the dam
during periods of unusual runoff. The spillway shall be located in stable formations not easily eroded, and shall extend
to a point well downstream from the dam. The following table shall be used to determine the necessary width of spill-
way to meet the above requirements. The top of the dam at all points shall be not less than 4 feet above the bottom of
the spillway.

The fallowing table shows the widths of spillways for corresponding drainage areas with an allowance of a mini~
mum freeboard between the maximum high water line and top of dam, of 2.3 feet, and maximum velocities of 3.5 feet
per second of time.

AREAS OF LOW RAINFALL INTENSITY AREAS OF mOB RAINFALL INTENSITY
AREA OF REQUIRED WIDTH OF AREA OF REQUIRED WIDTH OF AREA OF REQUIRED WIDTH OF
DRAINAGE BASI N SPILLWAY "W" AT DRAINAGE BASIN SPILLWAY "W" AT DRAINAGE BASIN SPILLWAY lOW" AT
ABOVE DAM NARROWEST POINT ABOVE DAM NARROWEST POI NT ABOVE DAM NARROWEST POINT
I 101 ACRES IN FEET 1M ACRES IN FEET IN ACRES IN FEET
20 8 2. 8 40. 76
,. 9 4. 9 450 84
60 11 6. 11 s.. 9.
s. " S. 18 ". 98
10. 16 ,.. " 6.0 '.5
". 21 12. .. 7.. 117
18. 25 ". s. 8.. 129
32. 29 16. " 900 ".
... " 18. 37 1000 15~)
s.. .. 2.0 43 1100 16.
... 38 22. 46 1200 169
4.. 42 24. 5. 1300 178
450 44 26. 53 1400 187
5.. 46 28. 57 1500 196
6.. Sl 3.. 6. 1600 2.3
7.. 55 32. 63 1700 212
8.. 59 ". 66 1800 '19
9.. ., ... 7. 1900 325
1000 66 38. 73 2000 323

ALL AREAS EAST OF THE CONTINENTAL DIVIDE BELOW AN ELEVATION OF 7000 FEET, ARE CONSID-
ERED AS BEING IN THE HIGH RAINFALL INTENSITY ZONE.

The above spillway widths may be reduced- at a point 50 feet below intake, by 25 per cent, where the spillway is
located the full length thereof in hard clay or shale, and by 50 per cent when located in hard rock formations, if the
slope or grade of the bottom is increased accordingly. The gra~e for clay and shale formati~ns should b~ 0.30 foot per
100 feet and for rock formations 0.90 foot per 100 feet. The WIdth of the entrance to the spIllway must m all cases be
one-thir'd wider than shown in the table, and the bottom should slope from the lower end of the funnel section, toward
the reservoir 1.0 foot in the distance of 50 feet, and the slope downstream should be 0.25 foot in a distance of 100 feet.

Borrow Pits-Pits from which materials are taken to build the dam, shall be cleared of all vegetable matter, and
no material shall be borrowed within a distance of 50 feet of any part of the dam. Materials excavated from the spill-

way, when suitable, may be used in building the dam.