2016-05-04_PERMIT FILE - C1982056 ‎(7)‎

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 5/4/2016
• Section_Exhibit Name: 2.06 Special Categories of Mining
• Media Type: D
• Archive: No

Calculation of these values indicates that along Fish Creek, the allowable change in soil conductivity will
be experienced with the application of 0.663 feet of irrigation water. The salinity threshold on Trout Creek
•
below -Middle Creek will lie exceeded with -the application of 0.98-6 feet of irrigation- water: Along Trout
Creek below Fish Creek, the threshold will be exceeded at 0.889 feet of water. The above demonstration
reveals that there is a theoretical potential salinization of irrigated lands using waters from Fish Creek and
along Trout Creek below Middle Creek. This value, however, ignores the fact that leaching is continuously
occurring, as a result of precipitation and irrigation. A significant amount of salt is removed in the
harvested crop and that precipitation of salts is naturally occurring in the soil profile.
The leaching requirement as defined in Handbook No. 60 is defined "as the fraction of irrigation water that
must be leached through the root zone to control soil salinity of any specified level". The equation used to
calculate the leaching requirement is given as:
where:
LR = Ddw = ECiw
Diw ECdw
LR =
Leaching Requirement;
Ddw =
depth of drainage water;
Diw =
depth of irrigation water;
Eciw =
electrical conductivity of the irrigation water; and
ECdw =
electrical conductivity of the drainage water.
For purposes of this evaluation, ECdw equals 2.0 mmhos/cm. The ECiw equals conductivity of 1.22
mmhos/cm for Fish Creek water and Trout Creek irrigation waters equal 0.82 rmnhos/cm at its confluence
with Middle Creek and 0.91 mmhos/cm below its confluence with Fish Creek. The leaching requirement for
these areas is calculated to equal 61, 41 and 46 percent, respectively.
• The required depth of irrigation water that is necessary to be applied is calculated by the formula:
where:
Diw = ( ECdw Dcw,
ECdw - ECiw
Diw = Required depth of irrigation water;
ECdw = Electrical Conductivity of the drainage water;
Eciw = Electrical Conductivity of the irrigation water; and
Dcw = depth of consumptive water use which is obtained from studies conducted by
Leonard Rice Water Engineers for the years 1978, 1979 and 1980 and collected by
the Colorado Department of Water Resources for the years 1983, 1984 and 1985.
The highest yearly average consumptive use value, for the 6 years studied was
found to equal 21.92 inches of water.
Calculation of the required depths of irrigation water to satisfy both the consumptive demands of
evapotranspiration and to satisfy the leaching requirement to maintain the soil salinity values below 2.0
mmhos/cm produces a value of 56.2 inches of water being applied to lands irrigated with Fish Creek water,
37.2 inches of water being applied to lands irrigated with Trout Creek waters below the Foidel Creek
drainage, and 40.2 inches of water from Trout Creek being applied to irrigated lands below its confluence
with Fish Creek.
Due to inherent inefficiencies of the existing irrigation systems, the actual quantities of water being applied
are substantially greater than those needed to satisfy the consumptive water use demands. According to
. data from the Colorado Division of Water Resources (CDWR) Office in Steamboat Springs,
MR 97-154 2.06-18 Revised 12/09/97