PERMFILE131517

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 20 PERMIT REVISION DURING THIRD FIVE-YEAR PERMIT TERM
• Media Type: D
• Archive: No

7. Colowyo agrees with the Division's finding that efforts to
• return the natural drainage portions to previous
configurations are not feasible. The explanation of how the
south drainage was determined to be stable is explained in the
T.R. under item 3 and follows similar reasoning as used by the
Division in determining the "North Drainage" to be in a
"somewhat stable configuration". In determining stability,
Colowyo as well as the Division, uses such factors as the
predominance of rock outcrops and other geologic control
within the drainage, the large component of rock on and near
the surface, the channel being naturally lined with rock in
several areas, and the ground immediately adjacent to the
channel having a good cover of native vegetation.
a. Areas which have had additional rock placed in them
have been described in the T.R. under item 3 and
includes the north drainage natural drainage
segment. Note that a large rain storm on 8/9/94
completely removed these rock check dams. This
drainage segment can be considered stable as
described above in 5. and below in b. & c.
b. & c. Colowyo contends that there is no such thing as a
truly stable natural drainage, and to try and
provide a suitable demonstration or prepare a
program for verifying stability within a natural
• drainage subjected to the randomness of natural
weather conditions, would be futile. By
definition, a drainage represents a dynamic measure
of change in a landform with water runoff energy
and erosional debris being channeled through a
drainage corridor causing scouring, downcutting,
deposition and enlargement. Therefore, change
within a natural drainage is to be expected.
Colowyo does realize that two distinct factors are
contributing to water flow within the south collection ditch
system, namely, natural weather contributions plus other
contributions due to Colowyo's activities. Natural weather
contributions are random, impossible to quantify, and can be
of such magnitude and intensity as to create tremendous flows
which will exceed all ditch design parameters specified in the
appropriate portions of Rules 4.05.1 and 4.05.3. Conversely,
flow contributions due to Colowyo's activities can be
quantified via Division approved SEDCAD hydrological modeling.
The jointly developed (DMG and Colowyo) SEDCAD model found in
T.R. 30 provides a suitable demonstration of the stability of
the natural drainage segments impacted by flow contributions
due to Colowyo's activities. The model shows expected flow in
both of these natural drainage segments as 0.00 cfs.
Therefore, these two natural drainage segments will not be
• impacted by flow contributions due to Colowyo's activities.