APPCOR11081

• Permit No: C1981048
• IBM Index Class Name: Application Correspondence
• Doc Date: 3/25/1981
• Doc Name: TRINIDAD BASIN MINING DELAGUA STRIP APPLICATION FN C-048-81
• From: MLR
• To: MIKE SAVAGE
• Media Type: D
• Archive: No

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DEPARTMENT OF NATIIN AL RESOURCES 999
D. Monte Pascoe, E.ecueive Director
M1N~;D LAND REi;LA111ATION
423 Centennial Building, 1313 Sherman Street
Denver, Colorado 80203 Tel. [phone]
David C. Shelton
Director
TO: Mike Savage
FROM: R. A. Domingue
RE: Trinidad Basin Mining, Delagua Strip Application
File No. C-098-81
Hydrologic Concerns
Z. Peak Flows: TBM has used the SCS Peak Flows manual for estimating peak
flows on their permit area. The application and presentation of the method
is complete except in regard to diversion ditch designs. Generally basin
shape varies greatly from the relationship used to derive the SCS nomography
in areas which have diversion systems. Estima'.es made in this office employing
the correction far basin share have been approximately 20~ greater for peak
flows than those generated by TBM. TBM must redesign the diversion/collection
system using revised peak flows employing the basin shape correction as
prescribed in Appendix E of Peak Flows in Colorado.
2, Ditch Velocities: Estimated velocities in diversion ditches designed by
TBM are high and erosive under conditions of the 10-yr. peak flow. The
value of Manning's n given by TBM (n=0.045) appears to be quite high given
the soils lining the ditches. Values of n greater than 0,04 suggest large
rock lined channels similar to natural streams. Does TBM intend to fully rock
line the ditches? Ditches of the greatest concern include 15-01, 22-D8, 22-D6
and 22-D1. TBM must:
(a) address the question of ditch velocities in a1I ditches under the
10-yr. peak flow and protect the ditches from erosion at the estimated
velocity;
(b) show that the use of n=0.045 is justified or choose an "n" which
more accurately fits the existing conditions.
3. Culvert Designs: TBM has continued to design culverts without taking
entrance head losses into accrount. Even assuming inlet control, culverts
designed at C-2, C-3, C-4, C-8 and C-IO are all undersized unless headwater
calculations, embankment protection and slope stability are addressed. TBM
must:
(a) redesign a1I culverts to eliminate any headwater; or
(b) show estimated headwaters, provide for an embankment slope stability
of 1.25 as per Section 4.03.1(3)(d)(ix) of the Regulations, show that
the embankment's stability will not be reduced by infiltration and
provide embankment protection from turbulence at the culvert inlet as
per Rule 9.03. Z (4) (e) (vi) (E) .
rt~~t~t. t~,l
March 25, 1981