REV95112

• Permit No: C1981071
• IBM Index Class Name: Revision
• Doc Date: 6/7/2000
• Doc Name: SL07 EXHIBIT 5 TO THE END OF INFORMATION IN PACKAGE
• Type & Sequence: SL7
• Media Type: D
• Archive: No

CYCC - .Sedimenr Yield Demonsrrnrion Eckman Park .Area 41
Hydrograph Response Shape, A unit hydrograph was chosen for each drainage area or sub-area model to
predict the runoff response. The hydrograph responses available in the SEDCAD+ model are slow, medium, and
fast. A slow response corresponds to a forested area or an area with a number of obstructions, where as a fast
response corresponds to an unvegetated or poorly protected area. For the demonstration, a medium runoff
response was chosen.
Drainage Basin Area. Representative one acre drainage basin areas were modeled for the reclamation area and
reference area being evaluated. Representative one acre unmined drainage areas were modeled to exhibit overland
flow throughout the length of the defined watershed. Representative one acre mined drainage areas were divided
into four sub-watersheds due to the presence of contour furrows throughout the reclamation blocks. Within these
areas, overland flow lengths are shortened with subsequent flow paths consisting of overland drainage, contour
furrow flow, and then combined flow along grassed waterways representative of areas of concentrated runoff.
Time of Concentration. Time of concentration (4) within each representative one acre drainage was calculated
with SEDCAD+ using the SCS Upland Method, as presented in Barfield, et al. (1981), page 100. Representative
one acre areas were used to derive hydraulic lengths and drainage paths. Average slopes for Eckman Park were
measured directly from 1" = 500' scale maps. These slopes were used as inputs for calculating both time of
concentration and Muskingum routing parameters where appropriate. Slopes of the contour furrows in the
reclaimed blocks were assumed at 0.5 %.
Curve Number. The runoff curve number (CN) is a factor relating the amount of rainfall to the amount of
mnoff for a given area. Tt is dependent upon the infiltration characteristics of site-specific soil types and the type
and amount of vegetation. Prior to disturbance, the mined areas encompassed the following soil types (Ref: Soils
Map, CYCC Permit No. C-81-071):
SOIL NAME HYDROLOGIC SOiL GROUP•
AABer Silty Clav D
AABer -Wavbe Com lex D
Arbor Silty Clav Loam D
Arbor-Moverson Com lex D
Binco Silh~ Clav Loam D
Buckskin Loam C
Bulklev Silty Clav Loam D
Cocheto a Loam C
Coutis Fine Sandv Loam A
Ga o Clav Loam B
Routt Loam C
Roxal Variant-LVIr1aI150n-Startnan Com lex C
Skvlick Loam B
Winevada-S litro Com lex B
Cvroborolls. Torriorthents-Rock Outcro Com lex Rock Outcro
Unnamed-Cocheto a Com lex C
• Hydrologic Soil Groups based on Routt County SCS dcslgnations.
Hydrologic Soil Groups for the reclaimed areas are assumed to be a mixture of the groups which were originally
stripped. The distribution of these soils within the mined area is as follows:
• i mn~enaronmaval4<Am~honJrel'urca~l Joc