ADDENDUM 6 TO APPENDIX VI-3

DESIGN AND CALCULATION DATA FOR DITCH 31

September 15, 2006

The following addendum contains the modifications to the drainage strategy for the Mining andReclamation Plan. This addendum includes the calculation sheets associated with the design ofDitch31. Ditch3l wi l l col lectdrainagefromport ionsofWatersheds Al,A2,andA3aspartof thereclamation plan for a portion of the refuse pile area. Ditch 31 will be remain following finalreclamation activities for the site.

Historically, Bermed Channel 31 has been designed for the 10 year-6 hour event and only for theflow from Watershed 30. However, Watersheds A1 , A2, and 43 provide flow to this structure (seeFigure 1). Additionally, as this structure is to remain as a permanent diversion, the channel shouldbe designed for the 1 00 year- 6 hour event. Therefore, the attached calculations provide the peakflows for Watersheds A1 , A2, and A3 for the 100 year-6 hour event. Also, the design calculationsfor channel sizing are based on the total flow from all three watersheds, Riprap has been sized forthe increased flow velocity.

Based on these calculations, the proposed channel modifications, should be able to convey the flowevents that are occurring within the channel.

0r 400'-

FIGURE 1. WATERSHED DRAINAGE AREAS

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SCSHYDRO

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W a t e r s h e d f . D . :WATERSHED A1

INPUT SUMMARY

STORM :Dis t . = SCS Type I IDep th = 1 - .90 i nchesDura t i on = 5 .0 h rs

T/'IATERSHED :A r e a = 2 2 . 3 0 a c r e sC N = 7 5 . 0 0

T i m e c o r r c . = 0 . 2 1 h r s

OUTPUT SUMMARY

Runoff depth:In i t ia l abst . r :Peak f low:

a t t ime :

0 .333 i nches0 . 567 i nches

t I . 78 c f s ( 0 . s24 i ph )3 .135 h r s

Triangular Hydrograph

SCSHYDRO

Calculat ions using

Prograrn

W a t e r s h e d I . D . :WATERSHED A2

INPUT SUMMARY

STORM :D is t . = SCS Type f fDep th = 1 .90 i nchesDura t i on = 5 .0 h r s

WATERSHED :A r e a = 2 . 7 0 a c r e sC N = 7 5 . 0 0

T i m e c o t r C . = 0 . 1 8 h r s

OUTPUT SUMMARY

Runoff depth:In i t i a l abs t r :Peak f low:

a t t ime :

0 . 3 3 3 i n c h e sO . 6 5 7 i n c h e s

1 . 6 0 c f s ( 0 . 5 8 8 i p h )3 . ] - 2 0 h r s

Triangular Hydrograph

SCSHYDRO

Calculat , ions using

Program

W a t e r s h e d I . D . :WATERSHED A3

INPUT SUMMARY

STORM :D i s t . - S C S T y p e I fD e p t h = 1 . 9 0 i n c h e sD u r a t i o n = 5 . 0 h r s

WATERSHED :A r e a = 6 . 0 0 a c r e sC N = 8 2 . 0 0

T i m e c o r r c . = 0 . 2 1 , h r s

OUTPUT SUMMARY

Runoff depth:fn iL ia l abs t r :Peak f low:

at. L, ime :

0 . 584 i nches0 .439 i nches

6 .e4 c f s ( r . 148 i ph )3 .135 h r s

EXISNNG*

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FIGURE 2, TYPICAL DROP STRUCTURE DETAIL

Ghannel ReportHydraflow Express by Intelisolve

Ditch 31 - Min

TrapezoidalBotom Width (ft)Side Slope (z:1)Total Depth (ft)Invert Elev (ft)Sfope (o/o)N-Value

CalculationsCompute by:Known Q (cfs)

Wednesday, Sep 13 2006, 8:25 PM

= 5.00= 2.00= 2.00= 1 .00= 4.00= 0.030

Known Q= 20.32

HighlightedDepth (ft)Q (cfs)Area (sqft)Velocity (fUs)Wetted Perim (ft)Crit Depth, Yc (ft)Top Width (ft)EGL (ft)

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Ghannel ReportHydraflow Express by Intelisolve

Ditch 31 - Max

TrapezoidalBotom Width (ft)Side Slope (z:1)Total Depth (ft)Invert Elev (ft)Slope (%)N-Value

CalculationsCompute by:Known Q (cfs)

= 5.00= 2.00= 2.00= 1 .00= 12.00= 0.030

Known Q= 20.32

Wednesday, Sep 13 2006, 8:26 PM

HighlightedDepth (ft) = 0.42Q (cfs) = 20.32Area (sqft) = 2.45Velocity (fUs) = 8.28Wetted Perim (ft) = 6.88Crit Depth, Yc (ft) = 0.73Top Width (ft) = 6.68EGL (ft) = 1.49

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