PROJ00462

• Contract/PO #: FS0036X
• Contractor Name: Idaho Springs, City of
• Contract Type: Loan
• Water District: 0
• County: Clear Creek
• Loan Projects - Doc Type: Feasibility Study

(b) Assumption A, inflow design flood, thunderstorm
rainfall

(1) From Figure 24, Page 58, reduction ratio is 6 or
multiply by O. 167

<'i.

Time
Ending, Hr.

Probable Max.
Thundersrprm
Rainfall, .. in.

Accum.
Reduce~
Rainfall, in.

Assumption A Design Storm

Accum. rainfall3 Incremental
in. Rainfall, in.

0.25 1.34 0.22 O. 78 0.78
0.50 3.24 0.54 1.89 1.11
0.75 5.80 0.97 3.39 1.50
1.00 11. 16 1.86 6.51 3.12
1.25 12.28 2.05 7.17 0.66
1.50 13.06 2.18 7.62 0.45
1.75 13.62 2.27 7.95 0.33
2.00 14.06 2.34 8.20 0.25
2.25 14.40 2.40 8.40 0.20
. -~ 2.50 14.68 2.45 _ 8.57 0.17
.J 2.75 14.84 2.47 8.66 0.09
.,j
3.00 14.95 2.49 8. 72 0.06
,--:~~" .,
.: ..' ~.;.
.'""
1 From Step 8, Column 3
2 Design arrangement accumulative PMP multiplied by O. 167

3 Average of values, Columns 2 and 3

(2) Obtain thunderstorm runoff curve number, CN,
from Table A-9, Appendix A, Page 544

Cover type: Brush, sage, grass or combinations,.
cover density at ground surface - 50% or less, Zone III,
Assumption A thunderstorm. eN is 85 so from Table 5,
Page 67 no adjustment in T is necessary.
c

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