3
I:\11\82323\0100\0122 TM\Feb14\11382323 TM PreFeasibilityHydrologyHydraulicsRevE 13FEB14.docx
Storm Depths (NOAA, 1973):
Storm Event
2-year 24-hour 10-year 24-hour
100-year 6-hour
Storm Depth (in)
1.4
3.0
3.24
Applications
Tc
Calculations
Sedimentation Pond
Volumes
Conveyance Channel, Riprap,
and Culvert Sizing
Storm event temporal distribution – Dimensionless design mass curve (Tyrell &
Hasfurther 1983)
Type II storm distribution
Manning’s n Coefficients:
Description
Manning’s n
Stability Capacity
Grass
0.030
0.035
Riprap
0.030
0.035
Mountain Stream
0.030
0.050
Corrugated Metal Pipe (CMP) 0.024
0.024
Haul Road Culverts:
Culverts are assumed to be corrugated steel with Manning’s n = 0.024
Length, available headwater depth, headwall configuration, downstream channel
geometry, and slope are assumed or estimated from available topography
Channel Assumptions:
Slopes for flow routing and channel sizing calculations are the average slope across
the entire reach
3H:1V side slopes
Minimum freeboard is 1 ft
4.0 CALCULATIONS
Basin area-weighted curve number calculations are presented in Table 1. Time of concentration
calculations are presented as Table 2. The HEC-HMS model parameters are included as Attachment A
and calculated 100-year frequency, 6-hour duration and 10-year frequency, 24-hour duration peak flows
are included as Tables 3 and 3a respectively. Preliminary channel sizing calculations are presented in
Table 4. Preliminary riprap sizing calculations are presented in Tables 5 and 5a. HY-8 Culvert sizing
model output is included as Attachment B. Pit dewatering pond sizing calculations are included as
Attachment C.
5.0 CONCLUSIONS AND DISCUSSION
Channel dimensions and revetment have been designed based on available topography and preliminary
facility designs. Dimensions and revetment requirements may change as the designs become more
detailed.
