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<br />I Table 3-2 I
<br />UDFCD Stream Names and Numbers
<br /> UDFCD Stream Appendix F
<br /> UDFCD Stream Name Number Stream Number
<br /> Coyote Run 8168 100
<br /> W ouz1es Gulch 8168-01 103
<br /> Prairie Dog Draw 8169 106
<br /> Rat Run 8170 119
<br /> Muskrat Gulch 8171 126
<br /> W oodrat Gulch 8172 131
<br /> Box Elder Creek 8100 200
<br /> Cardboard Draw 8173 204
<br /> Corrugated Gulch 8174 211
<br /> Empty Draw 8175 210
<br /> Younger Gully 8176 216
<br /> Statesman Gulch 8177 219
<br /> Deacon Draw 8178 223
<br /> (no name) 8179 226
<br /> Company Gulch 8180 229
<br /> Bender Drainage 8181 231
<br /> Drop Seed Drainage 8182 233
<br /> Forked Gully 8183 243
<br /> Beach Coulee 8184 247
<br /> Crossing Gulch 8185 249
<br />
<br /> Table 3-3
<br /> Summary of Area Adjustments
<br />Watershed Storm Need for Area Locations Where Area Area Adjustment
<br />Area (sq.mi.) Duration Adjustment Adjustments Were Applied Identifier
<br />0-10 2-Hour no - All tributaries I
<br /> - Upstream portion of
<br /> mainstem Coyote Run
<br />10-20 3-Hour yes - Middle portion of mainstem 2
<br /> Coyote Run (3.1 to 9,8 miles
<br /> upstream of north study
<br /> limit)
<br />20-30 6-Hour yes - Downstream 3,1 miles of 3
<br /> mainstem Coyote Run
<br />50-75 6-Hour yes - Mainstem Box Elder Creek 4
<br /> in study area and upstream
<br /> of study area
<br />
<br />Basin) (NOAA, 1973), One-hour depths for the 5-, 10-, and 50-year storm events were
<br />estimated from Figure 6 in the NOAA Atlas (NOAA, 1973),
<br />
<br />Six-hour duration rainfall depths were estimated for the 2-, 5-, 10-, 50-, and l00-year
<br />storm events by superimposing the study area onto the rainfall isopluvial maps provided in
<br />the NOAA Atlas (Figures 20-25) (NOAA, 1973). Three-hour duration rainfall depths
<br />were estimated using equation 4 in the NOAA Atlas, which is a function of the I-hour
<br />and 6-hour rainfall depths (NOAA, 1973), The 1-, 3-, and 6-hour rainfall depths for the
<br />500-year storm event were determined by plotting the 2-, 5-, 10-, 50-, and 100-year depths
<br />on log-probability paper and extrapolating, A summary of the 1-, 3-, and 6-hour depths is
<br />shown in Table 3-4,
<br />
<br />3.5 Rainfall
<br />
<br /> Table 3-4
<br />Summary of Unadjusted Rainfall Depths
<br /> Unadjusted Rainfall Depths (inches)
<br />Storm Event I-Hour 3-Hour 6-Hour
<br />2-Year 1.0 1.2 1.4
<br />5-Year 1.3 1.7 2,0
<br />10- Year 1.7 2,0 2.2
<br />50- Year 2.3 2,7 3.0
<br />100-Year 2,6 3,1 3,4
<br />500- Y ear 3,3 3,9 4.2
<br />
<br />3.5.1 <:riteria
<br />
<br />The design rainfall events modelled for the study area were developed using criteria from
<br />the Urban Storm Drainage Criteria Manual (USDCM) (UDFCD, 1969) and the National
<br />Oceanic and Atmospheric Administration (NOAA) Atlas (NOAA, 1973). Tables 4-1 and
<br />4-2 of the Rainfall Chapter of the USDCM stipulate criteria for general storm durations
<br />and adjustments to rainfall based on watershed area, Table 3-3 provides a summary of
<br />area adjustments, based on Tables 4-1 and 4-2 of the USDCM, used for this study.
<br />
<br />3.5.2 Rainfall Depths
<br />
<br />Rainfall depths for 1-, 3-, and 6-hour durations were determined from the NOAA Atlas
<br />(NOAA, 1973), One-hour rainfall depths were used to produce 2-hour duration storms
<br />according to criteria shown in Table 3-1 of the Rainfall chapter of the USDCM (UDFCD,
<br />1969). The I-hour depths were estimated for the 2-year and 100-year storm events using
<br />the equation provided in Table 11 of the NOAA Atlas for Region 1 (South Platte River
<br />
<br />3.5.3 Hyetographs
<br />
<br />A total of 24 hyetographs were developed for six recurrence intervals (2-, 5-, 10-, 50-,
<br />100-, and SOD-year), each having four area adjustments as shown in Table 3-3, These
<br />
<br />3-2
<br />
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