FLOOD10386

• County: Jefferson
• Community: Golden, Lakewood
• Stream Name: Upper Lena Gulch
• Basin: South Platte
• Title: FHAD - Upper Lena Gulch
• Date: 1/1/1993
• Prepared For: UDFCD
• Prepared By: Boyle Engineering Corporation
• Floodplain - Doc Type: Floodplain Report/Masterplan

represents an idealized section for routing computations and was estimated from the
topographic maps. The channel roughness coefficient was estimated from criteria outlined in
the USDCM. The channel routing parameters used in the model are presented in Table 3.
Future Basin Conditions
Land use and zoning maps provided by Jefferson County and the Cities of Golden and
Lakewood were used to identify projected ultimate future land use in the basin. Estimates of
the percent impervious area for the projected land use were made and entered into the
hydrologic model. Peak discharges for each of the recurrence intervals were computed for
future basin development conditions. Figure 5 shows a map of the basin which depicts the
projected future land use. Table 4 contains the peak discharges for selected design points for
each of the recurrence intervals under future basin development.
TABLE 4
Future Basin Conditions
Peak Flow Summary At Design Points (cfs)
Location 1Jb!r ~ 100-yr
Lena Gulch at Hogback 510 1,320 1,770
Lena Gulch at 6th Avenue 800 1,740 2,270
Lena Gulch at 1-70 1,440 3,920 3,810
nflow to Maple Grove Res. 580 3.080 3,980

For sub-basins with areas less than 90 acres, the CUHP requires that the time of concentration
for each sub-basin be estimated. The time of concentration used as input to the CUHPE/PC
model was estimated using the procedures outlined in the USDCM. The computed times of
concentration are shown in Table 1.
One-hour rainfall depths for the 10-, 50-, and 100-year recurrence interval rainstorms were taken
from the USDCM depth-duration-frequency information and are summarized in Table 2 below.
Table 2
1-Hour Rainfall
Recurrence Rainfall
Interval Depth (in)
10-yr 1.72
50-yr 2.35
100-yr 2.60
Channel routing parameters were developed for 54 conveyance elements from topographic
mapping provided by UDFCD and field inspection. These routing parameters include length of
conveyance element, channel bottom width, channel shape, channel invert slope, and a
channel roughness coefficient. The channel length and invert slope were estimated from USGS
7.5 minute quadrangle maps. The channel geometry used in the UDSWM2/PC model

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