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

Basin Parameters
Specific input parameters used in modeling runoff from the basins include: basin area; length of
the longest water course; length along the water course to the sub-basin's centroid; weighted
basin slope; percent impervious area; pervious and impervious interception losses; initial and
final infiltration rates, and the infiltration rate decay exponent. Table 1 summarizes the input
parameters to CUHPE/PC by sub-basin for projected future land use conditions.
The basin area, length of the longest water course, distance to basin centroid and weighted
slope for each sub-basin were measured from a photo enlargement of 7.5 minute USGS
quadrangle maps. The pervious and impervious interception losses were estimated to be 0.40
and 0.10 inches respectively as suggested in USDCM.
Basin infiltration properties were estimated using Horton's equation as outlined in the USDCM.
As part of the 1975 Master Plan study, numerous field infiltration tests were performed. The
measured initial and final infiltration rates reported in the 1975 Master Plan were used in this
study because they are representative of actual basin conditions and are based on more
detailed field analyses than the general criteria for infiltration rates presented in the USDCM.
The values reported in the 1975 Master Plan were used for all sub-basins except for the non-
forested areas of Apex Gulch and Jackson Gulch. The initial infiltration rate used for these sub-
basins was 3.00 inches/hour based on further information provided by UDFCD and the project
sponsors. The infiltration decay rate constant was estimated as 0.0009 to reach steady state
nfiltration within 30 to 60 minutes.

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