FLOOD07170

• County: El Paso
• Community: Manitou Springs
• Stream Name: Fountain Creek
• Basin: Arkansas
• Title: Hydrology for FEMA, Phase II
• Date: 2/1/1994
• Prepared For: FEMA
• Prepared By: RCE
• Floodplain - Doc Type: Floodplain Report/Masterplan

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6. LITTLE JOHNSON/SECURITY CREEK

6.1. Watershed Description

The Little Johnson/Security Creek watershed is located south of Colorado Springs and
incorporates the town of Security, The basin lies generally between the railroad which parallels
Fountain Creek on the west and the Windmill Gulch basin to the east The basin consists of three
distinct areas which drain to Crews Gulch: (1) the Little Johnson Reservoir area, (2) Security area,
and (3) the Widefield area (Figure 6,1),

The basin area of Little Johnson/Security Creek at the confluence with Crews Gulch, excluding
Windmill Gulch is 3,12 square miles, This includes a 0,51 square mile area above Canal #4 which
is partially diverted to Windmill Gulch (50 cfs diversion to Windmill Gulch), Windmill Gulch streamflow
is conveyed via a 12-foot diameter culvert directly to Fountain Creek and therefore bypasses the Little
Johnson/Security Creek system, However, during the 100-year event the conveyance capacity of the
culvert is slightly surpassed and the resulting overflow is contributed to the Security Creek drainage,
The drainage basin area of Windmill Gulch is 3,38 square miles which results in a total tributary area
of 6,0 square miles, An area west of Grinnell discharges into this basin from Big Johnson/Crews
Gulch basin,

The majority of the watershed is urbanized, Land uses include industrial and commercial
properties, but the dominant land use is residential. Soils are predominantly Type "A" and "B"
hydrologic types as categorized by the SCS with some type "C" soils along the railroad on the west
side of the watershed,

6.2. Previous Studies

Two previous studies were available for review: (1) the FIS - EI Paso County, Unincorporated
Areas (Ref, 6,1), and (2) the Little Johnson/Security Creek Drainage Basin Planning Study (Ref, 6,2),
The FIS used synthetic unit hydrographs to develop peak discharges, The Little Johnson/Security
Creek Drainage Basin Planning Study used methods previously specified in Colorado Springs drainage
criteria to compute peak discharges, However, this study estimated discharges associated with the
100- year, 2-hour storm duration with AMC III. Current specification require use of the 24-hour
duration storm with AMC II conditions,

Peak discharges at the confluence with Crews Gulch are presented in Table 6.1 for the two
studies,

6,1 Resource Consultants & Engineers, Inc,