FLOOD07224

• County: Jackson
• Community: Walden
• Basin: North Platte
• Title: Flood Plain Information Report Town of Walden
• Date: 2/1/1999
• Prepared For: Walden
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Table t
tOO-year Peak Flow Estimates for the Town of Walden

FFA Regression
Mean Basin Drainage tOO-year tOO-year
Slope Area Peak Flow Peak Flow
Stream Name and Location (feet/feet) (sq. mi.) (cfs) (cfs)
Michigan River at the Highway 125 0.134 180 1,240 1,880
bridge approximately 4,000 feet north
of Fifth Street
Illinois River at the Highway 125/14 0.133 240 2,550 2,300
bridge approximately 2,300 feet east
of Main Street

Based on the above results, it is suggested that 1,880 cfs be adopted as the 100-year flow for the
Michigan River, and 2,550 cfs be adopted as the 100-year flow for the Illinois River. The Town of
Walden should regulate the approximate floodplains on a case-by-case basis. FEMA requires that a
detailed floodplain analysis must be performed by a professional engineer and submitted by the
developer or development proponent for development projects involving more 5 acres or more than
50 units (whichever is more restrictive).

Hvdraulic Analvsis
Hydraulic methods used for the approximate floodplain delineations shown on the Town of Walden
FIRM panel are not available or have not been documented by FEMA. For future studies, an
approximate 100-year flood elevation at a particular location on the river may be obtained by using
the 100-year peak flow value (as provided in this report) in conjunction with an acceptable
hydraulic analysis. Hydraulic analyses for determining 100-year water surface elevations for
approximate floodplains may be performed using FEMA's Quick-2 computer program, the Corps
of Engineers' HEC-2 computer program, Flowmaster, or other acceptable hydraulic methods.
Channel and floodplain cross-sections may be obtained from detailed topographic mapping or from
field surveys. Cross-sections obtained from USGS quadrangle maps are not advised.

Floodolain Maooinl!:
The existing Flood Insurance Rate Map for Town of Walden depicts areas subject to 100-year
flooding based on approximate technical methods. The map does not show flood profiles, base
flood elevations, or sufficient detail in order for Town officials, engineers, developers, and land
owners to make floodplain determinations with any certainty. The Colorado Water Conservation
Board can be contacted to request technical assistance for approximate floodplain analyses as
needed.

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