FLOOD06660

• County: Douglas
• County: El Paso
• County: Elbert
• Community: Franktown, Parker
• Stream Name: Cherry Creek Watershed
• Basin: South Platte
• Title: Franktown Parker Tributaries fo Cherry Creek Watershed
• Date: 4/1/1960
• Prepared For: State of Colorado
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Sediment and erosion damages and benefits to agricultural land
are based on expected reductions in yields, The number of acres of land
estimated to be damaged during the next 50 years without a project
were calculated, Damage reduction was based on the reduction of peak
flow with the project installed and benefits were discounted to allow
for lag in accrual.

Floodwater damages to road grades and bridges used in the
evaluation were those obtained from state and county officials, Benefits
were estimated by relating expected reduction of peak flow to dollar
damage.

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In addition to the direct floodwater damages there are indirect
damages, such as interruption of travel, rerouting of traffic, cost
for extra feed for livestock, decreased milk production, extra cost
of marketing milk, and depreciation of property in the flooded areas.
Ten per cent of the direct floodwater damage was used as a conservative
estimate of the annual indirect flood damages.

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Restoration to former productivity benefits were calculated,
amounting to $1,453 annually, These are net benefits remaining after
floodwater damage with project installed, and production, harvesting
and associated costs deducted, These benefits are included in the
total of crop and pasture benefits shown in Table 7. Benefits were
discounted to provide for a 5-year delay in accrual,

Engineering Investigations and Cost Estimates

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Field investigations were conducted on all of the Franktown-
Parker Watershed tributaries above the principal damage areas to
locate possible structural sites, These investigations resulted
in the selection of 24 floodwater-retarding and combination floodwater-
retarding and grade stabilization structures and a floodwater diversion.
The difference between the designations ~floodwater-retardinif' and
ucombination floodwater-retarding and grade stabilizationn is mainly
geographic with respect to the relative location between structures
and gully headcuts, The same design criteria applies to both types
of structures. Consideration of site locations included topographic
conditions, economic feasibility, and existing facilities including
springs, roads, bridges, and culverts. Structural site locations are
shown on the Structure Location Map, Figure 2,

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Detailed topographic maps of the dam sites and pool areas were
obtained by planetable surveys on each of the proposed f"oodwater-
retarding and combination floodwater-retarding and grade stabilization
structures. Contour intervals of either four-foot or eight-foot were
used depending upon the steepness of the terrain, The information
obtained fram the geologic investigations made on the adjacent West
Cherry Creek Watershed (Public Law 566 watershed program now in
construction) is representative of the conditions which exist in the
Franktown-Parker Watershed. Structure site samples and borings were
deemed unnecessary for the planning investigations.