FLOOD03506

• County: Jefferson
• Community: Lakewood
• Stream Name: South Lakewood Gulch
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 8/1/1978
• Prepared For: Lakewood
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Floodp~ain controls are premised upon the concept that government should

protect the health, safety, and welfare of the citizens. It is a function

of government to protect the citizens from extraordinary costs of relief and

rehabilitation and to plan against social disruption and chaos which usually

occur during and after a major flood.

The Federal Insurance Administration "Depth versus Percent Damage" table

(January 21, 1974) was used to calculate dollar damage values for structures

and contents for the various levels of flooding. (Ref. 7). The actual market

valuation of structures was developed from Jefferson County current assessment

records. These values were the basis for estimating flood damage costs for

the 5, 10, 50, and 100-year flood events. The flood damage probability

distribution and annual damages for existing and improved conditions are

given in the Phase A report.

Nature possesses a prescriptive easement for intermittent occupancy of flood-

plains by storm water runoff. This easement cannot be subordinated to any

other use of the floodplain without costly compensatory control measures.

Encroachment upon this easement can adversely affect upstream and downstream

flooding.

Urbanization of a drainage basin modifies the natural hydrologic response

of that basin, usually in a manner to increase the rate and volume of runoff.

If floodplain lands are developed, drainage works may be necessary which

reduce floodplain storage. As a result, the upstream and downstream flood

damage potential may be compounded.

FLOOD DAMAGES

The floodplain of the 5, 10, 50, and 100-year design frequency were plotted

on I-inch to 100-foot scale mapping. The extent of flooding for each fre-

quency was then related to the ground and first floor level of the structures.

Damages were then tabulated for each frequency according to type of structure

and similarity of levels of flooding for each reach.

Federal and State flood damage mitigation efforts, including the Flood Disaster
Protection Act of 1973 (PL 93-234), the Water Resources Development Act of
1974 (PL 93-251), the State of Colorado Model floodplain Regulation (CWCB &
HB 10111), are all aimed at avoiding the floodplain occupancy mistakes of the
past. Thus, when projecting future flood damages it is appropriate to assume
no increase in "hazardous" floodplain occupancy within the 100-year flood-
plain.

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