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FLOOD05134
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FLOOD05134
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Last modified
1/25/2010 6:48:21 PM
Creation date
10/5/2006 1:17:08 AM
Metadata
Fields
Template:
Floodplain Documents
County
Jefferson
Community
Lakewood
Stream Name
South Lakewood Gulch
Basin
South Platte
Title
Flood Hazard Area Delineation
Date
7/1/1977
Prepared For
Lakewood
Prepared By
UDFCD
Contract/PO #
&&
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br /> <br />8 <br /> <br />I <br /> <br />I <br /> <br />SECTION IV <br /> <br />The actual floodplain map is a pictorial representation of the profile in <br />plan format which is used for land use planning purposes. <br /> <br />FLOODPLAINS <br /> <br />The floodwater surface area was delineated On a map at a scale of I-inch <br />equals 100 feet using normal and accepted hydraul ic engineering methods of <br />plotting. This map was reduced by one-half for publishing in this Report. <br /> <br />I <br /> <br />GENERAL <br /> <br />I <br /> <br />Floodplain delineation in a dependable manner is the cornerstone to reason- <br />able floodplain controls. Private property is being regulated for the <br />good of the private property owner, his neighbor, the general public, and <br />to reduce the liabil ity of government. The flood discharge and the flood- <br />plain boundaries must be established in accordance with reasonable and ac- <br />cepted engineering methods. <br /> <br />Prior to preparing the map, a field inspection of the floodplain was under- <br />taken to check the map for conformance to actual field conditions. <br /> <br />I <br /> <br />PRINCIPLES OF FLOODPLAIN CONTROLS <br /> <br />The overall purpose of floodplain controls is to: <br /> <br />I <br /> <br />Flood Frequency <br /> <br />. Protect the public health, safety, and general welfare, <br /> <br />I <br /> <br />The frequency of occurrence of the regulatory flood for land use regulation <br />purposes is the 1 percent flood event (lOO-year flood) with future develop- <br />ment. This flood has a 1 percent chance of being equalled or exceeded in <br />any given year. <br /> <br />. <br /> <br />Minimize flood losses in areas subject to flood hazards, <br /> <br />. <br /> <br />Promote the wise use of the floodplain, and <br /> <br />I <br /> <br />The 1 percent event criteria orovides for a basic waterway which will <br />function during larger, as we(l as smaller floods and is a reasonable <br />basis for public safety and protection. <br /> <br />. Provide for the preservation of floodways and floodplain storage <br />areas in order to protect those downstream from increased flooding. <br /> <br />I <br /> <br />Flood Magnitude <br /> <br />Floodplain controls are critical factors in drainage management. Success- <br />ful floodplain controls will preserve a reasonable path for floodwaters by <br />control I ing development in flood hazard areas, prevent loss of floodplain <br />storage volume and prevent the introduction of structures, property or <br />land uses into the floodplain which would result in damages. <br /> <br />I <br /> <br />The rate and volume of the 1 percent flood has been determined for <br />existing and future development and is presented in Section III. The flood <br />is defined using procedures of the Runoff Section of the Urban Storm <br />Drainage Criteria Manual supplemented by additional modeling techniques. <br /> <br />I <br />I <br /> <br />Flood Prof i 1 es <br /> <br />Floodplain controls are premised upon the concept that government should <br />protect the health, safety, and welfare of the citizens. It is a function <br />of government to protect the citizens from extraordinary costs of relief <br />and rehabilitation and to plan against social disruption and chaos which <br />usually occur during and after a major flood. <br /> <br />I <br /> <br />The floodwater surface profiles are computed using standard engineering <br />techniques. The basic procedure in determining the floodplain was the <br />HEC-2 backwater program developed by the U.S. Army Corps of Engineers. <br />A backwater program is necessary to determine the flow depth upstream of <br />the multitude of bridges, culverts, and various channel constrictions of <br />South Lakewood Gulch. (Ref. 5, 6). <br /> <br />Nature possesses a prescriptive easement for intermittent occupancy of <br />floodplains by storm water runoff. This easement cannot be subordinated <br />to any other use of the floodplain without costly compensatory control <br />measures. Encroachment upon this easement can adversely affect upstream <br />and downstream flooding. <br /> <br />I <br /> <br />I <br /> <br />The data base required for this program consists of cross sectional channel <br />shapes, roughness, and survey information about culverts and bridges. The <br />majority of the information is provided by I-inch to IOO-foot scale aerial <br />topographic mapping and surveyed culvert information. This was supple- <br />mented by a field trip in which detai led notes were taken to note various <br />soil, channel, and culvert conditions. The drawings of this report show <br />the 100-year floodplain for future basin development for the existing channel <br />This floodplain will be submitted to the Colorado Water Conservation Board <br />for official designation. <br /> <br />Urbanization of a drainage basin modifies the natural hydrologic response <br />of that basin, usually in a manner to increase the rate and volume of <br />runoff. If floodplain lands are developed, drainage works may be necessary <br />which reduce floodplain storage. As a result, the upstream and down- <br />stream flood damage potential may be compounded. <br /> <br />I <br /> <br />I <br /> <br />I. <br />
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