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Last modified
1/25/2010 7:09:02 PM
Creation date
10/5/2006 2:17:53 AM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
92
County
Jefferson
Community
Arvada
Stream Name
Ralston, Leyden Creeks
Basin
South Platte
Title
Major Drainageway Planning - Ralston/Leyden Creek, Arvada, Jefferson County, CO
Date
8/1/1977
Designation Date
1/1/1978
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br /> <br />VI-3 <br /> <br />I <br /> <br />I <br /> <br />1. Lowered groundwater table. <br />2. Controlled rising groundwater table after urbanization. <br />3. Reduced street maintenance costs. <br />4. Reduced street construction costs. <br />5. Improved movement of traffic. <br />6. Improved publ ic health environment. <br />7. Lower-cost open space. <br />8. Lower-cost park areas and more recreational opportunities. <br />9. Improved quai ity of streams. <br />10. Opportunities for close-in solid waste disposal sites, <br />11. Opportunities for lower building construction cost, <br />12. Opportunities for creating new water supplies. <br />13, Opportunities for lower insurance rates, <br /> <br />considered. It should be noted that in many cases, a 10-year design chan- <br />nel with 2 feet of freeboard can carry the 100-year frequency event without <br />overflowing; however, this is not generally true of box culverts, <br /> <br />I <br /> <br />I <br /> <br />Tables VI-3 and VI-4 tabulate the expected annual damages to be incurred <br />with each alternate for the 2-, 10-, and 100-year design frequency with a <br />100-year storm occurring after improvements on the reaches of Ralston and <br />Leyden Creeks. <br /> <br />I <br /> <br />FLOOD PLAIN ACQUISITION <br /> <br />I <br /> <br />These factors were considered in the unit cost prices and the estimation of <br />various alternatives, but do not affect the costs significantly between alter- <br />natives. <br /> <br />The cost of acquiring the 100-year flood plain was calculated by determin- <br />ing the actual number of houses, apartments, and commercial units which would <br />be purchased to clear the flood plain of structures. It should be noted that <br />the I imits of the flood plain will vary with removal of structures and that a <br />more specific flood plain analysis would be necessary to determine the specific <br />number and type of structures to be removed. <br /> <br />I <br /> <br />I <br /> <br />INTANGIBLE BENEFITS <br /> <br />I <br /> <br />Intangibles include those components of environmental appreciation which are <br />not directly quantifiable in terms of dollar value or dollars spent for <br />their use. Normally, intangibles accrue from the aesthetic, scientific, <br />educational, historical, and recreational aspects of natural and manmade <br />environments. One additional intangible benefit, peculiar to residents of <br />flood hazard areas, is the peace of mind which can be enjoyed by those <br />safeguarded from future flood damages. <br /> <br />Table VI-5 summarizes the structures, by reach,which would have to be removed <br />to completely clear the entire 100-year flood plain of structures. This, how- <br />ever, is only an index number because there would be no reason to clear the <br />entire flood plain when other measures exist, including flood insurance and <br />flood proofing. <br /> <br />I <br /> <br />IRRIGATION STRUCTURES <br /> <br />I <br /> <br />The inclusion of intangible benefits in the land use decision making process <br />presents obvious advantages. The methods by which they can be included, <br />however, are not so obvious. Benefit/cost analyses have been used to weigh <br />the merits of various alternative courses of action in terms of economic <br />efficiency. This requires that all benefits and costs be relegated a dollar <br />value, or they are not included in the benefit/cost decision making process. <br /> <br />Both Ralston and Leyden Creeks are crossed by the Church Ditch, Croke Canal, <br />and Farmers Highline Ditch. Costs for each crossing structure were included <br />in Reach 5 of Ralston Creek and Reach 3 of Leyden Creek. Due to the unde- <br />veloped state of the areas surrounding the ditch crossings, only minor damage <br />reduction benefits can be derived by the improvements to the crossings, but <br />it should be noted that these improvements would be critical in passing the <br />floodwaters downstream rather than having the flood flows transferred by the <br />ditches to other drainage basins or causing flooding in areas not subject to <br />flooding. <br /> <br />I <br /> <br />The 5.6 miles of urbanized channel on Ralston Creek and 1.8 miles on Leyden <br />Creek provide many opportunities to identify intangible benefits. revive <br />additional ones which have been destroyed by urbanization, and create new <br />one-s. <br /> <br />I <br /> <br />NONSTRUCTURAL STRATEGY COSTS <br /> <br />I <br /> <br />Costs used for the nonstructural strategy are given in Table VI-6. <br /> <br />FLOOD DAMAGES OF ALTERNATIVES <br /> <br />I <br /> <br />Each of the various alternatives will still incur expected damages when, for <br />example, the 100-year storm overflows a channel which is designed for the <br />2-year flow. These damages include channel erosion and structural damage <br />(covered in Annual O&M) and private home and shop damages which are included <br />under this subsection. The level of damaaes incurred will be dependent upon <br />the design frequency of the alternate and the frequency of the storm being <br /> <br />I <br /> <br />I <br /> <br />I <br />
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