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FLOOD03506
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Last modified
1/25/2010 6:27:29 PM
Creation date
10/4/2006 11:49:11 PM
Metadata
Fields
Template:
Floodplain Documents
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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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />SOUTH lAKEWOOD GULCH HYDROLOGY <br /> <br />Peak Flow for Various Frequencies <br />5-Year 10-Year 50-Year 100-Year <br /> <br />1. The shape of the South lakewood Basin is extremely long and thin, <br /> <br /> <br />with a length to width ratio of about 8. Whereas most typical <br /> <br /> <br />basins in the Denver Metropolitan area are relatively shorter and <br /> <br /> <br />consequently route flood flows much quicker, basin correlation tech- <br /> <br /> <br />niques would tend to overestimate flows on South lakewood Gulch. <br /> <br /> <br />2. This hydrological study involved the detailed analysis of five <br /> <br /> <br />separate subbasins, as well as the actual stream routing character- <br /> <br />istics of the basin. This combination of hydrology and hydraul ics <br /> <br /> <br />carefully considered percent of impervious area, slope, individual <br /> <br /> <br />subbasin shape, stream cross sections, and roughness factors. This <br /> <br />resulted in a more complete, specialized study of this particular <br /> <br /> <br />local area. larger, basin-wide studies tend to be oriented towards <br /> <br /> <br />overall basin effects and do not usually include the detail required <br /> <br />for a refined analysis in one local area. <br /> <br /> <br />3. The basin studied by the USACE was approximately 20 percent larger <br /> <br /> <br />than the 1,040 acres analyzed here. By del ineating the basin boundary <br /> <br /> <br />on standard U.S. Geological Survey maps, surface contours generally <br /> <br /> <br />suggest a larger tributary area than that used in this analysis. <br /> <br /> <br />However, recent field inspections have indicated that a large portion <br /> <br /> <br />of the lower basin that would otherwise be tributary is in fact cut <br /> <br /> <br />off by the Sixth Avenue Freeway. Drainage in this area would tend to <br /> <br /> <br />run along the frontage road just south of the freeway, eventually <br /> <br /> <br />finding its way into lakewood Gulch. No major problems were noted in <br /> <br /> <br />this area, except for the potential inundation of the frontage road <br /> <br />during extreme rainfall events. In addition to this basin modifica- <br /> <br /> <br />tion, others were made according to the local street grades in some <br /> <br /> <br />areas. In general, basin boundaries often diverge from those evident <br /> <br />from surface contours in urban areas. <br /> <br />The CUHP was used to prepare runoff hydrographs for each subbasin in South <br /> <br /> <br />lakewood Gulch. Individual hydrographs were then routed and combined by <br /> <br /> <br />the use of the Massachusetts Institute of Technology Catchment Model <br /> <br />(MITCAT). The combination of these two hydrological methods provides <br /> <br /> <br />for an economical and efficient analysis of the hydrologic response of <br /> <br /> <br />the basin. The various stream network and reservoir routing capabilities <br /> <br /> <br />of MITCAT allow for a flexible approach in analyzing future runoff con- <br /> <br /> <br />ditions, while the widely-accepted CUHP provides the basic input data for <br /> <br /> <br />the routing. A more detailed description of both CUHP and MITCAT is pre- <br /> <br /> <br />sented in the Hydrological Appendix. (Ref. 2). <br /> <br />Present Condition Peak Flows <br /> <br /> <br />Presented below in Table 111-1 is a summary of runoff flows under present <br /> <br /> <br />conditions for the 5, 10, 50, and 100-year frequency events. <br /> <br />TABLE 111-1 <br /> <br />PEAK RUNOFF FLOWS <br />PRESENT CONDITIONS <br />(All Values in Cubic Feet per Second) <br /> <br />In contrast to the flows presented above, the 1968 <br />utilizing basin correlation techniques indicated a <br />1,600 cfs at the mouth of South lakewood Gulch. This corresponds to the <br />1,150 cfs figure in Table 111-1, which is about 28 percent lower. There <br />are several reasons for this apparent discrepancy which are discussed as <br />follows: <br /> <br />Subbasin <br /> <br /> @ Addenbrooke Pond 120 180 <br />2 @ Rockmont Pond 340 500 <br />3 @ Fi rst Ave. Pond 400 610 <br />4 @ Wadsworth Blvd. 490 730 <br />5 @ lakewood Gulch 580 860 <br /> <br />210 240 <br />600 670 <br />730 810 <br />870 970 <br />1,040 1,150 <br />study by the USACE (Ref. 4) <br />100-year flow of about <br /> <br />Future Development Peak Flows <br /> <br /> <br />As discussed in Section II, the South lakewood Gulch drainage basin is <br /> <br /> <br />presently about 70 percent developed. Based upon future land use maps <br /> <br /> <br />provided by the City of lakewood officials, peak flows have been deter- <br /> <br /> <br />mined for the 5, 10, 50, and 100-year flood frequencies, and are presented <br /> <br /> <br />in Table 111-2 below. <br /> <br />111-2 <br />
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