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Last modified
1/29/2010 10:15:21 AM
Creation date
10/4/2006 9:09:38 PM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
121
County
Adams
Arapahoe
Douglas
Community
Denver Metro Region
Stream Name
Massey Draw and North Tributary
Title
FHAD - Massey Draw and North Tributary, SJCD South 6200 and Tributaries, Jefferson and Arapahoe Counties, CO
Date
5/1/1978
Designation Date
11/1/1978
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />16 <br /> <br />Where the IOO-year flood overtops controls such as banks, road crossings, or <br />dams, areas of "overland flowll are created downstream. OVerland flooding is <br />physically separated from flooding in the channel and flows at elevations in- <br />dependent of those shown on the flood profiles. The flow can be either back <br />toward or away from the channel. To differentiate between overland flooding <br />and "backwater" flooding in the channel, a dashed line delineates the flood <br />limit based on channel flood elevations. Both areas are included in the flood <br />hazard area, delineated in a solid line. <br /> <br />The third reach of Massey Draw extends from South Garrison Street upstream to <br /> <br /> <br />the Section 3-4 line. The area is presently unplatted and no dedicated drain- <br /> <br /> <br />age ROW exists. An area south of the channel near South Garrison Street will <br /> <br /> <br />be gravel mined. The upstream limit of the master planning study for Massey <br /> <br />Draw is in reach 3. The lOa-year flood plain averages 270 feet in width and <br /> <br /> <br />channel velocities average 8 feet per second. Overbank velocities, where they <br /> <br />exist average 5 feet per second. <br /> <br />Flood Hazard Area Description <br /> <br />The fourth reach extends from the Section 3-4 line upstream to a point where <br /> <br />the flood plain is confined within narrow limits (in Section 32). Near the <br /> <br /> <br />upstream end of this reach, the lOa-year flood overtops the right bank and is <br /> <br /> <br />conveyed primarily in the right overbank. The limited capacity channel hugs <br /> <br /> <br />the left side of the flood plain. The lOa-year flood plain is considerably <br /> <br /> <br />wider, averaging 610 feet, channel velocities average 5 feet per second and <br /> <br />overbank velocities average 4 feet per second. <br /> <br />To aid in describing the flood hazard area, each drainageway was subdivided <br /> <br /> <br />into reaches shown on Plate II. The first reach of Massey Draw extends from <br /> <br /> <br />South Wadsworth Boulevard through South Carr Street and includes the Meadow- <br /> <br />brook Heights subdivision. There is no dedicated drainage right-of-way and in- <br /> <br /> <br />dividual lots generally extend to the center line of the draw. The lOa-year <br /> <br /> <br />flood plain averages 160 feet in width, channel velocities average 8 feet per <br /> <br />second, and overbank velocities average 3 feet per second. The inadequate <br /> <br /> <br />culvert at South Carr Street causes road overtopping and probable failUre for the <br /> <br />two year and larger floods. South Wadsworth Boulevard is not overtopped during <br /> <br />the lOa-year flood. A reach of Stene Drive is affected by the overflow at <br /> <br /> <br />Carr Street, and one house could sustain structure and content damage. Damage <br /> <br />to landscaping and fencing could occur at four homes within the reach. <br /> <br />The fifth reach of Massey Draw includes all of the narrow flood plain reach from <br /> <br />the point in Section 32 where it widens out to the upstream limit of study. The <br /> <br /> <br />cross section reference numbers included are 390 to 500. The channel is narrow <br /> <br /> <br />and the banks are steep. The 100-year flood plain averages 50 feet in width and <br /> <br /> <br />the velocities average 9 feet per second. The Hogback Ridge, which divides the <br /> <br />upper and lower basins of Massey Draw, occurs within this reach. <br /> <br />The second reach of Massey Draw extends from South Carr Street through South <br /> <br /> <br />Garrison Street. It is presently unplatted and much of the area is being gravel <br /> <br />mined. No dedicated drainage right-of-way exists. An inadequate culvert at <br /> <br /> <br />South Garrison Street causes overtopping and potential for failure for the 5 <br /> <br /> <br />year flood and larger. The width of the main channel lOa-year flood plain <br /> <br /> <br />averages 330 feet and channel velocities average 5 feet per second. Channel <br /> <br /> <br />velocities are higher through a channelized stretch immediately downstream of <br /> <br /> <br />South Garrison Street. OVerbank velocities average 2 feet per second where they <br /> <br /> <br />exist. An extensive area is inundated by flood waters that overtop South <br /> <br /> <br />Garrison Street and the right bank at two locations. Flood depths there do <br /> <br /> <br />not correspond to channel profile elevations, because the flooding is physically <br /> <br />separated from the channel. This is an example of the designation "area sub- <br /> <br />ject to overland flooding" used on the drawings. <br /> <br />The first reach of the North Tributary of Massey Draw extends from South Wads- <br /> <br />worth Boulevard through South Carr Street. South Wadsworth Bouleward is not <br /> <br /> <br />overtopped during the lOa-year flood. but Allison Street and South Carr Street <br /> <br />are overtopped and failure is likely for floods greater than or equal to the <br /> <br /> <br />5 year and 2 year floods respectively. The drainageway is located along the <br /> <br /> <br />back property lines in the Meadowbrook Heights subdivision and no dedicated right- <br /> <br /> <br />of-way exists. Structure and content damage could occur at four individual <br /> <br /> <br />homes, and several outbuildings. Fence and landscaping damage might result at <br /> <br /> <br />seven home sites. Overtopping of the roadway at South Carr Street causes flood <br /> <br /> <br />water to flow along 900 feet of Brook Drive. The average lOa-year flood plain <br /> <br /> <br />width is 240 feet and the average channel velocity is 6 feet per second. Over- <br /> <br />bank velocities average 3 feet per second. <br /> <br />~ Leonard Rice Consulting Water Engineers, Inc. <br />
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