FLOOD04702

• Designation Number: 347
• County: Jefferson
• Community: Unincorporated Jefferson County
• Stream Name: Upper Lena Gulch
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Upper Lena Gulch
• Date: 1/1/1993
• Designation Date: 9/1/1993
• Floodplain - Doc Type: Floodplain Report/Masterplan

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the Pleasant View and Green Mountain tributaries just upstream of the Denver West Office Park

and 1-70, The drainageway passes through box culverts under 1-70 and into a series of ponds in

the lower portion of the Denver West Office Park, Downstream of Denver West, the channel

consists of various improved sections and meanders through residential areas and then under

Youngfield Street into Lakewood, Downstream of Youngfield Street it is unimproved and it

continues downstream through residential properties to a recently improved crossing under

20th Avenue and into Maple Grove Reservoir at the downstream end of the study area,

Historv

Basin development began in earnest in the early 1940's in the Pleasant View area of Jefferson

County, Over the years, the basin has seen continued growth in both commercial and

residential development The present location of the Mobile Premix Quarry, in the upper

portion of the basin, was originally opened to provide rock for the dam at Chatfield Reservoir,

Apex Gulch has seen the construction of an amusement park and shopping complex at

Heritage Square in Golden, The commercial deveiopments along U,S, Highway 40 upstream of

6th Avenue have increased runoff from this portion of the basin, Numerous residential

developments such as the Mountain Side Mobile Estates Trailer Park in Jefferson County and

the Applewood Hills and Applewood Glen areas upstream of 20th Avenue in Lakewood have

increased the amount of impervious areas in the basin and thereby increased storm runoff,

The historic path of Upper Lena Gulch has also been changed by development over the years,
The large Denver West Office Park along Interstate 70 modified both the location and capacity
of the Upper Lena Gulch channel, and increased the amount of runoff from the area,

Until recently, thorough flood records were not kept for Lena Gulch, Over the last 10 to 15

years, the level of attention paid to recording and monitoring flooding in this basin has

increased, The Urban Drainage and Flood Control District has installed automated flow

detection equipment in Lena Gulch and has incorporated this basin into its "ALERT" flood

forecasting network,

Historically, little information was compiled on the frequency or severity of flooding in the upper

basin, although it is known that relatively high frequency flood events have caused a number of

flood problems, A flood event on May 5, 1980 caused numerous damages in the basin,

especially in the reaches above Maple Grove Reservoir, The estimated flow for that event was

approximately 430 cubic feet per second (cfs), a little more than half of the 2-year flood,

On June 8, 1987, flooding occurred which reportedly had water overtopping 20th Avenue by 3
to 4 feet and had water overtopping the dam crests of the Denver West ponds by 1 to 2 feet
The estimated flow for this event was about 600 cfs measured at Alkire Street, which is slightly
less than the 2-year flood,

Another event on June 1, 1991 caused considerable flooding in the basin, Lena Gulch at
Isabell Street was overtopped, blocking access into and out of the nearby residential
subdivision,

These past events tell the story clearly that the potential for a great deal of damage from
flooding exists in this basin,

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