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 main channel. The split flow re-combines with the main channel just
upstream of South Golden Road.

Damages to some residential properties in this reach upstream of Camp George
West are expected. Some erosion damage to the main channel is also likely.

The main channel through this reach passes through several undersized
culverts. The culverts under Orchard Street and 10th Avenue are both
corrugated metal pipes which are undersized. Several residential structures in
this area of low density development are located directly in or near the edge of
the floodplain. The structure at South Golden Road at the downstream end of
this reach is a triple 20-foot wide by 3-foot high reinforced concrete box culvert
which is undersized. The existing culvert is about half blocked with sediment,
and flow overtops South Golden Road during floods greater than the to-year
event. Damages to structures and contents as well as to road pavement are
expected in this reach.

L-4

Sta. 272+40 to 289+40: Sheets 8-9

L-5

Sta. 289+40 to 312+00: Sheets 7-8

Downstream of the Pleasant View-Lena Gulch Confluence the mainstem crosses
the Welch Irrigation Ditch. The ditch crosses over the channel in a rectangular
concrete flume. The crossing under the flume is of inadequate capacity to
convey all flood flow and causes the ditch flume to be overtopped. Between the
Welch Ditch and the crossing at Isabell Street, the floodplain covers a broad area
of mostly underdeveloped property. However, in the vicinity of West 13th
Avenue and Isabell Street, a few residences lie in the floodplain. The culvert
under Isabell Street is undersized and causes the street to be overtopped. Flow
crosses Isabell and continues overland into the Denver West Office Park.
Damages to residential property in this reach are low due to the shallow nature of
the flooding. Minor erosion and pavement damage is expected around the
Isabell Street crossing.

Below South Golden Road, the channel is unimproved. Low flows meander
through a small area of low density residential development and then into Camp
George West. Through Camp George West the channel passes through two
undersized bridges. These bridges cause a significant backwater effect which
inundates a wide area. In addition, flow from the Pleasant View Tributary merges
with the floodwater from the mainstem on the Camp George West property just
upstream of the Pleasant View-Lena Gulch Confluence. The inundated land from
the combined Lena Gulch-Pleasant View flows covers an area approximately
400-feet wide by 1100-feet long. Fortunately this area is primarily undeveloped
and no major structures lie within the floodplain in Camp George West.

L-3

Sta. 223+00 to 272+40: Sheets 9-10

This reach lies entirely within the Denver West Office Park. Denver West is

divided by 1-70 with the majority of the development located downstream of 1-70.

While being the largest commercial development in the study area, Denver West

has very few stormwater related problems due to the drainage improvements

which were built into the development. The Lena Gulch channel has been

enlarged throughout the development and has adequate capacity for the 100-

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