FLOOD06450

• 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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VIII-5

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The 100-year flows will overtop these drainage facil ities, However, much
of the lOO-year flood plain under improved channel conditions overlaps with
the 100-year flood plain under improved channel conditions for Van Bibber
Creek. Certain damages will occur on these channels from lOO-year flows;
however, these damages are unavoidable if the discharge is to flow through
the construction formed by the inappropriate urbanization of the area.

For the 100-year flood, the grass-lined channel will have an average velocity
of 8.3 feet per second, a base width of 160 feet, an overbank depth of 4.4
feet, and 3 to 1 side slopes.

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The homeowners left in the 100-year flood plain are encouraged to obtain
flood insurance and to flood proof their dwellings.

Miller Street will have the existing bridge replaced with a 150 foot long
bridge. A transition to this bridge will extend upstream to Nelson Street.
Three cottage schools will have to be moved or removed in order to build
the transition to the bridge.

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The master plan improvements for this reach of channel are presented on
Sheets 19 and 20, These improvements will decrease the area of the flood
plain in this reach.

The master plan improvements for this reach of channel are given on Sheet 16.
These- improvements will decrease the area of the flood plain in this reach
will channel ize the lOO-year flow for the downstream European channel, and ~ill
alleviate the overtopping of Miller Street during a 100-year event.

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RALSTON CREEK FROM BELOW BROOKS DRIVE TO ABOUT LEE STREET - Station 152+00
to 202+00

RALSTON CREEK FROM BELOW OAK STREET TO BELOW SIMMS STREET - Station 230+00
to 265+00

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A European-type channel is to be used in this reach of Ralston Creek, For
the 100-year flood, this channel will have an average velocity of 7.6 feet
per second, a base width of 140 feet, an overbank depth of 6.3 feet, and
textured concrete sidewalls that slope at 0.5 to I, It wi 11 follow the al ign-
ment of the existing channel except where the existing channel makes 90 degree
bends. In these areas the European-type channel will bend in a gentle curve.
Transitions to grass-lined channels will be provided upstream and downstream
of this length of channel, A total of 44 residences and 3 separate garages
will be removed in order to build this channel. It is anticipated that most
houses will be purchased as they come on the market in order to minimize the
sociological impact of this portion of the master plan.

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A grass-lined channel is to be constructed in the vicinity of Oak Street.
The grass-l ined channel transitions to a European channel downstream of
68th Avenue. There are no improvements called for in the master plan for
Ralston Creek between 68th Avenue and Simms Street.

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Brooks Drive will have the existing box culvert replaced with a 160 foot long
bridge. Rensselaer Drive and 6lst Avenue wi 11 have the existing box culverts
replaced with 140 foot bridges.

For the 100-year flood, the grass-lined channel will have an average velocity
of 9.0 feet per second, an overbank depth of 9 feet, and 4 to 1 side slopes.
The European channel will have an average velocity of 10 feet per second,
an overbank depth of 9 feet, and vertical concrete walls, Transitions to
the existing channel will be provided upstream and downstream of this com-
bined length of improved channel. Some damages will be sustained adjacent
to these channels from the 100-year discharge. One house will be removed
to build this channel.

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The master plan improvements for this reach of channel are presented on Sheets
16 through 19. These improvements will decrease the area of the flood plain
in this reach and will alleviate the overtopping of Brooks Drive, Rensselaer
Drive and 61st Avenue during a 100-year event.

Oak Street will have the existing bridge replaced by an 80-foot long bridge
and 68th Avenue will have the structure replaced with a 70-foot long bridge,

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RALSTON CREEK FROM ABOVE LEE STREET TO BELOW OAK STREET - Station 202+00 to
230+00

The master plan improvements for .this reach of channel are presented on
Sheets 14 and 15. These improvements wi 11 decrease the area of th;' f1 ood
plain in this reach.and will alleviate the overtopping of Oak Street and 68th
Avenue during a lOO-year event.

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A grass-lined channel is to be constructed in this reach of Ralston Creek from
above Lee Street to Nelson Street and no improvements are to be constructed
from Nelson Street to below Oak Street,

RALSTON CREEK FROM BELOW SIMMS STREET TO XENON STREET - Station 265+00 to
303+00

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A grass-lined channel is to be used in this reach of Ralston Creek, For the
100-year flow, this channel will have an average velocity of 8 feet per second,
a base width of 68 feet, an overbank depth of 6 feet and 4 to 1 side slopes.
Transitions to the existing channel will be provided upstream and downstream
of this length of channel,

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