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-7

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LEYDEN CREEK FROM ABOVE ALKIRE STREET TO BELOW LEYDEN LAKE - Station 92+00
to 155+00

The master plan improvements For this reach of channel are given on Sheets 31
and 32. These improvements will decrease the area of the Flood plain in the
vicinity of the new structures, will alleviate the overtopping of the Church
Ditch and overtopping of Quaker Street will be decreased to meet the allowable
criteria of the Urban Drainage and Flood Control District. Due to the minimal
damage potential of the area, no erosion protection measures will be provided
to the channel in the master plan.

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A nonstructural modified channel is to be used in this reach of Leyden
Creek. The Croke Canal will be provided with a new flow limiter and spill
structure to enable separation of storm flows from the canal while still
allowing base flows to be intercepted by the canal. The new spill structure
will require the relocation of a segment of private road and the con-
struction of a length of grass-lined channel to carry flows to Leyden Creek.

LEYDEN CREEK FROM ABOVE THE TOWN OF LEYDEN TO STATE HIGHWAY 93 - Station 230+
00 to 371+50

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A new 40-foot long bridge will replace the existing pipe at Indiana Street
and the existing channel in the vicinity of the bridge will be increased
to handle the higher discharge.

A nonstructural modified channel is to be used For this reach of Leyden Creek.
A new 75-Foot long bridge will replace the existing pipe at Leyden Road and a
new structural plate steel pipe arch will replace the existing pipe at State
Highway 93. Transitions to the existing channel will be provided upstream and
downstream of both of these structures.

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The master plan improvements for this reach of channel are presented on
Sheets 34, 35, and 36. These improvements will decrease the area of the
flood plain in this reach, will separate storm Flows at the Croke Canal,
and will alleviate the overtopping of Indiana Street during a 100-year
event. Due to the minimal damage potential of this area, no erosion pro-
tection measures will be provided to the channel in the master plan.

This reach of channel has several private
out during the 100-year flood discharge.
have no measureable adverse eFFect on the
not provide for improvements.

roads and driveways that will wash
Because these private facilities
flood hazard, the master plan does

LEYDEN CREEK AT LEYDEN LAKE - Station 155+00 to 195+00

The master plan improvements for this reach of channel are given on Sheets
26 through 31. These improvements will decrease the flood plain in the vici-
nity of the new structures, will alleviate the overtopping of Leyden Road,
and will bring the overtopping of State Highway 93 into the allowable recom-
mended criteria of the Urban Drainage and Flood Control District. Due to the
minimal damage potential of the area, no erosion protection measures will be
provided to the channel in the master plan.

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The master plan includes nO governmental improvements to the Leyden Lake.
However, modifications by the owner to the Leyden Lake dam embankment and!
or spillway are important and necessary to meet current flood requirements
as establ ished by the State Engineer as a hazard exists to those down-
stream. The master plan downstream of the dam assumes no significant de-
crease in flood retention or increase in downstream flows as a result of
such modifications.

LEYDEN CREEK FROM THE CHURCH DITCH TO ABOVE THE TOWN OF LEYDEN - Station
195+00 to 230+00

The master plan presented in this report is for 58,000 feet of Ralston Creek
and 37,150 feet of Leyden Creek. Some of the master plan improvements are
corrective in nature due to the inappropriate urbanization of the area while
in other areas nonstructural flood plain management can be implemented due
to the fact that the waterway has been treated with respect and utilized as
an asset. Most of the structures and roadways in the existing 100-year flood
plain will be removed From the flood plain upon implementation of this master
plan. The owners of the structures projected to still be in the flood plain
after the implementation of this master plan are encouraged to obtain flood
insurance and to flood proof their dwellings.

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The existing flood plain for this reach is presented on Sheets 32,33, and 34.

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A nonstructural modified channel is to be used in this reach of Leyden
Creek. A new structural plate steel pipe arch will be located on the creek
to transport 100-year flood flows under the Church Ditch. A rock transition
to the pipe arch section will be used to help convey waters to the structure.

The flood plain shown will be submitted to the Colorado Water Conservation
Board by the Urban Drainage and Flood Control District for official designa-
tion. Upon designation, this flood plain can be regulated by JeFferson County
and the City of Arvada to stop imprudent development of the remaining open
lands and the Further abuses of these channels.

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The existing culvert at Quaker Street will be replaced with a 35-foot long
bridge. Transitions to the existing channel will be provided upstream and
downstream of the new structure.

The cost estimate for the master plan improvements can be found in Section
IX.

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