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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into upstream and downstream headwalls for aesthetic enhancement.
When design velocities through the structure exceed 10 feet per
second, riprap will be provided through the structure and upstream
and downstream of the structure. Structural steel pipe arches
cannot be used on skewed crossings due to the transfer of forces
along the corrugations through the arch.

RALSTON CREEK FROM ABOVE GRANDVIEW AVENUE TO ABOVE PIERCE STREET - Station
9+00 to 60+00

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5.

Drops and Checks. Channel drops will be used as needed to control
the hydraulic grade line and velocity to within reasonable slopes
and limits, Drops will be of concrete, riprap, or riprap in gabions;
be of pleasing appearance; have gravel filter blankets under the
rock to control undercutting; and be properly notched for the trickle
channel. Design must account for potential vandalism. Checks will
be end-protected to eliminate side cutting.

A European-type channel is to be used in this reach of Ralston Creek, Orig-
inally, the specific direction given by the Urban Drainage and.Flood Control
District for Phase B was for a grass-lined channel for this reach. However,
the additional constraint of the extension of Ralston Road from Lamar Street
to Sheridan Boulevard required a narrower channel in this area. From Lamar
Street to Pierce Street two channels were designed. A European-type channel
was found to be less costly than the recommended grass-lined channel because
of the structures that had to be removed in order to use a grass-lined channel
which met the criteria stated in the Denver Regional Council of Governments'
Urban Storm Drainage Criteria Manual, Volumes I and 2.

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4.

Irrigation Ditches. All irrigation ditches and laterals will be
provided for, though laterals are not shown on the Master Plan. On-
grade flumes will be used where feasible to reduce silt and main-
tenance problems. Capacity of crossings will be limited to cause
storm runoff in ditches to enter waterways. Irrigation ditch
crossings will be designed to obviate picking up the overflow from
waterways,

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RALSTON CREEK FROM CLEAR CREEK TO GRANDVIEW AVENUE - Station 0+00 to 9+00

For the 100-year flow, the master plan channel will have an average velocity
of 8.4 feet per second, a base width of 105 feet, a major channel depth of
flow of 9 feet and textured concrete side walls that slope at 0.5 to 1. It
will follow the alignment of the existing channel except where the existing
channel makes a 90 degree bend. In these areas, the European-type channel
will bend in a gentle curve. As a part of this master plan, the Colorado and
Southern Rai lroad bridge wi 11 be r"placed with a 120-foot long bridge, Ralston
Road will have the existing bridge replaced with a 155-foot long bridge, Lamar
Street will have the existing pipe replaced with a 120-foot long bridge, Noland
Street will have the existing pipes replaced with a liS-foot long bridge and
Pierce Street will have its bridge opening area increased by adding a new bay
to the existing structure. The Manhart Ditch will have its headgate moved up-
stream from the existing Ralston Road bridge to the drop at the Pierce Street
bridge. As an alternative, an investigation might be conducted into the feas-
ibility of purchasing the water rights at Lamar Street.

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THE MASTER PLAN

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The following pages describe the specific master plan improvements for
Ralston Creek and Leyden Creek on a reach by reach basis. The cost estimates
for these improvements are given in Section IX.

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A grass-lined channel is to be used in this reach of Ralston
100-year flow, this channel will have an average velocity of
second, a base width of 200 feet, a major channel depth of 5
side slopes.

Grandview Avenue will have the existing bridge replaced with. a 150 foot long.
opening structure. Transitions to the master plan channel WIll be provided
upstream and downstream of the new structure.

Creek. For the
7.5 feet per
feet and 4 to 1

The master plan improvements for this reach of channel are presented On Sheets
22 through 25. These improvements will decrease the area of the flood plain in
this reach and will alleviate the overtopping of the Colorado and Southern Rail-
road tracks, Ralston Road, Lamar Street, Noland Street, and Pierce Street during
the 100-year event.

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The master plan improvements for this reach of channel are presented On
Sheet 25. These improvements will decrease the area of the flood plain
in this reach and will alleviate the overtopping of Grandview Avenue during
a 100-year event.

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