FLOOD10481

• County: Douglas
• Basin: South Platte
• Title: Chatfield Reallocation Study - Roadway Analysis Study
• Date: 5/11/2004
• Prepared For: CWCB
• Prepared By: Sear Brown
• Floodplain - Doc Type: Floodplain Report/Masterplan

were obtained by comparing
The

The unit costs for the opinion of probable constlUction cost
recent bids of current roadway construction projects located in the Front Range.
costs were from publicly bid projects and are adjusted based on engineer's judgment
where appropriate to be consistent with the level of work expected for this project

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nvestlgations
,
On December 19, 2003, a site visit was held with EDA W, CWCB, Sear-Brown, and CTL
Thompson to make a visual observation of the existing soil conditions along the proposed
alignment. Mr. Frank Holliday, CTL Thompson. was selected to perform this review and
provide his conceptual level recommendations based on his knowledge of and experience
with the soils in this part of the Denver area. Mr. Holliday made a visual reconnaissance of
the types of soils present along the proposed roadway alignment to attempt to identify areas
of potential concern that may impact the feasibility or cost ofconstlUcting a roadway along
the alignment. Mr. Holliday's observations generally indicate that the soils northerly of the
Deer Creek crossing appear to be clay over claystone bedrock which are expansive type
soils, For the roadway southerly of Deer Creek appear to be a variable thickness of clays
overlying alluvial sands and gravels mixed with some cobbles and probably boulders. Mr.
Holliday provided some possible methods to deal with potential constlUction issues but did
not observe any geologic or geotechnical conditions that would preclude building the
roadway in the proposed alignment on the conceptual plan, For the complete text ofCTL
Thompson's observations, refer to the letter dated January 6, 2004 from CTL Thompson to
Sear-Brown

Route Selection
In the original concept plan there were two possible roadway alignments that were reviewed
by the design team. Both alignments were identical along the west side of the existing
reservoir to the point where the current roadway turns easterly around the southern side of
the reservoir towards the Platte River crossing, At this point one option was to use this
existing alignment and significantly raise the road\\'ay above the new water elevation and
effectively creating a causeway across the south end of the reservoir including a new bridge
crossing of the Platte River. The second option was to construct a new roadway around the
south end of the what would be the new r water
the Platte River.

evels and make a new crossing of
Both of these alignments were reviewed with State Parks and the design
team and it was decided by State parks that for operational concerns it would be preferable
to construct a new roadway around the south end of the expanded reservoir rather than to
build a causeway across it. To that end, a conceptual level design and cost estimate was
completed for only the option of extending a new roadway around the south end of the
expanded lake, The selected route would be a new roadway approximately 4 miles in
length including two new bridges

reservOl

hatlield

c

Sear-Brown was retained by The Colorado Water Conservation Board to work with EDA W
on the Recreational Mitigation Study and more specifically to analyze the cost impacts ofre-
aligning the main circulation roadway within Chatfield Park, The study consisted of several
meetings, discussions and on-site visits with the design team to detennine a feasible route
and extent of needed improvements, The product for this study was intended to be a
evel design for the roadway re-alignment along with an opinion of probable
The remainder of this study will outline the criteria utilized,
route selection results, conceptua evel design documents, and opinion
on cost

AnalysIs

Reservoir Roadway

conceptual
construction cost

InveStigatIOns
of probable construct

made,

r

raising the current nonnal water leve n the reservoi
evation of approximately 5444 per the base map drawings
nformation is based on the topography depicted in

Criteria

The re-alignment study is based on
approximately 12 feet to an e
created by EDA W. AI
EDA W base maps.
State Parks desires

freeboard above the normal water level that will
the roadway operatlOnat which results in a minimum roadway elevation of 5446.
Roadway sections are to be similar to the current Chatfield Park conditions with the
addition of a 4 foot wide paved shoulder for bicycle use per the request of State Parks
Geometric design criteria is based on design guidelines contained in "A Policy on
Geometric Design of Highways and Streets by American Association of State Highway
and Transportation Officials (AASHTO),
a) The roadway is assumed to be classified as a special purpose road - recreational road
b) A roadway section consisting of two II foot wide paved lanes, 4 foot wide paved
shoulders and a 10 foot wide vegetated clear zone on each side has been utilized,
c) The re-aligned roadway functions as a primary access roadway to the park facilities
and a 40 mph design speed is appropriate, Portions of the existing roadway are posted
at 35 mph currently.
d) For conceptual design purposes it is assumed that horizontal curves will be
superelevated to a maximum rate of 0,06 which established a minimum horizontal
radius for conceptual design purposes of approximately 521 feet.
There will be two bridge structures over the length of the re-aligned roadway, One at
Deer Creek and the other at the Platte River. Each structure is sized to accommodate the
ke trail for a total

keep

design

to have a 2 foot

2

3

4

5

de pedestrianlbi

roadway section plus guardrails and an 8 foot wi
structure width of approximately 42 feet wide.
Drainage structures have been located and sized based on a si

ng
of the

ew of eXIst
e\v

e rev
and a rev

cut verts along highway 2 (Wadsworth/Canyon Road)
topography along the proposed roadway alignment

upstream
existing

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