FLOOD10318

• County: Arapahoe
• County: Jefferson
• Stream Name: South Platte River
• Basin: South Platte
• Title: Chatfield Reservoir, Roadway Analysis Study
• Date: 2/3/2004
• Prepared For: CWCB
• Prepared By: Sear Brown
• Floodplain - Doc Type: Project

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Chatfield Reservoir Roadway Analysis

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 of re-
aligning the main circulation roadway within Chatfield Park. The study consisted of several
meetings, discussions and on-site visits with the design team to determine a feasible route
and extent of needed improvements. Tpe product for this study was intended to be a
conceptual level design for the roadway re-alignment along with an opinion of probable
construction cost. The remainder of this study will outline the criteria utilized,
investigations made, route selection results, conceptual level design documents, and opinion
of probable construction cost.

Criteria
1. The re-alignment study is based on raising the current normal water level in the reservoir
approximately 12 feet to an elevation of approximately 5444 per the base map drawings
created by EDA W. All design information is based on the topography depicted in
EDA W base maps.
2. State Parks desires to have a 2 foot freeboard above the normal water level that will keep
the roadway operational which results in a minimum roadway elevation of 5446.
3. 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.
4. 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 rlOad.
b) A roadway section consisting of two 11 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.
5. There will be two bridge structures over the length of the re-aligned roadway. One all
Deer Creek and the other at the Platte River. Each structure is sized to accommodate the
roadway section plus guardrails and an 8 foot wide pedestrian/bike trail for a total
structure width of approximately 42 feet wide.
6. Drainage structures have been located and sized based on a site review of existing
upstream culverts along highway 121 (Wadsworth/Canyon Road) and a review of the
existing topography along the proposed roadway alignment.