FLOOD10360 ‎(2)‎

• County: Washington
• Community: Otis
• Title: Preliminary Design, SW Drainageway, Railroad to Washington Street, Town of Otis Colorado
• Date: 1/1/1997
• Prepared For: Otis
• Prepared By: McLaughlin Water Engineers, Ltd.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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was completed using the HEC-2 computer program, The HEC-2 printouts are included in the Appendix
of this report, The downstream starting point for this analysis is the railroad, The existing culverts would
be under inlet control. (No new culverts are proposed for the railroad at this time). The combined culvert
capacities were calculated using a water surface elevation of 4,328,0,4,329,0 and 4,330,0, The calculated
capacities for each of these water elevations are 485, 625, and 800 cfs respectively, These flows and
elevations are the starting point for the analysis, with an assumed station of 9+00, and an invert elevation
of 4322.4, From the survey, it was determined there is positive grade following the proposed alignment
to Spruce and Vine Streets, From Vine Street west, the ground is essentially flat, which is why the
flooding occurs, and is slow to dissipate,

Reach 1, Railroad to 300'::1: Northeast of SpruceNine Intersection
No improvements are proposed from the railroad culverts to Station 16+00, which is where the existing
channel turns south, The first proposed work would be at Station 20+50, which is about 300 feet east and
north of Vine/Spruce Street intersection, The average slope from the lowest railroad culvert to Station
20+55 is ,003 ft/ft or about 3 feet in 1,000 feet,

Reach 2, Station 20+55 to Vine Street
The proposed channel would be a trapezoidal shape and have a base width of 20 feet and gradual side
slopes to existing grade, The channel would be graded to allow flow from the south (east of Vine Street)
to enter the system,

Reach 3, Vine/Spruce Intersection
At Vine Street, the road is to be lowered approximately 1,5 feet and gradually slope north and south to
allow proper traffic flow, The initial proposed grades are 5 %, It was pointed out that there is a water line
and sanitary sewer line at this location, The water line would proposed to be lowered, and the sanitary
sewer rerouted to avoid the conflict. Further design work is needed to verify the grades and alignment of
the sewer, The Vine Street road surface would then be fInished with gravel.

Reach 4, SpruceNine Intersection to Alley West of Vine
Spruce Street is proposed to be lowered from Vine Street west to the alley, about 200 feet, The grade may
be continued to Washington Street to improve that intersection and drainage from the south, The roadway
would affect the driveway on the south side of Spruce at the alley, The current grades are flat into the
driveway, and would increase to about 3 % with the lowering of Spruce. The street surface would be
concrete with curb and gutter,

96416.OO2IPRELIM

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