HomeMy WebLinkAboutDrainage Reports - 08/22/2003SEAR BROWN
1
August 18, 2003
Mr. Basil Harridan
Storm Drainage Utility
700 Wood Street
Fort Collins, CO 80521
ARCHITECTURE
ENGINEERING
PLANNING
CONSTRUCTION
209 South Meldwrn
Fort Collins,C080521
970.482.5922 phone
970,482.6368 fax
www.searbrown.com
RE: Drainage Addendum the Sage Creek Drainage and Erosions Control Report Dated
July 19,2003.
Dear Basil,
The Following is an addendum to the Sage Creek Drainage and Erosions Control Report
Dated: July 19,2003. The Addendum addresses the following items.
1. The historic off -site drainage pattern along the western Boundary.
2. The conveyance of the onsite drainage along the western boundary of the site.
Historic Western Boundary Offsite Drainage
Historically the drainage for Basin OS -I would drain to the north and east to a farm
access road with small drainage swales. The storm drainage flows would then follow
these roadside swales to the north and to point A where the flows would then flow into
McClellands Channel. In the time period from the approval of the drainage report and
the construction of the Sage Creek the access road has been removed. However by
observation there is still a broad shallow swale (2 to 3 inches deep) that still takes the
storm drainage flows to the north.
Western Boundary On -site flows.
In order to keep flows from going off -site to the west the lots are graded so that the
majority of the storm run-off grades to the east. The remaining strip of land adjacent to
the western property line (approximately 15 feet wide) of Sage Creek is graded with a
small swale (see swale cross sections A I a and Al b). The grade of this swale is set at 1 %
with a capacity of 0.44 efs. This is approximately twice the capacity required for the
flows calculated for the 100-year storm.
Conclusion
With the addition of the small swale on the Sage Creek Property the integrity of the
historic drainage pattern has been maintained
Yours Sincerely,
Jim Allen -Morley, P.E.
Project Manager
i j
Worksheet
Worksheet for Triangular Channel
Project Description
Worksheet
Sage Creek West Ditch
Flow Element
Triangular Channel
Method
Manning's Formula
Solve For
Discharge
Input Data
Mannings Coefficient
0.030 -
Slope
0.008000 ft/ft
Depth
0.30 It
Left Side Slope
4.00 H : V
Right Side Slope
4.00 H : V
Results
Discharge
0.44 cfs
Flow Area
0.4 ft'
Wetted Perimeter
2.47 ft
Top Width
2.40 ft
Critical Depth
0.24 It
Critical Slope
0.027782 ft/ft
Velocity
1.23 file
Velocity Head
0.02 ft
Specific Energy
0.32 ft
Froude Number
0.56
Flow Type
Subcritical
Project Engineer: Sear -Brown
untitled.fm2 The Sear -Brown Group FlowMaster v6.1 [614k]
07/22/03 04:25:54 PM 0 Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA (203) 755-1666 Page 1 of 1
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