HomeMy WebLinkAboutBUCKINGHAM PLACE, SECOND FILING - PDP/FDP - FDP150001 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTEEEEnnnnggggiiiinnnneeeeeeeerrrriiiinnnngggg
908 Laporte Avenue Fort Collins, Colorado 80521 970.219.2834 bob@apex-engineer.com
July 8, 2015
Mr. Glen Schlueter, P.E.
Stormwater Department
City of Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80521
RE: Final Drainage and Erosion Control Letter
Buckingham Place, Second Filing
Dear Glen,
We have prepared this final drainage letter for Buckingham Place, Second Filing for your review
and approval. The only comments received on the previous submittal were from Jesse Schlam
regarding Appendix C. Those comments are addressed in that attachment.
The existing property is an undeveloped 12,529 square-foot lot on the east side of Third Street
approximately 200 lf north of Lincoln Avenue. It is located in the Dry Creek Master Drainage
Basin. This project proposes to develop to single family residential lots on the property. The
following is a summary of the impacts to the drainage systems on and off the site. In addition,
supporting calculations and a drainage exhibit have been attached.
Floodplain
The project site is located within the Poudre River 500-year floodplain (Zone X, Protected by
Levee). “At-risk population and essential service” critical facilities are not allowed within the
500-year floodplain. No floodplain permitting is required for this project since single family
residential is not considered a critical facility.
Runoff
The existing site (Basin EX) drains to the east and has 0.02 cfs and 0.78 cfs of runoff leaving the
site in the 2-year and 100-year storms, respectively.
In the developed condition, approximately 0.15 acres (Basin A) drains to 3rd Street and 0.13
acres (Basin B) drains to the east. Runoff from Basin A is 0.17 CFS and 0.76 CFS for the 2-year
and 100-year storms, respectively. Runoff from Basin B is 0.02 CFS and 0.46 CFS for the 2-year
and 100-years storms, respectively.
Detention Storage
The entire site is estimated to be approximately 50% to 60% impervious when built out. The
Dry Creek Master Drainage plan estimated this area at 90% impervious. Due to the reduction
in the planned imperviousness, the size of the site, and the difficulty in providing detention we
are not proposing any detention storage with this project.
Water Quality
The small site, existing location of the Coy Ditch, and proximity to adjacent storm sewer make
it very difficult to provide structural water quality facilities. The residential site will have an area
of non-paved surfaces at the front and rear of the lot. These areas will intercept the
stormwater runoff from the roof and hardscape areas and provide water quality via
“disconnected impervious areas”.
Erosion Control
Erosion and Sediment Control devices will be implemented on the site as needed. The erosion
control consists of typical silt fencing within the lots and a gravel inlet protection for the existing
inlet in 3rd Street receiving runoff from the project. A separate Erosion Control Report has
been attached as Appendix C.
Summary
Due to the size of this small site, the proposed development of the site will have minimal impact
to the stormwater. The runoff from the site is less than what was originally planned for in the
Master Drainage Plan, therefore no on site detention or downstream improvements are
included with this project.
I appreciate your time and consideration in reviewing this submittal. Please contact me at (970)
219-2834 should you have any questions or concerns.
Best Regards,
Bob Gowing, P.E.
APEX Engineering
Attachments:
• Appendix A - Calculation of Peak Runoffs
• Appendix B - Erosion Control Report
• Appendix C – Grading Drainage and Erosion Plan