HomeMy WebLinkAboutDrainage Reports - 10/08/2015EN
NORTHERN
ENGINEERING
Dan Mogen, EIT
City of Fort Collins Engineering
281 North College Ave
Fort Collins, Colorado 80522
Re: 4825 Crest Road Home Expansion
Drainage Evaluation
Ilao'i q, ijrooka�occC �Sfaies
Dear Mr. Mogen:
"0,0t1ober 7; 2015.
der Fosse Cry Mos`.Ar, acsuw�e
o,s, Fo( -Bat'rK SZ.' h 40
The owners of the residence at 4825 Crest Road'in fort Collins would like to construct an
expansion onto their estate for personal use. Building permit plans have been submitted to
the City for approval. It was requested of us to.provide a grading, plan for the home and
evaluate the change in drainage from the property.
The property falls within the Fossil Creek Master Drainage Basin. The property, resides
within the Brookwood Estates Subdivision; platted in 1975 by Everitt:Enterprises, Inc_.
Currently, this property is developed estate lot. The subdivision would have been developed
under the criteria in place at the time of platting. Any effect of updates to drainage criteria
would be recognized by the Fossil Creek Master Drainage Plan and should not affect the
vested rights of property ownership.
It can reasonably be assumed that any drainage design for the property would have used
the old City.of Fort Collins Stormwater Criteria where an aggregate runoff coefficient of 0.45
would have been used for the subdivision with a 40% imperviousness. Any design for
downstream facilities to manage.runoff from this subdivision would also use similar values
for modeling. -
It is our opinion that the surface. improvements of the lot with a pro-rata share of the
subdivision improvements would be a representative sample for calculation of the fair
contributing imperviousness for the lot. We have delineated the lot and the entire adjacent
.roadway section as the lot's reasonable and conservative contribution to the stormwater
system. The property as proposed, including the adjacent roadway is calculated to_ be 17%
impervious and will fall well within the 40% imperviousness that would reasonably be
anticipated for buildout of a home within this subdivision during design and mod,'eling.
301 N. Howes Street, Suite 100, fort Collins, CO 80521 'I . 970.221.4158 I www.northernengineering.com
NORTHERN
ENGINEERING
We have attached the impervious calculations for your reference
We trust that this letter will satisfy the requirement for evaluation showing that the
proposed expansion is within impervious limits used for drainage design within the City.
Please contact Northern Engineering with any questions or concerns regarding this matter.
Sincerely,
Ryan Banning, P.E.
Project Manager
u
301 N. Howes Street, Suite 100, Fort Collins, CO 80521 I 970.221.4158 I www.northernengineering.com
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