HomeMy WebLinkAboutGrading Plans - 12/21/2021DRAINAGE LETTER
3019 MooRe LANE RESIDENCE
FORT COLLINS, CO
December 21, 2021
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: 3019 MOORE LANE RESIDENCE
FORT COLLINS, COLORADO
PROJECT NUMBER: U21034
Dear Staff,
��� UNITED CIVIL
Design Group
Grading/Stormwater Plan Accepted
(Building Permit Released)
Accepted by: Dan Mogen
Date: 12/21/2021
Tefft Acres
POR OF TR'10' DESC AS COM AT NW COR TR'10', ERLY ALG N LN
597.14 FT, SRLY 145.9 FT, WRLY 597.22 FT, NRLY 145.9 FT TPOB
United Civil Design Group, LLC. is pleased to submit this Drainage Letter for the 3019 Moore Lane Residence in Fort Collins,
Colorado. In general, this summary serves to document the stormwater impacts associated with the proposed site
improvements.
SITE LOCATION AND PROJECT DESCRIPTION
The 3019 Moore Lane Residence site (referred herein as "the site") is situated in the Northeast Quarter of Section 28,
Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, Larimer County, State of Colorado. More
specifically, the site is located immediately west of Moore Lane, approximately 450 feet north of the intersection with Moffett
Drive. The planned improvements consist of an expansion of an existing single-family residence.
EXISTING CONDITIONS
Hydrology
The site, located within the Spring Creek Drainage Basin, is approximately 2.00 acres, although proposed improvements will
disturb only approximately 0.15 acres within the site. The existing site drains via overland flow and native grass lined swale.
Runoff from the site generally drains from southeast to northwest, and ultimately reaches the Pleasant Valley and Lake Canal.
Portions of the site immediately south of the existing house generally drain east to west along the southern property line,
before ultimately reaching the Pleasant Valley and Lake Canal via overland flow.
Floodplain
The western portion of the site is located within a FEMA floodplain — FEMA Map No. 08069C0986G (see attachments). The
site is not located within a City of Fort Collins regulatory floodplain. No improvements or land disturbances are proposed
within the FEMA floodplain.
CITY REQUIREMENTS
As discussed above, the site is located within the Spring Creek Drainage Basin. Per information provided by the City of Fort
Collins, the sub-basin containing the site has an assumed imperviousness of 30% in the City's master drainage plan. City
drainage requirements for residential projects state that, "The water quantity detention requirements can be waived... if the
final percentage of hard surfaces including one half the adjacent streets or alleys is equal to or less than the percentage used
in the City's master drainage plan for your area of town." Thus, if the proposed site has a proposed imperviousness of less
than 30%, no detention is required for the project.
IMPROVED CONDITIONS
The proposed site improvements include expanding an existing single-family residence and replacement of existing sidewalks
in support of the structure. The expanded structure footprint is larger than the footprint of the existing structure, resulting
in an overall increase in impervious area. The table below summarizes the hydrologic impact associated with the proposed
site improvements relative to existing conditions. See the attached Impervious Area Exhibit to see the location of the new
impervious areas.
19 OLD TOWN SQUARE #238 � FORT COLLINS, CO 80524 � 970-530-4044 � www.unitedciviLcom
DRAINAGE LETTER
3019 MooRe LANE RESIDENCE
FORT COLLINS, CO
HYDROLOGIC SUMMARY TABLES
��'�`\ UNITED CIVIL
Design Group
Note that the area used in these calculations includes the 2.00-acre site, plus one half of Moore Lane adjacent to the site.
Runoff flows and drainage patterns for the improved site remain largely unchanged from existing conditions. On site drainage
basin boundaries are unchanged, and all flows are directed generally southeast to northwest to existing discharge locations
offsite, ultimately reaching the Pleasant Valley and Lake Canal. Downspouts from the proposed residence are planned to be
piped by the contractor away from the building and directed either towards the northwest portion of the site or towards the
existing roadside swale along Moore Lane before discharging and ultimately reaching the Pleasant Valley and Lake Canal via
overland flow.
DETENTION Sc WATER QUALITY
As the proposed site including half of the adjacent street has not exceeded the assumed imperviousness of 30% for the sub-
basin per the City of Fort Collins master drainage plan, detention requirements are waived for this residential project.
Proposed improvements include disconnected impervious areas separated by landscaped areas. Runoff from proposed
impervious areas discharge to existing landscape areas that act as grassed buffers and the existing native grass lined swale
on the site before reaching existing discharge locations offsite.
EROSION CONTROL
Erosion control, both temporary and permanent, is a vital part of any development project. For this project, the site
disturbance is less than 1 acre; therefore, a CDPHE Stormwater Management Plan (SWMP) is not required. However,
comprehensive erosion control measures are included with the site improvements. Refer to the Civil Construction Plans for
additional information. At a minimum, the following temporary BMP's will be installed and maintained to control on-site
erosion and prevent sediment from traveling off-site during construction:
• Sediment Control Log — a linear roll made of natural materials to trap sediment from sheet flow. Sediment Control
Log is a temporary BMP placed at the perimeter of disturbed area.
The contractor shall store all construction materials and equipment and shall provide maintenance and fueling of equipment
in confined areas on-site from which runoff will be contained and filtered. Temporary Best Management Practices (BMP's)
will be inspected by the contractor at a minimum of once every two weeks and after each significant storm event.
CONCLUSIONS
The drainage system proposed within this Drainage Letter provides adequate conveyance of the developed stormwater
runoff from the proposed improvements to existing discharge locations to the north and west of the site. No negative impacts
are anticipated to the City of Fort Collins Master Drainage Plan or adjacent properties and infrastructure due to the proposed
improvements. No detention is required for onsite runoff per City of Fort Collins requirements for this residential
development as the proposed site imperviousness is less than that assumed for the sub-basin by the City's master drainage
plan and runoff is adequately conveyed. Water quality considerations are being provided by the grassed buffers on the site.
19 OLD TOWN SQUARE #238 � FORT COLLINS, CO 80524 � 970-530-4044 � www.unitedciviLcom
*- Percent imperviousness for different area types based on Fort Collins Stormwater Criteria Manual recommended values.
DRAINAGE LETTER
3019 MooRe LANE RESIDENCE
FORT COLLINS, CO
��'�`\ UNITED CIVIL
Design Group
We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in
the Fort Collins Stormwater Criteria Manual (FCSCM). This summary was prepared in compliance with technical criteria set
forth in both the Urban Drainage and Flood control District (UDFCD) Urban Storm Drainage Criteria Manual and the FCSCM.
If you should have any questions or comments as you review this drainage summary, please feel free to contact us at your
convenience.
Sincerely,
United Civil Design Group, �LC
Prepared by:
Jacob Stein, EIT
Design Engineer II
/ Ii�
Kevin Brazelton, PE
Principal
ATTACHMENTS
Proposed Impervious Area Exhibit
FEMA Firmette (covering FEMA FIRM Panel 08069C0986G)
Op RE
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W 8837 p : #
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19 OLD TOWN SQUARE #238 � FORT COLLINS, CO 80524 � 970-530-4044 � www.unitedciviLcom
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