HomeMy WebLinkAboutHERITAGE PARK - MJA220001 - DOCUMENT MARKUPS - ROUND 3 - DRAINAGE REPORT (2)Preliminary Drainage Report
Heritage Park Apartments – Fort Collins, Colorado
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INTRODUCTION
The proposed Heritage Park Apartments Improvement Project is located within the Northeast Quarter of
Section 22, Township 7 North, Range 69 West of the Sixth Principal Meridian, City of Fort Collins, County
of Larimer, Colorado. The site is bound by:
· North: Existing Multifamily Development
· East: S Shields Street
· South: W Stuart Street
· West: Existing Multifamily Development
A vicinity map is provided below.
PROPOSED DEVELOPMENT
The site is approximately 16.29 acres and is an existing multifamily development previously known as
“Northwood Apartments” per the approved drainage plan dated 7/11/75. The proposed site improvements
include six additional dwelling unit buildings with associated driveways and landscape improvements, as
well as building and sidewalk additions to the clubhouse under separate permit and submittal.
EXISTING SITE INFORMATION
The Site is located within the Spring Creek Basin. Existing floodplain boundaries were provided by the City
of Fort Collins and are denoted on the proposed drainage map referenced in Appendix B. The Master Plan
for this basin is currently planned to be updated in 2022, according to the City of Fort Collins website.
Preliminary Drainage Report
Heritage Park Apartments – Fort Collins, Colorado
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Portions of this property are in the city-designated Canal Importation floodplain and floodway. The FEMA
FIRM Panel is 08069C0978G dated 5/2/2012. The Canal Importation Basin Master Drainage Plan Hydraulic
Evaluation and Mapping Update dated 7/22/14. The Flooding Solutions Map indicates that there are no
current upgrades to storm infrastructure near the site. No flooding, water quality, nor Master Plan
improvements are recommended within the vicinity of the Site. A proposed linear bioretention and modified
detention pond system is located within the existing floodplain. The remaining proposed buildings and
scope of site improvements are outside of the 100-year floodplain. No work is proposed within the existing
floodway.
The soil on the site is primarily Altvan-Satana Loam and Caruso Clay Loam, which are classified as
Hydrologic Soil Group B and D, respectively. The soil Classification Map can be found in Appendix A. This
Site is a part of the Spring Creek Master Drainage Plan, which is currently under revision and has not been
referenced in this design. The existing site is utilized as a multifamily development with associated
buildings, parking, and landscape areas.
HISTORIC DRAINAGE
The existing Site varies with slopes ranging from 1.5% to 35%. There is currently an onsite detention basin
in the northeast section of the property. The Site is split into five sub basins, A-1 to A-5, based on the
existing drainage map included in Appendix B. Basins A-2, A-3, and A-4 generally slope to the northeast
and are conveyed to the existing detention basin within Basin A-4. The flows within the detention basin are
then released into the existing storm infrastructure system along S Shields Street. Basins A-1 and A-5 are
conveyed south via sheet flow, and collected by existing inlets along W Stuart Street, that convey flows to
the existing storm system along S Shields Street.
The site is located within City of Fort Collins Federal Emergency Management Agency (FEMA) Flood
Insurance Rate Map Number 08069C0978G and the property being developed is designated as an area
outside of the 100-year floodplain. The updated FEMA maps is included in Appendix A.
Per the FEMA Flood Insurance Rate Map and City of Fort Collins Problem Identification Map, the Site is
not within a 100-year floodplain and therefore additional analysis and permitting will not be required.
DESIGN CRITERIA
The City of Fort Collins “Stormwater Criteria Manual, December 2018 Edition,” (Criteria Manual), the “Urban
Drainage and Flood Control District Urban Storm Drainage Criteria Manual” Volumes 1, 2, and 3 (Drainage
Manual), with latest revisions, and the “City of Fort Collins Low Impact Development Implementation
Manual, July 2017 Edition” (LID Manual) were used to prepare the storm calculations. Weighted impervious
values were calculated and used for the site area in accordance with the Criteria Manual and Drainage
Manual.
This Site is a part of the Spring Creek Master Drainage Plan, which is currently under revision. Existing
storm sewer infrastructure is present on the Site. An existing detention pond is present on the northeast
corner of the site.
Hydrologic Criteria
The 2-year and 100-year storm event were evaluated for this Site. Rainfall intensity values provided in the
Criteria Manual were utilized for the analysis. Impervious values for pavement, roof, and landscape area