HomeMy WebLinkAboutPLANETSCALE LIVING - PDP200015 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT (2)October 1, 2020
City of Fort Collins
Public Works and Development (Stormwater Department)
201 Laporte Ave,
Fort Collins, CO 80521
RE: Drainage Report – Low Impact Development
Project: 2020-006 (TT) Serdar Badem, 906 E Stuart St, Fort Collins, CO 80525
To Whom it may Concern:
This Drainage Report is for analysis of on-site drainage for Low Impact Development for Project 2020-006
(TT) Serdar Badem, 906 E Stuart St, Fort Collins, CO 80525. The project is in Fort Collins, Colorado and will
entail converting (remodeling) an existing childcare center into an affordable housing 4-Plex. The site
(parcel #9724106924) is located 850 feet west of S. Lemay Avenue and 1,200 feet south of E. Prospect
Road. Access is taken from E. Stuart Street directly to the south. The property is within the Low Density
Mixed-Use Neighborhood District (L-M-N) zone district and is subject to Administrative (Type 1) Review.
The existing drainage on site has no drainage structures and minimal surface flow (on-site or off-site).
Most of the existing site (Figure 1) consists of Concrete access and driveway; most of the southern portion
of the site, the concrete footprint of building, concrete patio and the remaining consists of
grass/dirt/gravel mixture with trees. The existing site is flat with minimal to zero slopes throughout the
site. To the east there is an HOA Easement that parallels the site and Springmeadows Court. The HOA will
not allow any construction and/or stormwater work within this area. Because of this limitation, the
project will be implementing Low Impact Development drainage solutions using City of Fort Collins
Stormwater Criteria Manual – Chapter 7, Section 6.0 and Appendix C – LID Implementation Manual.
Because of the inability to go of site with any of the on-site run-offs; the project will design LID solutions
that will improve the entire site.
Table 1 Below shows that around forty-two percent of the existing site is impervious (Areas 2 & 4) and the
remaining pervious areas (1 & 3) are limited because of no positive slope and random native material
mixed with dirt, grass, gravel and rocks. The proposed solution will be to implement Pavers and
Landscape Beds/Areas throughout most of the site, which will improve and be below the 1000 s.f.
requirement for LID water quality requirement (Table 1). No LID water quality requirement will be needed
for this site.
Table 1
Figures 1 (existing) and Figure 2 (Proposed) [correspond with Table 1]
Figure 1 - Existing
Figure 2 – Proposed
MAJOR DRAINAGE BASINS & SUB-BASINS
A. The site is not within a Floodplain; the site does not lie within the Regulatory Floodway Zone. (All
new construction is outside the floodway boundaries). There are no storm drainage structures
located in the property. All flows inflow and outflow are surface. The main site is made up of
existing building, parking and access road south front which is concrete. The northern/western
portion of the existing site is native grass / dirt / gravel. The existing southern access drive and
eastern concrete areas are standing water and minimal surface flows to eastern HOA easement
towards Springmeadows Court. This project will not be allowed to construct any drainage
structures or grading within the HOA Easement.
B. Drainage analysis – Mile High Flood District: Rational Method v.2 was used (spreadsheet-based
calculations for surface, %I runoff).
C. The proposed site is with an Urban Drainage Area. The site is LID and all drainage and runoff with
be onsite controlled with Pavers and landscaped control areas. The proposed site will match
exiting grades and historic flows.
D. Basins & Sub-Basins:
BASIN 1 – (0.25 Acres) Existing Site with existing structure; full area.
Sub-basin 1a - (0.024 Acres, %I 2) Runoff sheet flows from portion of northwest
corner of parking on pavement then flows south to north. Runoff flows across the
drive north to Sub-basin D.
Sub-basin 1b - (0.114 Acres, %I 40) Runoff sheet flows from portion of the proposed
parking lot, split in half and flows to sub-basins A (West) and C (East)
Sub-basin 1r - (0.05 Acres, %I 100) Runoff sheet flows from portion of northeast
corner of parking on pavement then flows south to north. Runoff flows across the
drive north to Sub-basin F.
Sub-basin 1c - (0.06 Acres, %I 2) Runoff sheet flows from portion of western paved
area mid-western to Northern portion of new paved area Sub-basin E.
Peak Flow, Q (cfs)
Sub-catchment Name
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
AREA 1a 0.00 0.00 0.00 .02 0.03 0.05 0.08
AREA 1b 0.05 0.08 0.12 0.20 0.27 0.36 0.57
AREA 1r 0.10 0.14 0.18 0.25 0.30 0.36 0.53
AREA 1c 0.00 0.00 0.01 0.05 0.07 0.11 0.20
FINISH FLOOR ELEVATIONS
The Finish Floors have been established to set at 4980.75. Proposed site will match flow patterns
and drain as per existing conditions.
FLOOD PLAINS
The site is not within a Floodplain; There is no documented history of flooding.
MAINTENANCE PLAN:
Owner will complete a monthly maintenance inspection once a month to clean and remove any
trash, debris and vegetation that is restricting or not allowing pavers and/or landscape areas to
drain. This will include any mowing or trimming of landscaped areas. Any repairs to the grading
because of washout and/or sedimentation will be removed.
CONCLUSIONS
Proposed construction will have minimal to no impact to the existing flows onsite / offsite. The
design drainage will provide measures that protect public health, safety, and the general welfare
of the proposed site and surrounding areas; plus have no impacts on public rights-of-way or
offsite properties.
The proposed project includes 856 sf (<1000 s.f.) of added/modified impervious area. The project will
treat 49.83% of this area (5458 sf) using permeable pavers and run-on to the pavers. The proposed project
provides 7.86% of new impervious area as permeable pavers (1520 sf) located in parking areas within the
site. The project will treat new impervious area using a combination of LID treatments (both permeable
pavers and landscape beds/areas). A summary LID Compliance Table is provided below.
Summary
In summary, the proposed project incorporates permeable pavers as the primary component of
stormwater LID treatment. The proposed solution will be to implement Pavers and Landscape Beds/Areas
throughout most of the site, which will improve and be below the 1000 s.f. requirement for LID water
quality requirement (Table 1). No LID water quality requirement will be needed for this site.
This project and memo are in compliance with the City of Fort Collins Stormwater Criteria Manual
(December 2018) and associated references to the latest version of the Urban Drainage and Flood Control
District Manual.
If you have any questions regarding this submittal, please do not hesitate to contact me by email at
apowell@pec-inc.co or by phone at (720) 409-2454. Thank you.
Adam A. Powell, PE
PEC Inc
(From Fort Collins Stormwater Criteria Manual - 6.0 Low Impact Development)
This Section of this Chapter presents information that is specific to the City of Fort Collins and may be a
significant deviation from the information presented in the UDFCD Manuals. Utilizing UDFCD
methodologies for Low Impact Development (LID) designs may not be accepted by FCU.
In February 2013, Fort Collins City Council adopted Ordinance No. 152, 2012, to incorporate provisions
implementing LID principles; with the goal to declare that the purpose of the City Stormwater Utility is
to provide an integrated, sustainable stormwater management program that reflects the community’s
values of protecting and restoring the City’s watersheds. This was subsequently modified and updated in
January 2016 with Ordinance No. 007, 2016 to allow for some added flexibility in the implementation of
the LID policy.
Reference: Both the initial LID ordinance, Ordinance No. 152, 2012, and the subsequent
ordinance, Ordinance No. 007, 2016, can be found on the City of Fort Collins website.
LID is simply defined as an integrated, sustainable stormwater management program that requires a
distributed, closer to the source stormwater runoff control that simulates natural processes and relies
mainly on filtration and infiltration to locally treat and manage stormwater runoff.
Integration of LID systems into the drainage design is required for all development projects in order to
comply with the City’s policies on LID, the requirements of this Manual, the City Code and the Land Use
Code. LID systems provide a higher degree of stormwater quality treatment than that provided with
standard water quality design. The implementation of LID systems requires one of the following two
options:
1) 50% of the newly added or modified impervious area must be treated by LID techniques and
25% of new paved (vehicle use) areas must be pervious.
2) 75% of all newly added or modified impervious area must be treated by LID techniques.
Impervious surfaces are defined as hardscape surfaces that do not allow stormwater to infiltrate into
the ground. Impervious surfaces include asphalt and concrete surfaces, concrete curbs, gutters,
sidewalks, patios and rooftops. (Impervious surface areas must be assumed for single family residential
lots when overall impervious areas are being determined for residential developments. The assumed
areas must then be included in LID calculations.) “Added” impervious area stated in the two options
above is further defined as existing vegetation (or pervious) areas becoming hardscape (or impervious)
areas. “Modified” impervious area stated in the two options above is further defined as existing
impervious areas on an existing site being removed and replaced with other impervious surfaces through
a redevelopment process (i.e. existing asphalt surface becoming a rooftop surface). Mill and overlay of
asphalt areas is not considered a “modified” impervious area. “Paved” areas, as stated in option 1 above
are generally considered to be private vehicle use areas only.
Reference: Refer to the City of Fort Collins LID Implementation Manual in Appendix C for
detailed information and requirements on LID systems.
(From Fort Collins Stormwater Criteria Manual - 6.2 Permeable Pavement)
The term “permeable pavement” is a general term to describe any one of several pavement systems that
allow infiltration of water into the layers below the pavement through openings within the pavement
surface. Use of permeable pavements is an accepted Low Impact Development (LID) practice in Fort
Collins and is often used in combination with other BMPs to provide full treatment and slow release of the
WQCV. In addition, there are some installations in Fort Collins that have also been designed with an outlet
control and increased depth of aggregate material in order to provide quantity detention in excess of the
water quality (80th percentile) storm event. Design considerations for permeable pavement systems are
presented in the LID Implementation Manual, included in Appendix C.
Included here are some general design requirements applicable for all types of LID system designs in
Fort Collins.
• Overall added or modified impervious areas that amount to less than 1000 square feet (<
1000 sf) on a site will not require LID system treatment for water quality.
• For development sites that are adding or modifying 1000 square feet of imperviousness or
more (≥ 1000 sf) are required to implement LID system treatment at the site. The LID system
is allowed to treat existing imperviousness in exchange for the newly added imperviousness
if the surface character is similar (e.g. existing pavement may be treated in lieu of newly
added rooftop)
• For single-family residential developments, LID must be placed in tracts or common areas
for ownership and maintenance by the HOA. LID systems installed as part of the
development requirement shall not be placed on single-family lots.
• LID is not required for private, single-family residential improvement projects that are not a
part of a larger subdivision project. (i.e. an existing lot in an older part of Fort Collins that is
being re-built)
APPENDIX A
(VICINITY MAP)
APPENDIX B
(N.O.A.A. ATLAS 14)
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2020
Page 1 of 3
4490240 4490260 4490280 4490300 4490320 4490340 4490360 4490380 4490400
4490240 4490260 4490280 4490300 4490320 4490340 4490360 4490380 4490400
494760 494780 494800 494820 494840 494860 494880
494760 494780 494800 494820 494840 494860 494880
40° 33' 52'' N
105° 3' 43'' W
40° 33' 52'' N
105° 3' 37'' W
40° 33' 46'' N
105° 3' 43'' W
40° 33' 46'' N
105° 3' 37'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 40 80 160 240
Feet
0 10 20 40 60
Meters
Map Scale: 1:887 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
95 Satanta loam, 1 to 3 percent
slopes
2.4 72.8%
101 Stoneham loam, 1 to 3 percent
slopes
0.9 27.2%
Totals for Area of Interest 3.3 100.0%
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2020
Page 3 of 3
APPENDIX C
Designer:
Company: 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
Date: 1-hour rainfall depth, P1 (in) = 0.80 1.09 1.35 1.78 2.14 2.54 3.63
Project: a b c
Location: Rainfall Intensity Equation Coefficients = 28.50 10.00 0.786
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
Overland
Flow Length
Li (ft)
U/S Elevation
(ft)
(Optional)
D/S Elevation
(ft)
(Optional)
Overland
Flow Slope
Si (ft/ft)
Overland
Flow Time
ti (min)
Channelized
Flow Length
Lt (ft)
U/S Elevation
(ft)
(Optional)
D/S Elevation
(ft)
(Optional)
Channelized
Flow Slope
St (ft/ft)
NRCS
Conveyance
Factor K
Channelized
Flow Velocity
Vt (ft/sec)
Channelized
Flow Time
tt (min)
Computed
tc (min)
Regional
tc (min)
Selected
tc (min)
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr
0.01 0.01 0.07 0.26 0.34 0.44 0.54 72.38 72.38 25.66 1.38 1.87 2.32 3.06 3.67 4.36 6.23 0.00 0.00 0.00 0.02 0.03 0.05 0.08
0.29 0.32 0.38 0.50 0.55 0.61 0.68 27.89 27.89 19.20 1.61 2.19 2.71 3.58 4.30 5.10 7.29 0.05 0.08 0.12 0.20 0.27 0.36 0.57
0.74 0.76 0.78 0.81 0.83 0.84 0.87 1.87 1.87 5.00 2.72 3.70 4.58 6.04 7.26 8.62 12.31 0.10 0.14 0.18 0.25 0.30 0.36 0.53
0.01 0.01 0.07 0.26 0.34 0.44 0.54 63.48 63.48 25.66 1.38 1.87 2.32 3.06 3.67 4.36 6.23 0.00 0.00 0.01 0.05 0.07 0.11 0.20
0.000 0.00 0.000
AREA 1b 0.11 85.00 0.001 0.00
25.66
10.70
AREA 1c 0.06 B 2.0 50.00
Cells of this color are for calculated results based on overrides
AAP
APPENDIX D
GRADING AND DRAINAGE PLAN
48IN DIA
18IN DIA
18IN DIA
24IN DIA
48IN DIA
24IN DIA
18IN DIA
12IN DIA
12IN DIA
12IN DIA
TURF
PROPERTY
LINE, TYP.
PROPOSED DRIVEWAY
WITH BELGARD DRAINSTONE
PROPOSED
PATIO
PROPOSED 5'
CONC. WALKWAY
1' CONCRETE
BORDER BAND
RESIDENT
PARKING
(BELGARD
DRAIN
STONE
FIELD)
OPTIONAL CONCRETE
BAND TO DELINEATE
RESIDENT PARKING
(MAY SUBSTITUTE WITH
BELGARD BAND)
PARKING
STRIPE
(TYP.)
1' BELGARD DRAIN
STONE BAND
TURF
5'-0"
9'-6" 12'-0" 5'-0"
PROPOSED
PERV. PAVER
FIELD
5'-0"
PROPOSED BIKE
RACK
N89° 08' 19.95"E
1029.569
PECPEC
1401 Wewatta St.
Unit 804
Denver. Colorado 80202
Email: apowell@pec-inc.co Phone: 720.409.2454
Proect anaement
Civil Enineerin
Conltin
PLAN VIEW - GRADING & DRAINAGE
north
PEC
A
B I
A = BASIN DESIGNATION
B = AREA IN ACRES
I = % IMPERVIOUSNESS
D D = DESIGN POINT DESGNATION
1
.25 -
1r
.05 100
1c
.06 2
1b
.11 40
1a
.02 2
Belgard Concrete Pavers
Compacted Subgrade, prepare
according to recommendations
in geotechnical report.
Compacted Aggregate Base -
minimum 6” thick. Asphalt or
cement treatment base can
be used over weak or
saturated subgrade soils
1” Bedding Layer, conforms
to ASTM C33 with <1%
passing 0.080 mm
Mirafi 160N Nonwoven Filtration Fabric on entire
bottom of aggregate base (extends under curb).
Jointing Sand,
Conforms to ASTM C144
Design Notes:
1. Cross section as shown is suitable for pedestrian and vehicular applications. Paver dimensions subject to aspect and plan ratio requirements. Contact
Belgard Commercial for product selection guidance based on the intended traffic loading.
2. Depth of aggregate base subject to site specific conditions (traffic loading, soil conditions, groundwater levels, climatic conditions). Contact Belgard
Commercial for design assistance.
3. When traffic flow is perpendicular to the direction of the header, the width of the header curb should be sufficient to ensure that a bouncing tire caused by
differential settlement will land on the header and not skip over it.
4. When using geotextile separation fabric, consult with the manufacturer to ensure the material has good drainage characteristics and is not prone to clogging.
5. Drain pipes may be required within the aggregate base depending on the permeability of the subgrade soils. Verify drainage needs with the geotechnical
engineer. Ensure drain pipes are able to daylight via gravity flow to surface, or connect to catch basin.
6. Techniseal HP Nextgel jointing sand conforming to ASTM C144 may be used in pedestrian and light vehicular applications. Please contact Belgard
Commercial for design assistance.
Top of installed pavers shall be 1/8”
to 1/4” above adjacent rigid surfaces
Concrete header curb, 12" to 24" wide (see
note 3), minimum 12" deep. Add rebar as
required (designed by others). Elevation to
be 1/4 in. below adjacent pavers and asphalt.
Existing grade
Mirafi 160N Nonwoven
Filtration Fabric - 12” wide at
all perimeters, turn up against
curb and cut even with the top
of pavers
TYPICAL PAVER DETAIL
LOC
LOC
LOC
LOC
PEC
10/1/2020
4-Plex Affordable Houseing - PRO
Fort Collins, CO
Version 2.00 released May 2017
7 0.07 0.00
19.20
AREA 1r 0.05 B 90.0 15.00 0.020 0.00 0.020 20 2.83 0.00
B 40.0 0.000 20 0.20 0.00
65.00 0.000
Rainfall Intensity, I (in/hr)
0.00 0.001 10 0.32 0.00 25.66
Peak Flow, Q (cfs)
Calculation of Peak Runoff using Rational Method
Runoff Coefficient, C Overland (Initial) Flow Time Channelized (Travel) Flow Time Time of Concentration
Subcatchment
Name
Area
(ac)
NRCS
Hydrologic
Soil Group
Percent
Imperviousness
AREA 1a 0.02 B 2.0
Select UDFCD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link)
Cells of this color are for required user-input
Cells of this color are for optional override values
I 𝑖𝑛/ℎ𝑟 =
a ∗ Pଵ
b + tୡ
ୡ
t୧
=
0.395 1.1 − Cହ
L୧
S୧
.ଷଷ
t୲
=
L୲
60K S୲
=
L୲
60V୲
Computed tୡ
= t୧
+ t୲
Regional tୡ = 26 − 17i +
L୲
60 14i + 9 S୲
Selected tୡ
= max t୫୧୬୧୫୳୫
, min Computed tୡ
, Regional tୡ
t୫୧୬୧୫୳୫=5 (urban)
t୫୧୬୧୫୳୫=10 (non-urban)
Q 𝑐𝑓𝑠 = CIA
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 15, Jun 9, 2020
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 11, 2018—Aug
12, 2018
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2020
Page 2 of 3