HomeMy WebLinkAboutLONGSTEIN SINGLE-UNIT DWELLING WITH ADU - FDP240014 - SUBMITTAL DOCUMENTS - ROUND 1 - Drainage Related Document
KEEFE CIVIL, INC
3125 Crockett Street
Fort Collins, Colorado 80526
(970) 215-6808
meg@keefecivil.com
October 3, 2024 Keefe Civil Project Number: 2024-017
Water Utilities Engineering
City of Fort Collins
700 Wood Street
Fort Collins, Colorado 80522
RE: 728 Cherry Street Drainage Memo
Parcel 9711240002
To Whom it May Concern:
The purpose of this letter is to describe the proposed site improvements and potential drainage
impacts at 728 Cherry Street (Exhibit A). The 0.088-acre project site is an undeveloped single-
family residential lot located on the north side of Cherry Street between North Grant Avenue and
North Loomis Avenue in Fort Collins, Colorado (Figure 1). The site is located within the Old
Town drainage basin.
Figure 1: Vicinity Map
728 Cherry Street Drainage Memo Keefe Civil Project No.: 2024-017
Page 2 of 3 October 3, 2024
The lot is bound by existing single-family residences to the north and west, Cherry Street right-of-
way to the west, and a gravel alley way to the east. Per the NRCS Soil Survey of Larimer County
(Exhibit B), the site entirely consists of Paoli fine sandy loam and is classified as being within
hydrologic soil group A. These soils are anticipated to have a high infiltration rate when
thoroughly wet and a high rate of water transmission.
Per the attached flood insurance rate map (Exhibit C), the lot is located within Zone X (Panel
08069C0979H). Zone X is defined as an area of minimal flood hazard and does not have a base
flood elevation associated with it. Also, the site is outside of any City of Fort Collins’ mapped
floodplain.
Historically, the site’s stormwater has drained with flat slopes towards either Cherry Street or the
dirt ally to the east. Based on field survey completed by King Surveyors, the dirt alley to the east
does not adequately drain stormwater to public right-of-way before impacting private property;
therefore, alley improvements are proposed to handle the increased stormwater flows. See
Exhibit D for drainage basins and stormwater flow patterns.
The proposed site improvements include a single-family home with basement, a gravel driveway
and parking, a concrete valley pan with alley grading improvements, and the removal of an
existing deck and shed. The grading plan was developed to match existing drainage patterns;
therefore, the developed basins are the same as the historic basins. Where possible, impervious
areas and downspouts shall be routed into pervious areas with landscaping to allow for project
stormwater infiltration and increased water quality with site runoff.
As indicated in the table below, the adjusted site impervious will increase by 1,696 square feet (sf).
Site Hardscape or Hard Surface
Draining Towards Alley
Historic Site Area
(sf)
Adjusted
Historic Area
(sf)
Developed Site
Area (sf)
Adjusted
Developed
Area (sf)
Concrete (100%) 0 0 235 235
Rooftop (100%) 55 55 1,430 1,430
Gravel (40%) 0 0 230 92
Deck (40%) 65 26 50 20
Total Impervious Area 120 81 1,945 1,777
Adjusted Site Imperviousness 1,696
Since the lot’s total adjusted impervious area increase is <5,000 square feet (sf), water quantity
detention requirements are not required for this development.
Based on the enclosed design, it is my professional opinion that the additional runoff generated by
these site improvements will not cause adverse impacts to downstream private properties. I hereby
attest that this letter for the final drainage design for 728 Cherry Street was prepared by me or
under my direct supervision, in accordance with the provisions of the Fort Collins Stormwater
Criteria Manual. I understand that the City of Fort Collins does not and will not assume liability
for drainage facilities designed by others.
728 Cherry Street Drainage Memo Keefe Civil Project No.: 2024-017
Page 3 of 3 October 3, 2024
Thank you for the opportunity to submit this drainage memo. Please do not hesitate to reach out
to me if you have any questions or comments regarding the above items.
Best regards,
Megan L. Keefe, PE / Manager
Keefe Civil, Inc.
Enclosures
Cc: Kirk Longstein, Property Owner
EXHIBIT A
LOT 24
LOT 25
LOT 26
LOT 27
50
0
2
50
0
3
5003
5002
5003
50
0
3
S0°00'21"W
70.00'
S89°54'55"E
55.00'
S0
°
0
0
'
2
1
"
W
70
.
0
0
'
N89°54'55"W
55.00'
FO
R
T
C
O
L
L
I
N
S
,
C
O
L
O
R
A
D
O
SHEET
72
8
C
H
E
R
R
Y
S
T
R
E
E
T
KE
E
F
E
C
I
V
I
L
,
I
N
C
31
2
5
C
R
O
C
K
E
T
T
S
T
R
E
E
T
FO
R
T
C
O
L
L
I
N
S
,
C
O
8
0
5
2
6
(9
7
0
)
2
1
5
-
6
8
0
8
ME
G
@
K
E
E
F
E
C
I
V
I
L
.
C
O
M
1 OF 1
GR
A
D
I
N
G
P
L
A
N
PROPOSED BUILDING
TOF = 5003.68
PROPERTY LINE
PROPERTY LINE
PR
O
P
E
R
T
Y
L
I
N
E
EXISTING HOUSE
PROPOSED CONCRETE VALLEY PAN
CHERRY STREET
NO
R
T
H
G
R
A
N
T
A
V
E
N
U
E
AL
L
E
Y
PROPERTY LINE / ROW LIMITS
** CAUTION: EXISTING
OVERHEAD UTILITY LINES**
EXHIBIT B
Hydrologic Soil Group—Larimer County Area, Colorado
(728 Cherry Street)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2024
Page 1 of 4
44
9
3
5
0
0
44
9
3
5
0
4
44
9
3
5
0
8
44
9
3
5
1
2
44
9
3
5
1
6
44
9
3
5
2
0
44
9
3
5
2
4
44
9
3
5
2
8
44
9
3
5
3
2
44
9
3
5
0
0
44
9
3
5
0
4
44
9
3
5
0
8
44
9
3
5
1
2
44
9
3
5
1
6
44
9
3
5
2
0
44
9
3
5
2
4
44
9
3
5
2
8
44
9
3
5
3
2
492471 492475 492479 492483 492487 492491 492495
492471 492475 492479 492483 492487 492491 492495
40° 35' 33'' N
10
5
°
5
'
2
0
'
'
W
40° 35' 33'' N
10
5
°
5
'
1
9
'
'
W
40° 35' 32'' N
10
5
°
5
'
2
0
'
'
W
40° 35' 32'' N
10
5
°
5
'
1
9
'
'
W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 5 10 20 30
Feet
0 2 4 8 12
Meters
Map Scale: 1:168 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 Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
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
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 19, Aug 29, 2024
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 2, 2021—Aug 25,
2021
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.
Hydrologic Soil Group—Larimer County Area, Colorado
(728 Cherry Street)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2024
Page 2 of 4
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
81 Paoli fine sandy loam, 0
to 1 percent slopes
A 0.1 100.0%
Totals for Area of Interest 0.1 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Hydrologic Soil Group—Larimer County Area, Colorado 728 Cherry Street
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2024
Page 3 of 4
Aggregation is the process by which a set of component attribute values is
reduced to a single value that represents the map unit as a whole.
A map unit is typically composed of one or more "components". A component is
either some type of soil or some nonsoil entity, e.g., rock outcrop. For the
attribute being aggregated, the first step of the aggregation process is to derive
one attribute value for each of a map unit's components. From this set of
component attributes, the next step of the aggregation process derives a single
value that represents the map unit as a whole. Once a single value for each map
unit is derived, a thematic map for soil map units can be rendered. Aggregation
must be done because, on any soil map, map units are delineated but
components are not.
For each of a map unit's components, a corresponding percent composition is
recorded. A percent composition of 60 indicates that the corresponding
component typically makes up approximately 60% of the map unit. Percent
composition is a critical factor in some, but not all, aggregation methods.
The aggregation method "Dominant Condition" first groups like attribute values
for the components in a map unit. For each group, percent composition is set to
the sum of the percent composition of all components participating in that group.
These groups now represent "conditions" rather than components. The attribute
value associated with the group with the highest cumulative percent composition
is returned. If more than one group shares the highest cumulative percent
composition, the corresponding "tie-break" rule determines which value should
be returned. The "tie-break" rule indicates whether the lower or higher group
value should be returned in the case of a percent composition tie. The result
returned by this aggregation method represents the dominant condition
throughout the map unit only when no tie has occurred.
Component Percent Cutoff: None Specified
Components whose percent composition is below the cutoff value will not be
considered. If no cutoff value is specified, all components in the database will be
considered. The data for some contrasting soils of minor extent may not be in the
database, and therefore are not considered.
Tie-break Rule: Higher
The tie-break rule indicates which value should be selected from a set of multiple
candidate values, or which value should be selected in the event of a percent
composition tie.
Hydrologic Soil Group—Larimer County Area, Colorado 728 Cherry Street
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/1/2024
Page 4 of 4
EXHIBIT C
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 10/1/2024 at 10:32 AM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
105°5'39"W 40°35'46"N
105°5'2"W 40°35'19"N
Basemap Imagery Source: USGS National Map 2023
4,514
752.3
FCMaps
This map is a user generated static output from the City of Fort Collins FCMaps
Internet mapping site and is for reference only. Data layers that appear on this
map may or may not be accurate, current, or otherwise reliable.
City of Fort Collins - GIS
572.0
1:
WGS_1984_Web_Mercator_Auxiliary_Sphere
Feet572.00286.00
Notes
Legend
3,430
Street Names
Parcels
FEMA Floodplain
FEMA High Risk - Floodway
FEMA High Risk - 100 Year
FEMA Moderate Risk - 100 / 500 Year
FEMA Map Panel
City Floodplains
City High Risk - Floodway
City High Risk - 100 Year
City Moderate Risk - 100 Year
Growth Management Area
Parks
Schools
Natural Areas
City Limits
World Hillshade
EXHIBIT D
50
0
3
50
0
2
50
0
2
50
0
3
5002
5003
500
3
CHERRY STREET
NO
R
T
H
G
R
A
N
T
A
V
E
N
U
E
AL
L
E
Y
CHERRY STREET
NO
R
T
H
G
R
A
N
T
A
V
E
N
U
E
AL
L
E
Y
DR
A
I
N
A
G
E
E
X
H
I
B
I
T
FO
R
T
C
O
L
L
I
N
S
,
C
O
L
O
R
A
D
O
SHEET
72
8
C
H
E
R
R
Y
S
T
R
E
E
T
KE
E
F
E
C
I
V
I
L
,
I
N
C
31
2
5
C
R
O
C
K
E
T
T
S
T
R
E
E
T
FO
R
T
C
O
L
L
I
N
S
,
C
O
8
0
5
2
6
(9
7
0
)
2
1
5
-
6
8
0
8
ME
G
@
K
E
E
F
E
C
I
V
I
L
.
C
O
M
1 OF 1
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
HISTORIC DRAINAGE BASIN
DEVELOPED DRAINAGE BASIN
PROPOSED
BUILDING
PROPERTY LINES
PROPERTY LINES