HomeMy WebLinkAboutLONG POND, WIRELESS TELECOMMUNICATIONS FACILITY - FDP - FDP180016 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTDate: July 11, 2018
City of Fort Collins – Development Review Center
281 North College Avenue
Fort Collins, CO 80524
(970) 221-6750
Tower Engineering Professionals, Inc.
500 E. 84th Avenue, Suite C-10
Thornton, CO 80229
(303) 566-9914
nconstantine@tepgroup.net
Subject: Drainage Report
Site Applicant Designation: Atlas Tower Site Name: Long Pond
Engineering Firm Designation: TEP Project Number: 67927
Site Data: 2008 Turnberry Rd. Fort Collins, CO 80524
Township 08, Range 68, Section 32
N 40° 36’ 53.67” (NAD ’83)
W 105° 02’ 15.74” (NAD ’83)
City of Fort Collins,
Tower Engineering Professionals is pleased to submit this “Drainage Report” regarding the proposed
wireless telecommunications facility.
The purpose of the report is to show that the proposed development will meet the stormwater
requirements of the City of Fort Collins. Based on our analysis we have determined that a stormwater
Best Management Practice (BMP) will not be required to meet the requirements for the City of Fort
Collins.
If you have any questions or need further assistance on this project, please give us a call.
Respectfully submitted by
Nicholas M. Constantine, P.E.
This PDP Drainage Report for the design of Long Pond – Proposed Telecommunications Facility was
prepared by me (or under my direct supervision) in accordance with the provisions of Fort Collins
Stormwater Criteria Manual and was designed to comply with the provisions thereof. I understand that the
City of Fort Collins does not and will not assume liability for drainage facilities designed by others.
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 2
TABLE OF CONTENTS
1) VICINITY MAP
2) INTRODUCTION
3) ANALYSIS CRITERIA
4) ANALYSIS PROCEDURE
4.1) Analysis Method
4.2) Analysis Results
4.3) Assumptions
5) ANALYSIS RESULTS
Table 1 – Drainage Area 1 Stormwater Quantity Analysis Results
Table 2 – SW Master Plan Drainage Area 1 Stormwater Quantity Analysis
Results
Table 3 – Drainage Area 2 Stormwater Quantity Analysis Results
Table 4 – SW Master Plan Drainage Area 2 Stormwater Quantity Analysis
Results
6) CONCLUSION
7) APPENDIX A
A.1) DA1 Stormwater Quantity Analysis Calculations
A.2) DA2 Stormwater Quantity Analysis Calculations
8) APPENDIX B
Stormwater Drawings
9) APPENDIX C
City of Fort Collins Floodplain Review Checklist
LEGEND
EXISTING PARENT
PARCEL BOUNDARY
EXISTING 50'
RIGHT-OF-WAY
3
TOWER ENGINEERING PROFESSIONALS 67927
(303) 566-9914
THORNTON, CO 80229
500 E 84TH AVE, SUITE C-10
www.tepgroup.net
SITE NAME:
LONG POND
VICINITY MAP
V-1
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 3
2) INTRODUCTION
The proposed telecommunication facility is located at 2008 Turnberry Road. The 4.51acre parent parcel
currently has 0.55 acres of weighted impervious surface. For a weighted impervious area value,
open/landscaped areas are considered 0% impervious, gravel is considered 40% impervious, and
roofs/concrete are considered 90% impervious, and asphalt is considered 100% impervious. The parcel
currently consists of a residential/farming development. A concrete dich runs along the southwestern
boundary and agricultural land borders the property to the east. The average slope of the site is
approximately 5% and is located in the Cache La Poudre River Watershed. Additionally, the proposed
site is not located in a flood plain according to FEMA panel # 08069C0981G dated June 17, 2008.
The scope of the project will encompass a 50’ x 50’ gravel compound and a 45’ tall silo tower on a
concrete foundation that is located 266’ off the eastern property line and 58’ off the northern property line
of the parcel. The compound will house concrete foundations for an equipment rack and
telecommunications cabinets. The site will be accessed using a 12’ wide gravel access road. The
construction will result in a weighted increase of 0.02 acres (643 SF) of impervious area or 0.29%
increase in impervious area of the parcel.
3) ANALYSIS CRITERIA
The stormwater quantity analysis was performed for this site using the Rational Method with the following
design criteria:
1) Type of Analysis: Pre/Post Runoff Analysis
2) Storm Events: 2, 10, & 100 Year Storm Events
3) Land Covers: Lawn, Gravel, Impervious
4) ANALYSIS PROCEDURE
4.1) Analysis Method
The Rational Method was used to analyze pre and post-development runoff for the 2,10, and
100-year storm events. The analysis was completed by applying the Rational Method in
conformance with the Fort Collins Stormwater Criteria Manual. The parent parcel is located on
the boundary between Fort Collins Drainage Basin 24 and 28. Each proposed drainage area
includes a portion of the parent parcel and 50% of the Turnberry Road Right-of-Way that falls in
its respective Drainage Basin. These drainage areas were chosen because they reflect the
entirety of the effects of the parent parcel and proposed development on any properties
downstream of the parent parcel and Fort Collins Drainage Basins 24 and 28.
4.2) Analysis Results
There is an increase in runoff for Drainage Area 1 between pre-development and post-
development flow of 0.02 cfs (0.64% increase) for the 2-year storm event, an increase of 0.05
cfs (0.94% increase) for the 10-year storm event, and an increase of 0.11 cfs (0.81% increase)
for the 100-year storm event for the drainage area effected by the proposed development.
The Planning Commission has a target impervious area of 9% for Basin 28. The post-
development runoff rates for Drainage Area 1 were above the allowable runoff flowrates by
0.10 cfs (3.30% runoff overage) for the 2-year storm event, 0.18 cfs (3.47% runoff overage) for
the 10-year storm event, and 0.46 cfs (3.48% runoff overage) for the 100-year storm event.
There is a 0.00 cfs (0%) increase in runoff for Drainage Area 2 since there will be no proposed
development within the boundaries of Drainage Area 2.
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 4
The Planning Commission target has a target impervious area of 45% for Basin 24. The current
runoff flowrates for Drainage Area 2 are below the allowable runoff flowrates by 0.65 cfs
(38.69%) for the 2-year storm event, by 1.11 cfs (38.68%) for the 10-year storm event, by 2.84
cfs (38.80%) for the 100-year storm event. Since there will be no proposed development within
the boundaries of Drainage Area 2, these values will not be affected.
4.3) Assumptions
1) Existing land cover has not changed since the aerial image was taken.
2) Existing topography has not changed since the Larimer County data was gathered.
5) ANALYSIS RESULTS
Table 1 – Drainage Area 1 Stormwater Quantity Analysis Results
2 Year 10 Year 100 Year
(cfs) (cfs) (cfs)
Pre-
Development 3.11 5.32 13.58
Post-
Development 3.13 5.37 13.69
% Increase 0.64% 0.94% 0.81%
Table 2 – SW Master Plan Drainage Area 1 Stormwater Quantity Analysis Results
2 Year 10 Year 100 Year
(cfs) (cfs) (cfs)
9% Impervious
Development 3.03 5.19 13.23
Post-
Development 3.13 5.37 13.69
% Runoff
Overage 3.30% 3.47% 3.48%
Table 3 – Drainage Area 2 Stormwater Quantity Analysis Results
2 Year 10 Year 100 Year
(cfs) (cfs) (cfs)
Pre-
Development 1.03 1.76 4.48
Post-
Development 1.03 1.76 4.48
% Increase 0.00% 0.00% 0.00%
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 5
Table 4 – SW Master Plan Drainage Area 2 Stormwater Quantity Analysis Results
2 Year 10 Year 100 Year
(cfs) (cfs) (cfs)
45% Impervious
Development 1.68 2.87 7.32
Post-
Development 1.03 1.76 4.48
% Runoff
Overage -38.69% -38.68% -38.80%
6) Conclusion
The following summary describes the measures used to meet the City of Fort Collins
stormwater requirements for the proposed tower site.
The stormwater runoff for the site will sheet flow off the property. The minor increases in
stormwater runoff shown in Table 1 and Table 3 are negligible and will not negatively impact
the downstream properties. Along with the small amount of increased run-off, the overall
imperviousness of the site increases by only 0.29%. Therefore, detention for this site is not
required since the site will continue to sheet flow the stormwater runoff at close to historic
values and downstream neighboring properties will not be affected.
The proposed site will comply with the City of Fort Collins stormwater requirements without the
implementation of a Stormwater Control Measure (SCM).
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 6
APPENDIX A.1
DA1 STORMWATER QUANTITY ANALYSIS CALCULATIONS
0.2 Channel Flow in Paved Pipes or Channels
K= 2 K= 2 0.4 Overland Flow on Paved Surface
L= 47.00 ft L= 47.00 ft 1.0 Channel Flow in Natural Channel
H= 0.40 ft H= 0.40 ft 2.0 Overland Flow on Grassed Surface
TC(AB)= 1.90 min T
C(AB)= 1.90 min
K= 0.4 K= 0.4
L= 13.00 ft L= 13.00 ft
H= 0.70 ft H= 0.70 ft Kirpich's Equation:
TC(BC)= 0.07 min T
C(BC)= 0.07 min
K= 2 K= 2
L= 406.00 ft L= 406.00 ft
H= 23.20 ft H= 23.20 ft
TC(CD)= 4.80 min T
C(CD)= 4.80 min
TC= 6.76 min T
C= 6.76 min
*See sheets DA-1 & DA-2 for flow paths
Tc =
K * ( L
3
/ H )
0.385
128
K-Values
Long Pond: Drainage Area 1
Segment A-B Segment A-B
Segment B-C
Segment C-D
Segment B-C
Segment C-D
Pre-Development Tc Post-Development Tc
Job Name:
Job Number:
ATotal sqft x = acres
Aimpervious sqft x = acres
AGravel sqft x = acres
Alawn sqft x = acres
Ci = 0.95 (Runoff Coefficients taken from Table RO-11
Cg = 0.50 of the Fort Collins Stormwater Critieria Manual)
Cl = 0.25
CTotal =
(Per Table RA-7 of the Fort Collins Stormwater Manual)
CF =
Q (cfs) =
*See sheet DA-1 for Land Cover
3.11 5.32 13.58
Q = C (unitless) * i (inches/hour) * A (acres)*Cf(unitless)
Design Storm Event (yr) 2 10 100
Design Storm Event (yr)
141,252
(AI*cI) + (AG*cG)+(AL*cL)
AT
Rainfall Intensity at Tc of 6.76 min.
11,075
3.792
0.295
3.243
=
0.254
(1 acre/43560 sqft)
(1 acre/43560 sqft)
67927
Date:
Date:
(1 acre/43560 sqft)
(1 acre/43560 sqft)
165,173
12,846
1.00 1.00 1.25
Design Storm Event (yr)
Tower Engineering Professionals, Inc.
326 Tryon Road, Raleigh, North Carolina 27603
(Ph) 919.661.6351 (Fax) 919.661.6350
Pre-Development Stormwater Runoff : Drainage Area 1
JCO
Checked by: MWC
Long Pond Calculated by: 7/11/2018
10
2.55 4.37
2 100
8.92
2
= 0.321
(0.295*0.95)+(0.254*0.5)+(3.243*0.25)
10
3.792
100
Job Name:
Job Number:
ATotal sqft x = acres
Aimpervious sqft x = acres
AGravel sqft x = acres
Alawn sqft x = acres
Ci = 0.95 (Runoff Coefficients taken from Table RO-11
Cg = 0.50 of the Fort Collins Stormwater Critieria Manual)
Cl = 0.25
CTotal =
(Per Table RA-7 of the Fort Collins Stormwater Manual)
CF =
Q (cfs) =
2
= 0.313
(0.341*0.95)+(0.0*0.5)+(3.451*0.25)
10
3.792
100
10
2.55 4.37
2 100
8.92
1.00 1.00 1.25
Design Storm Event (yr)
Tower Engineering Professionals, Inc.
326 Tryon Road, Raleigh, North Carolina 27603
(Ph) 919.661.6351 (Fax) 919.661.6350
SW Master Plan Stormwater Runoff : 9% Impervious (Basin 28)
JCO
Checked by: MWC
Long Pond Calculated by: 7/11/2018
67927
Date:
Date:
(1 acre/43560 sqft)
(1 acre/43560 sqft)
165,173
14,866
0
3.792
0.341
3.451
=
0.000
(1 acre/43560 sqft)
(1 acre/43560 sqft)
Design Storm Event (yr)
150,307
(AI*cI) + (AG*cG)+(AL*cL)
AT
Rainfall Intensity at Tc of 6.76 min.
3.03 5.19 13.23
Q = C (unitless) * i (inches/hour) * A (acres)*Cf(unitless)
Design Storm Event (yr) 2 10 100
Job Name:
Job Number:
ATotal sqft x = acres
Aimpervious sqft x = acres
AGravel sqft x = acres
Alawn sqft x = acres
Ci = 0.95 (Runoff Coefficients taken from Table RO-11
Cg = 0.50 of the Fort Collins Stormwater Critieria Manual)
Cl = 0.25
CTotal =
(Per Table RA-7 of the Fort Collins Stormwater Manual)
CF =
Q (cfs) =
*See sheet DA-1 for Land Cover
Tower Engineering Professionals, Inc.
326 Tryon Road, Raleigh, North Carolina 27603
(Ph) 919.661.6351 (Fax) 919.661.6350
Post-Development Stormwater Runoff : Drainage Area 1
RCL
Checked by: MWC
Long Pond Calculated by: 7/10/2018
67927
Date:
Date:
(1 acre/43560 sqft)
(1 acre/43560 sqft)
165,173
13,100
3.792
0.301
3.213
=
0.278
(1 acre/43560 sqft)
(1 acre/43560 sqft)
= 0.324
(0.301*0.95)+(0.278*0.5)+(3.213*0.25)
3.792
139,962
(AI*cI) + (AG*cG)+(AL*cL)
AT
12,111
3.13
2 100
8.92
Design Storm Event (yr) 2 10 100
5.37 13.69
Rainfall Intensity at Tc of 6.76 min.
Design Storm Event (yr) 10
Q = C (unitless) * i (inches/hour) * A (acres)*Cf(unitless)
Design Storm Event (yr) 2 10 100
2.55 4.37
1.00 1.00 1.25
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 7
APPENDIX A.2
DA2 STORMWATER QUANTITY ANALYSIS CALCULATIONS
0.2 Channel Flow in Paved Pipes or Channels
K= 2 K= 2 0.4 Overland Flow on Paved Surface
L= 275.00 ft L= 275.00 ft 1.0 Channel Flow in Natural Channel
H= 2.00 ft H= 2.00 ft 2.0 Overland Flow on Grassed Surface
TC(AB)= 7.86 min T
C(AB)= 7.86 min
TC= 7.86 min T
C= 7.86 min
*See sheet DA-1 for flow paths
Kirpich's Equation:
Tc =
K * ( L
3
/ H )
0.385
128
Long Pond: Drainage Area 2
Pre-Development Tc Post-Development Tc K-Values
Segment A2-B2 Segment A2-B2
Job Name:
Job Number:
ATotal sqft x = acres
Aimpervious sqft x = acres
AGravel sqft x = acres
Alawn sqft x = acres
Ci = 0.95 (Runoff Coefficients taken from Table RO-11
Cg = 0.50 of the Fort Collins Stormwater Critieria Manual)
Cl = 0.25
CTotal =
(Per Table RA-7 of the Fort Collins Stormwater Manual)
CF =
Q (cfs) =
*See sheet DA-1 for Land Cover
1.03 1.76 4.48
Q = C (unitless) * i (inches/hour) * A (acres)*Cf(unitless)
Design Storm Event (yr) 2 10 100
Design Storm Event (yr)
45,013
(AI*cI) + (AG*cG)+(AL*cL)
AT
Rainfall Intensity at Tc of 7.86 min.
1,842
1.229
0.153
1.033
=
0.042
(1 acre/43560 sqft)
(1 acre/43560 sqft)
67927
Date:
Date:
(1 acre/43560 sqft)
(1 acre/43560 sqft)
53,526
6,671
1.00 1.00 1.25
Design Storm Event (yr)
Tower Engineering Professionals, Inc.
326 Tryon Road, Raleigh, North Carolina 27603
(Ph) 919.661.6351 (Fax) 919.661.6350
Pre-Development Stormwater Runoff : Drainage Area 2
JCO
Checked by: MWC
Long Pond Calculated by: 7/11/2018
10
2.42 4.13
2 100
8.44
2
= 0.346
(0.153*0.95)+(0.042*0.5)+(1.033*0.25)
10
1.229
100
Job Name:
Job Number:
ATotal sqft x = acres
Aimpervious sqft x = acres
AGravel sqft x = acres
Alawn sqft x = acres
Ci = 0.95 (Runoff Coefficients taken from Table RO-11
Cg = 0.50 of the Fort Collins Stormwater Critieria Manual)
Cl = 0.25
CTotal =
(Per Table RA-7 of the Fort Collins Stormwater Manual)
CF =
Q (cfs) =
2
= 0.565
(0.553*0.95)+(0.0*0.5)+(0.676*0.25)
10
1.229
100
10
2.42 4.13
2 100
8.44
1.00 1.00 1.25
Design Storm Event (yr)
Tower Engineering Professionals, Inc.
326 Tryon Road, Raleigh, North Carolina 27603
(Ph) 919.661.6351 (Fax) 919.661.6350
SW Master Plan Stormwater Runoff : 45% Impervious (Basin 24)
JCO
Checked by: MWC
Long Pond Calculated by: 7/11/2018
67927
Date:
Date:
(1 acre/43560 sqft)
(1 acre/43560 sqft)
53,526
24,087
0
1.229
0.553
0.676
=
0.000
(1 acre/43560 sqft)
(1 acre/43560 sqft)
Design Storm Event (yr)
29,439
(AI*cI) + (AG*cG)+(AL*cL)
AT
Rainfall Intensity at Tc of 7.86 min.
1.68 2.87 7.32
Q = C (unitless) * i (inches/hour) * A (acres)*Cf(unitless)
Design Storm Event (yr) 2 10 100
Job Name:
Job Number:
ATotal sqft x = acres
Aimpervious sqft x = acres
AGravel sqft x = acres
Alawn sqft x = acres
Ci = 0.95 (Runoff Coefficients taken from Table RO-11
Cg = 0.50 of the Fort Collins Stormwater Critieria Manual)
Cl = 0.25
CTotal =
(Per Table RA-7 of the Fort Collins Stormwater Manual)
CF =
Q (cfs) =
*See sheet DA-1 for Land Cover
2
= 0.346
(0.153*0.95)+(0.042*0.5)+(1.033*0.25)
10
1.229
100
10
2.42 4.13
2 100
8.44
1.00 1.00 1.25
Design Storm Event (yr)
Tower Engineering Professionals, Inc.
326 Tryon Road, Raleigh, North Carolina 27603
(Ph) 919.661.6351 (Fax) 919.661.6350
Post-Development Stormwater Runoff : Drainage Area 2
RCL
Checked by: MWC
Long Pond Calculated by: 7/10/2018
67927
Date:
Date:
(1 acre/43560 sqft)
(1 acre/43560 sqft)
53,526
6,671
1,842
1.229
0.153
1.033
=
0.042
(1 acre/43560 sqft)
(1 acre/43560 sqft)
Design Storm Event (yr)
45,013
(AI*cI) + (AG*cG)+(AL*cL)
AT
Rainfall Intensity at Tc of 7.86 min.
1.03 1.76 4.48
Q = C (unitless) * i (inches/hour) * A (acres)*Cf(unitless)
Design Storm Event (yr) 2 10 100
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 8
APPENDIX B
STORMWATER DRAWINGS
D1
A1 B1
C1
A2
B2
DRAINAGE AREA 2 Tc
FLOW PATH
ANALYSIS POINT 2
DRAINAGE AREA 2:
1.23 ACRES
DRAINAGE AREA 1 Tc
FLOW PATH
ANALYSIS POINT 1
DRAINAGE AREA 1:
3.79 ACRES
EXISTING PARENT
PARCEL BOUNDARY
5050
5050
5045
5040
5035
5030
5025
PROPOSED TOWER
COMPOUND
EXISTING PARENT
PARCEL BOUNDARY
IMPERVIOUS
SURFACE
GRAVEL SURFACE
LAND COVER
POST-DEVELOPMENT LAND COVER TABLE
DA 1
AREA (FT²)
DA 2
AREA (FT²)
LAWN
D1
A1 B1
C1
A2
B2
DRAINAGE AREA 2 Tc
FLOW PATH
ANALYSIS POINT 2
DRAINAGE AREA 2:
1.23 ACRES
DRAINAGE AREA 1 Tc
FLOW PATH
ANALYSIS POINT 1
DRAINAGE AREA 1:
3.79 ACRES
EXISTING PARENT
PARCEL BOUNDARY
5050
5025
PROPOSED TOWER
COMPOUND
LAND COVER
EXISTING GRAVEL
DRIVEWAY
BARN
HOUSE
GARAGE
PROPOSED SILT FENCE. SEE
THIS SHEET FOR DETAILS.
5050
PROPOSED TOWER
COMPOUND
EXISTING PARENT
PARCEL BOUNDARY
PROPOSED TOWER
COMPOUND
EXISTING PARENT
PARCEL BOUNDARY
ZONE "X"
SECTION A-A
NOTES:
DRAINAGE AREA
MAPS II AND
GRADING & EC PLAN
SW-2 3
SITE NAME: LONG POND
JKW SCB
TOWER ENGINEERING PROFESSIONALS
OFFICE: (303) 566-9914
THORNTON, CO 80229
500 E 84TH AVE, SUITE C-10
FAX: (303) 566-9916
67927
0 10-10-16 DRAINAGE REPORT
SEE COVER
SHEET FOR SEAL
1 02-27-17 DRAINAGE REPORT
2 03-07-17 DRAINAGE REPORT
3 07-11-18 DRAINAGE REPORT
SOIL & EROSION CONTROL PLAN
QUADRANGLE MAP FEMA FLOOD MAP
SILT FENCE DETAILS
Drainage Report July 11, 2018
TEP Project Number 67927 Long Pond
Page 9
APPENDIX C
CITY OF FORT COLLINS FLOODPLAIN REVIEW CHECKLIST
City of Fort Collins Floodplain Review Checklist
100% Development Review Submittals
Instructions: Complete this checklist by marking all boxes that have been adequately
completed. Put an “NA” next to any items that are not applicable to this particular
submittal. Any boxes that are left blank and do not have an “NA” marked next to them
are considered incomplete.
Date of Review:_____________ Reviewer’s Name:____________________________
Plat Map
The following required items are on the plat:
100-year floodplain boundary
City
FEMA
Floodway boundary
City
FEMA
The benchmark number and elevation of benchmark
These items match the FIRM. (FEMA Basin)
These items match the Master Plan. (City Basin)
The benchmark number and elevation match with those published in the City of Fort
Collins benchmark system.
Site Plan
The following required items are on the site plan:
100-year floodplain boundary- FEMA and City
500-year floodplain boundary (if proposed structure is a “critical facility”
and a 500-year floodplain is mapped)
Floodway boundary
Erosion buffer zones
Restrictions related to use (ie. critical facility or no residential use of lower
floor if floodproffed mixed use structure)
Drainage and/or Grading Plan (or a separate Floodplain Sheet if it is too cluttered on
Drainage and Grading Plan)
The following required items are on the drainage and/or grading plan:
100-year floodplain boundary- FEMA and City
500-year floodplain boundary (if proposed structure is a “critical facility”
and a 500-year floodplain is mapped)
Floodway boundary
Erosion buffer zones
Cross-section locations
BFE lines
Lowest floor elevation of structures (bottom of basement or crawl space is
considered the lowest floor)
The floodplain and floodway boundaries are in the correct location and labeled
properly.
The cross-section and BFE lines are in the correct location and labeled properly.
Elevations are referenced to the appropriate datum:
FEMA basins – list in both NGVD 29 and NAVD 88
City basins – list only in NGVD 29
Floodway regulations have been met.
No fill in the floodway unless a hydraulic analysis shows “no-rise”.
No manufactured homes, except in an existing park, can be placed in the
floodway.
No changing a nonconforming non-residential or mixed use structure to a
residential structure.
Landscaping meets requirements for no encroachment in the floodway
without a hydraulic analysis to show “no-rise”.
No storage of materials or equipment.
A note is on the plans about the above floodway restrictions.
Critical facilities regulations have been met:
100 year – no life safety, emergency response or hazardous material
critical facilities
500 year Poudre – no life safety or emergency response critical facilities
Any pedestrian bridges in the floodway that are not able to pass the 100-year flow are
designed to be “break-away”.
Fences in the floodway will not block conveyance. Example: split-rail fence cabled
together to not float, flap at bottom of privacy fence to allow water through (flap at
BFE or above).
Any items in the floodway that can float (Example: picnic tables, bike racks, etc.) are
noted as being anchored.
Erosion Buffer Zone requirements have been met:
Design of any allowed development minimizes disturbance to channel bed
and banks.
No structures allowed.
No additions to existing structures allowed.
Any fencing is split-rail design and break-away, but cabled. Must be
oriented parallel to general flow direction.
No detention or water quality ponds.
No bike or pedestrian paths or trails except as required to cross streams or
waterways.
Road, bicycle and pedestrian bridges must span erosion buffer zone.
No fill.
No outdoor storage of non-residential materials or equipment.
No driveways or parking areas.
No irrigated vegetation and non-native trees, grasses, or shrubs.
No utilities except as necessary to cross streams or waterways.
No grading or excavation except as required for permitted activities in
erosion buffer zone.
No construction traffic except as required for permitted activities in
erosion buffer zone.
Any construction in the erosion buffer zone shows that it will not impact
the channel stability.
A note is on the plans about the above erosion buffer zone restrictions.
Any necessary floodplain modeling has been submitted and approved. All modeling
must follow the City’s floodplain modeling guidelines.
Special Poudre River Regulations
Poudre River Floodway Regulations have been met.
No construction of new residential, non-residential or mixed-use
structures.
No redevelopment of residential, non-residential or mixed-use structures.
No additions to residential, non-residential or mixed-use structures.
No fill unless hydraulic analysis shows “no-rise”.
Poudre River floodplain regulations have been met
No construction of new residential or mixed-use structures
No additions to residential structures
No additions to mixed-use structures if there is an expansion in the
residential-use area of the structure.
No floatable materials on non-residential sites
Information Related to Structures in the Floodplain
For structures in the floodplain, a table is shown that lists the following:
City BFE at upstream end of structure
FEMA BFE at upstream end of structure (if different than City BFE)
Regulatory flood protection elevation
Lowest floor elevation (bottom of basement or crawl space is considered
lowest floor)
Floodproofing elevation for non-residential structures (if applicable)
Garage slab elevation
HVAC elevation
The BFE at upstream end of structures are correct based on interpolation between the
cross-sections.
The regulatory flood protection elevation is correct.
The lowest floor and HVAC are at or above the regulatory flood protection elevation.
Elevations are referenced to the appropriate datum:
FEMA basins – list in both NGVD 29 and NAVD 88
City basins – list only in NGVD 29
A typical drawing detail is included for each foundation type proposed (slab-on-
grade, basement, crawl space) showing the elevation of the HVAC and lowest floor
elevation (which includes bottom of the basement or crawl space) relative to the BFE.
If garage is not elevated to the regulatory flood protection elevation, then a drawing
detail is included showing vent placement, size, and number.
There is 1 square inch of venting for every 1 square foot of enclosed area.
The bottom of the venting is not higher than 1 foot above grade.
The venting is on at least two sides, preferably on upstream and
downstream sides. (Does not have to be divided equally).
If a non-residential structure is to be floodproofed, one of these conditions is met:
All requirements on separate sheet titled “Floodproofing Guidelines” have
been met.
If floodproofing information is not submitted as part of the plans, then a
note is on the plans stating that floodproofing information will be
submitted at the time of the building permit application.
For manufactured homes, all submittal requirements on separate sheet titled
“Installation of a Mobile Home Located in a Floodplain: Submittal Requirements”
have been met.
If the floodplain use permit is not going to be submitted until the building permit is
applied for, then a note is on the plans stating that the floodplain use permit will be
submitted at the time of building permit application.
N/A
N/A
N/A
N/A
N/A
N/A
N/A
A note is on the plans stating that a FEMA elevation or floodproofing certificate will
be completed and approved before the CO is issued. This is required even if property
is only in a City floodplain.
Drainage Report
The site is described as being in the floodplain. Floodplain name and if the floodplain
is a FEMA or City-designated is described. Any floodway or erosion buffer zones on
the site are described.
The FEMA FIRM panel # and date and/or the Master Plan information is cited.
A copy of the FIRM panel with the site location marked is included in the report.
If a floodplain modeling report has been submitted, that report is referenced. The
reason for the floodplain modeling report is described.
If a FEMA CLOMR or LOMR has been approved for the site, the case number is
referenced. The reason for the CLOMR or LOMR is described.
If a FEMA LOMR is required after construction, this is stated in the report.
The location of the structures relative to the floodplain is described. If there is both a
FEMA and a City floodplain on the site, the location of the structures relative to both
is described.
The use of the structures is described. This is to determine if the structure is
residential, non-residential, or mixed-use. Also, structures in all 100-year and Poudre
River 500-year floodplains cannot be used as a critical facility. (See Chapter 10 of
City Code for definitions.)
The report describes how the development is in compliance with the applicable
floodplain regulation (Chapter 10 of City Code). (Examples: elevation of lowest floor
above regulatory flood protection elevation, floodproofing, floodway regulation,
erosion buffer zone regulation, no-rise, etc.)
The type of foundation construction for the structures (i.e. slab-on-grade, crawl space,
basement, etc.) is discussed in the report.
The type of foundation matches with the lowest floor elevations and grading plan.
If any of the garages are not going to be elevated above the regulatory flood
protection elevation, the hydraulic venting requirements are discussed.
For structures in the floodplain, a table is included (same table as on the
Drainage/Grading Plan) that lists the following:
City BFE at upstream end of structure
FEMA BFE at upstream end of structure (if different than City BFE)
Regulatory flood protection elevation
Lowest floor elevation (bottom of basement or crawl space is considered
lowest floor)
Floodproofing elevation for non-residential structures (if applicable)
Garage slab elevation
HVAC elevation
Elevations are referenced to the appropriate datum:
FEMA basins – list in both NGVD 29 and NAVD 88
City basins – list only in NGVD 29
If the floodplain use permit is not going to be submitted until the building permit is
applied for, then a note must be included in the report that states the permit will be
submitted at the time of building permit application.
If floodproofing information is not submitted as part of the plans, then a note must be
in the report stating that floodproofing information will be submitted at the time of
the building permit application.
A note is in the report stating that a FEMA elevation or floodproofing certificate will
be completed and approved before the CO is issued.
In the compliance section, Chapter 10 of City Code is listed.
Floodplain Use Permit
Floodplain Use Permit has been submitted for each structure.
Permit fee has been submitted
All information on permit matches the plans
All information on permit meets floodplain regulations
FEMA CLOMR Approval
FEMA has approved any necessary CLOMRs.
Additional Comments:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
N/A
N/A
N/A
N/A
N/A
Terms to Note
Lowest Floor Elevation – Elevation of the lowest floor of the lowest enclosed area
(including bottom of basement or crawlspace). This is not the same as finished floor. The
lowest floor should be distinguished from finished floor on plans and reports.
Regulatory Flood Protection Elevation – For all floodplains except the Poudre River, the
regulatory flood protection elevation is eighteen (18) inches above the base flood
elevation. For the Poudre River floodplain, the regulatory flood protection elevation is
twenty-four (24) inches above the base flood elevation. If there is both a FEMA and a
City BFE, the higher BFE should be used to determine the regulatory flood protection
elevation.
Additional floodplain terminology is defined in Chapter 10 of City Code.
NOTE: Issues specific to individual sites may arise that result in additional
requirements. These will be discussed during initial meetings with the applicant.
X
PRE-DEVELOPMENT LAND COVER TABLE
DA 1
AREA (FT²)
EXISTING PARENT
PARCEL BOUNDARY
IMPERVIOUS
SURFACE
GRAVEL SURFACE
LAWN
DA 2
AREA (FT²)
DRAINAGE AREA
MAPS I
SW-1 3
SITE NAME: LONG POND
JKW SCB
TOWER ENGINEERING PROFESSIONALS
OFFICE: (303) 566-9914
THORNTON, CO 80229
500 E 84TH AVE, SUITE C-10
FAX: (303) 566-9916
67927
0 10-10-16 DRAINAGE REPORT
SEE COVER
SHEET FOR SEAL
1 02-27-17 DRAINAGE REPORT
2 03-07-17 DRAINAGE REPORT
3 07-11-18 DRAINAGE REPORT
PRE-DEVELOPMENT LAND COVER MAP
PRE-DEVELOPMENT DRAINAGE AREAS MAP POST-DEVELOPMENT DRAINAGE AREAS MAP
POST-DEVELOPMENT LAND COVER MAP