HomeMy WebLinkAboutDrainage Reports - 03/12/1997r: Orm,ry OF Final Approved Report
FORT LOLLMUnI., IE ate
FINAL DRAINAGE REPORT
FOR
1ST STOP PLAZA MINOR SUBDIVISION
DRY CREEK DRAINAGE BASIN
PREPARED FOR
PATERSON AND ASSOCIATES
FEBRUARY 10,1997
STER'ART & ASSOCIATES, INC.
103 SOUTH MELDRUM STREET
FORT COLLINS, COLORADO 80521
970/482-9331
Table of Contents
1-2
Text of report
3
Vicinity Map
4-6
Drainage Calculations For Total Tract
7 - 10
Drainage Calculations For Basin "A"
11 - 13
Drainage Calculations For Basin `B"
14
Drainage Calculations For Basin "C"
15
Mass Diagram For Basin "A" & "C"
16
Outlet Ditch Capacity
17
Detention Pond Volume Table
18 - 20
Erosion Control Calculation
21
Erosion Cost Estimate
22
Variance Request
23
Flood Plain Use Permit
24 - 27
Easement Dedications
Addendum
Autozone and. Jax Pond Release Data
Pocket
Grading and Drainage Plan
' STEWART$,LSSOCIATES
Consulting Engineers and Surveyors
' February 10, 1997
Mr. Basil Harridan
Stormwater Utility
City of Fort Collins
' P.O. Box 580
Fort Collins, CO 80522
Dear Basil:
The following is the final storm drainage report for I st STOP PLAZA MINOR SUBDIVISION.
' The site is situate in the Southwest 1/4 of Section 1, Township 7 North, Range 69 West of the 6th
P.M., Fort Collins, Colorado. The site contains a net area of 3.5509 acres more or less. It is in the
Dry Creek Drainage Basin. The site is bounded on the West by North College Avenue, on the North
' by a retail area, on the East by undeveloped ground that had a previous agriculture use and on the
South by a retail area. The site slopes from West to East at an approximate slope of 0.75%. The
ground cover is buildings, asphalt and a good cover of weeds.
' The site is in the Dry Creek flood plain, and a triangular shaped area in the Northeast corner of
the site is in the Dry Creek floodway.
' The historic site contains the Pagoda Restaurant and its parking area. There is also an existing
asphalt area Iving North and Northeast of the restaurant on the site.
' On the developed site, the existing restaurant building will be demolished and three new buildings
and their parking areas will be constructed.
t The entire historic site including half of North College Avenue contains 3.76 acres and has a two
year historic runoff rate of 2.56 efs. The amount of detention required as calculated for the entire site
and using a discharge of 2.56 cfs is 25,350 cubic feet. However the entire developed site will be
divided into three sub -basins, which are further described below.
Basin "A" which is most of the developed net site contains 2.50 acres and will have onsite
' detention. The historic two year runoff rate is 1.91 cfs The detention volume required in Basin "A"
is 16,770 cubic feet when using a discharge rate of 1.91 cfs.
Basal `B" is the Northerly 0.95 acres and includes the North parking area and the part of the site
' which is in the Dry Creek Floodway. The two year historic runoff rate for Basin `B" is 0.40 cfs. The
required detention volume is 5,760 cubic feet. The Basin `B" detention pond will discharge into the
existing drainage ditch at a rate of 0.40 cfs.
' Basin "C" is the North College Avenue right-of-way and contains 0.31 acres. The two year
historic and developed runoff rate is 0.76 cfs. Curb and gutter will be installed on College Avenue
' and the runoff will flow South in College Avenue at the historic rate and into the site at the driveway.
' James H. Stewart
and Associates, Inc.
103 S. Meldrum Street
' P.O. Box 429
Ft. Collins, CO 80522
970/482-9331
Fax 970/482-9382
' Final Drainage Report
' 1st Stop Plaza Minor Subdivision
Page 2
' Due to the fact that the Basin "C" runoff is being diverted into Pond "A" and that the existing
drainage ditch does not have a great capacity, it has been planned to over detain in Pond "A" and
discharge at 1.24 cfs rather than at the allowable rate of 2.16 cfs. The volume of detention provided
' in Pond ` A" will be 21,924 cubic feet. Therefore the total discharge rate into the drainage ditch from
Basins "A" and `B" will be 1.64 cubic feet per second. The total detention volume required for a
discharge rate of 1.64 cfs is 27,684 cubic feet. The total volume designed for is 31,437 cubic feet.
' The high water line elevation for Pond "A" will be 4967.25 and the resultant depth of the pond
in the parking area at the curb opening will be 18 inches. A variance is requested to allow that depth
' at the outlet of the parking area.
The ponds will discharge into the existing abandoned irrigation ditch that runs along the East and
South property lines. The ditch flows Easterly and discharges into Dry Creek. Twenty foot wide
' drainage easements have previously been dedicated to the City of Fort Collins. Copies of the
recorded easements are enclosed in this report. The slope of the existing ditch is 0.15% and the ditch
' willbe modified to have across sectional area of 7 square feet. The capacity of the ditch will be 9.1
cfs. The discharge rate from JAX Surplus is 1.84 cfs and from Auto Zone is 0.42 cfs and from 1st
Stop Plaza is 1.64 cfs for a total of 3.90 cfs. The discharge rates for JAX Surplus and Auto Zone are
' included in the Addendum of the report.
EROSION CONTROL: The site is in the moderate rainfall and wind erosion zones. The
' existing building will be demolished and part of the existing asphalt will be removed. The overlot
grading will be done and the three building pads will be constructed. The three foundations will be
constructed as soon as the building pads are completed. A silt fence will be constructed along the
' North, East and South property lines. Straw bales will be placed at the discharge point of the
detention pond. After the discharge pipes have been completed, rock filters will replace the straw
bales and the ponds will become sedimentation traps. Straw bale dikes will also be placed in the
' existing outlet ditch.
The storm water runoff calculations, detention calculations, erosion control calculations and the
' grading and drainage plan are included as a part of this report. The erosion control cost estimate is
also enclosed.
This drainage report and the design of the drainage system are in compliance with the City of Fort
' Collins Storm Drainage specifications and criteria to the best of my knowledge.
If you have any questions regarding this report, please call.
' Sincerely,
Richard A. Rutherford, P.E. & L.S. ;.Q�otsrERF`�,
*: 5028 rrc � ,
1
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103 S. MELDRUM, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
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Consulting Engineers and Surveyors
103 S. MELDRUM, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
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Consulting Engineers and Surveyors
103 S. MELDRUM, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
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Consulting Engineers and Surveyors
103 S. MELDRUM, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
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Consulting Engineers and Surveyors
By: R A ,P_ Date: Or TZ� M 1, Client: A_c'm r.. Sheet No. ) 4- of
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Consulting Engineers and Surveyors
103 S. MELDRUM, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
By: 2 A,2 Date: J,t,v. 3y ti97 Client: PA r ERso" / Asro Sheet No. /,,5- of
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EMERGENCY SPILLWAY DESIGN
Weir Equation Q = C L (H) ^ 3/2
Q (cfs), C (weir coefficient), L (crest length, feet), H (energy head, feet)
See Table 704 in this Report for C factors
24 = Weir Length L in feet
3.1 = Weir Coefficient
Weir Shape Broadcrested
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Depth of
flow ft
Flow Over Weir
cfs
0.40
18.82
0.41
19.53
0.42
20.25
0.43
20.98
0.44
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22.46
0.46
23.21
0.47
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STEWART$,�,SSOCIATES PH. 482- 3311RF FAX 482-9380LLINS, CO 80521
Consulting Engineers and Surveyors
By: 2 AYE Date: — 9 Z/ ZI / Client: PA TEe rao A.rror . _ Sheet No. f� of _
Project: 1 c-;c iro f- PLA A M A.10r= ruRD�IV/r/n r
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CONSTRUCTION SEQUENCE
KOJECT: ISr SroP PI-AZA Mi&)op, fu 8. STANDARD FORM C
IQUENCE FOR 19 9_ ONLY COMPLETED BY: E A A!�- DATE: Nov. 13,199 L
Indicate by use of a bar line or symbols when erosion control measures will be installed.
jar modifications to an approved schedule may require submitting a new schedule for
proval by the City Engineer.
1447 YEAR
' MONTH TIF IMIA IM ITITIaIS ID IAJ ID
OVERLOT GRADING
ND EROSION CONTROL
Soil Roughening j
Perimeter Barrier
' Additional Barriers
Vegetative Methods
Soil Sealant
' Other f I I !
I i
INFALL EROSION CONTROL ! !
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters j
Straw Barriers
Silt Fence Barriers
Sand Bags
Bare Soil Preparation
Contour Furrows
Terracing
ET. Asphalt/Concrete Paving
Other
I ; i
FOVNDAT/ON i I i
' VEGETATIVE:
Permanent Seed Planting
' Mulching/Sealant j
Temporary Seed Planting j
Sod Installation
i
'Nettings/Mate/Blankets
Other
CXiS T, UuOiST v�egED
ORUCTURES: INSTALLED BY
rETATION/MULCHING CONTRACTOR
DATE SUBMITTED
1
MAINTAINED BY
APPROVED BY CITY OF FORT COLLINS ON
MARCH 1991
DESIGN CRITERIA
0q)
n
RAINFALL
PERFORMANCE STANDARD EVALUATION
-------------
STAHOARD
FORM A
PROJECT:
Is-t .f roP
P/-AZA
MiuoP,
-Cvg,
COMPLETED
BY: (2 A.
�.
DATE: Aza,.�
---------------------------------------------------------------------
DEVELOPED
ERODIBILITY
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EFFECTIVENESS CALCULATIONS
----------------------------
7------------ ---------------------------
PROJECT: 'IS-7- "-rOP PI-AZq M/uoje. SUE'D/VIrto v . STANDARD FORM B
COMPLETED BY: T2,A2., DATE:
i
Erosion Control
C-Factor
Method
Value
----------
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AREA
BASIN
(%)
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Comment
---------------------------
A OD
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---------------------------------
CALCULATIONS
F4c7-02 : (b00x asry) 4. (0,01 X 0.7W) +
(0,07x0.46) 1— i0,01 X A77)/3.T7'
Wro C FAcr0e. : / G371
3, S5-
O' 4101
wT D P FAcroe = 0. 80 x O,SO
1✓ F F. _ E1 — 0,46,1 x 0. 40] X /00 - 31, 6 %
W,
---------------------------------------------------------�
I/SF-8:1989
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STEWART$,LSSOCIATES
Consulting Engineers and Surveyors
January 8, 1997
'
Mr. Basil Harridan
Stormwater Utility
City of Fort Collins
P.O. Box 580
'
Fort Collins, CO 80522
Dear Mr. Hamdan:
The following is the cost estimate of the erosion control for Ist Stop Plaza Minor Subdivision.
1. 1330 L.F. of Silt Fence @ $2.00 $ 2,660.00
2. 5 Straw Bale Barriers @ $75 $ 375.00
3. Gravel Filter @ $100
4. Reseeding 101,059 S.F. @ $0.0149/F"T2 .
ESCROW REQUIRED= 1.5 x $3135
If you have questions regarding this cost estimate, please call.
Sincerely,
Richard A. Rutherford, P.E. & S.
President
5028
*
rrc
•. A
L• •• J
' James H Stewart
and Associates, Inc.
103 S. Meldrum Street
P.O. Box 429
' Ft. Collins, CO 60522
970/482-9331
Fax 970/482-9382
$ 100.00
$ 1,506.00
$ 4,703.00
1
' STEWART$,LSSOCIATES
Consulting Engineers and Surveyors
1
'
September 3, 1996
Mr. Basil Hamdan
'
Storm Water Utility
City of Fort Collins
P.O. Box 580
'
Fort Collins, CO 80522
1
Dear Basil,
This is to request a variance for 1st Stop Plaza Minor Subdivision to allow the depth of the
detention in the parking lot to be 18 inches.
The variance is justified due to the problem of having to provide detention even though a part of
the site is in the floodway. Often times when there is a floodway adjacent to a site, detention is not
required. This site requires the building to be elevated, the floodway to not be disturbed and onsite
detention to be provided. The three parameters do not allow the detention depth to be no greater
than 12 inches. The portion of the detention pond that will be deeper than 12 inches is located in the
Southeast comer of the parking lot and covers approximately 5500 square feet. In a 100 year storm
the 18 inch depth would involve 13% of the parking spaces.
If you have any questions regarding this variance, please call.
' Sincerely,
U .(f�
Richard A. Rutherford P.E. & L.S.
President
rrc
' James H. Stewart
and Associates, Inc.
103 S. Meldrum Street
�"0:6 A. Hu6z''o
GIST ro F`..�PO
ram:
T
*: 5028
p�6gery ism �.sp.
P.O. Box 429
Ft. Collins, CO 80522
970/482-9331
Fax 970/482-9382
(z3 )
' FLOODPLAIN USE PERMIT
TITIONER NAME: PATRQ,fnuASJec. ARrr+ve PgsEt!reel
DRESS: 1I3G E SrvAitr J-r. FrCec,crljs CO SoS•z.0 PHONE: 2Z/� ZY7_0
: ER NAME: JAA JeTX J• MDao^ GU rub N9N6 rgHy _fuE, TAti
48+'7807 / eosz& ADDRESS: A
PHONE• zz4-S7oz.
'3G/3 CAuwal��r Prfr•Gu. . DS }/ Pus Ly.Y�Roj�yE�l4r4,,,,
11GAL DESCRIPTION AND/OR ADDRESS OF PROPERTY: PA&T S.W.%a J•ec.1.'r? 4.je.G9#y
tee' i,.. -D M in 1)7 itA..-
SCRIPTION OF PROPOSED USE, TYPE OF CONSTRUCTION (ZONING). STRUCTURE ELEVATED
FLOOD PROOFED? IF FLOOD -PROOFED WILL HUMAN INTERVENTION BE REQUIRED?
17G I.11O II.11 d P11AI1 VI/_LI..'.. _ Rnf...G fI �•�.�.•��...p G`
l�ISTING GROUND ELEV: 49G 7 M.S.L.; FINISHED GROUND ELEV. Vw¢e Ir M.S.L.
LOWEST FLOOR ELEVATION (INCLUDING BASEMENT): 4969.zo M.S.L.
FLOOD -PROOFED, TO WHAT ELEVATION: +9&9•7-0 M.S.L.
SE FLOOD ELEVATION (BFE):
WIRM MAPS)
GULATORY BASE FLOOD ELEVATION:
FE + 1.5')
VARIANCE FROM ORDINANCE:
96Z7
M.S.L.
4969.z0 M.S.L.
YES* X NO
F Y/E-S�, ATTACH "APPLICATION FOR VARIANCE OF CITY OF FORT COLLINS FLOODPLAIN
nvnrvf Am TinTTeu I--
F PETITIONER DATE
USE PERMIT - APPROVED DENIED
OF CITY PERSONNEL
IMMENTS
.PPLICATION/PERMIT #:
DATE
kll->
i Cf i Y OF FORT COLLINS l
DEED OF DEDICATION FOR EASEMENT-5
KNOW ALL MEN BY THESE PRESENTS: These the undersigned C.V. LeForce of
Faith Realty and Development Co., being the owner of certain real property in Larimer
County, Colorado legally described in Deed Book 1361, Page 79, in the Larimer County
Records, in consideration of Ten Dollars ($10.00) in hand paid, receipt of which is hereby
acknowledged, and other good and valuable consideration, does hereby dedicate, transfer
and convey to the City of Fort Collins, Colorado, Municipal Corporation, for public use
forever a permanent easement for drainage in the City of Fort Collins, County of Larimer,
State of Colorado, more particularly described on Exhibit "A" attached hereto and by this
reference made a part hereof.
Witness our hands and seals this On5 4j4 day of February 1994.
Grantor: Faith Realty and
Development Co.
C. V. LeForce
Title:
State of CO Aoyf�,D o )
County of DeAw&./Z
The foregoing instrument was acknowledged before me this ' y/;�day of February,
1994, by C.V. LeForce of Faith Realty and Development Co.
Witness my hand and official seal.
My commission expires: KILEY J.
� 1 FREEMAN
r :-
h
Accepted by the City of Fort Collins on the jq� day of SU 1994.
J
' City Clerk
Or-
Iol
EXHIBIT A
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FAITH REALTY AND DEVELOPMENT CO.
LEGAL DESCRIPTION
A PERMANENT DRAINAGE EASEMENT SITUATED IN THE SOUTHWEST ONE -QUARTER OF
SECTION 1, TOWNSHIP 7 NORTH, RANGE 69 WEST OF THE SIXTH P.M., LARIMER COUNTY,
COLORADO, BEING MORE PARTICULARLY DESCRIBED AS FOLLOWS:
COMMENCING AT THE NORTHWEST CORNER OF SAID SOUTHWEST ONE -QUARTER OF
SECTION 1, THENCE SOUTH 00'39'11" WEST ALONG THE WEST LINE OF SAID SOUTHWEST
ONE -QUARTER, WITH ALL BEARINGS USED IN THIS DESCRIPTION RELATIVE THERETO, A
DISTANCE OF 1614.38 FEET; THENCE SOUTH 89'20'49" EAST A DISTANCE OF 40.00 FEET
TO THE NORTHWESTERLY CORNER OF LOT 2, BROOKS MINOR SUBDIVISION, RECORDED AT
RECEPTION NO. 93056058, LARIMER COUNTY RECORDS, THENCE SOUTH 89'20'49" EAST
ALONG THE SOUTHERLY LINE OF SAID LOT 2 A DISTANCE OF 190.00 FEET; THENCE SOUTH
89'25'59" EAST A DISTANCE OF 200.00 FEET TO THE SOUTHEAST CORNER OF SAID LOT 2;
THENCE NORTH 00'39'11" EAST ALONG THE EASTERLY LINE OF SAID LOT 2 A DISTANCE
OF 284.58 FEET TO NORTHWEST CORNER OF THAT TRACT DESCRIBED IN INSTRUMENT
RECORDED IN BOOK 1361 AT PAGE 79, LARIMER COUNTY RECORDS; THENCE SOUTH 89'12'36"
EAST ALONG SAID NORTHERLY LINE A DISTANCE OF 38.06 FEET TO THE TRUE POINT OF
BEGINNING OF THE HEREIN DESCRIBED DRAINAGE EASEMENT, THENCE CONTINUING ALONG
SAID NORTHERLY LINE SOUTH 89'12'36" EAST A DISTANCE OF 1242.95 FEET; THENCE SOUTH
00'47'24" WEST A DISTANCE OF 20.00 FEET; THENCE NORTH 89'12'36" WEST A DISTANCE
OF 1242.95 FEET, THENCE NORTH 00'47'24" EAST A DISTANCE OF 20.00 FEET TO THE
TRUE POINT OF BEGINNING,
CONTAINING AN AREA OF 24,859 SQUARE FEET OR 0.571 ACRES, MORE OR LESS.
DAVID L. FREEMAN
REGISTERED LAND
AUTOZONE, INC. I TITLEi NORTH COLLEGE EASEMENT AVENUE
PROPERTY I
PWPARED BY: JEHN & ASSOCIATES, INC.
5695 YUKON ST_ STE C, ARVADA, CO 80002 423-6036 DATE. FEBRUARY 22, 1994 1 SHEET 1 OF 2
CITY OF FORT CALLit43
(26 )
v- r'm W*�t
DEED OF DEDICATION FOR EASEMENT &-5"I4 AvI eM%'-
KNOW ALL MEN BY THESE PRESENTS: That the undersigned Mary D. Dreher and Ron
A. Dreher being the owners of certain real property in Larimer County, Colorado
legally described in Book 2157 Page 1164 in the Larimer County Records, in
consideration of Ten Dollars ($10.00) in hand paid, receipt of which is hereby
acknowledged, and other good and valuable consideration, does hereby dedicate,
transfer and convey to the City of Fort Collins, Colorado, a Municipal
Corporation, for public use forever a permanent easement for drainage in the City
of Fort Collins, County of Larimer, State of Colorado, more particularly described
on Exhibit "A" and outlined on Exhibit "B" attached hereto and by this reference
made a part hereof.
It is understood by the undersigned that, by acceptable of this dedication,
the city of Fort Collins will not accept the duty of ain�tenance of such easement.
Witness our hands and seals this day of� \'� v 1994.
ATTEST:
Title: i.c:rt'ti':s-.
State of rc"Z ' )
)ss
County of
Grantor
By:
Title: c. A
By:
•J
Title: (( (L
The forgoing instrument was acknowledge before me this )� day of
-1 --% 1994,by N-v1,y --:c>. _Y�c:i.\�LL� as
anfl� as
Witness my hand and official seal.
My commission expires:'1 0
Notary Public
4
Accepted by the City of Fort Collins on the _� day of BTU
1994.
City Clerk
1� t ,r .
r Ri,•
A PERMANENT DRAINAGE EASEMENT SITUATED IN THE NORTHWEST ONE OUAR'ER OF THE
SOUTHWEST ONE QUARTER OF SECTION 1. TOWNSHIP 7 NORTH, RANGE 69 WES . OF THE
SIXTH P.M., LARIMER COUNTY, COLORADO, BEING MORE PARTICULARLY DESCRIBED AS
FOLLOWS:
COMMENCING AT THE NORTHWEST CORNER OF SAID NORTHWEST QUARTER OF THE SOUTH-
WEST ONE QUARTER OF SECTION 1. THENCE SOUTH 00'39'11" WEST ALONG THE WEST LINE
OF SAID NORTHWEST QUARTER OF THE SOUTHWEST ONE QUARTER, WITH ALL BEARINGS
USED IN THIS DESCRIPTION RELATIVE THERETO. A DISTANCE OF 476.58 FEET; THENCE
SOUTH 89'21'04" EAST A DISTANCE OF 40.00 FEET TO THE NORTHWESTERLY CORNER OF
TRACT ONE, AS DESCRIBED IN INSTRUMENT RECORDED IN RECEPTION NO. 86002283,
LARIMER COUNTY RECORDS; THENCE CONTINUING SOUTH 89'21'04" EAST ALONu- THE
NORTHERLY LINE OF SAID TRACT ONE A DISTANCE OF 215.48 FEET; THENCE SOUTH
43'56'50" EAST A DISTANCE OF 302.09 FEET TO THE NORTHWE57ERLY CORNER OF PARCEL
THREE, AS DESCRIBED IN BOOK 2157 AT PAGE 1164, LARIMER COUNT'' RECORDS, SAID
POINT BEING MARKED BY AN IRON PIN, THE TRUE POINT OF BEGINNING OF THZ HEREIN
DESCRIBED DRAINAGE EASEMENT; THENCE SOUTH 89'20'49" EAST ALONG THE NORTHERLY
LINE OF SAID PARCEL THREE A DISTANCE OF 15.00 FEET; THENCE SOUTH 00'29'48" WEST
A DISTANCE OF 74.48 FEET; THENCE SOUTH 00'30 38 WEST A DISTANCE OF 101.06 FEET;
THENCE SOC'44'58" WEST A DISTANCE OF 440.92 FEET; THENCE SOUTH 16'10'49" EAST A
DISTANCE OF 22.55 FEET TO A POINT ON THE SOUTH LINE OF SAID PARCEL THREE;
TH_NCE NORTH 89'12'W WEST A DISTANCE OF 20.91 FEET; THENCE NORTH 16`IO'49" WEST
A DISTANCE OF 19.42 FEET TO A POINT ON THE SOUTHERLY LINE OF THE TRACT DESCRIBED
!N DEED BOOK 8906, PAGE 127 , LARiMER COUNTY RECORDS: THENCE S8S'20'49" EAST
A DISTANCE OF 5,00 FEET TO THE SOUTHEASTERLY CORNER OF SAID TRACT:
THENCE NORTH 00'44'58" EAST ALONG THE WESTERLY LINE OF SALC PARCEL THREE A
A D'STANCE OF 443.85 FEET; SAID POINT BEING MARKED BY AN IRON P:N: THENCE NORTH
00'30'38" EASI A D157ANCE OF 101.03 FEET TO AN IRON PIN WITH CAP LABELED LS 1650
THENCE NORTH OC'29'48" EAST A DISTANCE OF 74.45 FEET TO THE TRUE POINT OF
BEGINNING.
CONTAINING AN AREA OF 9,681 SQUARE FEET OR 0.222 ACRES MORE OR LESS.
AUTOZONE, INC.
TITLE- NORTH COLLEGE AVENUE P
'5695AYU ONYS?E ST EC, AQWADASCO SM02 423-6036I rATE- • SEPTEMBER 21. IS93 S,4EET 1 OF 2 '
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.iEHA1 � AS;rOttATEs XNu
'QPPKavEp A14ReM 31,/955-
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I. GENERAL
A. LOCATION
This proposed site for an AutoZone Auto Parts Store is situated on a track of land in the
northwest 114 of the southwe—s�T/4 o�S6don--T,Tam ship 7 North, Range 69 West of the
6th Principal Meridian. More specifically it is located at 1180 North College Avenue in the
City of Fort Collins, County of Larimer, State of Colorado between Hemlock Street and
Conifer Street.
B. DESCRIPTION
The site consists of two tracts. Tract 1 contains 2.112 acres and is the site of the proposed
development. Currently the parcel is occupied by Modular Sales, a mobile sales business.
Ground cover is primarily gravel, except for a 159 x 100' area of asphalt in the southwest
comer of the tract along North College Avenue. The undeveloped southeast comer of the
tract is covered with natural grasses and weeds. A triangular parcel of land of
approximately 0.42 acres has been subdivided off of the east end of Tract 1 along the
existing irrigation ditch and deeded to James E. Quinlin.
Tract 2 contains 0.635 acres and is located south of Tract 1. It is presently undeveloped
and there are no plans at this time to change that. Ground cover consists mainly of natural
grasses and weeds.
The entire site slopes slightly to the east and southeast at approximately 1 %. The property
is zoned "HB" - Highway Business - and is bounded on the north, south and west by
various other businesses. An existing irrigation ditch, which flows east and southeast to
Dry Creek, borders the property on the east.
11. EXISTING HYDROLOGIC CONDITIONS
The site presently drains east and southeast overland to the existing irrigation ditch along
the east property line which eventually makes its way east to Dry Creek. The site falls
within the Greenbriar/Evergreen Major Drainage Basin. Offsite flows from the Kechter
property to the south are minimal due to grading from the existing building located adjacent
to the west property line of Tract 1. The Grenz property adjacent to the west line of Tract 2
contributes minimally to offsite runnoff flowing east toward the existing irrigation ditch,
however, those flows do not impact the proposed development within Tract 1. There are no
offsite flows from the property to the north.
The proposed site is located within the 100-year floodway of Dry Creek. An analysis of
floodplain development has recently been prepared by Dr. Daryl B. Simons, P.E., and Mark
A. Severin, P.E., of Simons and Associates, Inc., of Fort Collins dated September 1993,
revised March, 1995. In the original report, a lowest habitual floor elevation had been set at
1
' 4972.03 with a regulatory base flood protection elevation of 4970.36. The revised report
determined that the 100 year water surface elevation was 4970.25 with the regulatory
' floodway elevation of 4970.94. The revised report reflects the changes in the grading plan
with the existing finished floor elevation of 4971.46. The report was based on an HEC-2
' model which accounted for the blockage due to the proposed structure as well as the
compensating effect of proposed grading for the site and detention pond. Flow conveyance
below the 100-year water elevation in the detention pond was assumed to be ineffective.
' The analysis showed that the proposed structure and grading would decrease the 100-year
floodplain elevation by 0.04 feet and a decrease of 0.03 feet would occur for the 100-year
floodway elevation. The building will be floodproofed to an elevation of 4971.96. See
' Flood Proofing sheet in the back of this report
' III. HYDROLOGIC PROCEDURE
The Rational Method has been utilized to determine the magnitude of the stomrwater runoff
' from the site for both the 10 year and the 100-year storm events for the developed
conditions and for the 2 and 100 year storm events for the historic conditions. Calculations
' have been performed to determine the volume necessary to detain the difference between
the two-year historic and the 100-year developed flows. Water from the proposed
detention facility will be released at the two-year historic rate. Rainfall intensities and runoff
' coefficients were obtained from the City of Fort Collins Storm Drainage Design Criteria and
Construction Standards Manual. Average flow velocities were obtained from the Urban
Drainage and Flood Control District's Criteria Manual.
Rainfall performance evaluation, effectiveness calculations and construction sequence for
erosion and sediment control have been performed as per the City of Fort Collins
' specifications and requirements
IV. DEVELOPED HYDROLOGIC CONDITIONS
' The site has will be graded to allow overland flow to the northeast and southeast comers of
the proposed development. Runoff from those two developed sub -basins will be released
through curb cuts into concrete channels and diverted into the proposed detention pond in
the southeast comer of Tract 1. The two concrete channels have been designed to
' accommodate 133% of the developed 100 year storm flows and will meet behind the
southeast comer of the building. The storm flows will be diverted from the concrete
channels to the detention pond through a grass lined channel with a concrete trickle
' channel designed to contain the 10 year developed flow. The grass lined channel has
been designed to contain 133% of the 100 year developed flows. A 1' high berm will be
constructed along the east property line of the Kechter property to prevent any offsite flows
' from entering the development.
The detention pond will release into the existing irrigation ditch along the east property line
' at less than the 2 year historic rate of 0.42 cfs. The existing irrigation ditch flows south and
1
' The detention pond will release into the existing irrigation ditch along the east property line
' at less than the 2 year historic rate of 0.42 ds. The existing irrigation ditch flows south and
then east to Dry Creek and recent field surveys and open channel indicate ample capacity
in the unimproved channel, from the discharge of the pond, with over V of freeboard.
' Outlet flow control from the detention pond will be regulated by a 37 diameter hole cut into
a 12" corrugated aluminum stand pipe that will be welded to the 12" corrugated aluminum
outlet pipe. Bottom of pond elevation will be 64.25 while the top of the outlet structure is
' set at 67.13. A notch will be cut into the existing box release the 100 year event at the 100
year historic rate of 3.43 ds. The pond will provide 12,223 cubic feet of volume for the 100
year event An V long weir will be constructed along the east end of the detention pond for
' an emergency overflow. The top of the pond will be set at 67.20 to allow for 1' of freeboard
in the pond.
' Hay bale barriers will be placed around all earth moving construction prior to construction
for sediment control. Detention pond excavation and site grading will remove the
necessary quantity of earth along the floodplain to satisfy the floodplain development
' report requirements to allow for a zero rise in the floodway water surface elevation during
the 100 year storm event Hay bales shall remain until grass cover has been well
testablished after construction.
V. CONCLUSIONS
' This proposed drainage plan meets all requirements and specifications from the City of Fort
Collins Storm Drainage Design Criteria and Construction Standards Manual. Furthermore
' this plan follows all the recommendations of the Stormwater Utilities Department of the City
of Fort Collins with respect to compliance with the master drainage plan.
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A'PG.COVED APRIL 191¢
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The following report represents the results of a drainage investigation for a proposed
building addition to the existing "JAY" located at 1200 North College Avenue, Fort
Collins, Colorado. The purpose offs investigation is to determine the effects of the
proposed development on the area's existing drainage conditions and to determine the
improvements, if any. The appropriate sizing for any proposed improvements has been
determined so that the improvements may be incorporated with the construction of the
project. The conclusions and recommendations presented in this report are based upon
the proposed site development plan; proposed site grading construction plans; on -site
observations; and the available topographic information. The analysis was performed in
accordance with the City of Fort Collins "Storm Drainage Design Criteria and
Construction Standards" manual.
The entire "JAY" site is irregular and contains approximately 5.9 acres. The portion of
the site that is currently being considered in conjunction with the proposed building
addition is the area situated between the existing structure and Conifer Street. This are:
is approximately 50 feet from the building to the curb and approximately 360 feet parall,
with Conifer Street. The site is located in the drainage basin boundary known as the DR
CREEK BASIN. The site is located within the "Floodway" as depicted on the DRY CREE
DRAINAGEWAY PLAN.
EXISTING CONDITIONS
The area being considered is used as an access drive and temporary parking. Several
trees and a landscaped strip have recently been established in the area between the curt
and the access drive. The ground surface has been graded to drain away from the
existing structures toward the street. The area between the existing structures and
Conifer Street slopes from South to North toward Conifer Street at rates varying from
3.5% to 0.7%. The area does receive a minor amount of run-off from the roofs to the
South. The run-off generated on the parking lot to the West flows southwesterly toward
the southern boundary of the site and then overland in a poorly defined drainage ditch tc
Dry Creek. Run-off from the northern portion of the site that flows onto Conifer Street is
directed to the East in the existing curb and gutter. The run-off which is directed along
the curb and gutter ultimately flows into the detention facilities located at the intersecti(
of Conifer Street and Redwood Drive.
The proposed construction is to consist of the addition of approximately 3,500 square fee -
of building together with associated access driveway and parking. The proposed building
addition will be situated in an area between existing structures. The building addition
area is presently used as an open storage area. The storage area has a concrete floor and
is partially enclosed by a metal structure. A paved access drive and parking area to be
constructed will provide a one-way east bound drive lane and parking for 17 cars. The
drive and parking will be located between the structure and Conifer Street. Access to the
site is to be provided through existing driveway cuts located at the east and west sides of
the existing structures. The proposed site plan indicates that the eastern third of the site
is to remain vacant. This investigation has considered that the access drive to the East o
the existing structures will be paved as a part of this construction or at a future date.
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' The current City policies require that the difference between the historic rate of run-off
and the developed rate of run-off be detained onsite. The release rate is to be no greater
than the 2 Year Storm historic rate. The City's policies normally require that the flows in
t the adjacent streets be incorporated with the onsite detention requirements. Conifer
Street has been constructed and slopes from West to East at a grade of approximately
0.4%. In order to divert the flow from the gutter onto the site and then route the flow
t through an onsite detention facility, it would be necessary to have a minimum of 2.5 feet
of drop between the point that the flow would exit the gutter to the point that the flow
would reenter the gutter. This is not physically possible due to the extremely flat
topography on the site and the flat gutter slope of the existing street section. Therefore a
variance to the City's policy with regard to the detention of the adjacent street flows is
being requested.
t EROSION CONTROL MEASURES
Erosion control considerations have been made based upon the short term, i. e., during
construction activities and the long term, through the life of the facility. The long term
measures incorporated to eliminate erosion are the proposed methods and materials to
be used to provide a surface covering for the driveways, parking areas, walkways and th(
landscaped open areas. The structure and hard surfaced areas will provide a covering to
deter erosion. The landscaping will provide a combination of plantings and ground
covers to deter erosion.
The short term erosion control method to be incorporated into the construction
requirements for the project is the placing of a "Sediment Trap" at the detention pond tc
' retain mud and debris onsite. The proposed construction area is exempt from providing
wind erosion measures since it is less than one acre in area. The schedule for
construction activities is anticipated to be: April 11- April 22, perform demolition, site
' preparation, and related construction; April 25 - May 6, foundation construction; May 9 -
July 19, building construction; June 6 - July 1, construct parking and drives, and install
landscaping and signage.
' CONCLUSIONS AND RECOMMENDATIONS
' 1. The proposed development will retain the existing drainage patterns.
2. The site is located in the DRY CREEK BASIN. The site is located within a defined
' floodway or flood plain.
3. All development is to be performed in accordance with City of Fort Collins criteria. A
' request for a variance to the City's policy with regard to the detention of the adjacent
street flows is made as a part of this investigation. It is not physically feasible to rout
the flow from the street through on -site detention facilities and back onto the street.
' 4. Onsite detention of stormwater is required by the City of Fort Collins. The volume of
run-off estimated to be the difference between the existing and the proposed conditioi
' is 5,042 cubic feet. This volume has been determined based upon the difference
between the run-off from a 2 Year Storm at the current condition and the run-off
from a 100 Year Storm at the proposed conditions. The flow is to be released at a
controlled rate not to exceed 1.84 c.f.s.
5. The City of Fort Collins Standards for temporary erosion control measures are to be
' incorporated with the construction activities.
2
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