HomeMy WebLinkAboutHARMONY SCHOOL SHOPS PUD - PRELIMINARY - 42-89D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND
EROSION CONTROL STUDY
FOR HARMONY SCHOOL SHOPS
FORT COLLINS, COLORADO
October 13, 1995
Prepared for:
GT Land Inc.
3555 Stanford Road
Ste. 100
Fort Collins, Colorado 80525
Prepared by:
RBD, Inc.
209 South Meldrum
Fort Collins, Colorado 80521
(970)482-5922
RBD Job No. 226-045
T:DINC.
Engineering Consultants
209 S. Meldrum
Fort Collins, Colorado 80521
303/482-5922
FAX: 303/482-6368
October 13, 1995
Mr. Basil Hamdan
City of Fort Collins
Utility Services Stormwater
235 Matthews Street
Fort Collins, Colorado 80522
RE: PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY FOR THE
HARMONY SCHOOL SHOPS PRELIMINARY P.U.D.
Dear Basil:
We are pleased to submit to you, for your review and approval, this Preliminary Drainage and
Erosion Control Study for the Harmony School Shops Preliminary P.U.D.. All computations
within this report have been completed in compliance with the City of Fort Collins Storm
Drainage Design Criteria.
We appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Respectfully,
RBD Inc. Engineering Consultants
Prepared by: Reviewed by:
Ar 441
Bill Taylor David K. Thaemert, P.E.
Design Engineer Water Resources Engineer
Denver 303/458-5526
TABLE OF CONTENTS
DESCRIPTION PAGE
I.
GENERAL LOCATION AND DESCRIPTION ..............................
1
A. Location.......................................................1
B. Description of Property ...........................................
1
II.
DRAINAGE BASINS ..................................................
2
A. Major Basin Description ...........................................
2
B. Sub -Basin Description ............................................
2
III.
DRAINAGE DESIGN CRITERIA ........................................
3
A. Regulations....................................................3
B. Development Criteria Reference and Constraints ........................
3
C. Hydrological Criteria .............................................
3
D. Hydraulic Criteria................................................3
E. Variance from Criteria ............................................
3
IV.
DRAINAGE FACILITY DESIGN .........................................
3
A. General Concept.................................................3
B. Specific Details..................................................4
V.
STORM WATER QUALITY ............................................
5
A. General Concept.................................................5
VI.
EROSION CONTROL ................................................. 6
A. General Concept.................................................6
VII. CONCLUSIONS...................................................... 6
A. Compliance with Standards ......................................... 6
B. Drainage Concept................................................6
REFERENCES............................................................7
APPENDIX
VICINITY MAP............................................................I
HYDROLOGY.............................................................2
DETENTION.............................................................13
PRELIMINARY DRAINAGE AND
EROSION CONTROL STUDY
FOR HARMONY SCHOOL SHOPS
FORT COLLINS, COLORADO
GENERAL LOCATION AND DESCRIPTION
A. Location
' The Harmon School Shops is located on the northeast corner of Harmon Road
Y P Y
' and Timberline Road intersection: It is bounded by Sunstone Village 7th and 8th
Filing to the north and Harmony Road Mobile Home Park to the northeast. The
northwest corner of the property is clipped by the extension of Milestone Drive
' currently under construction at the time of this study. The Sunstone Village 7th
Filing and this property share a drainage easement for a detention pond east of
Milestone Drive. The piece of land on the southeast corner of Milestone Drive
' and Timberline Road is planned to be Diamond Shamrock gas station and is not
included within this development. Directly east of the site is an undeveloped
parcel of land zoned for commercial use.
' The site location can also be described as situated in the Southwest 1/4 of Section
32, Township 7 North, Range 68 West of the 6th P.M., City of Fort Collins,
' Larimer County, Colorado. The site location can be seen on the vicinity map in
the Appendix.
B. Description of Property
Harmony School Shops contains approximately 19.9 acres, more or less. Presently
' the property is undeveloped agricultural land and the historic site of Old Harmony
School which is to remain as part of the development. The above mentioned
detention pond is landscaped with small trees and shrubs. Two large cottonwood
' trees stand in the southwest corner of the property near the school structure and
are proposed to be preserved as well. Topographically the site gently slopes from
' southwest to northeast at approximately 1.0 percent.
The Warren Lake ditch crosses the southwest corner of the property in a
' southeasterly direction from Timberline Road to Harmony Road. There are no
major drainageways contained within the site.
The project is a commercial development comprised of a large complex containing
two large retail store outlets and one smaller retail store. Along the perimeter of
the property is two fast food restaurants and three retail stores and/or business
' office complexes. Lot 9 north of Milestone Drive is proposed as retail stores
and/or business offices.
II. DRAINAGE BASINS
'
A. Major Basin Description
The proposed Harmony School Shops lies within Reach 2 of the Fox Meadows
'
drainage basin and Basin 1 of the Timberline Farms Master Drainage Plan. Other
than the undeveloped land parcel just east of the Harmony School Shops site,
'
Timberline Farms drainage basin is built out primarily with a residential
development known as Sunstone Village. The site is largely influenced by this
development downstream and north of the subject site. Stormwater discharge in
'
this basin is limited to the 2-year historic runoff as determined by the 1989
Timberline Farm P.U.D. SWMM update of Fox Meadows Master Drainage Plan.
Warren Lake Ditch will require some modifications and realignment but otherwise
'
will not be affected by this development. For clarity this preliminary drainage plan
neglects any alignment of the ditch. Upon preliminary approval, the owner will
seek an acceptable realignment of the ditch with the ditch owner which will then be
'
incorporated into the final design.
B. Sub -Basin Description
The site is located at the top of the Fox Meadows drainage basin and receives
offsite contributing runoff from the north half of Harmony Road fronting the site
and five sub -basins of Sunstone Village 7th and 8th Subdivisions. Under
developed conditions historic runoff patterns will be maintained to the north and
'
east. Other than some minor runoff from greenbelt areas no significant flows will
affect the property to the east.
'
Stormwater discharge is limited to the predetermined discharge of the shared
detention pond located to the north. This pond is referred to as Detention Pond
No. 1 in the Timberline Farms P.U.D. Master Drainage Plan performed by
'
Engineering Professionals in September, 1989 and Sunstone Village 7th and 8th
Subdivision P.U.D. Preliminary and Final Storm Drainage Reports. Discharge
'
from this pond is limited to 12 cfs and flows north via pipe and grass swale in a
drainage tract between Harmony Mobile Home Park and Sunstone Village
Subdivision to Detention Pond No. 2 south of Caribou Drive. A copy of the
Timberline Farms Master Drainage Plan Map is included for reference in the
'
Appendix.
DRAINAGE DESIGN CRITERIA
A.
C.
E.
Regulations
The City of Fort Collins Storm Drainage Design Criteria is being used for the
subject site.
Development Criteria Reference and Constraints
The Fox Meadows Master Drainage Plan, Timberline Farm P.U.D. and Sunstone
Village 7th and 8th Subdivision P.U.D. Preliminary and Final Storm Drainage
Reports are the governing drainage criteria for Harmony School Site stormwater
development. As previously mentioned the existing built out nature of the
surrounding property also has a major impact on the drainage design of the
proposed development.
Hydrological Criteria
The Rational Method for determining surface runoff is used for the project site.
The 2-year, 10-year, and 100-year storm event criteria, obtained by the City of
Fort Collins, is used to determine the design rainfall and resulting runoff values.
Detention pond sizing by FAA Method is used to determining required detention
volume. These calculations are included in the Appendix of this report.
Hydraulic Criteria
All hydraulic calculations within this report have been prepared in accordance with
the City of Fort Collins Drainage Criteria and are also included in the Appendix.
Variance from Criteria
No Variances are being sought for the proposed project site.
DRAINAGE FACILITY DESIGN
A. General Concept
Harmony School Shops is intended to develop in accordance with the Master
Drainage Plan for Timberline Farms. Runoff from the Harmony Schools Shops
will be routed to Pond No. 1 where it will be detained and released at a rate of 13
cubic feet per second as stipulated in the Master Drainage Plan and subsequently
recognized in Sunstone Village 7th and 8th Subdivision P.U.D. Preliminary and
Final Storm Drainage Reports.
B. Specific Details
The site is divided into six sub -basins as shown on the drainage and grading plan
included in the Appendix. Please refer to the drainage plan for the following
discussion.
Sub -basin 1 encompasses a large area on the south and east sides of the site.
Generally runoff will accumulate and flow easterly toward the east parking lot then
turn and flow north to the detention pond. Flows will be conveyed from the
parking lot to the pond through slot inlets in the curb on the low end of the lot. A
small portion of the rear or north parking lot will be utilized for detention storage
not to exceed one foot in depth. The area used for storage will be that which lies
within the 4957 contour and is anticipated to hold approximately 0.5 acre feet.
This is the only proposed parking lot storage on the site.
Sub -basin 2 drains the west parking lot north to the detention pond. Flows will be
conveyed by gutter and cross -pan to a sidewalk chase drain discharging into the
pond. The side slope of the pond at this discharge point will be rip -rap protected
to reduce erosion. No flows from this sub -basin will enter Milestone Drive.
Sub -basin 3 collects rainfall on the western side of the development adjacent to
Timberline Road and south of Milestone Drive. This runoff accumulates as gutter
flow and discharges into the south flow line of Milestone Drive where it runs north
to the south sump inlet in Milestone Drive.
' Sub -basin 4 gathers rainfall from residential backyards of Sunstone 8th Filing and
the north one half of Harmony School Shops Lot 9. These flows will be routed
east to a proposed culvert which will tie back into the existing culvert under
' Milestone Drive. A concrete trickle channel will be constructed in the bottom of
the swale to facilitate drainage in this low slope reach.
'
Sub -basins 5 and 6 include the north side of Milestone Drive and the balance of
Lot 9. These flows collect in Milestone Drive and discharge through a sump inlet
'
in the north side of Milestone Drive.
Sub -basin 7 is the south half of Milestone Drive. Street flow capacities have been
'
checked to insure compliance under City of Fort Collins Design Standards. An
overflow discharge weir into Pond No. 1 at this point will insure maximum
allowable street depths will not be exceeded in the event of debris blocking the
'
inlets in Milestone Drive.
Sub -basin 8 is the east side of Timberline Road. During the time of this study
Timberline Road was in the midst of a major widening/reconstruction project along
'
the entire frontage to the Harmony School Shops site. Stormwater runoff for this
'
portion of Timberline Road is addressed in a number of drainage studies. The
Preliminary and Final Drainage Report for Sunstone Village Subdivision, 8th Filing
addresses the segment from Milestone Drive north to the sag curve/storm drain
inlet adjacent to the Sunstone Village Subdivision. The segment from Milestone
Drive South to Harmony Road is included in the Drainage Report for the
Timberline Road Improvements. The Drainage Report for Milestone Drive
Extension also addresses drainage issues in Timberline Road.
As designed Timberline Road releases no flows to the Harmony School site. The
newly constructed extension of Milestone Drive also receives no flows from
Timberline Road. Surface runoff north of Milestone Drive as well as detention is
' accounted for in the improvements to Timberline Road that accompanied the
development of Sunstone Village Subdivision 8th Filing. The area of Timberline
Road, Harmony Road to Milestone Drive, will be accounted for in detention while
' allowing runoff to continue its present path.
Preliminary investigations into the existing volume size of Pond No. 1 have
determined the pond size to be inadequate to store the developed volume of
rainfall, therefore the pond will need enlarging to meet City of Fort Collins
t detention volume requirements. In addition, the outlet works will require
redesigning and reconstruction. The existing pond and the accompanying 18 inch
outlet pipe is very shallow. The total length of the existing pipe is 110 feet. The
' remainder of the reach to Pond No. 2, approximately 800 feet, is a grass lined
swale with a concrete trickle channel invert.
' Presently the apparent high water elevation appears to be at elevation 4957.0 and
the pond bottom or invert of the existing discharge pipe is 4954.9. The developer
proposes to provide the required detention by deepening the existing pond,
reworking the discharge outlet, and installing a discharge pipe the entire distance
between Pond No. 1 and Pond No. 2. Preliminary hydraulic calculations show that
this approach is practical and is not anticipated to adversely affect the hydraulic
' characteristics of Pond No. 2. It is believed installation of the pipe will cause
minimal disturbance to the existing vegetation within the drainage tract and
provide a superior transmission facility between Ponds 1 and 2 while providing the
' necessary detention storage.
V. STORM WATER QUALITY
A. General Concept
' The water quality of storm water runoff is required to be addressed on all final
design of utility plans. During the final design phase we will seek to find an
' acceptable method for treatment of storm water runoff.
VI. EROSION CONTROL
A. General Concept
This development lies within the Moderate Rainfall Erodibility Zone and Moderate
Wind Erodibility Zone per the City of Fort collins zone maps. At the time of final
design we will address and utilize various Best Management Practices in
compliance with the City of Fort Collins Design criteria to minimize erosion during
construction of the Project.
VII. CONCLUSIONS
A. Compliance with Standards
All computations completed in this report are in compliance with the City of Fort
Collins Storm Drainage Design Criteria Manual. In addition all computations and
release rates are consistent with the master plan "Timberline Farms P.U.D.
Drainage Report" prepared by Engineering Professionals, Inc. in 1989.
B. Drainage Concept
The proposed drainage concepts adequately provide for the transmission of
developed on -site runoff, provides ample detention avoiding the need for parking
lot detention; improves the existing transmission facility to Pond No. 2.
G
REFERENCES
1. Storm Dranage Design Criteria and Construction Standards, City of Fort Collins,
Colorado, May 1984, revised March 1991.
2. Erosion Control Reference Manual for Construction Sites, City of Fort Collins, Colorado,
January 1991.
3. Master Drainage Plan for Timberline Farm P.U.D., by Engineering Professionals, Inc.,
September, 1989, revised November, 1989.
4. Sunstone Village 7th Subdivision P.U.D. Preliminary and Final Storm Drainage Report, by
Land Services, Inc., June, 1993.
5. Sunstone Village 8th Subdivision P.U.D. Preliminary and Final Storm Drainage Report, by
Land Services, Inc., June, 1993, revised August, 1993.
6. Final Storm Drainage and Erosion Control Report for Milestone Drive, by Land Services,
Inc., June, 1995.
7. Final Drainage Report for Timberline Road, by Northern Engineering, July, 1994.
7
APPENDIX
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LAND SURFACES IN THE DENVER REGION.
REFERENCE: "Urban Hydrology For Small Watersheds" Technical
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DETENTION
11
F1
1
�7,
!' DATA ENTRY FORMS
HYDRO POND
DATA ENTRY PREPARATION FORM
I.
FAA Method
1.
Project Title���p
2.
Basin Data: Basin Number
Basin Area ��,
2�
acres
Runoff Coefficient
3.
Rainfall Statistics
• Provide either rainfall
formula
or table:
(a) Rainfall Formula: One -Hour
Precipitation
inch
C1 =
C2 =
C3 =
(b) Rainfall Table:
Duration (min) 5
10
20 30 40
50
Intensity' (in/hr) to
��
��'� 41 �•5
�,O
Duration (min) 60
80
100 120 150
180
Intensity (in/hr) 2 %
2.05"
/.70 1-41_'5� /•/91
/-Dj
4.
Allowable Outflow Rate: 2
cfs
5.
Outflow Adjustment Coefficient
K:
Icig (Figure 1)
II. Hydrograph Routing Method
Project Title:
Inflow Hydrograph:
. Starting Time:
14
DETENTION POND SIZING BY FAA METHOD
DEVELOPED BY
JAMES C.Y. GUO, PHD, P.E.
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF COLORADO AT DENVER
EXECUTED ON 10-04-1995 AT TIME 09:44:17
PROJECT TITLE: Harmony School Shops Detention Pond I
**** DRAINAGE BASIN DESCRIPTION
' BASIN IDNUMBER = 1.00
BASIN AREA (acre)= 28.22
RUNOFF COEF = 0.95
I
***** DESIGN RAINFALL STATISTICS
DESIGN RETURN PERIOD (YEARS) = 100.00
'INTENSITY(IN/HR)-DURATIONOZN) TABLE IS GIVEN
DURATION 5 10 20 30 40 50 60 80 100 120 150 180
INTENSITY 9.0 7.3 5.2 4.2 3.5 3.0 2.6 2.1 1.7 1.5 1.2 1.0
t ***** POND OUTFLOW CHARACTERISTICS:
MAXIMUM ALLOWABLE RELEASE RATE = 12 CFS
OUTFLOW ADJUSTMENT FACTOR = .99
AVERAGE RELEASE RATE =11.88 CFS
AVERAGE RELEASE RATE = MAXIMUM RELEASE RATE * ADJUSTMENT FACTOR.
***** COMPUTATION OF POND SIZE
-----------------------------------------------------
RAINFALL RAINFALL INFLOW OUTFLOW REQUIRED
DURATION INTENSITY VOLUME VOLUME STORAGE
MINUTE INCH/HR ACRE -FT ACRE -FT ACRE -FT
0.00 0.00 0.00 0.00 0.00
5.00 9.00 1.68 0.08 1.59
10.00 7.30 2.72 0.16 2.55
15.00 6.25 3.49 0.25 3.25
20.00 5.20 3.87 0.33 3.55
25.00 4.68 4.35 0.41 3.94
' 30.00 4.15 4.64 0.49 4.14
35.00 3.83 4.98 0.57 4.41
40.00 3.50 5.21 0.65 4.56
45.00 3.25 5.45 0.74 4.71
' 50.00 3.00 5.59 0.82 4.77
55.00 2.80 5.73 0.90 4.83
60.00 2.60 5.81 0.98 4.83
' 65.00 2.46 5.96 1.06 4.90
70.00 2.32 6.06 1.15 4.91
75.00 2.19 6.11 1.23 4.88
80.00 2.05 6.11 1.31 4.80
' 85.00 1.96 6.21 1.39 4.82
90.00 1.88 6.28 1.47 4.81
95.00 1.79 6.32 1.55 4.77
' 100.00 1.70 6.33 1.64 4.69
-----------------------------------------------------
THE REQUIRED POND SIZE = 4.914496 ACRE -FT
' THE RAINFALL DURATION FOR THE ABOVE POND STORA
GE= 70 MINUTES
OPEN CHANNEL FLOW ANALYSIS: FLOW IN A PIPE
' Developed by Dr James Guo, Civil Eng Dept, U of Colorado at Denver
Metro Denver Cities/Counties and UD&FCD Pool Fund Study
----
User-- KEVIN GINGERY RBD INC. FT. COLLINS COLORADO .............................
' ON DATE 10-13-1995 AT TIME 11:53:15
** PROJECT TITLE: Harmony School Shops - Preliminary
' ** DESIGN INFORMATION _ . I.1O _-1___ Sue.et� E___ PP c
PIPE (EQUIVALENT) DIAMETER(INCHES) = 21.00
PIPE ROUGHNESS MANNING N = 0.013
PIPELINE SLOPE (FT/FT) = 0.0040
DESIGN FLOW RATE (CFS) = 10.04
Z i z4 Ala P--_091 F_ 4!rT2., cT-
** NORMAL FLOW CONDITIONS: 12�rss,
FLOW CENTRAL ANGLE (DEGREE) = 359.28
' FLOW DEPTH (FEET) = 1.75
FLOW AREA (SQ FEET) = 2.41
FLOW VELOCITY (FPS) = 4.17
' SPECIFIC ENERGY (FT) = 2.02
SPECIFIC FORCE (KLB) = 0.21
FLOW FROUDE NUMBER = 0.00
NOTE: FROUDE NUMBER--0 MEANS FLOWING FULL.
** CRITICAL FLOW CONDITIONS:
' FLOW CENTRAL ANGLE (DEGREE) = 220.773
FLOW DEPTH (FEET) = 1.18
FLOW AREA (SQ FEET) = 1.73
FLOW VELOCITY (FPS) = 5.82
' MINIMUM SPECIFIC ENERGY (FT) = 1.71
MINIMUM SPECIFIC FORCE (KLB) = 0.18
SLOPE (FT/FT) = 0.0063
' -NERGY (FT) = 1.71
MINIMUM SPECIFIC FORCE (KLB) = 0.18
' SLOPE