HomeMy WebLinkAboutSite Certifications - (16)Drainage Certification
for
Phase's I & II
Fairbrooke Heights P.U.D.
fetia�,�c-cG�oc�cvo�s Fort Collins, Colorado
C
May 29, 1998
a
Prepared For:
Mr. Eric Booton
Loveland, Colorado
Prepared By:
Northam Engineedng Services, Inc
420 & Howes, Suite 202
Fort Collins, Colorado 80521
Phone: (970)2214158
Project Number: EBP; 9748.00
E N G I N E E R I N G
May 29, 1998
Basil Hamdan
The City of Fort Collins
Stormwater Utility
235 Mathews
Fort Collins, CO. 80522
RE: Drainage Certification for Phase's I and II
Fairbrooke Heights P.U.D.
Project Number: 9748.00
Dear Basil:
This report provides supporting documentation of our review of the as -built drainage
improvements and grading for the above referenced project. This project was divided into
three phases on August 21, 1997. This certification includes the first two phases of the
development with the third phase, which is the multi -family portion, scheduled for
completion within a year.
Please contact me at 22I-4158 if you should need clarification of the enclosed
information.
Sincerely;z
NORTHERN,.ENGINEERING SERVICES, INC.
a
Iti1ary B`=`Woliniadie-, P.E.
?,if
420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159
Final Drainage Certification
for
Phase's I & II, Fairbrooke Heights P.U.D.
Fort Collins, Colorado
May 29, 1998
I. Introduction
This report summarizes a comprehensive review of the as -built, on and off -site
drainage improvements and, final grading for the Fairbrooke Heights P.U.D. development.
A partial certification for this project was performed previously by CDS Engineering which
is dated July 24, 1997. This report is intended to serve as an adjunct to this prior
certification.
Construction of the off -site improvements, which include the Tract C Detention
Pond (Pond) and the relocated Pleasant Valley and Lake Canal (PV&L), has been completed
thanks to the cooperative efforts of the City of Fort Collins (City), Icon Engineering (Icon),
Northern Engineering (Northern) and the developer, Mr. Eric Booton (Developer).
Subsequent to the flood of July 28, 1997, modifications were made in the field to the off -site
improvements by the City, which deviate from the approved Final Utility Plans for
Fairbrooke Heights P.U.D. (Plans). These changes included: modifying the Pond grading in
the vicinity of Lots 40-44, raising the east embankment and providing a side -weir in the
relocated PV&L ditch, raising the pedestrian bridge crossing and, modifying the Pond outlet
pipe. Since these improvements are not consistent with the approved Plans and were not
designed by Northern Engineering, they will be excluded in this certification and will be the
responsibility of the City. V f,,,, 7
Certification of the relocated PV&L ditch has been provided by CDS Engineering
and is dated April 10, 1998 (see Section A and Plan Sheet 11/14). This was completed at
the request of Gerrard Excavating and has not been reviewed by Northern, although
supporting documentation from CDS Engineering is provided with this report.
II. Documentation
"Red -lined" Plans have been included with this report which provide documentation
of the as -built survey information. Only those sheets which are pertinent to the drainage
certification are provided. The following is an accounting of the sheets contained in the
approved Plan set and an explanation of each.
Plan Sheets 1/14 and 2/14 are the Cover and Overall Utility sheets respectively and
are not relevant to the overall drainage certification.
Plan Sheets 3/14- 5/14 document the as -built street elevations for the development.
Field survey information shown on these plans was provided by CDS Engineering in July
1997. Spot elevations at high and low points, cross -pans and flowlines were verified and
deemed to be within an acceptable range.
Plan Sheets 6/14 and 7/14 are the Sanitary Sewer Plan and Profiles and are not
relevant to the overall drainage certification.
Plan Sheet 8/14 is the Final Grading and Erosion Control Plan. Finished grades of
those lots not affected by the Pond regrading have been verified. Final grading on Lots 40-
Drainage Certification for
Phase's I and II of Fairbrooke Heights P.U.D.
May 29, 1998
Northern Engineering Services, Inc.
50, which are adjacent to the Pond, will be verified by the City due to changes in,the grading
as stated previously.
Plan Sheet 8A/14 is the Phase I Grading, Drainage and Erosion Control Plan and will
not be included in this overall certification.
Plan Sheet 9/14 is the Final Drainage Plan and will not be included in this overall
certification since it is a duplicate of Sheet 8/14.
Plan Sheet 10/14 is the Storm Sewer Plan and Profile and documents the as -built
survey information of Storm Sewer Line's A and B. Field survey information shown on this
plan was provided by CDS Engineering in July 1997. Elevations of pipe inverts and inlet
5 flowlines were verified and deemed to be within an acceptable range.
Plan Sheet 11/14 is the PV&L Ditch Relocation Plan and Profile. The ditch
relocation was certified by CDS Engineering on April 10, 1998, at the request of Gerrard
"'N Excavating Inc., and this sheet provided to Northern by CDS.
Plan Sheet 12/14 is the Final Detail sheet which includes details of the side -weirs,
pond overflow structure and others. Notes on each detail are included on this Plan which
identify the party responsible for the certification and the field survey information used. It
should be noted that the as -built survey information on the Modified -Existing Side -Weir is
not consistent with the design detail. Two incidents occurred in the construction of the
weir. First, it was discovered during the field survey for this drainage certification (by CDS
in July 1997), that there was a 0.25-foot bust in the design survey information provided by
Landstar Surveying, which resulted in the existing weir being 0.25-foot lower than what was
used for design. Secondly, it also turns out, that the portion of the weir which was to be
v extended was staked and then constructed incorrectly. The impact which these
discrepancies present are being considered as part of an overall analysis of the Pond and
appurtenant ditches. The information shown on Sheet 12/14 for the Modified -Existing
�� to Side -Weir does not imply that the weir is acceptable, rather, it is intended only to document
the existing as -built information.
�0 Y Plan Sheets 13/14 and 14/14 are the General Detail sheets and are not relevant to the
overall drainage certification.
III. Field Survey Information
The field survey information used to complete this certification was collected on
three separate occasions by three separate consultants, CDS Engineering, Icon Engineering
and Northern Engineering.
CDS Engineering conducted the initial survey in July 1997, prior to the flood of July
28, 1997. Survey information was gathered on; street grades, storm sewer inverts, swale
cross -sections, PV&L ditch relocation cross -sections, Tract C Pond grading and pond related
appurtenances and finished lot grading. Subsequent to the flood however, some of this
information was no longer valid due to the accumulation of sediment in the Pond, swales
and ditches. Information relating to the streets and storm sewers is considered accurate and
Page 2
Drainage Certification for Northern Engineering Services, Inc.
Phase's I and II of Fairbrooke Heights P.U.D.
May 29, 1998
has been utilized, where noted, in this certification.
Icon Engineering conducted a field survey on May 6, 1998. This survey gathered
information on the relocated PV&L ditch, the Pond, pond outlet storm sewer and side -weirs.
The only information used from this survey, in conjunction with this certification, was data
for the Temporary Side -Weir, shown on Sheet 12/14.
Northern Engineering conducted a field survey on May 27, 1998, which included a
profile and cross -sections of the emergency Overflow Swale located between Lot's 24-25 and
36-37. Existing residences are located on Lot's 24 and 25 and Lots 36 and 37 are currently
vacant. Cross-section A -A on Sheet 8/14 identifies the location of the section between the
existing residences. This section is considered marginally adequate to convey the 57.5 cfs
design flow (including freeboard) within the 15.5-foot easement (see Section B). The cross-
section located on Lot's 36 and 37 does not reflect the design detail provided on Sheet 8/14.
It is suggested that this section be constructed and certified as part of the individual lot
certification since the grading will most likely be disturbed during construction of homes on
these lots.
IV. Conclusion
To summarize, the drainage certification for this development is to be completed by
three parties, the City of Fort Collins, Northern Engineering Services and CDS Engineering,
as outlined previously in this report. This report provides supporting documentation from
Northern and CDS.
A separate report, prepared by Northern Engineering Services, will document the
SWMM and HEC-2 modeling associated with the Pond and, appurtenant ditches and weirs,
based on as -built survey information. This report will be submitted to the City of Fort
Collins Stormwater Utility Department on May 29, 1998.
To the best of my knowledge, belief, and opinion, the drainage facilities were
constructed in substantial compliance with the design intent of the approved drainage report
and Utility Plans with the exception of the Overflow Swale section at Lot's 36-37 which can
re rectified as stated previously.
Page 3
No Text
April 10, 1998
CDS Project No. P96-8717 _
Mr. Bill Nicholl
GERRARD EXCAVATING INC.
1739 S. County Road 13C
Loveland, CO 80537
Dear Bill,
This letter and the field notes attached hereto are to
serve as certification that CDS Engineering has performed an
as constructed survey and a comparison to the design grades
shown on the plan prepared by., Northern Engineering Services.
In summary it is my opinion that the bottom of the
channel has been constructed as close as possible to Northern
Engineering's design grades.
Sincerely,
i
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Enclosures
165 2nd Street S.W.. Loveland, CO 80537 . (970)667-8010 a Fax: (970) 567-8024
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As -Built Overflow Swale; Q100x1.33= 57.5
Worksheet for Triangular Channel
Project Description
Project File
d:\projects\ebp\ebp.fm2
Worksheet
As -Built Overflow Swale
Flow Element
Triangular Channel
Method
Manning's Formula
Solve For
Channel Depth
Input Data
Mannings Coefficient 0.035
Channel Slope 0.011900 ft/ft
Left Side Slope 4.500000 H : V E —J 4—
Right Side Slope 4.500000 H : V
Discharge 57.50 cfs
Results
Depth
1.75 —ft
,�n •.1 :>`yr—i = i • L I
Flow Area
13.79
ft'
Wetted Perimeter
16.14
ft
Top Width
1`15.75
ft
Critical Depth
1.59
ft
Critical Slope
0.019900 ft/ft
Velocity
4.17
ft/s
Velocity Head
0.27
ft
Specific Energy
2.02
ft
Froude Number
0.79
Flow is subcritical.
As -Built calculations
for the Emergency Overflow Swale
at Section A -A on Sheet 8/14
05/27/98 FlowMaster v5.13
02:24:45 PM Haestad Methods, Inc. 37 Brookside Road Waterhury, CT 06708 (203) 755-1666 Page 1 of 1
Triangular Channel. Analysis & Design
Open Channel. - Uniform flow
/3z
Worksheet Name: Fairbrooke
Heights
Comment: Overflow Swale at
Inlet B-3; Easement Width
Solve For Depth
-
Given Input Data:
Left Side Slope..
4.00:1 (H:V)
Right Side Slope.
4.00:1. (H:V)
Manning's n......
0.035
Channel Slope....
0.0089 ft/ft
Discharge........
57.50 cfs
Computed Results:
Depth............
1..93 f:t
Velocity.........
3.84 fps
Flow Area........
1.4.98 sf.
Flow Top Wi.dt:h...
1.5.48 ft�-
Wetted Perimeter.
15.96 ft.
Critical Depth...
1.67 ft
Critical Slope...
0.0198 ft/f.t
Froude Number ....
0.69 (flow is
Subcritical)
Open Channel Flow Module, Version 3.42 (c) 1991
Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708
Calculations from the approved
Drainage Report for Fairbrooke Heights P.U.D.
Water Utilities
Stormwater
City of Fort Collins
Mary Wohnrade
Northern Engineering Services, Inc.
420 S. Howes, Suite 202
Fort Collins, Colorado 80521
June 22, 1998
Dear Mary:
The City of Fort Collins Stormwater Department (City) has reviewed the report entitled "Storm Drainage
System. Evaldation at Brown Farm Tract C Pond" submitted by your company. The following comments
are provided below for your review.
l . Please include a Table of Contents for the text.
2. It appears from the text and review of Sheet I of 1 that as -built information (i.e., for the realigned
PV&L and the east and Icon weirs) was not used in the analysis. Lidstone and Anderson has
completed an analysis of the PV&L for a hydrology update of the Canal Importation Basin. The City
will provide this HEC-2 run for your usage in the evaluation of the realigned section. This should
allow for a more accurate analysis.
3. Please plot the HEC-2 water surface elevations on Sheet I of I to verify the location of the area of
inundation.
4. Please provide further explanation in text on the development of the table on page C I/ in appendix.
5. Please review and modify as necessary the cross-section numbered 178.10 in HEC-2 run FLD-
ME.DAT; should it not be 178.15?
6. Please provide split flow output for FLD-ME.DAT and FLD-RELO.DAT for the 30 minute runs.
7. Please review and modify whether the outlet pipe for the detention pond is inlet or outlet control;
provide documentation for both calculations.
8. Please provide a SWMM schematic for the Fairbrooke area — pertinent to this report.
9. The overland flow length for sub -basin 99 is too long. It should be less than approximately 250 feet
for developed conditions; please review and modify the width to incorporate a more developed
condition overland flow length.
10. Please explain why the % imperviousness was changed for sub -basin 99.
11. In the appendix, it is stated that conveyance element 199 will be removed from sub -basin 99. Please
explain why, and if it is to be removed, it has not yet been removed from SWMM.
12. Please explain why the Manning's n was changed for conveyance elements 168, 169, 170 and 171.
13. Please review and modify the diversion and total Qs for conveyance elements 504 and 506. The total
Q should be greater than the diverted Q.
14. Please provide an explanation as to why conveyance element 501 and 170 when added together in
the SWMM output do not sum to conveyance element 500.
233 N-lathews Street • P.O. Box 580 • Fort Collins. CO 80522-0580 • (970) 221-6589 • FAX (97/0) 221-6239
15. Please provide an explanation for the loss in flow in the west channel below the west weir as
indicated on Sheet 1 of 1 — the flow goes from 153.2 cfs (at the west weir) to 123.1 cfs to 105.7 cfs,
without any inflows or outflows.
16. Please discuss the effect of extended cross -sections, 286.6 and 357.27, on the output in the HEC-2
run FLD-RELO.OUT starting on page E2/.
17. Please explain the difference in water surface elevations between your balanced HEC-2 elevation of
10.62 feet and the SWMM elevation associated with 105.7 cfs (for CE 169) plus 40 cfs canal base
flow of approximately 11.12 feet. As written in the text and modeled in SWMM, the 40 cfs base
flow in the realigned canal was subtracted out, thus producing a discharge of 105.7 cfs at CE 169 as
shown in SWMM and on Sheet 1 of 1. In order to compare the HEC-2 and SWMM water surface
elevations, the 40 cfs should be added to the 105.7 cfs, which equates to a water surface elevation on
your rating curve on page C6/ (for 145.7 cfs) of 11.12 feet. These two elevations, 10.62 and l 1.12,
do not agree. As stated above, please explain this difference.
As per the City of Fort Collins Storm Drainage and Design Criteria Manual, particularly Section 1.3 (see
also sections 3.1.2 and 9.2), "The planning and design of the system shall not be such as to simply
transfer the problem from one location to another or create a more hazardous condition downstream.
Although improvements may not have to be made upstream or downstream of a subdivision, provisions
shall be made in every subdivision, in the form of an easement or drainageway for the 100-year storm to
pass through that subdivision'. Thus pertaining to the overall functioning of the detention pond and
realigned PV&L, the documentation within this evaluation must show the system will function per this
criteria. The 100-year existing upstream flow must pass safely through this system and not create a
problem which is worse than existing conditions (i.e., conditions existing before Fairbrooke Heights
development). Once this condition is achieved, certification of the drainage system can be considered.
The certification submitted on June 2, 1998 will need to be modified to reflect any changes to your
analysis and design.
Please incorporate the above comments into a final report and submit to the City for review. If you have
any questions, please call me or Sue Paquette at 221-6589.
Sincerely,
Il
Susan L. Duba Hayes, P.E.
Senior Utility Engineer, Master Planning
cc: Glen Schlueter, Development Review