HomeMy WebLinkAboutCORRESPONDENCE - GENERAL CORRESPONDENCE - MBF02-01EXHIBIT A
SCOPE OF WORK
for
OLD TOWN BASIN
BASELINE HYDRAULIC ANALYSIS AND FLOODPLAIN MAPPING
L GENERAL
A. BACKGROUND
The Old Town Basin is located in north -central Fort Collins, Colorado, and is characterized
as the area between the Cache la Poudre River on the northeast, the West Vine Basin on the
northwest, the Spring Creek Basin on the southeast and south, and the Canal Importation
Basin and Larimer County Canal (LCC) No. 2 to the west. The basin encompasses 2,120
acres, including approximately 400 acres on the Colorado State University main campus.
The Old Town Basin currently receives inflows from the Canal Importation Basin in the
form of storm runoff which overtops the LCC No. 2 at nine locations. The CSU portion of
the Old Town Basin exports runoff to the Spring Creek Basin at six locations. Runoff
otherwise exits the Old Town Basin along its north/northeast boundary to the Poudre River.
For all practical purposes, the basin is entirely urbanized with few constructed detention
ponds for attenuating flood peaks. However, drainage in the north -central portion of the
basin is currently facilitated by the recently constructed Howes Street Outfall, which collects
runoff along Laporte Avenue, Maple Street and Cherry Street between Howes Street and
Mason Street, and conveys it north to the Poudre River. Major flooding potential in the
southeastern portion of the basin has been largely mitigated by the recently constructed
Locust Street Outfall which collects and conveys runoff from a corridor extending from CSU
at Locust Street to the Poudre River near Myrtle Street. Finally, the Oak Street Outfall
project is currently being designed to alleviate flooding in the northeastern portion of the
basin and along College Avenue north of Olive Street.
B. PURPOSE
Recent hydrologic modeling of the basin was completed by Anderson Consulting Engineers,
Inc. as documented in the February 2001 report, "Old Town Basin Master Drainage Plan
Update (Partial Baseline Analyses)." As part of the 2001 study, hydraulic analyses and
floodplain mapping were completed for the northeast portion of the basin. The focus of the
current study is hydraulic modeling of the remaining reaches within the Old Town Basin that
exhibit the most severe flooding potential. The study includes the delineation of 100-year
floodplain, and hydrologic modeling only the extent necessary to revised previously -defined
or add new flow diversions along the hydraulic analysis reaches. This study is limited to
analyses and modeling based on fully developed basin conditions (which also reflects
existing development conditions within the Old Town Basin) with existing drainage
facilities.
C:IWINDOWSITEMPICOFC141-OLD TOWN-SOW-REV2.doc 1 December 31, 2001
1 W 1111:3118:1
BUDGET
for
OLD TOWN BASIN
BASELINE HYDRAULIC ANALYSIS AND FLOODPLAIN MAPPING
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ACEPROJECTNO.: COFC14.1
ear
Engineer
Engineer Engineer
1 Operator
Admin.
Other
PREPARED BY., GJK
I I
Direct
DATE., 1212112001
$93/hr
$67/hr $57/hr
$501hr
$451hr
Costs
Task/Description
Hours
Hours
Hours
Hours
Hours'
Cost
Hours
C.
1. DATA COLLECTION AND REVIEW
22
to 20
0
0
52
$3,856
2. MAPPING
36
96
$6,216
26 6 28
0
3. BASELINE HYDROLOGY
50
186 138
70
0
4"
$28,478
126
4. BASELINE HYDRAULICS
504 272
162
8
1072
$69,450
5. TECHNICAL DOCUMENTATION
32
12 18
106
$6,826
8
36
6. TECHNICAL / BACKUP INFORMATION
42
20 32
16 i
24
134
$8,950
6 6
7. ADMINISTRATION I DOCUMENTATION
20
0
8
40
$2,964
OTHER DIRECT COSTS (reproduction, mileage, etc.)
$1,600
$1,600
OUTSIDE SERVICES:
Water and Earth Technologies, Inc.
3,800
$3,800
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COFC141-OLD TOWN BUDGET -REVS XLS 12131101
C. GLOSSARY
Listed below are words commonly used in this Scope of Work. The definition of the words
is as they pertain to this Agreement.
• Base model: the hydrologic or hydraulic computer input to SWMM or HEC-2/HEC-
RAS which contains the most current, up-to-date information utilized by the City.
• Baseline hydrology: analysis of basin to determine future condition hydrology with
existing drainage facilities in place.
• Residual floodplain: is the floodplain which would remain for future watershed
conditions with future drainage facilities in place.
• Residual floodway: is the floodway which would remain for future watershed conditions
with future drainage facilities in place.
• Existing condition: the current, at the time of the study, state of the drainage basin
including current imperviousness, area, width, slope, and drainage facilities currently in -
place.
• Developed (future) condition: the future state of the drainage basin determined by full
development of the watershed and represented by future imperviousness, area, width, and
slope.
• Historical condition: the state of the drainage basin before development.
• Professional: the consultant awarded the contract and preparer/engineer of the Master
Drainage Plan.
• NGVD of 1929: unadjusted National Geodetic Vertical Datum used by FEMA in local
Flood Insurance Studies.
• City Benchmark System: survey utilized by the City of Fort Collins originally located on
the bonnets of fire hydrants, now relocated to more permanent sites; elevations on the
City Benchmark System are the same as the unadjusted NGVD of 1929.
• Existing drainage facilities in place: the drainage infrastructure in place at the time of
the study.
II. BASELINE ANALYSIS
A. DATA COLLECTION AND REVIEW
1. The Professional shall meet initially and as appropriately thereafter (up to five additional
times) for all work involved in the Baseline Analysis to:
a. Insure compliance with the services required by the Agreement.
b. Obtain existing data and general information, including known problem areas within
the drainage basin.
c. Avoid duplication of effort whenever possible by utilizing existing information
available from other agencies applicable to this study.
d. Provide updates on the status of project tasks and budget on a weekly basis.
2. The Professional shall furnish to the City, for their review and approval, detailed
scheduling including target dates for the completion of each phase of the project.
C. I WINDOWSITEMPICOFC141-OLD TOWN-SOW-REV2.doc 2 December 31. 2001
The Professional shall review all information provided by the City, as well as pertinent
information within the study area available from other individuals or agencies including,
United States Geological Survey, Colorado Department of Transportation, and Colorado
Water Conservation Board.
4. The Professional shall utilize the City "Storm Drainage Design Criteria and Construction
Standards" manual and the FEMA "Flood Insurance Study Guidelines and Specifications
for Study Contractors" where appropriate and applicable.
5. Field data collection shall be undertaken by the Professional to verify and obtain the
necessary information. The collection of field data may include the following areas:
general data collection and hydraulic analysis.
a. General
Obtain new 1-foot contour mapping, field survey notes and benchmarks from the
City and Rocky Mountain Consultants.
ii. Investigate existing major drainage facilities and street configurations along the
flow paths identified in Section D.
b. Hydraulic Data
HEC-RAS cross -sections will be located on project mapping. Cross sectional
data will be identified from contour mapping and available field survey data.
For the purposes of this project, field survey data will include all data collected
as part of the hydrologic model update for the Old Town Basin by Anderson
Consulting Engineers.
ii. Photographs shall be taken of areas depicting representative locations selected
for defining Manning's roughness coefficients used in analyses.
B. MAPPING
The City will provide digital mapping of all areas east of Sherwood Street to be used for this
study. This mapping has been prepared by Rocky Mountain Consultants (RMC) for the area
from Laurel Street on the south, to north of Cherry Street.
The Professional shall be responsible for preparing a complete ortho-photo topographic map
of the study area using RMC's topography for the area east of Sherwood Street, the City's
1999 topography between Sherwood and Shields Streets, and the City's 1999 aerial
photograph as a base. The Professional will ensure compatibility of RMC's map with the
City's 1999 aerial photograph and topographic map, including the feathering of all even -
numbered contours between RMC's map and the City's 2-foot contour map. The
Professional shall also be responsible for producing all other maps necessary for the study,
including coordination with the City Surveyor who will collect spot elevation information to
supplement the available mapping.
C:I WINDOWSVEMPICOFC141-OLDTOWN-SOW-REV2.Aoc 3 December 31, 2001
C. BASELINE HYDROLOGY
The baseline hydrologic model was completed by Anderson Consulting Engineers in
February 2001 as documented in the report, "Old Town Basin Master drainage Plan Update
(Partial Baseline Analyses)." The Professional shall revise the model as necessary to add or
revise flow diversions along the hydraulic analysis reaches. Up to a total of 22 flow splits
will be revised or added to the model. Potential flow diversions that would not result in
more than 15 percent of the incoming discharge being diverted may or may not be
incorporated into the hydrologic model depending on other hydrologic and physical
conditions in the vicinity of the flow split.
The purpose of this portion of the study is to better define flow splits within the hydraulic
modeling reaches, using more detailed methods than previously applied. This effort is
intended to promote consistency between the hydrologic and hydraulic models while
eliminating all flow splits from the hydraulic models. Existing FLO-2D flow splits will not
be modified; as they represent the use of a more detailed methodology for determining flow
splits than the proposed one-dimensional method. All new or revised flow diversion rating
curves will be based on HEC-RAS split flow analyses. The basin map and schematic will be
revised to reflect additional flow diversions and design points.
The base model will be documented in the hydrology/hydraulic modeling technical
appendices, including: sub -basin parameters, conveyance elements, design points, flow
diversions, and detention ponds (i.e., inclusion of outlet pipe and/or weir component in rating
curve). This information will be provided in the technical documentation, as well as on
drawings, with all backup information included in the technical appendix. Except for
revisions made as part of the current study, the hydrologic modeling reporting and
documentation from the Anderson Consulting Engineers 2001 report/appendices will be
included without modification.
Hydrology shall be based on a 2-hour storm duration with a 5-minute interval, and all
appropriate modeling parameters and input shall utilize current recommended City criteria.
Any deviation from City recommended parameters shall be documented with rationale and
justification. All input and output data shall be provided to the City on computer disks
which can be read by an IBM PC or compatible.
The following hydrologic information will be converted to GIS/ArcInfo data and provided to
the City: (a) subbasins as polygon data; (b) conveyance elements as line data with
directionality embedded; (c) linking the subbasin and conveyance element data to separate
spreadsheets of SWMM input data; (d) detention ponds, diversion elements, inflow
hydrographs, and selected nodes as point data; (e) linking the conveyance element,
diversion, and node data to a spreadsheet of SWMM summary output containing the
resulting discharges at selected locations; (t) linking the detention pond data to a
spreadsheet of pond results for the 100-year event to include active storage volume,
maximum ponded water surface elevation, peak release rate separated into overtopping
discharge and normal outlet discharge; and (g) attributing the inflow hydrographs with a
location identifier, linked to a table of inflow hydrograph ordinates.
C. IWINDOWSITEMMCOFC41-OLDTOWN-SOW-REV2.doc 4 December 31, 2001
D. BASELINE HYDRAULICS
I. Hydraulic calculations shall be performed using the HEC-RAS 3.0 hydraulic model to
define water surface profiles for the various frequencies (i.e., 2-, 10-, and 100-year) for
future basin development conditions with existing drainage facilities in place. Data input
and output files for final models will be provided on disks which can be read by an IBM
PC or compatible.
All assumptions and rationale shall be documented and discussed in the technical
documentation or provided in the technical appendix (i.e., channel slope, methods to
determine starting water surface elevations, backwater effects, Manning's n, discharges
correlated to SWMM elements, procurement of cross -sectional data, split flows, and
other analysis). All cross -sections shall be drawn on available maps, and datum
referenced with topography.
2. Models will be developed using new mapping provided by the City and Rocky Mountain
Consultants, supplemented with existing field survey data. The Professional will submit
a drawing showing cross-section locations with topography and contours.
3. Hydraulic models and detailed floodplain mapping will be prepared for the following
reaches:
Laporte Avenue: Howes Street to west of Whitcomb Street
Meldrum/Sherwood Streets: Laporte Avenue to Mountain Avenue
Mountain Avenue: Howes Street to Shields Street
Mountain/Washington split flow path to Magnolia/Sherwood intersection
Magnolia Street: College Avenue to Wayne Street
Mulberry Street: College Avenue to Shields Street
Mason Street: Mulberry Street to Oak Street
Howes/Canyon/Whitcomb/Loomis/Gordon/Wayne: Magnolia St to Mulberry St
Myrtle Street: Peterson Street to Howes Street
College Avenue: Myrtle Street to Olive Street
The reaches identified above are those flow paths within the Old Town Basin that
generally exhibit 100-year flows in excess of 200 cfs. The level of detail associated with
the detailed hydraulic modeling effort is reflected in the budget for Task 4. The budget
assumes that two to three cross sections will be defined in the vicinity of each street
intersection with only one cross section between intersections.
Other areas where 100-year flows approach 200 cfs and in which approximate methods
will be used to determining flooding potential include the following:
Cherry Street: Howes Street to Grant Avenue
Laporte Avenue: Loomis Avenue to Park Street
Oak Street: Grant Avenue to Washington Avenue
Washington Avenue: Oak Street to Akin Street
Grant/Washington Avenues: Magnolia Street to Mulberry Street
Mulberry Street: Riverside Avenue to Whedbee Street
Myrtle Street: Howes Street to Sherwood Street
Shields Street: Mulberry Street to Myrtle Street
C. I W/NDOWSITEMPICOFC/41-OLDTOWN-SOW-REV2.doc 5 December31, 2001
Myrtle Street: Shields Street to City Park Avenue
Plum Street: Shields Street to City Park Avenue
Floodplains will not be delineated for the areas analyzed by approximate methods,
consisting primarily of estimating flow depths by assuming normal flow conditions at
selected locations.
4. Hydraulic calculations shall be presented to the City for review and approval when
completed in accordance with the schedule.
The Professional shall prepare two sets of drawings (i.e., AutoCAD) one that shows the
100-year floodplain and the other showing flood profiles for future basin conditions with
existing facilities in place. These drawings will be prepared at an appropriate scale on
11"xl7" sheets; an index map will be included. The floodplain drawings will be
prepared on topographic maps with appropriate screening and photographic quality to
allow for reproduction in the final report. The information portrayed shall include:
a. Limits of the 100-year floodplain based on developed conditions with existing
drainage facilities.
b. Location and orientation of all cross -sections used in hydraulic computations.
c. Profiles showing the bottom of the channel or thalweg, 10- and 100-year water
surface profiles for developed conditions with existing drainage facilities.
d. Selected base flood elevations.
Floodplain information shall be converted to Archifo data for input into the City's GIS.
Data to be converted shall include: (1) 100-year floodplain as polygons, with shallow
flooding areas (if any) defined as separate polygons; (2) cross sections as lines, with
cross section number and model name attributes, linked to a spreadsheet of 100-year
water surface elevations and other hydraulic data as outlined in the City's "Master Plan
Drawing Standards" [December 4, 2001]; and (3) base flood elevations as lines, with
100-year water surface elevation and model name attributes.
6. The Professional shall prepare a tabulation of flood hazard information for each cross-
section. This shall include cross-section number, base line stationing, thalweg elevation,
discharge, and WSEL for the 2-, 10- and 100-year events. For the 100-year event, top
width of flow and channel velocity will also be included for developed basin conditions
with existing drainage facilities in place.
A table shall be prepared presenting 2-, 10-, and 100-year flow depths, velocities, and
travel times (i.e., time to peak from the hydrologic model) at major road crossings and
pertinent drainage features identified by the City.
8. Products from the baseline hydraulics shall include:
a. Technical documentation discussing the above information.
b. Hydraulic model (HEC-RAS) based on fully developed condition hydrology with
existing drainage facilities in place.
c. Floodplain mapping.
C: IWINDOWSITEMACOFC141-OLDTOWN-SOW-REV1.doc 6 December 31, 2001
E. TECHNICAL DOCUMENTATION
The Professional shall prepare written technical documentation upon completion of the
hydrologic modeling, hydraulic analysis, and floodplain mapping efforts. The technical
documentation will describe and discuss data/inforniation obtained for Paragraphs II. A., B.,
C. and D, including the following:
1. All product descriptions presented in Paragraphs II. A., B., C. and D.
2. A brief statement to clarify the Professional's understanding of the Agreement and any
action taken by the entities involved that modified, limited or expanded such
understanding.
3. A map depicting the drainage basin, sub -basins, and study corridor.
4. A summary of data obtained from the entities involved.
5. Summary of findings.
6. Pertinent charts, graphs and material utilized.
7. The technical documentation is to be verified, stamped and signed by a principal of the
Professional.
8. The information in the report will be sequential and orderly. As a final product, the
following data will be presented in the technical documentation:
i. Any pertinent information from previous work;
ii. Any deviation from City recommendations or requirements;
iii. SWMM sub -basin parameters;
iv. Detention pond rating curves which have been developed or modified for this project
including data on allowable release rates, peak outflow, and 100-year water surface
elevation (i.e., weir, pipe, and total discharge presented);
v. Design flows for each frequency storm event and development condition if different
from the original analysis;
vi. Reference to all calculations and materials used by the Professional to prepare this
study. Reference material shall be included with the final submittal as a Technical
Appendix, as described in Paragraphs III (Technical and Backup Information).
9. Technical documentation will be prepared in a three-ring binder and will contain
narrative description and drawings reduced to 8.5"xll" or 11"x17" figures; oversize
sheets will be included, as necessary, to promote the understanding of the study.
C:IWINDOWSITEMPICOFC141-OLDTOWN-SOW-REV2doc 7 December 31, 2001
10. One (1) copy of the draft technical documentation shall be submitted to the City for
review purposes.
11. One (1) copy of the final technical documentation shall be prepared and submitted
subsequent to review by the City and modification by the Professional.
III. TECHNICAL AND BACKUP INFORMATION
A. One copy of all pertinent calculations and references to materials used and one set of original
text and a hardcopy of all sheets in the reports shall be furnished to the City with the draft
technical documentation. All computer -generated drawings (i.e., AutoCAD) shall also be
submitted to the City on disk with the draft technical documentation. All revised computer -
generated drawings (i.e., AutoCAD) and final Archifo data (i.e., line work, shape data, and
tables) shall also be submitted to the City on disk with the final technical documentation.
B. Pertinent calculations to be provided to the City shall contain only final calculations. All
non -pertinent preliminary calculations, duplications, or items that would detract from the
clarity of the submittal shall not be included.
C. All pertinent calculations, backup information, and computer printouts shall be bound in 3-
ring binders and indexed. A table of contents describing the well -marked sections shall be
included.
D. Copies of all final computer model input and output files shall be provided on disks which
can be read by an IBM PC or compatible.
E. The following applies only to that information which promotes the understanding of the
study; preliminary and/or iterative information is not included. All documents, drawings,
plans, reports, studies, surveys, maps, photographs, photographic negatives, specifications,
work notes, worksheets, data and other materials prepared, made, compiled or used by the
Professional hereunder, whether finished and completed or not, shall be the property of the
City and may be reproduced, distributed and published in whole or in part without
permission or any additional payments or fees to the Professional or others. Upon
completion of services provided for hereunder, or upon termination of this Agreement, said
documents, drawings, plans, reports, studies, surveys, maps, photographs, photographic
negatives, specifications, work notes, worksheets, data and other materials, whether finished
and completed or not, shall be delivered to the City by the Professional, and organized in
such manner as to permit it to be easily identified.
IV. SCHEDULE
A. An estimated schedule is presented in Exhibit "C. The schedule shall be updated as needed.
B. The Professional shall submit work called for to the City for written approval by the City.
The City will provide approval or the reason for the lack thereof, within forty-five (45) days
after each submittal.
C:IWIND0WSITEMPIC0FCJ4J-0LDTOWN-SOW-REV2.Aoc g December 31, 2001
C. Prior to the City furnishing such approval to the Professional, the City will obtain as
applicable, comments from any other parties to this Agreement.
V. DOCUMENTATION
The City will appoint a Project Manager who shall represent the City in matters related to the
work under this Agreement. The Professional shall identify key staff for the study. It shall be
the Professional's responsibility to document all meetings and telephone conversations between
the Professional and any representatives of the City, and deliver documentation to the City
Project Manager within five working days.
VI. QUALITY CONTROL
It is understood and agreed that all work performed under this Agreement shall be subject to
inspection and approval by the Stormwater Division of the City of Fort Collins, and any maps or
data not meeting the specifications set forth in the Agreement will be replaced or corrected at the
sole expense of the Professional.
C:IWTND0WSITEMPC0FC141-0LDTOWN-SOW-REV2.doc 0 December 31, 2001