HomeMy WebLinkAboutTask Order No. 10004 with T-O Engineers for Flood Study on Eight Mile CreekTask Order No. 10004
Preliminary Study
Scope of Work
Letter of Map Revision (LOUR) Submittal
Flood Study of Eight Mile Creek
Silverstone and Silverstone Campus Subdivision Areas
Client: City of Meridian
Consultant: T -O Engineers, Inc.
April 2, 2009
This Task Order is issued by City and accepted by the Engineer pursuant to the mutual promises,
covenant and conditions contained in the Master Agreement between the above mentioned
parties dated March 18, 2009.
Purpose
T -O Engineers completed a flood study on Eight Mile Creek in a cooperative effort between the
Kevin Spencer Company and the City of Meridian in June 2008, referred to herein as the "2008
study". The 2008 study demonstrates higher 100 -year base flood elevations compared to the
existing FEMA maps. The higher flood elevations result from improvements to Overland Road,
tiling of Eight Mile Creek south of Overland Road, and installation of culverts at South Jade
Way and South Topaz Way. The City intends to ultimately submit the 2008 study, with
modifications as necessary, as a Letter of Map Revision (LOMR) to FEMA for approval and
implementation of the modified base flood elevations into the effective FEMA maps and Flood
Insurance Study.
The purpose of this Task Order No. 10004 is to complete preliminary hydraulic study efforts. The
majority of this Task Order is for extending the 2008 site-specific hydraulic analysis to satisfy the
FEMA requirement for matching existing mapped floodplain parameters at the limits of the
future LOMR submittal. The end product of this Task Order is a working hydraulic model within
the limits of the LOMR submittal. The hydraulic model will provide information on the upstream
extents of the higher flood elevations in the 2008 study and guidance for completion of the
remaining analysis necessary for submitting the future LOMR.
Scope of Work
1) Additional Analysis Required by FEMA.
Assist City in requesting 1989 hardcopy model input data and results plus back-up materials
from FEMA via FEMA's external data request process. Construct duplicate effective 1989 model
in HEC -RAS using 1989 FEMA HEC -2 hardcopy output.
Assess differences in streamline coordinates between 1989 and 2008 study due to overland flow
paths across parking areas. Determine any difference in flood elevations due to flow path
changes. Conform streamline coordinates of 2008 study to FEMA water surface profiles for
consistency in the Flood Insurance Study.
Extend 2008 study upstream (east of Silverstone Campus Subdivision) approximately 1,500 feet
to accomplish FEMA requirement for matching existing flood elevations at the study limits.
Collect survey data on approximately 7 cross sections and adjacent topography for mapping
floodplain. Layout and survey cross sections and topography with field extension up to estimated
limits of floodplain based on flood elevations from the upstream end of the 2008 study.
Update flood study to reflect any fill or floodplain encroachment after the original survey done
for the 2008 study. It is assumed that there is fill on Lot 12 in Silverstone Campus and three
buildings have been constructed subsequent to the 2008 study.
Develop models of 10 -year and 500 -year flood events to update existing FEMA model.
Run model through FEMA parameter checking software and document results.
Collect additional field topographic survey between original 2008 cross sections in the
Silverstone area and combine with survey data of upstream extension east of Silverstone. Create
digital terrain model and topographic contour work maps required by FEMA.
Transmit updated hydraulic model to City engineering staff, discuss results of model and assess
implications for completing future LOMR submittal.
Estimated Fee
The estimated fee for completing scope item #1 is $19,913.75. Accordingly, this Task Order
seeks approval for a budgetary allocation not to exceed $20,000.00. Estimated components of the
fee are detailed in the attached spreadsheet. The estimate is based on what is known and
reasonably foreseeable but no guarantee is expressed that the scope and estimate are all inclusive
and that no other items/tasks be required throughout the process.
Assumptions and Exclusions
The following assumptions have been made in developing this scope of work and estimated fee.
Additional services may be required if the assumptions do not remain valid in the process of
completing the work. Additional or excluded services may be added by amendment of the
agreement.
1) It is assumed FEMA will accept termination of the future LOMR at the north edge of
Overland Road with a known differential in flood elevations north (downstream) of Overland
Road. Flood elevations higher than FEMA regulatory values were revealed in a separate site-
specific study for lands north of Overland Road previously completed by Consultant. The
submittal to FEMA will characterize the relative insensitivity of the flood elevations at Overland
Road (and upstream) to the flood elevations downstream of Overland Road as a proposed basis
for FEMA approval. The City reviewed this finding and proposed submittal approach to retain
FEMA values north of Overland Road for purposes of mapping continuity with FEMA Region X
staff on December 19, 2008. At that time, FEMA did not object to the approach.
2) It is assumed the City will not enter into a joint LOMR submittal with landowners north of
Overland Road to extend the flood study downstream.
3) It is assumed that the flood study of conceptual improvements to I-84 and Eagle Road
completed by Connecting Idaho Partners (CIP) is not submitted to FEMA by CIP, the City of
Meridian or as a joint submittal with this proposed scope of work.
4) It is assumed the LOMR submittal qualifies for the FEMA definition of "improved
methodology and/or data" and is therefore exempt from a submittal fee. Submittal fees, if
required by FEMA, would be paid directly by the City to FEMA.
5) It is assumed that no new fill or development will occur within the limits of the flood study
after beginning work on the updated hydraulic analysis, any future LOMR submittal, or during
the FEMA approval process. Any such fill may require revision of the study.
6) Ada County will not require revision of the flood study as a condition of the County signing
the Community Acknowledgement form for the future LOMR application.
7) The City will obtain permission to survey on private property.
8) FEMA has established regulatory flows for 8 -Mile and 5 -Mile Creeks and those flow were
used in the 2008 study. It is assumed that FEMA will not require a hydrologic study to modify
the flows.
9) The City will provide the Consultant with relevant products prepared by other consultants in
conjunction to approvals for the Silverstone developments including a Record of Survey, design
plans for construction affecting Eight Mile Creek, and final plats, prior to the Consultant proceeding
with the Work.
10) The Nampa and Meridian Irrigation District does not have review or approval authority over the
LOMR submittal and neither the City or County will request comment from the District.
11) The City does not need to obtain written or e-mail permission from Kevin Spencer Company for
Consultant to use the 2008 study on behalf of City. Permission for use is assumed because of the
existing release forms provided by Kevin Spencer Company and signed by the City.
12) City has possession of the reputed 1989 flood study output and it is assumed that no digital
version of the model is available based on conversations with contractor that completed the 1989
study. If the City's external data request to FEMA produces a digital HEC -2 model, then it can
be imported directly into HEC -RAS with somewhat less effort and data conversion than
anticipated in this scope.
13) It is assumed that differences in streamline coordinates between the 1989 and 2008 studies
arising from piping of Eight Mile Creek and overland flow paths through parking areas do not
significantly affect the computed flood elevations. Based on this assumption, the streamline
coordinates in the 1989 study can be retained in the water surface profile in the Flood Insurance
Study without having to revise streamline locations in the water surface profile upstream of the
study area along the remainder of Eight Mile Creek.
14) No floodway will be delineated on Eight Mile Creek. The current FEMA maps do not
tiesignate a floodway on Eight Mile Creek and the 2008 study area has been platted as a
cubdivision. Property within the contemplated extension of the 2008 study will be subject to City
#r County requirements for proposed development to demonstrate limitations of base flood
-levation surcharges to less than one foot.
15) The City will lead coordination efforts with FEMA including requesting the 1989 model and
back-up work products, confirmation of receipt of submittal, establish a FEMA case number and
contact person, inquiries as to status of FEMA review and approval.
16) City will develop landowner location, contact summary and FEMA required flood elevation
notification letters for properties affected by 2008 study. Consultant will provide City with
FEMA template for notification letter.
CITY OF MERIDIAN
By.
TAMMY de -'EER®, AYOR
5 Dated: —C'- &ACr
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Attest:
JAYCW L. HOLM AN, V
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Approved asto Contenf 110,
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BY: Steven E. Holt, cretary
Dated: /
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