HomeMy WebLinkAboutItem 06.jDate: 16 April 2012 Item No.
APPROVE AMENDED PROPOSAL FROM BARR ENGINEERING CO. TO PREPARE
THE APPLICATION FOR A LETTER OF MAP REVISION (LOMR) OF THE MARION
BRANCH SOUTH CREEK DRAINAGEWAY
Proposed Action
Staff recommends adoption of the following motion: Move to approve the amended
proposal from Barr Engineering Co. to prepare the application for a Letter of Map
Revision (LOMR) of the Marion Branch South Creek drainageway.
Overview
At its February 21, 2012 meeting, the City Council approved a proposal from Barr
Engineering Co. (Barr) to prepare the application for a Letter of Map Revision (LOMR)
of the Marion Branch South Creek drainageway,
During Barr's preparation of the LOMR application submittal, it was determined that the
existing field conditions were not accurately reflected in the current stormwater model.
City staff is recommending a change to the project's work scope to include updating the
hydrology to accurately reflect existing field conditions. The change in work scope will
create a hydrologic and hydraulic mode! that will depict stormwater flows based on
existing field conditions and incorporate existing public storm sewer improvements,
thereby providing accurate floodplain information.
Attached is an amended proposal from Barr Engineering Co. providing the additional
scope of services and estimated costs for updating the hydrology.
Primary Issues to Consider
• Will the change in project scope impact the project schedule? The change in
project scope is not expected to impact the project schedule.
Supporting Information
• Barr Engineering Co. Amended Scope of Services, dated April 11, 2012
� ALA'.. ;
Zachary V Johnson.._.
Interirre'ity Engineer
Financial Impact: $7
Related Documents (CIP, ERP, etc.):
Budgeted: No Source: Utility Fund
(Environmental Resources)
Notes: The additional cost for the change in work scope results sn a total project cost of $30,800. The
initial project cost was $23,400.
April 11, 2012
Mr. Zachary Johnson
City of Lakeville
2019.5 Holyoke Ave.
Lakeville, MN 55044
Re: Change Order #1 — Lake Marion Branch LOMR: Hydrology Update
Dear Mr. Johnson:
resourceful. naturally. BARR
engineering and environmental consultants
This letter sets forth changes to the Agreement dated February 23, 2012 between the City of Lakeville and
Barr Engineering Company regarding the proposal for completing the Lake Marion South Creek Letter of
Map Revision (LOMR) (proposal dated February 6, 2012).
Barr Engineering has updated the HEC -RAS model with survey data provided by City staff on March 30,
2012. Model results indicate that the 1- percent floodplain, is not entirely contained within existing City
outlets. It is Barr's understanding that the City is interested in updating the hydrology to determine if the
1- percent inundation mapping could be contained within existing City outlots.
The primary benefit associated with updating the hydrology is that the City would be sure that the
floodplain is mapped based on the best available data that reflects current field conditions. However, it is
possible that revisions to the hydrology could result in similar flows to FEMA's effective flows or even
increased flows. Updates to the hydrology will require review and approval by the Interagency Hydrology
Review Committee (IAHRC) before a LOMR application can be submitted to FEMA.
Based on discussions with City staff on April 2, 2012 . it is Barr's understanding that the City would like to
amend Barr's scope of service to include updating the hydrology to reflect current field conditions.
Therefore, the scope of professional consulting services we will provide is modified as follows:
• Barr will modify the XP -SWMM model developed by the VRWJPO to reflect existing held
conditions along the Marion Branch of South Creek between the Lake Marion outlet and Dodd
Boulevard.
• XP -WMM model modifications will include adding additional subwatershed divides at road
crossings and to infiltration basins along the creek, updating hydrologic parameters, and verifying
storage and hydraulic model inputs along the Marion Branch of South Creek.
• Hydrology along the Marion Branch of South Creek from the XP -SWMM model will be input .
into the HEC-RAS model to calculate the 1- percent floodplain and floodway along the creek.
Prepare an IAHR.0 submittal documenting the updates to the hydrology.
Barr engineering Co, 4700 Wes 77th Street Suite 200, Minneapolis, MN 55435 952.832.2 www.barr.com
Mr. Zachary Johnson
Apr 11, 2012
Page 2
The cost for the additional scope of services listed above is $7,400. Therefore, the overall authorized
project budget will be increased from $23,400 to $30.800. It is anticipated that the additional tasks
defined above will not impact the project schedule.
If this Change Order to our Agreement is satisfactory, please provide written notification to proceed with
the project scope, as amended.
Sincerely,
Scott Sohiech, PE, CFM
Vice President
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