HomeMy WebLinkAbout02 08 2016 Flood Study Report
SURFACE WATER MODELING AND FLOOD DAMAGE REDUCTION STUDY
JOINT WORKSHOP
February 8, 2016, 5:00 PM
Prior Lake City Hall, Parkview Conference Room
INTRODUCTION In the spring of 2014, the Prior Lake Spring Lake watershed experienced
record amounts of precipitation which led to a historic flooding event. This
event triggered many questions and highlighted the need to update tools
that help inform decisions and policies of the organizations within the
watershed. In particular modeling of the watershed needed to be updated
and flood mitigation strategies for future events evaluated.
The current model was developed in 1995 to determine flood elevations
on Prior Lake. This model was approved by FEMA and established the
flood elevation for Prior Lake at 908.9 feet. Since this model was
completed more precise topographic information has been made
available. In addition, the precipitation data used by the industry to
calculate storm runoff has been updated (Atlas 14).
A review of the flooding event was held at a September 22, 2014 joint
work session. One of the items discussed was a collaborative effort with all
three organizations, Watershed District, Spring Lake Township, and the
City of Prior Lake, to complete the needed flood study.
PLSLWD, working with the City of Prior Lake and Spring Lake Township,
has been working with the selected consultant to complete that study which
included updating modeling of the watershed, review of flood-related issues
and historical projects, identification and evaluation of a suite of potential
flood reduction strategies, and creation of an implementation plan.
The scope also included a public input process that engaged a broad range
of stakeholders and included local units of government, lake associations,
the agricultural community and private landowners. Attachment 1 is the
agenda for this meeting. Attachment 2 shows the project process and
public meeting components.
CURRENT
CIRCUMSTANCES
There has been a considerable amount of work over the last ten months
in relation to modeling of the watershed, developing flood reduction
strategies, and evaluating those strategies in relation to benefits and
costs. The study is at a point where input is needed from the policy
makers as to what priorities should be used in the final draft of the study.
This joint meeting of the Spring Lake Town Board, Prior Lake Spring Lake
Watershed District Board and the Prior Lake City Council has been
scheduled to review the Surface Water Modeling and Flood Damage
Reduction Study and obtain the needed input. Staff from all three
organizations as well as the engineering consultant will provide a
summary of the modeling and technical evaluation of various strategies
that could be used to reduce the risk of flood damage.
To aid in the discussion a number of handouts have been attached.
Each handout will be reviewed in greater detail at the work session.
Attachment 3 Shows a map of the options. Attachment 4 is the summary
of the scoring criteria and scoring of the options. Attachment 5 shows the
impact of the various options on the level of Prior Lake and the
corresponding property and access impacts.
Staff will also help facilitate a dialogue on a number of policy issues to
help refine the final outcomes of the study. These policy questions were
presented to the Advisory Group at a meeting on February 4, 2016.
Feedback from the group is incorporated below.
1) Should public dollars be used to protect public infrastructure (i.e.
sanitary sewer and water utilities)?
There was fairly consistent support that the City has a responsibility to
protect and minimize damage to public infrastructure. In particular it is
imperative that sanitary sewer and water systems remain
uncompromised to minimize any health and safety issues.
2) To what degree should access be provided?
Building from the first policy question, streets and more importantly
the access that streets provide was considered separately. The
Advisory Group found three street/access priorities. These priorities
included access for emergency services, major transportation routes
(CR21), local access.
3) To what degree should public dollars be used to protect or assist
in the protection of private property?
The Advisory Group had a variety of opinions on this topic. There
were some who felt it was a government’s responsibility to provide
access to properties through public rights-of-way, however not
necessarily protect the property itself. However, there was not
specific feedback on temporary access disturbances including
frequency and duration. Some felt that public dollars should not be
used to make specific improvements to private property (i.e. flood
proofing or buyouts) but did support strategies such as upstream
storage. Some felt that flooding with a longer duration between
events was okay, but we should consider protecting homes that get
flooded on a greater frequency (i.e. every 25 years).
Staff is seeking specific feedback as to the level of protection that should
be considered. With this direction a final suite of strategies will be
developed, an implementation plan suggested and identification of
funding opportunities. Once the study documents are finalized a final
community meeting will be held to solicit input from the general public.
Finally the study will be presented to each organization for consideration
of approval/adoption.
The last topic of the night will be to discuss the upcoming state bonding
bill. This bill provides an opportunity to fund a portion of the potential
project(s) identified with the study. Staff will provide a summary of the
legislative process and discuss support for a request.
SURFACE WATER MODELING AND FLOOD DAMAGE REDUCTION STUDY
JOINT WORKSHOP
Monday, February 8, 2016
5:00-6:50 p.m.
Prior Lake City Hall
5:00-5:10 p.m. Welcome, Introductions & Purpose of the Meeting
Ken Hedberg, Mayor
Kathy Nielsen, Clerk, Spring Lake Township
5:10-5:15 p.m. Focus of the Meeting & Key Questions
Karen Chandler, Facilitator & Engineer, Barr Engineering
5:15-5:30 p.m. History of Flood Protection
Diane Lynch, District Administrator, PLSLWD
Katy Gehler, Public Works & Natural Resources Director
5:30-5:35 p.m. Study Process
Katy Gehler
5:35-6:00 p.m. Options Review
Diane Lynch
6:00-6:40 p.m. Policy Questions
Katy Gehler & Karen Chandler
6:40-6:45 p.m. 2016 Bonding Bill Legislative Effort
Diane Lynch
6:45-6:50 p.m. Wrap-up
Karen Chandler
Update the Watershed Model &
Gather Information
Public kick-off meeting: February 19, 2015
Provided overview of the project
Solicited input on flood damage reduction scenarios
Evaluate Flood Reduction Options
Identify Flood Reduction Options
Finalize Implementation Plan
Develop Watershed Model
1st Advisory Group Meeting: May 7, 2015
Gathered feedback on model results, flood damage reduction scenarios and
evaluation criteria/matrix
2nd Public Meeting: May 28, 2015
Will provide feedback on options evaluation criteria, review modeling results,
and recommend flood mitigation goals
Watershed Modeling to Evaluate Options
2nd Advisory Group Meeting: February 4, 2016
Gather feedback on modeling results & possible mitigation options
Farmer Listening Session: February 3, 2016
3rd Public Meeting: March
Review draft implementation plan
Prepare Final Recommendation: April
Watershed District/City/Township Meetings: April
Board/council approval/adoption of implementation plan
Stormwater Management & Flood Mitigation Study
Advisory Group –
Provides input from
key stakeholders
throughout the
project. Includes
PLSLWD’s Citizen
Advisory Committee
(CAC), City of Prior
Lake’s Lakes Advisory
Committee (LAC),
Lake Associations,
watershed district
managers, and
elected officials.
Public –
Generates flood
mitigation ideas,
stays informed on
the process, and
assists in reaching
out to inform the
wider community
regarding the status
of this planning
effort.
2015
FEB
MAR
APR
MAY
JUNE
through
DEC
2016
JAN
FEB
MAR
APR
Project Process UPDATED:
January 2016
Joint Flood Study Meeting: February 8, 2016
Meeting with Watershed District/City/Township to gather feedback on
modeling results and possible mitigation options
Option #2: Increase Prior Lake Outlet
Increase the capacity of the Prior Lake outlet
structure to 85 cfs
(20 cfs greater than current conditions).
Cost: $3M 100-year flood level: 905.4
Option #1: Spring Lake Storage
Install an outlet structure on Spring
Lake, raising the existing Spring Lake
100-year flood level by 1.2 feet.
Cost: $4.1M 100-year flood level: 906.3
Option #3: Upstream Storage
Work with upstream landowners to
create storage at nine (9) upper
watershed priority sites.
Cost: $2.9M 100-year flood level: 905.8
Option #4: Combine Options #1, #2 & #3
By installing all three options above, there is a
chance for the greatest amount of flooding
reduction on Prior Lake.
Cost: $10M 100-year flood level: 904.4
Surface Water Modeling &
Flood Damage Reduction Study
Option #6: Actively Manage Outlet
Actively manage the low-flow gate on the
Prior Lake Outlet Structure
(assumes full capacity above NWL)
Cost: $0.1M 100-year flood level: 906.6
Option #5: Flood-proofing
Flood-proofing for at-risk
primary structures.
Cost: $35M
Option #0: Existing Managed
Protection
Existing Conditions. Manage protection through
temporary protection on as-needed basis.
Cost: $1M 100-year flood level: 907.1
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Option #0:Existing Managed Protection 0 0 50 -10 0 40 1 40
$1M
Option #1:Spring Lake Storage 2 200 -116 10 -40 56.5 4.1 14
$4.1M
Option #2:Increase Prior Lake Outlet 0 400 13 10 -80 343 3 114
$3M
Option #3:Upsteam Storage 6 330 -65 20 -20 271 2.9 93
$2.9M
Option #4:Combine Options #1, #2 & #3 6 670 -196 10 -60 430 10 43
$10M
Option #5:Flood-Proofing 0 535 25 10 0 570 35 16
$35M
Option #6:Actively Manage Outlet 0 100 45 20 -20 145 0.1 1450
$0.1M
*This chart was last updated on 2/5/16.
Obstacles: Does not improve access to residential properties, businesses, and public roads. Concerns of safety due to
inaccessible properties.
Obstacles: Would require necessary approvals and support from Prior Lake Outlet Channel partners. Potential to cause
engative effects during drought conditions.
Obstacles: Continued impacts to structures on Prior Lake. Concerns of safety due to inaccessible properties. Project
readiness is a limitation.
Obstacles: Would require necessary permits & approvals, as well as easements/agreements on 261 properties. Impacts
to landowners on Spring Lake. Minimal risk of negative effects to Prior Lake during drought conditions.
Obstacles: Need to secure necessary permits & approvals, as well as support from Prior Lake Outlet Channel partners.
Potential impacts to landowners downstream.
Obstacles: Would require necessary permits for water control structures. Need to secure easements or purchase land on
120 properties. Impacts to landowners in upper watershed.
Obstacles: Need to secure necessary permits & approvals. Impacts to landowners in upper watershed and downstream.
Potential for negative effects during drought conditions.
Options Score Card
Each option was scored based on the following criteria. Each criteria was weighted based on
importance to project implementation.
Water Quality and Natural Resources Benefits
Minimizes downstream pollution impacts &/or deposition of sediments
Restores wetlands to their native conditions
Controls impact of artificial drainage systems
Enhances the effectiveness of existing BMPs (improves upon prior investment)
Provides additional/improved habitat for fish and/or wildlife
Stormwater Management Benefits
Increases stormwater storage &/or reduces runoff rates
Provides opportunity for groundwater recharge &/or improves drought tolerance
Reduction of peak Prior Lake 100-year flood level
Improved level of Prior Lake flood protection
Restores Natural Hydrology
Feasibility Issues
Legal authority:
Level of effort required to secure permits and necessary approvals
Is there current access to the property in order to implement the project?
Will we need to secure easements or purchase property?
Project readiness:
Amount of time needed to prepare/prep for the project
Amount of time need to complete the project
Human Impacts
Improves access to area roadways & businesses
Public acceptance/Stakeholder Groups Impacted:
People/communities downstream of Prior Lake
Prior Lake land owners
Spring Lake land owners
Upper watershed landowners (including Arctic Lake interests)
Risk Factors
Potential for the project to cause detrimental effects during drought conditions.
Potential for the project to cause detrimental effects downstream/upstream.
Cost of Project
Total cost of project
Funding Opportunities
Scoring Criteria
902
902.5
903
903.5
904
904.5
905
905.5
906
906.5
907
907.5
908
908.5
909
2-year 5-year 10-year 25-year 50-year 100-year 500-year
Option #0: Existing Managed Protection ($0.2M)
Option #1: Spring Lake Storage ($4.1M)
Option #2: Increase Prior Lake Outlet ($3M)
Option #3: Upstream Storage ($2.9M)
Option #4: Combine Options #1, #2 & #3 ($10M)
3 primary structures ($1.5M to buyout)
1 inaccessible property
16 primary structures ($8M to buyout)
20 inaccessible properties
6 primary structures ($3M to buyout)
8 inaccessible properties
29 primary structures ($14.5M to buyout)
27 inaccessible properties
38 primary structures ($19M to buyout)
39 inaccessible properties
49 primary structures ($25.5M to buyout)
58 inaccessible properties
69 primary structures ($34.5M to buyout)
87 inaccessible properties
91 primary structures ($45.5M to buyout)
118 inaccessible properties
105 primary structures ($52.5M to buyout)
134 inaccessible properties
133 primary structures ($66.5M to buyout)
138 inaccessible properties
Current FEMA 100-year flood level: 908.9
2014 peak flood level: 906.2
No-Wake Level: 904.0
Ordinary high water level: 903.9
Normal water level: 902.5
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Revised FEMA 100-year flood level: 907.1 (not yet approved)
Flood Impacts on Prior Lake