Second Public Meeting Prior Lake-Spring Lake Watershed Surface - - PowerPoint PPT Presentation

▶
second public meeting
SMART_READER_LITE
LIVE PREVIEW

Second Public Meeting Prior Lake-Spring Lake Watershed Surface - - PowerPoint PPT Presentation

Aug 08, 2023 139 likes •354 views

Second Public Meeting Prior Lake-Spring Lake Watershed Surface Water Modeling and Flood Damage Reduction Study Greg Wilson Barr Engineering Company May 28, 2015 resourceful. naturally. Meeting Outline Project Update Summarize major

slide-1
SLIDE 1
  • resourceful. naturally.

Second Public Meeting

Prior Lake-Spring Lake Watershed Surface Water Modeling and Flood Damage Reduction Study Greg Wilson Barr Engineering Company May 28, 2015

slide-2
SLIDE 2
  • resourceful. naturally.

Meeting Outline

  • Project Update

– Summarize major themes from the first public meeting – Recap 2014 monitoring

  • Preliminary Modeling and Universe of

Options

– Overview of model calibration to 2014 flooding – Preliminary results of 100-year flood event

2

slide-3
SLIDE 3
  • resourceful. naturally.

Themes from First Community Meeting

  • How were you impacted by 2014 flood?

– Damage to structure, shoreline, lawn/yard – Sandbagging and pumping for extended period – Road closures, loss of recreational use

  • What issues, concerns, possible remedies

would you like considered?

– Upstream storage and management of flow* – Modification to outlets/outlet operation – Water quality concerns – Flood-proof homes and use other storage basins

3

slide-4
SLIDE 4
  • resourceful. naturally.

Themes from First Community Meeting

  • For you, the most important outcome of this

study would be…

– Better management of lake levels; never let water to get to 904.5’ – More proactive flood response; estimate each spring if Prior Lake is going to flood – Slow down upstream water/manage inflows – Improving/protecting long-term water quality – Don’t exacerbate downstream (of PLO) impacts

4

slide-5
SLIDE 5
  • resourceful. naturally.

Themes from First Community Meeting

  • Other comments/suggested strategies

– Flood-proofing/buyouts – Enlarge Prior Lake outlet channel or provide new pipe – Re-establish overflow under TH13 – Emergency pumping to Campbell Lake/other basins – Let water out of PLO sooner—901 feet MSL or permanently/temporarily lower control elevation – Control Spring Lake outlet/permanent dam – Upstream storage (Buck Lake and CD13)

5

slide-6
SLIDE 6
  • resourceful. naturally.

Results of 2014 Monitoring—Spring Lake

7

Spring Lake Outlet Channel Dam In Place Spring Lake No-Wake Restrictions

908.5 909 909.5 910 910.5 911 911.5 912 912.5 913 913.5 May-01 May-16 May-31 Jun-15 Jun-30 Jul-15 Jul-30 Aug-14 Aug-29 Sep-13 Sep-28 1 2 3 4 5 6 Lake Level (ft) Rainfall (in) Daily Rainfall Spring Lake Elevation No-Wake Level (904.0)

Crest: 913.3 5" rainfall

Crest Crest of f 913.3 .3 on June 21, , 2014

slide-7
SLIDE 7
  • resourceful. naturally.

Results of 2014 Monitoring—Prior Lake

8

900.5 901.5 902.5 903.5 904.5 905.5 906.5 May-01 May-16 May-31 Jun-15 Jun-30 Jul-15 Jul-30 Aug-14 Aug-29 Sep-13 Sep-28 1 2 3 4 5 6 Lake Level (ft) Daily Rainfall (in) Daily Rainfall Prior Lake Elevation No-Wake Level (904.0)

Outlet Structure Discharging (above 902.5) Crest: 906.17 5" rainfall

(NWS Chanhassen)

Crest Crest of f 906.2 .2 on June 30, , 2014

slide-8
SLIDE 8
  • resourceful. naturally.

Watershed Map

9

slide-9
SLIDE 9
  • resourceful. naturally.

Results of 2014 Monitoring

10

slide-10
SLIDE 10
  • resourceful. naturally.

Results of 2014 Monitoring

11

slide-11
SLIDE 11
  • resourceful. naturally.

Results of 2014 Monitoring

12

Provide more Storage, Slow the Flow Increase outflow rate

slide-12
SLIDE 12
  • resourceful. naturally.

Calibration to 2014 Event Prior Lake Elevation

slide-13
SLIDE 13
  • resourceful. naturally.

Calibration to 2014 Event Spring Lake Elevation

slide-14
SLIDE 14
  • resourceful. naturally.

“What-if” Mitigation Strategies used in Modeling Scenarios

18

  • Increase upper watershed storage

– Utilized 1,000 ac-ft. storage by restricting flow at 3 locations

  • Increase Spring Lake storage

– Raised peak elevation by 1.2 ft. to 915.1’ – Raised peak elevation by 2.0 ft to 915.9’

  • Modify Prior Lake outlet structure

– Increase flow to 65 cfs (and 85 cfs) when lake level is > 902.5’

  • Combination of three scenarios (upper watershed

storage, Spring at 914.3’ & 85 cfs from Prior Lake)

slide-15
SLIDE 15
  • resourceful. naturally.

“What-if” Modeling Results for Mitigation Strategies

19

slide-16
SLIDE 16
  • resourceful. naturally.

“What-if” Modeling Results for Mitigation Strategies

20

slide-17
SLIDE 17
  • resourceful. naturally.

“What-if” Modeling Results for Mitigation Strategies

21

slide-18
SLIDE 18
  • resourceful. naturally.

“What-if” Modeling Results for Mitigation Strategies

22

slide-19
SLIDE 19
  • resourceful. naturally.

Selection Matrix for Flood Mitigation Options

  • Criteria that will be summarized for each

alternative:

– Life-cycle costs—incl. construction, O&M, loss

  • f property use/value

– Benefit—measured by flood peak reduction – Other benefits or impacts—water quality improvement(s), wetlands, habitat, etc. – Feasibility of reduction mechanisms—legal authority, regulatory controls, education, eligibility for outside funding, readiness

23

slide-20
SLIDE 20
  • resourceful. naturally.

Questions??

24