Management Board Minutes 4-30-2013

Jim provided an overview of 8 potential scenarios to mirror pond sedimentation problem and the 4 scenarios the tech advisory committee recommends moving forward

Jim gave summary of tech engineering report and permitting report

  • Inter-fluve report states pond is functioning as a lake not a river
  • Sediment is soft and gooey and not good top soil, mostly sand
  • 380,000 cubic yards of volume throughout bottom of pond
  • Sedimentation rate is about 1400 cu ft per year
  • There are 2 to 3 meters of sediment at bottom of channel and is much deeper as you move away from channel
  • Hydraulic suction is recommended as the best sediment removal technique

SCENARIOS

A – Do Nothing
Mostly mudflats with a well-defined channel

B- Dam in place with full sediment removal Extensive open water

  • Full sediment removal cost is $18M
  • Repeat dredging every 30 to 50 years

C -dam in place partial removal

D- Dam in place partial redistribution of sediment

  • Designer dredging requires subsurface bank stabilization
  • Use dredge material to create islands, wetlands and park land requires location to de-water sediment
  • Sediment deposition will occur mostly immediately below Galvaston bridge where ongoing dredging can take place

E- Remove dam and no active sediment management

  • Possibility for aggressive pioneer specie invasion in mudflats and wetlands including protected species
  • We can create an amenity that will then be regulated
  • Could pursue “safe harbor” approach

F – Remove dam reconstruct channel with sediment management

G- Remove dam with active sediment management and channel relocation

  • Creates more land on east side of channel
  • This is an aggressive manipulation of channel

H -Partial dam removal and stepped water terraces

Management Board voted 10 in favor and 1 opposed to advance scenarios A, B, D and G for further study

Next meeting to be held in June

Document: MIRROR POND MANAGEMENT BOARD Notes 04-30-2013

2013_03_22_Opp_Const_100sc

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