Dredging Creeks and the Inlet

February 2018 Update

Ice jams

  • DPW has been using effluent (treated wastewater) from the Ithaca Area Wastewater Treatment Facility (IAWWTF) to melt ice and free up the flow of water in Cascadilla Creek
  • Effluent is 40-50F
  • They have to run hoses (with DEC permission) from the IAWWTF to the creek
  • Ice jam mitigation comes out of overtime contingency in the budget

DPW would like permanent piping from IAWWTF to the creeks:

  • Install pipes in the ground leading to Cascadilla Creek so they can simply notify the DEC and turn a valve to start de-icing
  • Project would need funding and DEC approval
  • They’d also like to have outlets at Cayuga and Cascadilla to address jams further up the creek and by Lake St to address issues in Fall Creek
  • This would resolve another issue: effluent has chlorine and the DEC is concerned about adding chlorinated water to the creeks. Permanent piping would have dechlorination at the end like the effluent outlet into the lake
  • Would also mitigate overtime costs
  • Can be turned on and off in contrast with hoses which need to be constantly flowing to avoid freezing
  • Dredging may not solve the ice jam problem. Hence the effluent system.
  • DPW will put in request for a capital project and compare with the cost of overtime, equipment rental, fire department time, etc.

Dredging

When Cayuga Lake’s water level is lowered in the winter creek levels are lower too, exposing gravel bars. Ice gets caught there.

The US Geological Survey has mapped the bottoms of the inlet and creeks. They’re also doing a flood study and examining the impact of dredging on potential flooding, modeling water flows from creeks into the lake for 2, 50, 100, and 500 year flood events. They will be preparing maps (but not FEMA maps, which affect flood insurance requirements and rates) with conservative modeling of flood zones. A cost-benefit analysis will be performed based on that study. FEMA could provide money if those studies show dredging is effective.

Future: Look at watersheds throughout the county and their contributions to water in the city. Look at whether levees should be higher.

Inlet
  • Permit and plans for the dewatering facility in Southwest Park (behind Wegmans) are complete
  • Construction will start this year (2018) and hopefully finish by end of this year
  • DEC will perform hydraulic dredging of the inlet: barges will suck up silt which is 90% water to be dried at the dewatering facility. More detail on dewatering at the bottom of this page
  • No timeline is set on when dredging will actually occur
  • $13 million allocated
Cascadilla Creek
  • $2 million for Cascadilla Creek dredging
  • TG Miller has developed a dredging plan for Cascadilla Creek. DPW has requested 2 scenarios: one for as deep as it was “originally” (records are hazy), one for 1 ft below that (this means lowering the depth by roughly 3-4 ft vs 4-5 ft)
  • Permits will be acquired this year (2018) with dredging to start in 2019
  • Working with the DEC for permits to dredge
  • Dormitory Authority of State of NY holds and dispenses the money
  • The City Harbor project at Johnson Boat Yard will install a sea wall which will help with dredging.
  • The developers of that project want to start in 2019 so our dredging efforts can coincide
  • DPW is planning to install sediment traps along Cascadilla Creek, which will make it easier to pull material out. The traps will be deep spots in the creek with definable bottoms where sediment will accumulate
  • DPW is collecting samples from bottom of Cascadilla to figure out what the sediment can be used for. Developers can use gravel. Gravel pits in the area can hold the muddier stuff. Contaminated sediments have restrictions on use: highly contaminated sediment must be landfilled
  • The amount of dredging will depend on cleanliness of the spoils as more contaminated sediment will be more costly to dispose of

Six Mile Creek

  • Awaiting USGS study to see what mitigation makes most sense

May 2016 Update

In May 2016 Lisa Nicholas of the City’s Planning, Building, Zoning, & Economic Development department presented an update on the dredging effort to Common Council’s Planning and Economic Development Committee. To watch the presentation click here (and if the link doesn’t work, head to ithacany.pegcentral.com and click on “05-11-16 Planning and Economic Development Committee Meeting”). The presentation starts 23 minutes into the video. A summary of the presentation follows:

Background

In 2012 the state allocated $13 million to restore the inlet ($2 million was also allocated to the city in 2008 for dredging Cascadilla Creek, which has not yet happened). The DEC is the lead on this project. Within the inlet also lies a navigation channel under the control of the state Canal Corporation, so they share some responsibility as well.

Additional history on the flood control channel can be found in this Ithaca Journal article.

Project Summary

The project will occur in 4 phases:

Phase 1 – Design and construction of the sediment management (dewatering) facility
Sediment management will be located in the southwest corner of the city near Walmart. The DEC has a draft design now and it’s currently going through environmental review. An optimistic estimate of when design and construction of the facility will be complete is end of 2017. $2 million has been spent on design. Construction is conservatively estimated to cost $4 million.

Phase 2 – Dredging
Sediment will be pumped by vacuum and piped to the dewatering facility. The plan is to go down 1.5 feet, but places may be identified where they have to go deeper. If the aforementioned optimistic schedule works out, dredging could begin in 2018. We don’t really know if the money left over after design and construction of the facility will be sufficient to complete the dredging (unlikely).

Phase 3 – Dewatering
Drying (dewatering) in the sediment management facility can take 2-4 years. The wet sediment is put in geotubes and water slowly seeps out.

Phase 4 – Storage of the dewatered sediment
The current plan is to spread the sediment onto the same plot of land that the dewatering facility will sit on. Apparently the city has resold sediment in the past for reuse, but nothing has been planned in that vein at this time.