Sedimentation transport studies carried out for Tamar Lake Inc by consultants BMT WBM using the recently completed 3D hydrodynamic model of the Tamar have shown that the construction of a barrage at Long Reach will almost completely eliminate new silt accumulation in the Tamar and deliver a net export of residual silt over time with each significant flood event.
Specifically, the study focussed on the critical areas of Home Reach/Yacht Basin and between the barrage and the estuary entrance at Low Head.ir-leasing.ruбизнес

The studies showed that with the removal of the current flocculation zone from Tamar Island/Freshwater Point to downstream the barrage, and the complete removal of the asymmetrical tidal action, the incoming new silt from the catchment travels in suspension one way through the lake and beyond the barrage gates.
The net result in this area is an almost clear freshwater lake with a constant level of 0.3m below the current high tide.
The studies also show that over time with each flood event that tops the Trevallyn Dam, residual silt on the bed of Home Reach/Yacht Basin will be eroded downstream, never to return.
Mechanical agitation in the form of raking could be used to increase the rate of erosion of this residual silt.

As new silt from the catchment enters the Tamar principally in times of heavy rainfall, this silt
suspended freshwater travels through the barrage gates as they are opened on an ebb tide, and are
carried out to Bass Strait with limited mixing (and hence flocculation) due to the greatly reduced tidal
prism in this area.
The net result is no reduction in water clarity of this pristine marine environment, and even less silt
deposition than in the current tidal environment.

It is estimated in the study, that once the barrage is installed and the gates are closed, the lake will
transition from salt to fresh water in 4 to 12 months, depending on rainfall in the catchment.
The 3D studies also confirmed the long held view that with the current level of pollution entering the
Upper Tamar Reaches from sewage treatment plants and catchment and urban runoff, the concept is
not viable as it will not meet water quality standards for a freshwater lake.
3D modelling is now in progress to assess whether the proposed Launceston Sewage Improvement
Plan (LSIP) will reduce the pollution loads sufficiently to meet freshwater lake environmental
standards.
The Tamar Lake concept involves the installation of a barrage, just south of the Bell Bay port in Long
Reach, to separate the Tamar into a 60km long freshwater lake and reducing the tidal estuary section
to 20km.
The benefits include:

Tamar Lake Inc is a not-for-profit member funded Incorporated Association with the mission to
demonstrate to government and the community the viability of the Tamar Lake concept to transform
the economic potential of Launceston and the Tamar Valley.
Formed in 2010, the company has commissioned 10 studies that looked at all aspects of the technical,
environmental and economic feasibility of the concept.
Should the water quality issues be resolved with a funded commitment for the implementation of the
TasWater Launceston Sewage Improvement Plan, Tamar Lake Inc will give the community the
opportunity of evaluating and expressing their support or otherwise in a broad based Social License
program before a decision is made to proceed to detailed planning and approvals phase.
Full details on the Tamar Lake project and a summary of the results from all the studies carried out
are available from their web site at www.tamarlake.com.au.
Questions on this release may be directed to Robin Frith, President of Tamar Lake Inc, on 0419 176
096 or email to robin@robinfrith.com.au.