Tamar River silt – dredging not the answer

Silting in the Tamar River, Tasmania. Dredging is not the answer, says a new report. Credit: Water S.O.S. Tasmania The research, published in the journal Estuaries and Coasts involved assessing historical charts, maps and photos to identify factors contributing to the problem. The researchers concluded that excessive siltation was directly linked to changes in the tidal system caused by human activity

Siltation in the upper Tamar region has been a problem since Launceston was founded in 1806. The research shows that events such as the construction of dams and the diversion of a major tributary of the Tamar align with increased silt deposits in the upper estuary.

Traditionally, the response to siltation has been dredging.

‘Siltation has continued to occur despite over 100 years of dredging. It's an indication of a system in adjustment,’ says co-author Professor Jenny Davis of Monash University.

‘Our results show the siltation is the result of massive reductions in water flows due to activities such the draining of tidal wetlands for housing development and agriculture, and the reduction and redirection of inflows to generate hydroelectricity.’ 

‘The damage is quite severe. The upper estuary that was once Launceston’s commercial, recreational and aesthetic centre, has been reduced to a muddy trickle at low tide and a shallow, non-navigable pond at high tide.’

Professor Davis noted that some of the stressors on the river system, such as the damming of tributaries, are irreversible.

‘Some sustainable restoration activities include increasing tidal volumes by re-creating tidal wetlands, and the delivery of variable environmental flows from the Trevallyn Dam,’ says Professor Davis.

‘The study has enabled us to identify that water is the major issue in the degraded estuary, not silt. We need to increase tidal and river flushing to rehabilitate the sytem.’

Source: Monash University