Notes for boating on the Gordon River
The lower Gordon River is a narrow estuary within the Tasmanian Wilderness World Heritage Area. Its geomorphology is in itself of World Heritage significance. Its beautiful, and delicate, landforms are the legacy of progressive sedimentary filling of the steep sided river valley after it was drowned by rising sea levels following the end of the last ice age.
These soft sediment shoals and banks are susceptible to erosion by boat wake. The lower Gordon River, along with other the sheltered waters of some other inlets, estuaries, rivers, lagoons and lakes are suffering unnatural and largely unnecessary erosion as a result of boating activities.
History of Gordon River Bank Erosion
The lower Gordon River has been a tourism venue for over a century. By 1985, local Parks and Wildlife Service rangers had noticed that the river banks were starting to collapse. Ancient huon pines and myrtle beeches were toppling into the river.
It became apparent that the wake from cruise boats was responsible for erosion and that speed limits were required to minimise the impact. In 1987, following studies and an ongoing monitoring programme, a nine knot speed limit for vessels greater than 8 m in length was applied to some three quarters of the length of the estuary.
By 1988, monitoring had shown that while the rate of bank retreat had slowed in those areas where speed limits had been introduced, erosion was still occurring. Cruise boats were then restricted from travelling further than the Heritage Landing boardwalk which was built 13.5 Km from the mouth. Following the construction of Heritage Landing in 1989, the rate of erosion slowed dramatically, however by now some 80% of banks had been affected and seriously destabilised, so the problem was far from completely solved.
In 1992 after much consultation, a voluntary users code was produced to guide private visitors to the river in how to reduce damage caused by their vessels. However, people were beginning to question why the Parks and Wildlife Service still regarded the erosion as a matter of serious concern and there were even pushes from some quarters to increase speed limits or re-open closed reaches.
A series of radiocarbon dates on bank sediments obtained in 1993 proved that most banks had been stable for thousands of years, while those nearer the mouth had been very strongly depositional. On those banks it wasn’t the absolute rate of erosion that mattered as much as the reversal of geomorphic process from deposition to erosion. Together with the data from ongoing monitoring, this supported implementation of a further reduction in commercial vessel speed to
six knots in 1994.
In 1994 Sir Max Bingham QC was commissioned to head an Inquiry into Gordon River Tourist Operations. The principal outcomes were a new licensing regime which gave priority to environmental protection and a management plan for the lower Gordon that recognised the three major aims of World Heritage Area management: protection, presentation and rehabilitation. Replacement of the existing cruise fleet with vessels designed for low wake characteristics was encouraged.
As part of the Bingham Inquiry the wave characteristics of all commercial vessels were measured by the Australian Maritime College (AMC). The tests were repeated and expanded upon in 1995 and again in 1997 when a new, twin hull cruise vessel was proposed.
Other studies set speed limits for individual cruise vessels based on their modelled wake characteristics. This allows a speed limit to be set, a licence issued and the operator to gain finance before construction of the vessel commences.
Erosion caused by private boats
As the erosion caused by commercial traffic was progressively reduced, the impact of private vessels became relatively more significant. Speed limits were only applied to vessels greater than 8 m in length because it was then believed than the lower waves from small, planing boats were less erosive. Experimental work has shown, however, that this is incorrect. Wave speed is linked to boat speed so despite their lack of height the waves from a planing boat carry a lot of energy because they are moving fast. When these powerful waves hit the bank they cause significant erosion.
Further details of the Lower Gordon River Erosion is available on the Department of Primary Industries and Water web site.
How you can help minimise your impact
A guide to help boaters minimise the impact of their activities, Wake Up? Slow Down!, is available from the Department of Primary Industries and Water web site.
Among the ideas given in this brochure are:
- Be aware of different banks and beds – use your experience to recognise vulnerable landforms
- Keep your speed down – observe speed limits, voluntary and compulsory
- Travel slowly on the river and take the time to troll a line or admire the scenery
- Only use recognised landing places
- Observe the banks carefully when you’re on the water – keep an eye on any changes and report problem areas to the Department of Primary Industries and Water or the local Parks and Wildlife service base
- When planning a trip to one of the more remote waterbodies check with the local PWS Ranger regarding any access conditions that might apply (see list of contacts)
- Have a quiet word with boat drivers doing the wrong thing – better still, slip them a copy of this brochure
- For more information, visit the website – http://www.dpiw.tas.gov.au/inter.nsf/WebPages/LJEM-6HZTAB?open
- For information on minimal impact boating, see Better Boating.