Does the weight of riparian trees destabilize riverbanks?

In contrast to the generally accepted stabilizing effects of riparian veget ation, the surcharge of trees on riverbanks has been widely implicated as a source of bank instability. Fieldwork conducted along the Latrobe River in Victoria, Australia shows that the bank-destabilizing effects of surcharge , due to silver wattle (Acacia dealbata), are minimal. Field observations i ndicate that it is unlikely that the weight of silver wattles growing on an otherwise stable bank section will directly cause mass failure. Observatio ns of deep-seated failures and silver wattle stands on the Latrobe River in dicate that where average-sized slump-blocks support an average number of a verage-sized silver wattles, the trees represent only 4.1% of the total sat urated slump mass. Infinite slope stability analysis indicates a threshold of around 48 degrees where banks become prone to shallow-planar slide failu res as they steepen. Where bank sections are inherently unstable and prone to shallow-planar slide failure, the additional weight of the trees may con tribute to overall instability. However, manipulation of other stability pa rameters within reasonable constraints negates the effect of surcharge so i t is not possible to demonstrate conclusively a destabilizing influence of silver wattles. Copyright (C) 2000 John Wiley & Sons, Ltd.