Impacts of Recreational Boating on River Bank Stability: Wake Characteristics of Powered Vessels

"March 2008".

Project Number: Assessing the impacts of recreational boating activities on river bank stability - M/BUS/226.

MDFRC item.

1 of 3 reports associated with project see (Impacts of Recreational Boating on River Bank Stability. A Literature Review) and (Impacts of Recreational Boating on Bank Stability in the River Murray).

The purpose of the current study was to estimate the potential of powered recreational boats to increase bank erosion along the Murray River near Echuca-Moama. In particular the study considers whether wake boats substantially increase the rate of erosion relative either to other boat types or other factors than lead to erosion in this section of the river. The study clearly showed that wake boats can produce waves with greater erosion potential than other types of powered vessels that use the Murray River near Echuca. This is not surprising given that wake boats are both designed and operated to produce maximum wash. That is not to say that other boat types do not have the capacity to contribute to bank erosion. Jet skis and runabouts also produced wakes with both high peak and total energy density; jet skis, runabouts and ski boats all produced waves with similar levels of total power. The amount of sediment suspension caused by boat traffic varied with location and was estimated at between 0.45 and 3.6 kg/ metre of bank/hour in the Echuca region. In comparison, based on background turbidity levels, the total suspended solid load passing a given point in the river was estimated to be 25.4 tonnes/hr. When the potential for erosion from boat induced waves is compared to the potential from other sources, including flow and wind induced waves, it was estimated that overall, boat wakes only contribute to a small percentage of the total energy expended on the river bank at Echuca. Most of the energy expended on the river bank in this region is associated with river flow, with a smaller additional contribution from wind-induced waves.