Impact of the 1978 floods on the channel and floodplain of the lower Macdonald River, N.S.W.

Abstract

Summary Moderate to heavy rainfall over the lower catchment of the Macdonald River in March and May/June 1978 resulted in two moderate floods at St Albans with return periods of 11.11 and 3.63 years, respectively. The March flood resulted in about 0.30 m of bed aggradation, substantial river bank erosion and deposition of sand splays. The June flood resulted in about 0.10 m of bed degradation. This divergence in river response to the two events is due to the episodic supply of large volumes of sediment from river bank erosion during bankfull floods and the subsequent reworking of the sediment by lesser floods.