“The Effects of Catchment Land Cover Change on Sedimentation in Back Lake, Merimbula, NSW.”

Mapping of the catchment was undertaken to determine the extent and distribution of land cover changes. It was found that expansion of the existing development on the floodplains of Merimbula Creek occurred in the 1970s. Further development requiring the clearance of vegetation on the northern margin of Back Lake has occurred from 1999 to present. A rapid decrease in vegetation occurred between 1972 and 1975, causing an 11% reduction in forested area. Mapping highlighted the widespread clearance that occurred as a result of development and the impacts of this were examined with cores extracted from Back Lake. The cores retrieved demonstrated that there has been a significant change in the sediment supplied to Berrambool Creek. Clay horizons in the most recent stratigraphic record were present throughout the creek in thicknesses varying from 14.5cm to 23cm. The clay layers were not identified elsewhere in the estuary, suggesting that the cause of the sedimentation occurred locally. It was concluded that the likely cause of the clay deposits was the removal of native vegetation from the adjacent land causing increased surface runoff and soil erosion enhanced by rainfall events. Predictive modelling using a Coastal Eutrophication Risk Assessment Tool (CERAT) estimated that the loss of sediment into the lake through surface runoff and Total Dissolved Solids (TSS) is exacerbated through the clearance of vegetation. TSS volume increased by 282% using estimated future clearance conditions. Limited change was seen with the conversion of forest to urban area. This study concluded that there is a need for effective management of sediments within development sites. The monitoring of lake conditions can provide data that can be used to assess the effectiveness of sediment management practices. Additionally, monitoring data can provide a baseline to assess anthropogenic impacts, which may assist in effective ecological management of the estuary