River catchments are dynamic and vulnerable systems that can change markedly when exposed to human impact. Changes induced since European settlement in Australia are of particular interest because impacts can be almost impossible to reverse. A measure of catchment degradation may be determined using accumulation in lakes. Along the east coast of New South Wales, both the rate of sediment infill and the stage of infill reached differ between coastal lagoons as a function of physical characteristics within their catchments, including the erosive power of rainfall, the intrinsic susceptibility of the soils to erosion, as well as the combined effect of slope angle and length. The amount of human development also plays a role in that the nature and extent to which the natural vegetation is disturbed, and practices that control erosion, may influence sediment loss. Sediment accumulation rate in a lake has its own value, but when placed in the context of natural resource planning, it is retrospective and may not be the most efficient approach to land management in catchments. Thus, there is a need to forecast degradation; however, most research has tended to focus on “universal” applications that were designed to achieve exact values. Simulations using empirical, physical, and processbased techniques do offer another option. The effectiveness of the generated models can be tested by comparison with historic and prehistoric rates of sediment accumulation in coastal lagoons. A small coastal catchment, Lake Wollumboola, located north of Jervis Bay, NSW, was selected for testing simulated soil erosion, using the Revised Universal Soil Loss Equation in combination with GIS, since it offers the opportunity for measurement of sediment accumulation in its terminal lagoon. This integrative approach allows the modelling of soil erosion in coastal catchments as a response to changes in land use. Using hypothetical scenarios, the nature and extent of catchment degradation and erosion can be predicted for past, present and future conditions.