Calculating flow into coastal lakes from water level measurements

Some coastal lakes in New South Wales have narrow channels to the ocean. Runoff from the catchment elevates water levels within the lake because of the constricted nature of the entrance. Freshwater inflow affects many ecological processes in these lakes. Often freshwater inflow comes from multiple sources and is difficult to measure directly. Water level is easy to measure and is commonly measured for flood management purposes. A simple dynamical model can represent features of water level in such lakes to a good approximation. This is demonstrated by comparing model output with measurements of tidal oscillations and tidal pumping within the lake. Residuals of modelled water level relative to measurements within the lake are statistically analysed to estimate freshwater inflow to the lake. Comparisons of freshwater inflow with other estimates of catchment runoff are favourable.