Incorporating a temporal function (i.e. to analyse data over time) into the spatial environment of GIS has been developed and applied in the assessment of the evolution of Nash Bank, South Wales. A stringent programme of monitoring, including annual bathymetric surveys of the bank, is carried out as part of the requirements of aggregate dredging and provides suitable data to analyse changes in bank levels over time. Traditionally GIS has been used to assess the evolution of such coastal landforms by creating a digital terrain model (DTM) for each of the bathymetric datasets and then performing a simple calculation whereby one DTM is subtracted from an earlier one. However, a simple difference in levels between any two snapshots in time can be misleading when trying to evaluate long-term rates of change. The new GIS tool has been developed that calculates such rates (i.e. the time trend) by incorporating a linear regression formula. The results are then plotted out by the tool into GIS as a DTM, in which each individual data cell represents a rate of change (time trend) at that particular location, allowing a clear temporal analysis to be presented for the whole area.