Hydrogeological characterisation of catchments using hydrogeomorphic analysis of regional spatial data (HARSD): Characterisation of Axe Creek Catchment, Victoria, Australia

Recent significant developments in Geographical Information Systems (GIS) were used to develop new methods for hydrogeomorphic classification of large catchments. The new methodology takes account of the important role geology has in forming topography through differential weathering, erosion and deposition. These events in turn influence the formation of the geomorphic and hydrogeomorphic characteristics of the catchments. The new methodology was applied to the Axe Creek sub-Catchment within the Campaspe catchment in north-central Victoria. Hydrogeomorphic maps were prepared using a digital elevation model (20 m grid). The HydroGeomorphic Units (HGUs) showed very good correlation with detailed traditional geomorphic mapping done previously for the subcatchment. The HGUs reflected most of the major geological features of the area, including the Whitelaw fault (reverse thrust slip fault) extending in a NW-SE direction, the N-S strike of the steeply dipping Ordovician rocks, the gentle ridges where softer rocks occur in the northeast, and the major drainage lines. Groundwater level maps were prepared for the catchment using regression between the water levels and the surface elevation and controlled by the hydrogeomorphic classification and vegetation cover. Broad scale and detailed flow regimes were also constructed and fluxes calculated. Salt loads from two gauging stations were used to calibrate the fluxes. Detailed downhole electromagnetic surveys were used to estimate the salt contribution from the different HGUs. Recharge was calculated from borehole hydrographs and separated into two major components. These were seasonal recharge to the top aquifers, which eventually discharges to the streams or leaves the catchment as underflow, and a residual (annual cumulative) recharge which causes an annual rise in water level of 0.01-0.2 m yr(-1). The hydrogeomorphic classification will be used by Landcare groups to apply suitable management scenarios in order to reduce recharge and saline water discharge into rivers.