The Geographe Catchment includes a number of poorly drained flats, wetlands and river systems. The Vasse Wonnerup Wetlands provide habitat for thousands of waterbirds every year and are included on the list of internationally recognised RAMSAR Convention wetlands. Over 30,000 individual waterfowl have been recorded in the system at any one time. This short film “Life on the Water: The Vasse Wonnerup Wetlands” provides an insight into this special place on Busselton’s door step. In addition to this, there are 16 predominant watercourses in the catchment, including the Carbunup, Buayanup, Lower Vasse, Sabina, Abba, Ludlow and Capel River systems.
European settlement has seen many changes to the catchment’s hydrology. Originally very few waterways flowed directly into Geographe Bay, instead they flowed into an extensive chain of coastal wetlands and emptied into the Vasse or Wonnerup Estuaries. Hydrological change in the catchment started as early as the 1880s when the Capel River was diverted from the Wonnerup Inlet into Geographe Bay through the Higgins Cut. From this time until the 1950s, a series of hydrological alterations were made. Floodgates were installed near the mouths of the Vasse and Wonnerup Estuaries during the early 1900s to prevent flooding of the surrounding agricultural land with salt water. These floodgates have since enabled the Busselton town site to expand into land that was previously inundated during winter. The floodgates have also served to maintain fresh–brackish water within the system for a longer period than would have occurred under ‘natural’ conditions.
Geographe Bay also receives flow from groundwater sources. The catchment is underlain by the superficial aquifer, which is approximately 10m thick. Below this lies the Leederville aquifer, which in turn is underlain by the older and larger Yarragadee aquifer. Both the Leederville and Yarragadee are confined aquifers that are recharged by direct infiltration of rainfall on the Blackwood Plateau. The Capel River is the only waterway that actually intersects the Leederville aquifer, which is the reason it is a perennial river system. All other waterways receive contributions only from the superficial aquifer and surface runoff.