Mapping land cover changes (1947-2004) in the Lang Lang Catchment, Victoria
The Lang Lang Catchment has long been rated as having poor water quality even though it has the least urban sprawl of any catchment in the area controlled by Melbourne Water. The catchment is the largest under Melbourne Water jurisdiction and exhibits a wide variation in terms of geology and geography. Documented changes in the stream channels and sediment yield into the Westernport Bay are monitored and are shown to be mainly due to clearance of the dense forests within the contributing catchment, a land-cover change that progressed inexorably from the days of first European settlement about 150 years ago.
Studies of the Lang Lang catchment already published by Melbourne Water and CSIRO research programmes all link the progress of soil erosion to the history of land clearance but time series quantification is lacking, as is any derivative of it with reference to geographical variation in the catchment. In this study, the results of time series mapping using orthorectified mosaics of land cover change detection for the period 1947 to 2004 in each sub-catchments are presented.
Land use after clearing refers mainly to grazing, agriculture and dairying, all commendably viable in this area because of reliable rainfall and fertile soil. The results of net canopy change are used to quantify how much canopy cover has declined and attempts of reforestation by plantation have come nowhere near compensating for amount of land cleared. It seems that the relevant Catchment Management Authorities have not taken geographical variation of the catchment into account where modern digital spatial data handling methods can facilitate.
Although the stream water quality monitoring data is not ideal for immediate correlation with land cover change pattern analysis for each sub-catchment, it is shown that re-vegetation expenditure would probably yield most rapid return on investment if focussed upon selected areas of the sub-catchments. In reference to terrain attributes and land cover change history, site selection for a vegetation cover rehabilitation programme has been achieved.