Date of Award

1996

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Science, Technology and Engineering

First Supervisor

Dr Pierre Horwitz

Second Supervisor

Stephen Connell

Abstract

The Bremer river catchment, on the South-coast of Western Australia, is typical of most river catchments in this region in that it has been seriously affected by sedimentation, salinisation and eutrophication brought on by the gradual dominance of agricultural land management practices. Vegetated rehabilitation and changed agricultural land management practices (ie minimum / zero tillage) have now been widely adopted throughout the catchment in response to these degradation issues. This study examined the potential impact minimum / zero tillage, vegetated rehabilitation and remnant vegetation could have on both a farm and catchment wide scale. A Geographical Information System was developed to identify spatial variability evident throughout the catchment. Three zones were developed by the system to account for spatial variability. Field studies were undertaken to sample the surface runoff flow from areas under the Remnant Vegetation, Vegetated Rehabilitation and Minimum / Zero Tillage land management practice in each of the three zones. Runoff was sampled using a modified Gerlach trough. Runoff sampling was synchronised with the occurrence of the first rainfall I runoff event of the year. Phosphorus, sediment and salt concentrations were the main parameters analysed in the runoff samples collected. Following statistical analysis, the results for these parameters were extrapolated to a load per hectare figure. Further analysis of the catchment GIS was undertaken to determine the area of each zone and areas under each land practice in each zone. Two series of modelling scenarios, using the extrapolated load data, were used to determine the immediate and long term restorative effects increasing areas of vegetated rehabilitation could have on both a zone and catchment basis. This study concluded that minimum / zero tillage in the catchment, in combination with further wide-spread adoption of vegetated rehabilitation will have the capacity to reduce catchment degradation caused by eutrophication and sedimentation. Its extensive implementation can address these two forms of degradation by decreasing runoff concentrations of phosphorus and sediment. Salinity problems in the catchment will be indirectly effected through resulting changes to the groundwater table. Additional changes to current land management practices are also necessary for instance fertility testing and fertiliser application-on-need should be incorporated into the minimum / zero tillage land management practice if they haven't been already.

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