The Normanby River is the fourth largest river system flowing into the Great Barrier Reef (GBR) lagoon, and the largest on Cape York. Grazing is the most extensive land use in the catchment, with low density grazing occurring across the majority of the catchment. Horticulture (bananas, passion fruit, etc.) within the catchment is mainly limited to the rich clay soils around Lakeland, on the upper reaches of the Laura River. Elevated nutrient levels have been measured in the Laura River near Lakeland, associated with horticulture and fertiliser use. Land use in the catchment has also significantly increased erosion and increased levels of sediments entering waterways.
A rainfall simulation study was undertaken in April 2015 to assess and compare the runoff and water quality from various soil types and management practices (including grazing, horticulture and roads) within the Normanby and Endeavour River catchments. Simulations were undertaken on a combination of 19 differing soil type/land use/management practice combinations.
• 1 X Lakeland Rainfall Simulator demonstration/field day
• 3 X Lakeland horticulture rainfall simulation runs
• 3 X Grazing rainfall simulation runs
• 1 X Grazing demonstration/ field day
• 3 X Laura grazing simulation runs
• 1 X Endeavour Valley horticulture demonstration/field day
• 3 X Endeavour Valley horticulture rainfall simulation runs
Simulated rainfall was applied to each plot at a rate of approximately 80 mm/hr for one hour. Runoff rates were manually measured from the outlet of each plot by recording the time taken to fill a measured volume. Water quality samples were collected at 5 or 10 minute intervals (6 samples collected from each simulation run), depending on when runoff commenced. Water samples were chilled on collection, and sub-sampled and filtered at the end of each day. Nutrient samples were then frozen, and the sediment samples kept cool, and submitted to the laboratory for analyses.
In summary, the results of this rainfall simulation study are supported by those observed from other studies. A final technical report has been received. The results highlight the potential for elevated sediment and nutrient runoff losses if the soil type is not managed appropriately.