Climate Change Impacts on the Sediment Load for the Nogoa Catchment of the Fitzroy Basin

Climate Change Impacts on the Sediment Load for the Nogoa Catchment of the Fitzroy Basin

The likelihood of changes to mean annual total suspended solids (TSS) was assessed for the Nogoa catchment (Figure 1) by perturbing input data to the E2 Model according to quantified ranges of climate change for 2030. These ranges incorporate the range of global warming according to the IPCC Third Assessment Report and regional changes in temperature, rainfall and potential evaporation encompassing the results from nine different climate models. The wettest, driest and average climate scenarios for the region were used in hydrological models to assess changes in water flow for the Nogoa catchment of the Fitzroy Basin (Nogoa River and Theresa Creek). Changes in land use (cropping, grazing) were applied to the models and sediment loads in the waterways were simulated under existing and climate change conditions. Changes in climate, water flow and sediment loads were measured against a base period from 1961-1990.

The dry scenario for 2030 was associated with a mean temperature increase of 1.4 degrees C, 9% lower annual rainfall, 10% higher evaporation and 10-13% lower annual flow. The wet scenario for 2030 was associated with a mean temperature increase of 0.9 degrees C, 2% higher annual rainfall, 2% higher evaporation and 10-13% higher annual flow.

The range of change in TSS from the driest and wettest extremes of regional climate change indicate a wide range of change in mean annual TSS ranging from approximately -11% to +12% for Craigmore (southern part of catchment) and -33% to +38% for Theresa Creek (northern part of catchment) by 2030. These changes in TSS were influenced by land use. Doubling cropping land use at the expense of grazing was associated with higher sediment loads and decreasing cropping in favour of grazing with lower sediment loads.

The combined sediment loads for Craigmore (0.541 Mt/year) and Theresa Creek (0.477 Mt/year) was 1.02 Mt/year for the base scenario which corresponds with an independent study at Duck Ponds (at the end of the Nogoa catchment), where a mean annual sediment load of 1.23 Mt/year was estimated.

Increased sediment (and nutrient) load in the watercourses of the Nogoa catchment may increase the amount of sediment deposition onto coral reefs and the ocean floor, increase turbidity and water temperature and restrict aquatic animal and plant processes. The removal of topsoil may also reduce the production of terrestrial animals and plants.

The use of agricultural land by the cropping and grazing sectors influences runoff, flows and sediment deposition into watercourses. A wet climate change scenario in 2030 may create more cropping, whereas a dry scenario is likely to create more grazing, probably at the expense of cropping. Managing these systems to maintain good groundcover slows runoff and reduces sediment loads. The use of sustainable agricultural management practices will help reduce the risk of damage to terrestrial and aquatic resources and help maintain agricultural productivity.