WaterCAST sediment and nutrient modelling Scott Wilkinson May 2009 Water for a Healthy Country

Outline Current modelling strengths and uncertainties Reef Rescue monitoring and evaluation (modelling) Issues with daily modelling and model coupling

SedNet: sediment river network budget model Hillslope erosion Gully erosion Streambank erosion Hillslope delivery Floodplain deposition Reservoir/ lake deposition River link Yield from upstream links Yield to downstream link Wilkinson et al., 2004

Sediment and nutrient loads to the GBR Sedimentation rates Load monitoring Load modelling Brodie et al., 2009

SedNet N and P budgets Downstream yield Nutrient concentration P equilibration, denitrification Tributary supply River bank erosion Gully erosion Subsoil sediment nutrient concentration Hillslope erosion Topsoil sediment nutrient concentration HSDR, Nutrient enrichment ratio Channel resuspension, Channel, Floodplain, reservoir and lake deposition Diffuse dissolved loss (O&I) Nutrient delivery ratio Point sources Reservoir dissolved nutrient loss Denitrification Wilkinson et al., 2004

Particulate and dissolved nutrient species Particulate Dissolved inorganic Dissolved organic Brodie et al., 2003

Source areas and processes (Brodie et al., 2003) Contribution to suspended sediment export Yield Supply Deposition Supply

Uncertainties in catchment sources Basin source contributions >30% uncertainty Sub-catchment source contributions Gully density CV = 50–200% Input data improvements Gully mapping Vegetation cover Remediation response?

Model purpose Identify source processes and locations Assess their connectivity to downstream waterbodies Simulate the effect of planned management actions to set targets Evaluate the effectiveness of land management changes Modelling the effect of extreme events (eg bushfires) Load time-series for input to receiving water models (water quality and ecology models) Investigating climate change effects

Reef Rescue M&E Social & economic characteristics DEEDI, Science providers Land use & management Practices Regional bodies, industry Improvements in water quality DERM, science providers Subcatchment & end of catchment loads DERM Marine monitoring program GBRMPA, Science providers Plot / paddock models DERM, Regional bodies, science providers Catchment models DERM, science providers Receiving water models GBRMPA, science providers Water quality / ecosystem health GBRMPA, science providers Monitoring Modelling $2 - $3 million available ($1.2 million committed this year – Qld Govt) $2.5 million committed – Aust Govt Reporting & Evaluation Reporting & Evaluation Oversight: DPC Contributors: GBRMPA, DERM, industry, Regional bodies, science providers Coordination: TBA $0.25 – 0.5 million committed to reporting $0.9 million committed to design & set up – Aust Govt Cross regional analysis Contributors: TBA Coordination: TBA DERM: Department of Environment and Resource Management (formerly NRW & EPA) DEEDI: Department of Employment, Economic Development and Innovation (formerly DPI&F) GBRMPA: Great Barrier Reef Marine Park Authority

Options for modelling river load time-series Lumped statistical modelling of measured concentrations Sediment rating curves etc Distributed statistical modelling of measured concentrations EMSS, E2 Process modelling and disaggregation to daily SedNet Lumped statistical model WaterCAST daily process modelling By end 2010?

WaterCAST sediment model Hillslope erosion Gully erosion Streambank erosion Hillslope delivery Floodplain deposition Reservoir/ lake deposition River link Yield from upstream links Yield to downstream link Deposition/ re-suspension in channel

Model calibration Parameter estimation methods for automatically calibrating to observed water quality data Attempting to identify the response to practise change in a noisy climate-driven signal Wilkinson et al., 2009

Modelling resolution, timescale and complexity Adding complexity can reduce performance Process understanding Data available for parameterisation and evaluation Complexity increases at finer resolution and/or timescale e.g. water balance modelling (Grayson and Bloschl, 2000) (Jothityangkoon et al., 2001)

Model coupling issues Incorporating river load monitoring to improve modelling of the temporal dynamics Rating curve or statistical modelling (Kuhnert et al) Coastal fringe not well represented Estuarine trapping and remobilisation Fitzroy Tidal flows Load dependence on climate sequence Stochastic analysis? Command-line model control

References Grayson, R., Bloschl, G., Spatial modelling of catchment dynamics, Chapter 3 In: Grayson, R., Bloschl, G. (Eds.), Spatial patterns in catchment hydrology, Cambridge University Press (available at Jothityangkoon, C., Sivapalan, M., Farmer, D.L., Process controls on water balance variability in a large semi-arid catchment: downward approach to hydrological model development. Journal of Hydrology 254, Brodie, J., McKergow, L.A., Prosser, I.P., Furnas, M., Hughes, A.O., Hunter, H., Sources of sediment and nutrient exports to the Great Barrier Reef World Heritage Area. Report Number 03/11, Australian Centre for Tropical Freshwater Research, Townsville. Wilkinson, S., Henderson, A., Chen, Y., Sherman, B., SedNet User Guide, Version 2. Client Report, CSIRO Land and Water, Canberra. Wilkinson, S.N., Prosser, I.P., Rustomji, P., Read, A.M., Modelling and testing spatially distributed sediment budgets to relate erosion processes to suspended sediment yields. Environmental Modelling & Software 24, , doi: /j.envsoft