WaterCAST sediment and nutrient modelling

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

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

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

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

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

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

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

8. 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?

9. 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

10. $2 - $3 million available ($1.2 million committed this year – Qld Govt) $2.5 million committed – Aust Govt $2 - $3 million available Social & economic characteristics DEEDI, Science providers Monitoring 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 Modelling Cross regional analysis Contributors: TBA Coordination: TBA Reporting & Evaluation Oversight: DPC Contributors: GBRMPA, DERM, industry, Regional bodies, science providers Coordination: TBA Reporting & Evaluation $0.25 – 0.5 million committed to reporting $0.9 million committed to design & set up – Aust Govt 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 Reef Rescue M&E

11. 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?

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

13. 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

14. 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)

15. 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

16. References • Grayson, R., Bloschl, G., 2000. Spatial modelling of catchment dynamics, Chapter 3 In: Grayson, R., Bloschl, G. (Eds.), Spatial patterns in catchment hydrology, Cambridge University Press (available at www.hydro.tuwien.ac.at/publications/hydrol-proc.html),51-81. • Jothityangkoon, C., Sivapalan, M., Farmer, D.L., 2001. Process controls on water balance variability in a large semi-arid catchment: downward approach to hydrological model development. Journal of Hydrology 254, 174-198. • Brodie, J., McKergow, L.A., Prosser, I.P., Furnas, M., Hughes, A.O., Hunter, H., 2003. 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. www.actfr.jcu.edu.au/reports/2003/index.htm. • Wilkinson, S., Henderson, A., Chen, Y., Sherman, B., 2004. SedNet User Guide, Version 2. Client Report, CSIRO Land and Water, Canberra. www.toolkit.net.au/sednet. • Wilkinson, S.N., Prosser, I.P., Rustomji, P., Read, A.M., 2009. Modelling and testing spatially distributed sediment budgets to relate erosion processes to suspended sediment yields. Environmental Modelling & Software 24, 489-501, doi: 10.1016/j.envsoft.2008.09.006.