Modelling catchment erosion, sediment and nutrient transport in large basins.

A framework is proposed here to model catchment erosion, suspended sediment and phosphorus transport. It consists of two major components: an upland catchment model and an in-stream model. The upland model simulates streamflow (Q), suspended sediment (SS) and associated phosphorus (P) using rainfall data, and is calibrated to daily streamflow time series under historic conditions. Empirical relations are used to derive SS from P and Q. The in-stream model routes Q, SS and P from teh outlet of upland catchments or in-stream nodes to nodes downstream. The upland conceptual rainfall-runoff model is parametrically efficient and very effective in predicting streamflow. The in-stream transport model can infer sources (resuspension and bank erosion) and sinks (settling) within a reach. Aerial photographs are used to assess the on-site effects of climate and land cover/use on erosion and the drainage network. Changes in land cover/use and the effects on the drainage network are related to the parameters in the rainfall-runoff model so that associated effects on Q (and hence SS and P) can be assessed. This modelling framework is being prototyped on the Namoi Basin ni northern New South Wales, Australia and in the Ping Basin, Northern Thailand.

Figure 21.3: Modelling framework for upland catchments