Open Cut » Environment
The project aimed to develop a user friendly catchment/landscape based erosion model, based on the existing hillslope model MINErosion 3.01; a standalone database of soil and spoil physical and chemical properties that can be used with the erosion model as well as for other purposes and a standalone climate database of rainfall erosivity and its spatial and temporal variation for the entire Bowen basin that can be used for the erosion model and for other purposes.
MINErosion 3.01, which was written in Visual Basic v 5, was updated, upgraded and rewritten as MINErosion 3.1 using the current version of Visual Basic 8 and successfully validated for event based erosion using data collected from erosion plots during ACARP projects C1629, C4011 and C10037. The imbedded soils database was expanded with the inclusion of multiple samples from 6 mine sites. MINErosion 3.1 is a standalone hillslope model to determine suitable combinations of slope gradient, length and vegetation cover needed to control erosion to acceptable levels and can be used to assist in the design of the post-mining landscape.
A user friendly Catchment/landscape model MINErosion4.1 was developed to operate as a raster grid cell based concept. It links MINErosion 3.1 with the ESRI ArcGIS 9 which was used to divide the catchment/landscape into a series of raster grid cells and to calculate the relevant catchment hydrological parameters. Each grid cell is then tagged with the values of slope, water flow directions, flow accumulation, soil characteristics as well as vegetation cover. MINErosion 3.1 procedures are then applied to each grid cell to calculate the amount of soil erosion; however, as MINErosion 3.1 is applicable to simple hillslopes, it predicts the net erosion from that hillslope. As slopes may change between the grid cells, a deposition routine was developed to determine whether sediment is to be deposited or simply routed and moved to the next grid cell. The sediment carried by the flow is then routed in the direction of the catchment outlet. Outputs from MINErosion 4.1 are event erosion rates, sediment deposition rates and annual erosion rates for each raster cell and these are presented as maps using Arc GIS. Offsite sediment and water discharges from catchments can be determined from the rasters that makes up the catchment outlets. Other GIS programs can be used, but at this stage they are not automated and needs to be handled manually.
As MINErosion 4.1 is a landscape based model, it should be able to address the effect of spatial variability of soil/spoil characteristic on potential erosion. Composite samples (consisting of 3 to 5 subsamples) were collected from 6 to 8 sites across the mine site that are considered as sufficiently different materials. Samples were collected from 6 mine sites and a total of 97 samples were analyzed for physical and chemical properties using the same methods that was used to develop the soil database for MINErosion 3.01. These samples are now included in the soils database for both MINErosion 3.1 and 4.1 and consist of a total of 133 soil and spoils from 17 mine sites. In the future, if other mine sites are interested in the variability of potential erosion across their mine sites, they can conduct similar sampling and analysis and add these to the current database.
A stand alone soil/spoil database was developed by combining the erosion database and other relevant soil and spoil data that were published in ACARP reports or made available by mine sites. These were samples from project C12031 and from a BHP survey of the Liskeard project area.
An erosivity database for Central Queensland was developed based on previous work on Australian rainfall erosivities. This work was conducted using daily rainfall records from 75 sites across Central Queensland and generated detailed maps of rainfall erosivities for various Annual Recurrence Intervals as well as annual erosivities with a spatial resolution of 5 km x 5 km.