What are Emerson class numbers?

Answer 1

Soil dispersion potential is the likelihood that soils will release a cloud of fine clay particles when brought into contact with water. These clay particles may remain suspended for an indefinite period of time, resulting in turbid, 'dirty' water, which can impact on plant and animal life in and around our waterways and in Moreton Bay. Scientific studies focussing upon the health of the Brisbane River and Moreton Bay have demonstrated that sedimentation of these particles is threatening seagrass meadows in the Bay, with corresponding impacts on Bay ecology and specific species such as dugong, green sea turtles and fisheries. Note that soil dispersion can occur without the influence of slope, mechanical action or run-off velocity, ie. in 'still water', so it is imperative that run-off from dispersive soils is retained and treated on-site wherever practicable (even on smaller sites), before release into the natural or constructed stormwater system. Soil dispersion potential is measured as the Emerson Class number (a simple semi-quantitative dispersion test), which considers soil consistency, depth, and in some cases established soil electro-chemical data. Note that weathered parent rock substrates can show dispersive tendencies also. Dispersive soils usually contain significant amounts of clay, with at least moderate levels of chemically exchangeable Sodium, if they are not buffered by salinity.