Large parts of the irrigation areas of the Murray Darling Basin have shallow watertables that
threaten crop productivity and financial sustainability of irrigated agriculture due to soil
salinisation and waterlogging.
Planning for environmentally sustainable and economically viable management of these
problems requires the development, testing and application of mathematical models which can
integrate our understanding of water and salt movement with economic assessment of
different cropping decisions at a farm scale.
These mathematical models can help in proper selection of agronomic and engineering
options to reduce recharge to aquifers and rise of watertables and thereby minimise
waterlogging and salinity problems.
This paper gives mathematical details and sample applications of SWAGMAN (Salt Water
and Groundwater Management) Farm, a farm scale hydrologic economic model that integrates
agronomic, climatic, irrigation, hydrogeological and economic aspects of irrigated agriculture.
Optimum land uses for a given farm are determined by optimising an economic objective
function using mixed integer non-linear optimisation techniques.
SWAGMAN-Farm has been applied to several farms in irrigated areas of southeast Australia.
Model results show that for given hydro-climatic and irrigation conditions some land use
types result in overall discharge from soil and groundwater while others induce groundwater
recharge: a proper selection of crops can help reduce waterlogging and salinity problems and
ensure economic viability of farms.