PERTH residents should place the benefits of reducing the huge environmental problem of salinity above the costs of diverting saline water to the ocean through the Swan River, US drainage expert Wayne Scaggs said.
Mr Scaggs was the keynote speaker at the Salinity Engineering Conference held in Perth last week and is a University of North Carolina professor and a member of the US Drainage Hall of Fame.
He said any project to lower water tables, whether to stop salinity or waterlogging, required a good outlet to drain into.
He said mismanagement in the San Joaquin Valley had led to the closure of one of the biggest drainage districts in the US.
Drainage water was diverted into the Kesterton Reservoir because the ocean was not a viable option, but this caused a build-up of selenium and other elements that led to water fowl deaths and huge litigation.
"The take-home message here is not that evaporation basins won't work, but to start with a good outlet first then work out the rest," Mr Scaggs said.
He said it was important to know exactly what was going into an evaporation basin and whether it could be safely held.
The ocean remained the best possible outlet for drainage water, but this was an expensive option.
Mr Scaggs said WA people should be supportive if diverting drainage water through the Avon and Swan Rivers was decided to be the most effective solution for Wheatbelt salinity.
"If I was living in Perth my concern would not be that this water was coming into my river, but that it could help get rid of a huge environmental problem," he said.
"If you don't do anything, you're going to have a situation where the environmental consequences are unacceptable."
Mr Scaggs said the bulk of global drainage was in irrigated areas, and the dryland salinity challenge facing WA was unlike anything in the world.
"It's not a problem you can import a strategy for because it's not been experienced on this scale anywhere else - it's very exciting from a researcher's point of view but very frustrating for farmers and the community.
"I suggest using all the tools available, and that includes drainage both deep and shallow, surface water management, groundwater pumping - all these things should be done if you hope to succeed."
Mr Scaggs said some WA people were convinced if they drained in the middle of valleys, with a good outlet, they would succeed, while others suggested more lateral drainage, which would be dependent on the hydrological conductivity of the particular soils.
"In very general terms some of your soils might respond very well to a single ditch or a few ditches several hundred metres apart, while others might need them much closer together," he said.
Mr Scaggs said agriculture as we know it would not be possible without drainage - but the focus of engineers in recent years had changed from maximising yields and profits to minimising environmental impacts.