MASSIVE floodplain harvesting by Queensland and NSW irrigators is a scandal of tragic proportions.

Queensland irrigators diverted a record volume of water out of the Murray Darling Basin in the midst of the worst drought on record.

That should make their counterparts downstream very angry indeed.

Queenslanders diverted 1.014 million megalitres from the Darling catchment in 2007-08, with the bulk stored in private irrigation dams.

The previous record was 910,000 megalitres in 2003-04.

As Victorian Farmers Federation Water Council chairman Richard Anderson rightly argues - it makes a joke of the term "sharing" the basin flows.

Queenslanders inevitably roll out the argument that they only harvest 5 per cent of the basin's yields.

But in a drought year like this, 1.014 million megalitres is a dam sight more than 5 per cent of what's available in the basin.

The Queensland Government has long mounted the argument that it needs a chance to develop its share of the resource, following the signing of the Murray Darling Basin cap agreement in 1995.

Victoria, NSW and South Australia governments cut Queensland some slack, with the Sunshine state agreeing to establish draft Water Allocation and management Plans by 1998.

But a decade after the deadline was set, Queensland has still not finalised its resource operation plans.

In the meantime, the cowboys of the Queensland irrigation industry jumped on their bulldozers and tripled the capacity of their on-farm dams, from 535,000 megalitres in 1995 to 1.87 million megalitres in 2002.

What should also worry southern basin irrigators and their communities is that northern NSW irrigators also boosted their private dam capacity, despite their government signing on to the cap in 1995.

In NSW, private dam capacity has grown by 330,000 megalitres since 1995 to 1.33 million megalitres

Together NSW and Queensland irrigators now have at least 3.208 million megalitres of storage capacity on their farms, with most of them holding less than 40 per cent of their capacity.

Even if it buckets down in the north again this summer don't expect to see a flood of water flowing down the Darling into the Murray River at Wentworth.

In fact, the NSW Government's failure to monitor and regulate floodplain harvesting means no one knows exactly how much of this water will be harvested in any one year.

The NSW Government has implemented a floodplain management plan, but has no idea of what's out there and is considering grandfathering all diversion structures constructed since 1995.

Floodplain harvesting gives NSW and Queensland irrigators a powerful avenue to maximise the efficiency of their dams.

NSW irrigators in the Darling basin have two means of harvesting water.

Firstly, they can pump direct from a river or stream, under licence, based on river heights reaching defined trigger points. Many of these irrigators have annual volume limits on what they can take. But if they don't reach that limit this season they can add the shortfall to next year's limit.

Secondly, many NSW and Queensland irrigators engage in floodplain harvesting, which entails building an array of diversion banks and channels across the floodplain to capture flood water and divert it to their ring tank dams.

In many cases these diversion channels act as massive storages in their own right.

The floodplain diversions are neither monitored nor regulated by the NSW Government.

In fact, the NSW Government has relied on legislation derived from English law, which has made no mention of floodplain harvesting for most of the past century to manage the basin.

The other aspect of these ring tank dam developments that should worry all irrigators is the evaporation losses they incur each season, which are in the range of 1.8 to 2m.

Most dams are just 2-3 metres deep, meaning they lose more than half their volume in evaporation each season.

Any sane person looking at this issue would conclude the only real means of controlling these diversions is to meter all these private dams.

The MDB is engaged in a trial at the moment metering a handful of private dams.

But the Federal Government should accelerate this program, to protect the resource.

The big question is whether Federal Water Minister Penny Wong has the power and persistence to insist on the NSW and Queensland Governments metering these dams.

The Commonwealth could phase in metering, starting with all dams with a capacity greater than 100 megalitres.

Given the power of metering technology today it would be possible to automatically read these meters, with random audits used as a back-up.

As Prof Richard Kingsford argues, when the Murray Darling Basin Cap was implemented "floodplains went missing".

It's time we brought the floodplain and the Darling's diversions back under a far more rigorous cap.