He set about putting up small “leaky weirs” of rock, concrete and timber so the stream, instead of running straight through the property, “stepped” down through it in a series of ponds. At the head of each pond, particularly the first one, Andrews planted reeds.

Reeds provide several mechanical functions.

Their roots and litter build up the stream bed, spreading and slowing water and ponding it upstream.

They strain out debris and sediment. Before it reaches Andrews’s research site at “Tarwyn Park”, the stream runs through an unfenced bare gully visited by cattle—but the water in the ponds downstream of the reeds is perfectly clear.

A wall of 2-3 metre high phragmites can slow the progress of minor floods, but are flexible enough to withstand the power of major floods.

Under the Andrews/Marshall system, when floodwaters hit the pools or billabongs banked up behind leaky weirs, they lose some of their force as they encounter another body of water. If the pond isn’t too deep between stream banks, the flood is forced out onto the floodplain, where much of its remaining destructive power is dissipated.

As the waters spread and slow, soil and debris drops out, feeding the plain with nutrient.

But reeds are only part of Andrews’s (and Marshall’s) story.

Immediately before and after “Tarwyn Park”, the gully that carries the stream is deep, the water flowing a metre lower than the surrounding paddocks. Not so on the property. Because of the leaky weirs, the stream water level here is only slightly below the top of the streambank.

On “Tarwyn Park”, as with every natural waterway on a floodplain, the stream tracks through an elevated bed of sediment it has deposited over hundreds of years. The stream is therefore the highest point of the plain.

Because Andrews has lifted the water level with his leaky weirs, that means that the water is also higher than much of the plain.

What Andrews proved at “Tarwyn Park” is when the stream level is kept high relative to the floodplain, water can gravity-feed from the stream out to the edges of the plain, creating an underground reservoir of water.

After 1994, I visited “Tarwyn Park” again in 2002 and 2008, when the rest of Bylong not under an irrigation sprinkler was dry and dusty.

Both times there was rich green feed on the “Tarwyn Park” floodplains, and not an irrigation sprinkler in sight. The pasture was being irrigated from beneath, from an evaporation-proof storage in the soil.

Andrews reckons that millions of litres of water are banked in the soils of “Tarwyn Park”. In dry times, as the stream level falls, some of that water socked away in the soil runs back into the stream, keeping it running constantly through the driest summers—even though it might be dry upstream.

The stream on the Marshall property shows similar resilience in drought, to the benefit of not only the Marshalls but of those downstream.

There is far more to the ideas and engineering of Andrews and Marshall than just charging in and damming waterways (please folks, don’t do this at home!) but that’s not the purpose of this post.

We’re just considering one principle, that of the “leaky weir”, the bank of rocks, timber or reeds, or a beaver dam, that banks up water without forming a complete barrier to flow.

In Canada, leaky weirs form lakes. In Australia, properly designed, they form ponds or billabongs, and if conditions are suitable, fill the surrounding soil profile chock-full of evaporation-proof moisture.

On my 2002 visit to Andrews, he said the Murray-Darling Basin would be “stuffed” if a massive effort wasn’t made to hold water back up in the catchments so it could feed through in dry times.

Andrews is a man of bold statements, so I didn’t pay much attention at the time. I’m paying attention now.

What would have resulted, I wonder, if at every suitable point on every minor tributary of the Murray-Darling catchments, leaky weirs had been installed in the 1990s?

Presumably, the millions of megalitres of water that might have been stored in ponds and soil would still be contributing to the Murray’s now-faltering flow.

It would be no replacement for big general rains, but the river and its tributaries—and the wildlife, farms and towns that depend on them—could be in much better shape.

(In a similar vein, what might be the effect of increasing soil health away from the streams? In his Masters degree, northern NSW farm manager Glenn Morris calculated that because humus can hold four times its weight in moisture, increasing humus levels by two per cent across the Murray River catchment alone would increase the catchment’s water-storage capacity by 34 million megalitres.)

Out of curiosity, I consulted Charles Sturt’s account of his explorations along the Macquarie, Murrumbidgee and Murray rivers from 1828-1830. He mentions “reeds” 132 times (and “natives” 389 times).

These rivers are too big to enable the reed-bed leaky weirs that Andrews believes were common on smaller waterways, but reeds still tamed and filtered the flow.

Remarking that near its junction with the Murrumbidgee, the Murray river valley was at least four miles (6.4 km) across, Sturt wrote:

“It is to be remarked, that the bottom of the valley is extremely level, and extensively covered with reeds. From the latter circumstance, one would be led to infer that these flats are subject to overflow, and no doubt can exist as to the fact of their being, at least partially, if not wholly, under water at times.”

On the Macquarie, Sturt lived in apprehension of his expedition getting lost among the “huge belts of reeds that appeared to extend as far as the the eye could reach”.

There is no magic bullet for the problems of the Murray region, particularly if it doesn’t rain.

But while we wrangle about State water rights and dam releases, we might also consider the role of Australia’s beaver, the reed, and all that it can represent in mitigating future disaster.

(10.04.09: edited for clarity)