CONTROLLING WATER FLOW

Our farm at Glen Aplin is blessed with both a river frontage and an area which was a swampy flood plain when we bought the property in 1992. That swampy area had an eroded gully, was over grown with tussock grass and thistles, and also dotted with deep holes.  It was infested with blackberry brambles, riddled with rabbit warrens and I hardly ventured to enter the area for fear of snakes. When I saw my little Jack Russell Terrier dog fall into one of the steep sided holes filled with water and that he couldn’t get out without assistance, I decided something must be done. Eberhard, is almost pedantic about tidiness, so the sight of this wild area affronted him and neither of us thought it gave a pleasant outlook for our Das Helwig Haus B&B guests.

With the assistance of neighbours we burned off the tussock grass and brambles. We employed a contractor with a grader to level the region, filling in all the holes, but still leaving the eroded gully. Then we went to the Queensland Department of Primary Industries and paid for a water engineer to design two dams with a connecting water course and an overflow towards the river. In 1996 contractors were hired to undertake this work. No sooner were the earthworks completed and before they could move their machinery off our land a week of steady summer rain filled our dams and river to overflowing. To illustrate what happened I will used photographs taken in 2008.

Flood entry

The Stanthorpe Shire Council built three of these culverts which channel flood water under Mt. Stirling Road and into our first dam.

By 2008 the trees that I had planted along the channels and behind the largest dams were well established. The channels from the road carried the flood water into our first small dam, constructed as a horseshoe shaped pond.

Overflowing dam

When the dam was full the water flowed out in a broad shallow channel. The next photo shows this channel as it now is, in a period of drought.

Spillway

The water then rushed down the shallow watercourse we had created to replace the eroded gully, carrying the flow to the larger dam.

Flood in channel

Note the drop in this photo. Because that first flood came immediately after the shallow channel was constructed and before we could get grass planted to hold the soil, erosion occurred cutting the channel once more into a gully configuration. It eroded back creating what Peter Andrews calls a headwall. I quote from Back from the Brink. Water dropping over a low rise will start to create a hole below. As more water falls, the hole grows deeper, which means that water falls further and has more energy, which in turn means that the growth of the hole accelerates. A headwall erosion of a creek bed always begins this way.

Headwall drop

The flood water rushes down this channel until the channel turns left where the water begins to spill over between willow trees onto the grassed flood plain on the right.

Flooding over the banks

The entry to the dam is shallow and narrow, as the water engineers wanted most of the water to pass by the dam. Any farmer would wonder why they are constructing a dam only to have most of the water bypass it.

Dam entrance

We discovered that following heavy rain there was such a torrent of water rushing down off the hard high country of Mt. Stirling and beyond, the engineers were wise in designing a flood plain immediately behind the wall of the dam. As this was already grassed at the time the dam was constructed no erosion occurred as the water sheeted across this area.

Broad overflow

This is the richest soil now on our land as the grass catches silt and other nutrients as the water flows across the wide space between our land and boundary fence. The cultivated fields beyond the boundary fence are portion of the farm owned by our Cannavo neighbours.

Geese feed on green grass

Even when apparently dry, this land will have water moving slowly beneath the surface. It stays green twelve months of the year.

Another channel

Just below this flat area two small eroded gullies cut into our land under the boundary fence drain water from the Cannavo farm and create another headwall into which our sheeting water spills. I’ve prevented further erosion of this area by allowing tall rushes to grow and dissipate the energy of the rushing water on its final journey to the river. Should the river be in flood prior to our land flooding, the river water will back-flow up this channel maintaining the same level as the flooded river.

Although the engineers had planned to have a large volume of water flow past the dam, we found that so much water entered the dam that it rose above what had been planned as the high-water mark and spilled over at the far corner. This spilling water then found its way behind the end wall of the dam and over a grassy meadow before reaching the main water channel. Running down this steep bank, it started to erode cuttings into the edge. I tell the tale in my book Wildflowers, wilderness and wine of how I had another wide and shallow spillway created at that end of the dam to carry excess water in a separate stream to the river.

Last spillway

We broadcast grass seed into the dry dust of this spillway and were able to establish a grass cover before the next flood.

Full and overflowing dam

Geese enjoy floodwater

The above photo shows the new, grassed spillway carrying off excess water from the overfilled dam during a flood. When the flood ends and the water in the stream steadies to a normal pace, the level of water in the dam drops to the planned high-water mark and stays at that level until the stream no longer flows. This flow in a good wet season may continue for six months continuing to spread out across the grassed flood plain behind the dam. In my next post I will explain how Peter Andrews believes such flows can be sustained and erosion corrected. As the subtitle of Back from the Brink says, Australia’s landscape can be saved.  See www.sustainableinsight.com.au

Book cover

Das Helwig Haus B&B owned by Eberhard and Fay Helwig is situated at Glen Aplin, near Stanthorpe on the Granite Belt of southern Queensland, Australia.

This is a region noted for Australian wildflowers, four wilderness National Parks and sixty wineries. In 1997 Eberhard and Fay established the Remembrance Field of red Flanders poppies, a European wildflower.

To obtain Fay’s book Wildflowers, wilderness and wine email Fay on helwig@halenet.com.au

Internationally it is available on the Amazon.com website.  http://www.amazon.com/gp/product/B002ACXQ0M/sr=8-1/qid=1244294755/ref=olp_product_details?ie=UTF8&me=&qid=1244294755&sr=8-1&seller=

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