A dam story in pictures

(Two dams in actuality)

On a 4.4Ha block alongside a country road this wetland and watercourse was changed to construct two dams.

There is a certain amount of consternation from downstream residents as to the effects that these dams may have on the watercourse that used to flow freely through the block. It has now been dammed across with water now being released from the dams to be fed downstream through this culvert pipe.

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The main culvert pipe (outside the property with the dams) that delivers most of the water into the watercourse that runs through residents’ properties downstream.

The series of images following were taken from outside the property about this time last year or a little later as the dams were being constructed. The first sequence was taken from the road adjoining the property to the east and then went onto a private road thus semi-circling the property.

The second sequence was taken the next morning from slightly different vantage points.

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Here are the first ten images taken from along the main road.

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This second sequence starts from the road (first two images of this group) and then the images are taken from a private roadway.

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These eight images are the last taken on the first day. This one shows the donga opposite a Rural Residential area with new houses.

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These two images are the start of a group of photos taken the next day. The first is taken from a sealed road from an adjoining property showing its dam built many years back.  The second shows the main road (note the power lines) across to the hills looking approximately east.

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These photos show more of the northern end of the property looking from the western side. There is a dam wall visible in the centre of the image to the left, probably it is the upper dam wall.

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The crepe myrtle in full flower on an adjoining property indicates the pictures were taken around a year ago, i.e. in mid-late February or March. The water shown near the blackboys is likely to be from an upstream neighbour. The final photo in this series looks across a dam in the neighbour’s property which is to the west of the property of interest.

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This aerial photo was taken on 19 February 2017 which is around the time that the ground photos were taken, probably prior because there is little sign of dam walls. There appear to be two pieces of yellow earth-moving equipment near top. The block is triangular with the long side parallel to the road.

All in all there have been dramatic changes made to this piece of land that was once a wetland with a stream flowing through.

Sudden heavy rain and flooding

Not only bushfire, but another threat to safety

Late in November 2017 I had been doing research about rainfall events and the effects on water flow of the stream at our place. I’ve been recording rainfall most days in a garden diary since buying here in early 2006 as well as temperatures. Sometimes heavy rains have coincided with photos of the stream and the flows.
Generally we have noticed over the 12 years we’ve been here that the catchment is very responsive. Some heavy rain will be followed within a few hours by a rise in the level of the stream. A real cloudburst, say of 20 mm in an hour will show up within a short time of a few hours. This is not the effect of spring water, it is surface water flowing down hillsides and into the stream.
On Saturday, 7 September 2013, the day of a Federal election, I spent the morning at the Balingup Primary School handing out electoral material. Late morning large clouds gathered and we had a torrential downpour that lasted maybe an hour or so. When I returned home by about 1 pm I checked out the stream once the rain had stopped. It was running at the highest I have seen it, with water being almost over the bridge.

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In this flash flood after heavy rain, the level was about 1m above the usual level. It was lapping up to the bridge. A few minutes before it was even higher.

See first photo, taken at 1.23 pm. The second photo shows water roaring out of two medium sized pipes.

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Water was also pouring out from two other points, namely via the spillway under the bridge, and a channel nearer the hillside that goes under the track to the hill. See third and fourth photos for the latter. See how gravel has started to be washed off the track and down its sides. Water can be very destructive when it floods.

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Then from near the bridge I videod the scene, taken at 1.26 pm. The level had been even higher, it had gone over the track leading up the hill. Note the rather worried-looking dog, Joanna, who wasn’t very happy about the flood.

With the video, note the sheer volume of water going through, it pushed a wooden platform/deck into the stream, so it has power.


I checked today with one of our farming neighbours as to whether this sudden rise of at least a metre within an hour or so of the downpour might be due to a dam release. She was adamant that upstream from them the owners did not do dam releases to any extent, the flow was due to water streaming down off the hillsides of surrounding farms and hurtling down to the course of the stream and the wetland now known as 155 Grimwade Road.My 2013 diary tells me that at 9 am the next day 28 mm had fallen in the previous 24 hours. From memory nearly all the rain fell over the short period about noon on Saturday.

Are short, heavy showers frequent here in Balingup that could cause this sort of stream rise? On 10 February this year 24 mm was in the gauge at 9 am, followed by 14 mm the next day. On 20 July there was 29.5 mm in the gauge at 9 am. This small sample shows we can get heavy showers in a short timeframe.

Conclusion: with a heavy downpour now and only the overflow pipes in the dams newly built upstream from us, with a pipe needing to be manually opened by opening a valve to let water come out from the bottom of the dam and the small side pipe to cope with the flow, the water could potentially go over the top of the dam. The water in the dams is quite near the crests, much higher than that recommended by dam experts which is to have a gap (the freeboard) of at least 600mm, better 1 m, from the water level to the crest. If water does go over the crest, erosion can bring about a breach to the dam.
It may also be too much for the new culvert pipe under the track to the farming neighbours and cut off the two farms west of the new dams.

Dams need to be engineered for purpose, taking into account likely weather events, eg heavy showers in a short time-frame. Expert advice is needed to build dams that are structurally sound and will not risk the safety of neighbours either up- or down-stream. Perhaps more standardised rules and regulations are needed in this area to reduce risk of dam failure.

As for us downstream, how would we fare if the new dams breached after heavy rain??

Lower Dam, 28 November, 2017.  IMG_7003

Lower Dam showing water level near the top of the dam walls. It is recommended that freeboard (the distance between the water level and the top of the dam walls) be at a minimum of 600 mm, better, 1 m.