Prevention of the next potentially disastrous flood

After having to rebuild infrastructure again, and again, after big floods the Queensland State Government is now considering preventative measures.

Premier Campbell Newman has pledged to flood-proof parts of disaster-prone Queensland, by shifting suburbs to higher ground, raising highways, and building new levee banks.

Before taking this action further careful planning should be taken. While all these ideas have merit there are others that also should be seriously considered.

Furthermore, building new levee banks is not a good solution for many areas. It is disastrous when levee banks are broken or over-topped. The height has to be just right and who knows how high the next flood will be. Floods of 1893, 1841 and perhaps 1824 were higher than that in 2011. Furthermore, with global warming we can expect even bigger and more frequent floods than those.

Levee banks are probably unsuitable for the Brisbane River flood plain although they may possibly be useful in the Toowoomba region where conditions are different. Levee banks have failed in areas like New Orleans in USA, Northern Japan where they failed to stop the 2011 tsunami, and in China where hundreds of thousands of people have lost their lives when levee banks failed in the past.

More attention should have been made to flood-proofing after the 2011 floods. Instead much of the attention went on management and legalistic blame-finding in the control of Wivenhoe Dam. 753 submissions were made to the Flood Commission about what to do and very few of these have been followed up. There were several suggestions of merit that were totally overlooked. The least the Commission could do was to check out the merit of these concerning issues such as relief to Wivenhoe Dam (other than water level control), relief to the Brisbane River below the dam, and relief to the rainfall situation.

Relief to Wivenhoe dam can be effected by diversion of water below Somerset Dam to North Pine River. Another way is to divert water from Billies Crossing to North Pine River. Both of these involve tunnels. Further relief could be gained by extending Atkinson Dam to take overflow from Wivenhoe via a channel.

Diversion of water from below Somerset Dam to North Pine River

Reedy Ceek is just below Somerset Dam and extends east into Byron Creek. The D'Aguilar Range separates Reedy Creek from North Pine River. It is proposed to join Reedy Creek to North Pine River with a tunnel through the range terminating at a point near where Laceys Creek joins North Pine River. This gives a fall of about 10m over a distance of about 19 km which is enough slope for the water to run down. To get a greater head of water the tunnel could go about 3km further to a point below Lake Somerset dam. This greater head of water could allow for a shorter tunnel.

The positive aspect of this is that a considerable amount of water can be diverted from entering Wivenhoe Dam.

Negative aspects are that the tunnel is long and therefore costly, and that the water will be diverted into Lake Samsonvale and North Pine Dam. The North Pine waterway out through Petrie will need to be able to take a larger flow, and may need some modification.

Diversion of water from the Billies Crossing area to North Pine River

Like the above proposal this idea is to divert water easterly through a tunnel into North Pine River. Billies Crossing is on the easterly side of Lake Wivenhoe and about 8 km north of the dam wall. The exit for the tunnel will be near The Basin which is at the south-western corner of Lake Samsonvale. The distance is about 19km and the fall is roughly 30 m.

The positive aspect of this tunnel is that it directly drains Wivenhoe Dam and so has a bigger catchment than the Reedy Creek tunnel. It also has a greater fall.

The negative aspects are the same as for the Reedy Creek tunnel. It must be noted that the work for this proposal has been done from commercial contour maps. With more accurate surveying the tunnels may prove to be somewhat shorter. For Australia 19 km may seem to be a long tunnel but the World's longest is the Delaware Aqueduct in USA which is 137km long and it was built in 1945 for carrying water. The Epping to Chatswood rail tunnel in NSW is 13 km long.

Both tunnels divert water into North Pine River so care is needed not to overwhelm that river and cause a flood downstream. Timing and flow rates will need careful control.

Diversion of water into a renewed Lake Atkinson

This proposal is for a big extension of the Lake Atkinson Dam which will help alleviate flooding by itself. I do not have details as it was suggested by another geologist friend. His proposal was to enlarge the dam greatly by excavation. Once there is a bigger dam in place then some overflow from Wivenhoe Dam can be channelled into Atkinson Dam. The channel would be about 10km long.

Relief to the Brisbane River below the dam could involve a new dam on the Bremer River, a channel connecting the Brisbane River to the Logan River, straightening strategic parts of the Brisbane River, and deepening strategic parts of the Brisbane River.

A New Dam on the Bremer River

This will alleviate flooding to some extent. The main problem is finding a suitable place for it as the land is fairly flat. Western River joins the Bremer River near Lanefield south of Rosewood. This would require a dam about 4 km long and could interfere with the township of Rosewood. Mount Walker Lower is a possibility, and if that is not suitable then the Mount Walker area should be considered.

The advantages of such a dam are obvious. The land is not overpopulated except near Rosewood.

The only serious disadvantage is the flat nature of the country for a large dam.

Between Rosewood and Ipswich and west of Amberley airport is a large swampy area. Jeebropilly and Ebenezer open cut coal mines are in this area. My friend Evan suggested large scale excavation in this area. The coal, which is widespread in the area may be sub-economic at present but its value would help to pay for the excavation works, especially at the current price of coal. Coal extends out to Rosewood. The only problem with this might be increased bird life which could be a nuisance to the Amberley airport assuming that there are no proposals for it to be re-sited elsewhere.

Connecting Brisbane River to Logan River

Two possible routes for canals between the Brisbane River and the Logan River are being considered. More work is needed on this with better survey information than I have available at the moment.

The first to consider starts at Goodna on the Brisbane River and essentially goes south following a tributary for about 12 km then cuts across Oxley Creek and joins a tributary of the Logan River. Another possibility is to construct it just west near Round Mountain but it seems that the ground there is too hilly and would make for too much excavation.

The second route is from the bend in the Brisbane River at Fig Tree Pocket. This joins up with Oxley Creek for about 7 km then crosses over bare ground for about 4 km to join a tributary of the Logan River from Algester to Woodridge, then it goes into the Logan River.

The advantage of either of these connections is that it takes a load off the Brisbane River. The biggest disadvantage is that the extra load on the Logan River has to be addressed. Some work may be needed on the water-way between Logan and Beenleigh. Another disadvantage is that in the longest alternative there is about 10 km of new ground to be cut and the river tributaries and creeks will need to be deepened. Furthermore, it is yet to be demonstrated that there is enough slope for the canals to operate efficiently. The Fig Tree Pocket connection will give only partial relief to localities up stream such as Jindalee.

Straightening the Brisbane River

This may not be popular with people at certain locations along the river. Straightening the river will allow it to flow faster. When the water gets away more quickly there is less flooding. Of course, much depends on the tides as well. To maintain the beauty of the river the canals for shortening the river could be gated so that the shortening could be controlled time-wise.

Canals for shortening could be at:

• The Oxley Creek junction with the Brisbane River, near Lake Manchester, to the north-west;
• Across Kholo Road;
• Across the end of Somerville Road, Karalee;
• Across Priors Pocket;
• Graceville to Fig Tree Pocket;
• Across Long Pocket;
• Vulture Street to Dutton Park; and
• Kangaroo Point.

It must be noted that the Brisbane River is an entrenched river and was a canyon during the last Ice Age. Unlike normal meandering rivers it has cut deeply through some tough rock (when the sea level fell). Putting canals across some parts of the river could be an expensive business from the engineering point of view.

At Kangaroo point, for example, the banks are high so it would probably be better to put a short tunnel across it than a canal. This would alleviate the need to put a bridge over the canal.

A full study needs to be made to access the relative value of straightening the river in alleviating floods.

Deepening the Brisbane River

The river would run faster if it were deeper. This would help reduce flooding to some extent depending on the tides. When the river was a canyon 12,000 years ago it was about 30m deep. It has since been filling up with sand, silt and mud. Until recently the river was dredged for its sand resources. This has been stopped as it was thought it was muddying the river. It used to be a beautiful clear river in Aboriginal times. There is some doubt now that dredging is the main cause of the opacity of the river. It seems that other factors are more important.

Dredging will help the flow of the river if the dredging is done in the right places. As with straightening the river, we do not know if dredging in the right places will have a major or minor effect. This awaits further study.

The flood potential would also be reduced if the river was widened. This would apply particularly at certain localities where constrictions occur. Any building that constricts the flow should be removed. It exacerbates flooding and is at risk itself.

Relief to the rainfall situation involves a unique suggestion that I made involving the use cloud seeding to prevent the rain reaching the Brisbane catchment area in flood seasons. This should work very well when cloud seeding can be carried out over the sea. Many people do not realise that cloud seeding works, despite having a shaky early history.

Cloud seeding is normally done to bring rainfall to certain areas. The concept here is to use it for keeping rain away from a given area. The usual problem about whether or not the cloud has the potential to rain does not apply here as the cloud is expected to rain anyway. Seeding in this case is to control the time and hence the place of rainfall. Although this is a new concept it is hard to see why heavy rain clouds should not be easier to precipitate than milder clouds in more barren areas.

Cloud seeding has been used successfully in Tasmania since the 1960s where catchment in the dam increased by 30%. "Warm cloud" seeding experiments have also been conducted in Queensland by the Australian Bureau of Meteorology. It is used also used in the Snowy Mountains to precipitate snow.

Furthermore, it also was used at the Beijing Olympics to keep Beijing dry during a rainy season, and it worked. It has also been used in Jakarta late last month to prevent further flooding after 50,000 people were made homeless and early results suggest it has had some success (http://www.abc.net.au/rural/news/content/201301/s3678824.htm).

The only problem with this concept is that it needs proving and can only be really tested in a rainy season.

In conclusion there is no single solution to flooding and several measures should be used together. It is hoped that the government will take note of at least some of the 753 suggestions made to the Commission in 2011 and take account of levee banks that have failed in various parts of the world.

Further study is obviously needed and some ideas may be modified. I would like to see at least one measure for diverting water from Wivenhoe Dam, at least one measure for controlling the Brisbane River flow, and some serious research into cloud seeding to prevent unwanted rainfall over the Brisbane region. I believe the building of new dams is already being investigated.