Submission to the Senate Committee on:

Management of the Inland Rail project by the Australian Rail Track Corporation and the Commonwealth Government

From: The Soil Conservation Group. Date: 11th November 2019

Re: Floodplain crossings,

We, a group of mainly ex-Queensland Government soil conservationists, would like to provide comment with regard to your committee’s terms of reference of route planning and selection process as well as engagement on route alignment, relating to the proposed route across the Condamine , Macintyre River (and other) floodplain(s).

In summary we argue that: • As a matter of good land use and management along with best use of agricultural land, floodplains should be avoided for a project like this if possible. • If alternate routes are not feasible, effective consultation with all stakeholders who have roles to play in the implementation of good floodplain management is required so that a shared committed approach is developed. • Flows on floodplains should be as shallow and slow as possible to minimise soil erosion risk i.e. spread as much as possible. Any infrastructure on floodplains should be designed to accommodate this principle. If infrastructure must be above flood levels, viaducts spanning entire floodplains are an appropriate means of satisfying this requirement. • Regardless of the method used to traverse the floodplain(s), ongoing maintenance of structures and their surrounds to minimise flow concentrations with resultant soil erosion and siltation is essential.

Members of our group have (collectively) many years’ experience solving soil erosion issues on the Darling Downs uplands and floodplains, including those associated with transport infrastructure. This experience has shown us the wisdom of prevention rather than cure - it can take years to rehabilitate and heal erosion scars (if at all) after a single major erosion event. As well, the eroded soil is deposited elsewhere, creating another set of problems such as siltation and flow diversion.

Taking the rail line across floodplains, and in particular, the Condamine River and Macintyre River floodplains, could, if not appropriately designed, constructed and maintained, create many soil erosion issues that could be difficult and expensive to control both on and off site. Once started, controlling soil erosion on floodplains can be difficult, not only from a technical aspect but also from a social point of view. A co-ordinated approach between all affected landholders is required as what one landholder does often has a cascading impact on downstream landholders.

Thus, it is essential, in developing actions to minimise any soil erosion risk, a two-way inclusive active participation process be used. The Soil Conservation Services Branch of the former Queensland Government Department of Natural Resources (QDNR) successfully used this approach when developing a flow management plan for the floodplain of the Upper Condamine floodplain (UCF). During the consultation phase of the UCF project, many factors that influence overland flow and stream flow were identified. Some of these are: direction of cultivating farm land and alignment of standing crops, presence and alignment of fences, plough banks, rank grass growth, infrastructure such as roads and railways (alignment, height and cross drainage facilities), and infrastructure (head ditches, tail drains, ring dams and the like). This information was collated into a publication outlining management practices to minimise soil erosion on floodplains (QDNR, 1999).

One learning that came out of the UCF project and other observations was that it is best to keep flows as spread and shallow as possible – any concentration of flows resulted in soil erosion, loss of crops and productivity, siltation of roads and so on. As a consequence, Local Governments and the Main Roads Department redesigned and built roads on floodplains to have a low profile to allow maximum spread of flows with consequent low flow velocities.

It is recommended in the Yelarbon to Gowrie Corridor Options Report, (AECOM, 2017), that flow velocities on floodplains be no more than 1m/s – their modelling shows, for the events they reported, the estimated peak velocities in the Condamine River floodplain to be mostly less than 1m/s. This is probably satisfactory for the cracking black clay soil present on the Condamine floodplain provided it has a well anchored vegetative cover. The report goes on to say that drainage will be designed to ensure that velocity of flows be maintained at existing level. However, that report also recommends that the outlet velocities of culvert discharges be kept below 2.5m/s – it does not differentiate between pipe and box culverts but pipes will have the higher discharge velocities. Flows at that velocity (2.5m/s) will result in soil erosion, not only to the land downstream but most likely to the line embankment. If culverts are to be used then there is a need for well-maintained energy dissipaters and flow spreading structures at their outlets to bring flow velocities down to acceptable levels.

If infrastructure such as the railway line here has to be above flood levels, then viaducts that have minimal impact on flow paths and allow flows to pass under them in a spread fashion are the preferred option. Whilst there may be soil erosion around pylons during flows, the level of this is minimal compared to that which may arise from use of culverts.

Thus, in order to minimise soil erosion risk as much as possible, viaducts should be used to cross the full extent of floodplains – regardless of any extra upfront cost.

A further problem with regard to use of culverts is the threat of blockages. Whist it is acknowledged that hydraulic modelling to investigate the impact of up to 20% culvert blockages was carried out for the Condamine River floodplain, it is not clear in the report mentioned above how that blockage was spread across the floodplain. If the blockage occurred in a single section of the floodplain, which is likely if an upstream landholder has just baled a paddock, the resultant impact of flow diversions, inundation etc. would be different than if the blockage is evenly spread across the floodplain. The impact of blockages being unevenly distributed needs to be investigated and solutions developed.

It is normal that, for any floodplain modelling exercise, the maximum amount of base data possible be utilised. The UCF project collated much data including workshop outcomes (including runoff flow paths), on-ground topographic survey information, and digitised flood information for the floods of 1956, 1975, 1976, 1981, estimated flow levels and velocities and infrastructure affected for 1 in 20 and 1 in 100 year floods. The data is held by the Queensland Government. It does not seem that AECOM accessed this data for their modelling exercises.

It is imperative that, regardless of the method used to traverse the floodplain(s), maintenance of structures is essential. This should include slashing vegetation regularly, distribution/removal of silt deposits and filling of any eroded areas caused by the railway (and not just the right of way).

In summary:

• Floodplains should be avoided for a project like this if at all possible. • Effective consultation with all stakeholders is required so that a shared committed on- going approach to floodplain management is developed. • Flows on floodplains should be as shallow and slow as possible to minimise soil erosion risk. • Erosion is a genuine and significant concern on floodplains. It can take years to rehabilitate and heal erosion scars (if at all) after a single major erosion event. • To minimise soil erosion risk as much as possible, viaducts should be used to cross the full extent of floodplains – regardless of any extra upfront cost. • Ongoing maintenance of structures and their surrounds to minimise and manage flow concentrations is essential. • Extensive data on the Condamine River flood plain is held by the Queensland Government, but it does not seem that AECOM accessed this data for their modelling exercises.

Signed G Bass, 40 years experience T Donnollan, 40 years experience C Knowes,-Jackson 40 years experience D Muller, 40 years experience M Genrich, 35 years experience J Klein, 40 years experience P Govern, 30 years experience J McLatchey, 55 years experience E Power, 10 years experience B Rowlings 30 years experience G Smith 30 years experience B Stone, 55 years experience G Titmarsh, 40 years experience L Ward, 40 years experience

Reference Queensland Department of Natural Resources, 1999. Better Management Practices. Floodplain Management on the Darling Downs.