Botched Flood Prevention Scheme: How not to do it

Exemplified by the Actions of Perth & Kinross Council regarding the River Ruchil at Comrie, Perthshire, Scotland.

In the late 1990’s Perth & Kinross Council vandalised the banks of the River Ruchil at Cultybraggan Farm Comrie on the pretext of carrying out a flood prevention programme which they were clearly incompetent to do. There was a serious lack of co-ordination with such bodies as SEPA and SNH, as the government had not given them any authority in matters of flood prevention. The situation at the time (and continuing to the present day) was that the local authority was responsible and did not need to take advice from those who were expert on river management, be they SEPA, SNH or other authorities in Universities or wherever. While Perth & Kinross Council did contact both SEPA and SNH the end result was that Perth & Kinross Council went ahead with their own scheme administered by their roads department. They were warned against the consequences of their misguided plan, but neither SEPA nor SNH had any power to stop them, although it would appear that the efforts of these bodies were not very strenuous in this regard. Because the matter was outwith their remit, they did not bother too much. They did however advise against bunding; i.e. pilling up rounded stones from the river bed into high banks.

Figure 1

Click here to enlarge image (147KB)

This was all the more ironic as SNH had recently funded a farm conservation plan as an initial essential step for Cultybraggan Farm applying for an environmental grant under the Countryside Premium Scheme. In the proposed application, Farm and Wildlife Advisory Group (FWAG) had emphasised the very high conservation value of the bank of the River Ruchil at the farm. The plan was to fence off the river bank more effectively and to manage grazing for the benefit of the flora and wildlife. In the event a local government department destroyed it with blundering incompetence.

The result, illustrated in Figure 1, is appalling ecological vandalism for which Perth & Kinross Council never formally apologised or offered any recompense for their misdirected, ill-informed and totally arrogant actions. Not only were thousands of pounds of taxpayers' money wasted but the local environment was severely damaged. It is interesting that in terms of current government policy that funding of environmental schemes is to be largely devolved to local authorities. As mentioned above, flood prevention schemes remain at a local authority level but with encouragement (but only encouragement) to seek advice from those who are expert. What confidence can we have in whatever this or other local authorities may do next? What sort of “sustainable” environment is achievable in the face of such ignorance on the part of local government?

The following is a report on the River Ruchil project written by Dr David Gilvear, Senior Lecturer in Fluvial Geomorphology and River systems, University of Stirling, for the Scottish Wild Rivers Project.

(This paper can be viewed in image format as originally published here).

Opening the floodgates

In late 1997 a partnership between the Project, Scottish Wildlife Trust and Perth and Kinross Council was set up to take forward flood alleviation on the Water of Ruchil after flood intervention works had ended in disaster. The Ruchil responds quickly to rainfall; its small catchment, steep gradients and limited floodplain mean that water levels rise quickly. Improved farmland and the village of Dalginross occupy the floodplain near Comrie, restricting its natural flood-cushioning function.

In 1993 and again in 1997, when there was a peak flood flow of 250 cubic metres per second, houses in Dalginross were damaged, and Perth and Kinross Council, which has a statutory responsibility for flood protection, employed a consultant to find a solution. This preliminary consultancy identified failings in the design and maintenance of the existing flood embankments and recommended the construction of a hump with culvert pipes in the raised driveway to Dalginross that bisects the floodplain, to allow the floodplain to function more naturally.

In November 1997, before the Council had received this consultant’s report, Council engineers took matters into their own hands in the belief that they were protecting the local community. Contractors felled trees, re-sectioned the existing channel and excavated a new channel along the course of an old river bed, now partly filled with natural floodplain woodland, which had historically served as a natural flood overflow. The new channels had flattened beds with no natural riffles or gravel bars, and the excavated gravel was piled into high, steep, unvegetated banks, killing the vegetation which had naturally anchored the river bank. This work, while well-intentioned, failed to take account of dynamic river processes and has now seriously destabilised the river both up and downstream. What followed was nature’s lessons for human ‘solutions’:

Ironically, there is serious erosion on the main channel close to Dalginross, including the loss of some bankside trees that had survived the re-sectioning, and the popular bankside path and houses are threatened.
Tonnes of gravel have blocked the entrance to the old, re-excavated channel.
In February 2000 floodwaters breached the ‘island’ separating the two channels.
Bank erosion also moved upstream of the modified reach to over 200 metres above the channel division by March 2000. Here mature trees collapsed into the channel along with large chunks of bank, removing the riverbank path and undercutting a fence. This reach also deepened considerably, losing its previous pattern of pools and riffles.
In some places, the artificial banks have been wholly removed by floods, and erosion has affected woodland that was undisturbed, before and during the works. After high flows, large trees toppled by erosion lie on exposed gravel bars or even bridge the channels.
Higher sediment flow is likely to have affected aquatic life lower in the river system.
Natural marginal vegetation has been lost along the engineered sections, allowing exotic invasive plants such as Japanese Knotweed to establish.
It is likely that there have been effects further downstream on the River Earn.

Working with the river

The partners immediately sought the help of a leading fluvial geomorphologist with a practical understanding of river processes to advise on restabilising the river. While the river will find its own equilibrium in time, and in a less-populated location the most cost-effective solution would be to leave it to stabilise naturally. However the continued threat to houses at Dalginross means that interim measures are needed. The consultant recommended low-intervention interim work to confine the current problems:

The placing of a V weir upstream of the modified section to provide bank protection, stabilise the river bed and prevent instability from moving further upstream.
The removal of excess tree debris from this reach as it gathers to avoid channel blockage.

The low-cost, low-intervention work suggested by the original consultant, if applied at an earlier stage, could have saved a huge cost to the local authority as well as safeguarding the river environment. The remedial work recommended by the second consultant will, it is hoped, help to restabilise the river.

Flooding - a national issue

Rivers are natural and dynamic systems that react to climate, geology, geomorphology and land use and, importantly, transport sediment as well as water. As the example of the Ruchil shows, changes to any single factor can alter and destabilise the whole river system, and it is difficult to predict how the system will restore its equilibrium or how long this will take. For example:

Widening upsets sediment flow leading to erosion and deposition equivalent to the scale of the initial work.
Deepening leads to bed instability, which leads to bank collapse, more sediment and a wider channel.
Straightening makes the overall channel shorter and steeper, so water velocity, sediment transport and erosive power increase.

Flooding is now a crucial issue in Scotland, one that must be tackled carefully if we are to avoid problems like the Ruchil. Climate change is expected to increase rainfall, and with it the costs of flooding - unprecedented flooding in recent years have caused hundreds of millions of pounds worth of damage across Scotland.

Modern land use on our floodplains; drainage, housing and roads, channels water into rivers quickly, causing water levels to rise dramatically after rain. Engineered structures such as flood embankments separate the river from the floodplains that are vital relief valves for storing floodwater and dissipating energy! The reduced ability of the floodplain to store water worsens the effects of flooding, leading to erosion and even more engineering to protect inappropriate development-it is a vicious circle. It is vital that we take a strategic view of flood management that takes full account of the natural role of the floodplain and the dynamic nature of river systems. Short-term solutions all too often mean enormous long-term financial and environmental costs.

“This case highlights very well that many present day problems concerning rivers would not have arisen if past management had paid greater attention to the natural processes occurring within the river system. We can’t get away from the fact that rivers are constantly changing. Nature creates the most effective channels for conveying sediment as well as water. Sooner or later we pay the price for interference.”

Lessons

The Ruchil site and Comrie demonstrates that rivers cannot be “controlled”, that it is so often best not to interfere with natural river processes, but that low-intervention techniques are the best option if action is necessary.
Rivers and natural and dynamic systems that react to a range of factors and changes to any single factor can destabilise the whole river system at huge cost and environmental cost.
If floodplains are allowed to function naturally, rivers will look after themselves.
There is a serious lack of awareness of river processes at all levels and a tendency to look to engineers rather than river experts for answers. Decision-makers must be given access to good practice guidelines and training and know how to consult those affected and where to seek advice. Flooding is a national issue, and an increasingly important one give the compelling evidence of the flooding impact of climate change predicted for Scotland. National government must take the lead on flood management and ensue that there is integration between national and local government and a consistent approach across Scotland.
Flood Appraisal Groups based on best practice should be established for every catchment according to the guidelines set out in NPPG7 Planning and Flooding.

Further Editorial Comment

Perth & Kinross subsequently sought professional advice from a Professor in a University in England. The proposal was that vanes made of rocks projecting into the river be strategically placed to influence the flow and thereby hope to save the banks from further erosion. However this is clearly dependent on the Council promptly removing fallen trees from the river, which would otherwise get stuck on these vanes and cause blockage and acute flooding upstream. Observing the activities of the Council in this regard over the following two years they were shown to be ineffectual at promptly removing fallen trees, stating that they would do so when time and conditions permitted and stressing that it cost £2000 per time. Clearly, in spite of their verbal assurances that they would comply with this condition, they had no intention of doing so in a manner that would be effective. The result would very probably be flooding of the best arable fields on the farm with massive loss of the top soil. However, Perth & Kinross Council along with all other Councils have no responsibilities for what effect their flood prevention schemes may have on the properties of others outwith their urban settlements - i.e. farms do not matter. For his reason I have not given permission for such vanes to be placed in the river as far as the bank of the Ruchil at the farm boundary is concerned, although permission has been granted to place rock stone at the banks (but not projecting into the river).

When one hears so much from Government bodies and their agencies (such as SNH and SEPA) about the importance of the environment, it beggars belief that when its comes down to it flood prevention and the management of a highly ecologically important river is left to a roads department that knows nothing about rivers and cannot even manage the local drainage systems on their own roads effectively (1) (and as evidenced from the minutes of the Local Community Council).

Also extraordinary is the building of new houses on a floodplain, planning permission having been given by Perth & Kinross Council. Is local government really up to the job of protecting the environment? Is local governnent really an appropriate body to assess how modulated funds taken from farmers should be used for the benefit of the rural community?

References

1. Irvine, WJ (2002). Flood Prevention. Land-Care, 22 November 2002. (View Article).

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25 November 2002