PRIORITY RECOMMENDATIONS
PRIORITY RECOMMENDATIONS
There were six priority recommendations, of which five related to rain and the sixth related to severe weather events in general.
Design Issues
Recommendations 1 and 2 were identified to address the concern that the increase in rainfall, suggested by climate change predictions, could result in design elements which do not adequately cater for specific rainfall events where use is made of historical rainfall data.
- Recommendation 1: Revise the parameters for the design storm for surface water drainage performance. This could be achieved by continuing the use of historical information but for an increased return period, or by basing the approach on further research on rainfall changes arising from climate change.
Action: This has been addressed by revision of the relevant design standard, HD33/06 of the Design Manual for Roads and Bridges (DMRB), where paragraph 6.2 requires a sensitivity test of drainage systems for a 20 per cent increase in rainfall intensity of the design storm. This approach should enable current climate change predictions to be taken account of in the design process.
Status: Complete
Case Study: A876 Upper Forth Crossing at Kincardine
This project was one of the first major projects to be procured following publication of the Scottish Road Network Climate Change Study, and the drainage requirements for this contract, which includes attenuation ponds to control the rate of drainage release, were set to take account of climate change predictions. Construction began in Spring 2006.
- Recommendation 2: Revise the parameters for the design storm for watercourse structures. This could be achieved by continuing the use of historical information but for an increased return period, or by basing the approach on further research on rainfall changes arising from climate change.
Action: The design process for watercourse structures is less well defined within DMRB in terms of hydraulic capacity and no revisions have been made as yet. Other design guidance used for this purpose, such as the Culvert Design Guide — CIRIA Report 168, varies in whether it addresses climate change. Recent guidance issued by the Scottish Environment Protection Agency (SEPA) in the form of a scoping study regarding climate change and hydrological parameters refers to the need for some allowance for climate change effects but does not propose a specific approach. Representations on this matter are being made by Transport Scotland to other Overseeing Organisations within the relevant technical board and consideration may be given to the introduction of a design standard specifically addressing hydraulic capacity of watercourse structures.
Status: Progressing
Operational Issues
Recommendations 3 and 4 were identified to address the concern that the increase in rainfall suggested by climate change predictions could result in the exacerbation of flooding on the existing road network, particularly in areas already known to flood periodically.
- Recommendation 3: Identify locations where flooding of the road network has occurred and develop potential solutions for evaluation on a cost/benefit basis, prioritising those areas where repeated flooding has occurred.
Action: A number of schemes have been brought forward to address flooding concerns, although at present no consolidated schedule of such works has been created. The work being undertaken to develop an asset management plan for the trunk road network should afford the opportunity for works of this nature to be prioritised.
Consultation papers have also been released by the Government in January 2008 for the Scottish Climate Change Bill and the Flooding Bill. The Climate Change Bill addresses the need for legislation to help Scotland adapt to its changing climate and proposes various reporting mechanisms on actions being taken to adapt to climate change. The Flooding Bill will cover all aspects of planning and preparing for flooding.
Status: Progressing
Case Study: A90/B9108 Flooding at Boddam Junction (Aberdeenshire)
Within recent years there have been a number of flood events at the A90/B9108 Boddam Junction, resulting in closure of the A90 and B9108 and considerable damage to a number of private properties. An investigation has been carried out and measures to reduce the risk of flooding have been designed and are in the process of being taken forward. Improved maintenance of adjacent culverts, which was part of the recommended solution has been implemented.
- Recommendation 4: Pre-emptively clear detritus from channels/watercourse structures in known areas of flooding risk in response to predicted heavy rainfall.
Action: It is considered that this practice forms a requirement of the current term contracts for management and maintenance of the trunk road network.
Status: Complete
Case Study: Culvert Clearing Operations — A9 Backburn culvert (Blackford)
The current term maintenance contracts require six-monthly inspections of culverts, following which vegetation, debris and silt are removed to ensure the free flow of water. At some locations significant works are required to remove accumulated silt deposits within the culverts.
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Research Issues
Recommendation 5 was identified to address the concern that the increase in rainfall, combined with the changes in seasonal soil moisture condition, suggested by climate change predictions could result in catchments responding in a different manner to that described by current mathematical models, potentially increasing runoff volumes.
- Recommendation 5: Undertake further research in respect of catchment runoff estimation parameters, and provide guidance on possible risk-based design approaches, including evaluation of alternative solutions on a cost/benefit basis.
Action: Research is currently being undertaken by others (Centre for Ecology and Hydrology, Wallingford) into developing more accurate models of long-term catchment response. The effects of variations introduced by climate change will subsequently be modelled. The full publication of UKCIP 08, which is anticipated in November 2008, is awaited to progress this research. Further guidance on this issue will therefore draw on the results of this research, when completed.
Status: Pending
Policy Issues
Recommendation 6 was identified to address the concern that the general increase in severe weather events suggested by climate change predictions could result in a reduction in levels of service and safety for road users.
- Recommendation 6: Consider using the Variable Message Sign (VMS) network to provide a greater level of locally relevant information to road users on predicted severe weather events, expressed in terms of probability of occurrence.
Action: A series of weather event-related standard messages have been developed and are used on Variable Message Signs around the network during winter, being deployed in response to forecasts of specific weather events. The messages do not provide a probability of occurrence but they do reflect the forecast nature of the prediction. The decision has also been taken to expand this service to cover the whole of the year, in particular to allow messages for high intensity summer rainfall events to be developed for use. It is the intention to implement this service expansion in summer 2008.
Status: Complete
Case Study: Variable Message Signs
Traffic Scotland currently operate 118 Variable Message Signs on the motorway and trunk road network and, as part of the Traffic Scotland action plan, the aim is to expand the number to some 250 VMS within five years. Since 2005 a series of severe weather-related messages have been introduced, with their deployment being supported by detailed weather forecasts supplied by the Met Office. This has enabled Transport Scotland, via Traffic Scotland, to routinely provide important information to road users to assist them in travelling safely.
