UK roads faced one of their toughest tests last autumn - the wettest since records began - and the results for most were not good. While the dramatic pictures of last October's flooding will eventually fade from memory, the resulting state of the road network is likely to serve as a reminder for some time to come.
The immediate effect of the heavy rain included a rapid rise in potholes and collapsing road edges, not to mention damage to culverts, bridges and other structures. In the following weeks saturated slopes gave way to the forces of gravity resulting in landslips which saw roads blocked and eroded. Potholes and other defects also increased as wet roads were subjected to frost action. Temporary repairs proved to be just that.
Kent and East Sussex were both badly hit by flooding and the resulting repairs are expected to top £7.3M and £5M, respectively. East Sussex suffered a total of 28 landslips on its highways following the heavy rain and some of the roads still remain closed or restricted by traffic management.
'Since last autumn we have seen a dramatic increase in the rate at which potholes are appearing, ' says East Sussex County Council assistant operations director Chris Walker.
'One of the most widespread problems has been failure of carriageway edges, particularly on uncurbed roads.'
'Minor repairs were undertaken as soon as was practicable but some of the larger defects, where structural damage was more severe, and landslip stabilisation will have to wait until geotechnical investigations and engineering designs can be carried out.'
Meeting the cost of repairs is a big concern to local authorities.
Many have had to scale down and prioritise routine maintenance and divert funds to repair flood damage. However, the government has a scheme known as the Bellwin Funds which is available to local authorities to cover uninsurable emergency work following natural disasters such as floods.
Nonetheless, local authorities must pay for the repairs before they can reclaim the cost and the fund only covers emergency work, not long term remediation of subsidence and structural damage. Bellwin grants are also only available after councils have spent more than 0.2% of their total annual budget on repairs following a single, provable flooding incident, adding red tape to the clean up process (NCE 31 May).
'The scale of damage to Kent's roads as a result of the winter floods is huge, ' says Kent County Council strategic planning director Pete Raine. 'We can divert some money to part fund the cost of repairs, but we cannot meet the full cost alone. Without government help we will be caught between mending most of the county's roads badly, or mending only some of them well.'
Last month the government announced that it will make an extra £12M available to fund repairs to flood damaged roads and invited councils to bid for this extra cash by the end of June. However, initial estimates of the national repair bill are expected to exceed £45M.
Many road defects could not be permanently repaired until ground water levels had dropped, but by the time they were low enough foot and mouth restrictions were in place, limiting access in rural areas.
'Gloucestershire was pretty badly affected so we scaled down both emergency repair and routine maintenance work to avoid spreading the infection.' says Gloucestershire County Council network maintenance manager Phil Brain. 'We got away lightly on flood damage compared to many other counties but the heavy rainfall did cause several landslides which have partially blocked roads.'
North Yorkshire has suffered badly with both foot and mouth and flooding. 'Localised flooding in June last year caused structural damage to Mercury Bridge in Richmond, which meant we had to postpone 23 other planned structural maintenance projects and divert funds to repair the bridge, ' says Mike Moore, North Yorkshire County Council director of environmental services.
'The flooding has also brought a new problem in the form of springs. Ground water levels were so high in some areas that previously unrecorded springs appeared in roads, causing severe damage. Several bridges were also badly affected including a listed stone road bridge in Kirby Malzeard. It suffered severe structural damage and will have to be completely rebuilt at a cost of around £300,000.
'Most local authorities which suffered flood damage also emphasise that if roads had been in better condition beforehand, they might have fared better. But they acknowledge last autumn's rainfall was exceptional and believe they will cope in the long term if it proves to be a one-off.
But if the floods are the result of climate change and become more frequent then more government help will be needed.
Cutting edge solution
Highway authorities keen to increase the durability of carriageway edge repairs could find help from a new product developed by RMC.
'Haunches of minor roads fail mainly because heavy traffic often leaves the paved surface to allow vehicles to pass on a restricted carriageway width, ' says RMC divisional technical manager Gordon Lemon. 'Rainwater collected in the resulting rut causes softening of the vulnerable subbase and road foundation.'
RMC's solution is a bespoke asphalt mix designed to provide the exact properties of compactibility, impermeability and abrasion resistance - all of which are critical.
'The newly formulated material fulfils all these criteria by adopting a gap graded mastic bound mixture with a high bitumen content in relation to the coarse aggregate content.
A conventional penetration grade bitumen is used, but a unique mixing sequence produces a durable aggregate matrix, ' claims Lemon.
The new material has been designed as a sub-base, road base and binder course replacement layer in one so can be placed in one layer in the excavated road edge. The required compaction is achieved with around three passes of a vibrating plate or small roller and is completed with the application of a wearing course layer.