The impact of flooding due to our changing climate and rising sea levels is a major issue for highways authorities and their surveyors as they battle the elements to keep existing networks open and safe to use and consider the design of new roads.
Faced with keeping on top of flood risk, technology could provide the insight the authorities need to help guide the decision making process. Much of this will come from historical data collected that will show the extent of past flooding.
For example, the winter storms of 2013 affected large parts of the Thames Valley with houses, shops and roads flooded and inaccessible. SphereVision took a boatmounted 360 degree video capture system to Chertsey to record test footage of the disaster. Linked to online mapping, the digital images clearly show the flood affected roads. This kind of visual information has the potential to help with flood proofing existing roads or in planning alternative, new routes that are less likely to be affected.
Also in Surrey, the area around Chobham Common was affected over recent years. Surrey Heath Borough Council had been working actively on flood alleviation works and employed LiDAR data supplied by Bluesky to model the flow of water across the common and surrounding areas.
‘Using the LiDAR data we have been able to run a watershed analysis on this hugely important and sensitive site. We have identified at least one medieval bund; used to retain water, in Glovers Ponds on the common and we hope to be able to reinstate this and other historic drainage pools to attenuate flood water coming off the com- mon. We are also hoping to use the LiDAR data to work out cut and fill volumes for the work to reinstate the bund in order to gain an accurate understanding of the project costs,’ says James Rutter, GIS manager at Surrey Heath BC. In North Wales, the A470 trunk road runs through the valley of the River Conwy. This is an area that floods dramatically, being very wide and opens out into a long tidal reach. In 2011, a major road improvement project (Tanlan Penloyn scheme north of Llanrwst) between the Welsh Government (WG) and Balfour Beatty was completed. A WG spokesperson commented on the part that data played in the work.
‘The information supplied by the flood modelling did dictate the level of the new road for this scheme, as it was developed as part of the then Environment Agency Wales’ new flood protection scheme for the Conwy Valley. The scheme was developed as a flood barrier to those properties to the east of the new road. Also, the impact that the new road would have in reducing the valley storage during times of future flooding was modelled. In addition, several modelling scenarios were run and some of these did make an allowance for climate change,’ the spokesperson says.
On new schemes original ground levels and data is usually obtained through LiDAR - unless other modelling or terrain data is available. A ground model is created along with a base flood model, and the alignment and level data of the new route (or routes) is added to the flood model in order to assess the potential flooding impact the new route (or routes) may have. Depending upon the outcome of the modelling, the route or level may be adjusted to minimise the impact the specific route may have on future flooding.
‘If the route is within a flood area, then flood modelling is used during the planning stage of a new road. Also, historical data plays its part in the flood modelling process. These days with the advance in the computer design models, 3D views and fly-throughs are created and are part of the design process,’ says the spokesperson.
JBA Consulting model potential flood risks across England and Wales
Aerial photographs and detailed 3D elevation models from Bluesky’s newly launched Map Shop are helping JBA Consulting model potential flood risks. The aerial photomaps, LiDAR data and DTM (digital terrain model) are being used for testing JFlow – the consultancy’s award-winning hydraulic modelling software. In addition, the data are being utilised in the preparation and delivery of training courses for the software. Maps produced using JFlow have been used to assess flood risk by a large number of government and insurance clients in locations all over the world. The Bluesky LIDAR data provide the boundary conditions for a number of model test cases that are used to verify the accuracy of new versions of the software. The aerial photomaps, meanwhile, are used by JBA to illustrate the numerous ways in which JFlow can be applied.