Pioneering research, carried out by scientists at Durham University, has shown that rural land use, if carried out at the right locations, could help reduce the catchment scale
flood risk, even for extreme flood events such as those experienced in Carlisle, UK, in January 2005.
Ian Pattison, a research post-graduate at the University, has been developing a novel, downscaling approach using statistical analysis and computer modelling. This helps to understand how the magnitude and timing of peak flows from each of the Eden’s major sub-catchments interact to produce flooding at Carlisle. He then investigated a variety of rural land use measures, such as woodland planting, reducing soil compaction and the placement of large woody debris in the river channel, to see what effect they might have on downstream flood risk. Results from the modelling studies show that the impact of these measures on the timing of peak flows from specific tributaries could potentially reduce the downstream flood risk even for extreme events.
Making such a link between rural land use and catchment scale flood risk has proved very difficult in the past. One reason for this, as Ian explains; “is that land use changes can impact the relative timing of peak flows from one tributary in a river system compared with another as well as the magnitude”. For example, if land use changes cause peak flows from two tributaries to coincide in time, downstream flood risk will increase. Alternatively, if the peak flows can be
separated in time, the downstream flood risk could be reduced. Critically, this effect means that the same measure can either reduce or increase flood risk, depending upon where it is implemented in the catchment area.
Separating flood peaks in time is something which other ALFA partners are also looking to achieve. For example, in France the IIBRBS aim to store water from the River Seine in La Bassée to allow the flood peak from the River Yonne to discharge first, thus reducing the downstream flood risk from the River Seine in Paris.
Picture 1: Flooding - Warwick Road Carlisle – January 2005 (photo courtesy of the Environment Agency)
Picture 2: Map of the River Eden catchment showing the major sub-catchments
