Impacts of sediment and debris from Natural Flood Management

The impact of flooding is widespread and there are a number of factors increasing risk globally including urbanisation, economic growth and increased climate variability. A range of responses, both traditional and more innovative, are advocated by experts, the public and the media. The agencies responsible must balance these options based on clear evidence. The challenge is less about devising new measures, but more about how to combine various options and to assess the impact across the whole system. This requires greater understanding of impacts and how options positively or negatively interact.

This proposal focuses on one option that has recently attracted increased interest - natural flood management. This seeks to reduce peaks and consider timings through working with natural hydrological and morphological processes to manage sources and pathways by which water and sediment enter watercourses. However, there is a concern that natural flood management will increase the amount of sediment and debris in the system. Whilst sediment and debris are important for river and ecosystem sustainability, they can increase flood risk in the upstream with, for example, the blockage of small bridges/culverts or in the downstream with the accumulation of debris from across a catchment impacting bridges and buildings. This project will explore which of these effects is most significant and whether their relative significance varies spatially and temporally. It will also investigate where debris impacting urban areas comes from: upland areas, local tributaries or from more direct riparian sources?

The project outcome will be better understanding of sediment and debris processes in order to develop the evidence base. A full analysis of the impact requires understanding at a number of scales (reach, river network, catchment) and understanding of their interaction. However, the existing studies of sediment and debris in natural systems are mostly focused on a single scale. A detailed analysis carried out solely at a reach or floodplain scale cannot feasibly be extended to a whole catchment so in this project the student will use novel approaches at each scale and link the analysis across scales in an innovative manner through parameterisation and transfer of information.

The PhD will focus on the Aire catchment and answer the following research questions:
How much sediment and debris enters the system?
How does sediment and debris move within a single reach?
How are the different scales connected in terms of sediment and debris?