Assessing the Effectiveness of Natural Flood Management at a catchment scale

Overview

Flooding, and management, cost the UK £2.2billion per year. Under current economic pressures, flood policy is shifting from entirely flood defences to broader management strategies. This includes “Natural Flood Management” (NFM) which aims to restore the natural functioning of catchments to store water and slow the flow. Examples of NFM, shown in Figure 1, include tree planting, leaky dams and river restoration, along with agricultural land management. These work with hydrological processes, including increasing infiltration of rainfall into the soil, storing water on the floodplain and increasing the flow resistance to flow within the channel to attenuate the flood peak (taking the top of the peak).

However, despite NFM gaining popularity with policy makers and flood action groups, a lack of scientific evidence on its effectiveness and advice about how to go about implementing such an innovative approach are limiting its success.

There are two gaps in current knowledge relating to the effectiveness of NFM. First, at the intervention scale, we do not understand how much hydrological processes are modified by the NFM feature. Second, at the larger sub-catchment and catchment scale, we have limited knowledge of how the effect of interventions combine together and propagate through the river system. The importance of how sub-catchments interact in terms of tributary synchronicity is essential to understand in terms of larger scale scheme design (Pattison et al., 2014).

This project aims to develop specific guidance on how NFM schemes can be designed to optimise and monitor their effectiveness at different spatial scales.

Objectives
1) Carry out laboratory experiments and field trials to determine how interventions, e.g. leaky dams, can be designed to increase their effectiveness.
2) Develop models to design NFM schemes at the catchment scale to optimise for performance.
3) Optimise methods to work with policy makers and landowners to broaden the implementation of NFM to large catchments.

Methodology

This project will utilise a mixed methods approach, combining field monitoring, hydrological modelling and stakeholder engagement.

Field trials will seek to form a process-based understanding of how individual NFM features function, for example using a wide range of soil property tests to study the role of agricultural management in flood mitigation, and fluorescein dye tracing to upscale impacts to larger scales using estimates of travel times. Laboratory tests, such as rainfall simulation or flume experiments will allow controlled experiments to optimise individual feature design.

Hydrological modelling will be used to test the catchment scale impact of different “What if”  scenarios on flood risk. Furthermore, optimisation techniques will be utilised to determine the best locations to put different NFM interventions.

Finally, the student will consult with a large number of environmental catchment management stakeholders to understand the factors which govern what type of NFM features are popular and what measures could be put in place to overcome barriers of implementation. This would be through a series of questionnaires and focus groups.

Project Timeline

Year 1

Undertake a comprehensive literature review and develop detailed project objectives, particularly around which NFM interventions will be focussed upon, and design experiments to test their effectiveness in controlled systems.

Year 2

Continue field monitoring of NFM interventions and undertake complementary experiments to assess their effectiveness. Develop models for larger scale assessment of effectiveness and techniques through which approaches can be optimised.

Year 3

Finalise data collection and analysis. Work closely with stakeholders to ensure key messages are translated into practice.

Year 3.5

Thesis and publication writing

Training
& Skills

In addition to the core training provided by IAPETUS2, you will undertake specific training on numerical hydrological modelling and optimisation techniques which will be provided by the supervisors and through dedicated courses arranged by HR Wallingford and the Environment Agency. You will also attend a 5 day Annual Catchment Science Summer School, led by internationally leading hydrologists. Further training opportunities will be accessed through the British Hydrological Society. The student will get the opportunity to present their research at a range of national and international conferences, to build communication and networking skills. You will be a member of the Water Group at Heriot Watt University, which run a series of seminars and training workshops.

References & further reading

Pattison I, Lane SN. (2012). The link between land use management and flood risk: a chaotic conception? Progress in Physical Geography, 36, 72-92

Pattison I, Lane SN, Hardy RJ, Reaney SM , (2014), The role of tributary relative timing and sequencing in controlling large floods. Water Resources Research, 50, 5444-5458.

Further Information

Dr Ian Pattison
Institute of Infrastructure and Environment, EGIS, Heriot Watt University
i.pattison@hw.ac.uk

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