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Natural Flood Management in the United Kingdom: Developing a Conceptual Management Tool

Proceedings of 2013 IAHR Congress
© 2013 Tsinghua University Press, Beijing
ABSTRACT: Natural flood management (NFM) is increasingly adopted as a crucial element within the
UK sustainable flood management strategy. This utilises a non-structural multi-benefit approach, whereby
the landscape’s natural ability is restored or adapted to reduce flood risk by permanently or temporarily:
retaining flood water, providing attenuation, promoting sediment deposition and transport, and adjusting
the geomorphology formations of river systems (Flood Risk Management (Scotland) Act, 2009). Despite
the drive for NFM, it is well-recognized that there is a significant lack of evidence that NFM techniques
are actually effective in reducing flood risk at all scales of (sub-) catchment. Simultaneously, NFM
“multiple benefits” require evidence based quantification in order to fully evaluate and appraise NFM
techniques as a substitute or to compliment hard engineered flood defences. Thus, within the UK the full
range of NFM is being specifically assessed for this, and the associated cost-benefit, by way of field
monitoring in a number of demonstration catchments but still requires extensive research. The aim of this
paper is to identify variables, based on evidence and literature, which are suitable for monitoring the
impacts, multiple benefits and ecosystem services (ES) of NFM techniques, specifically; riparian
vegetation and bund runoff attenuation features (RAFs). The variables identified are translated in a
conceptual management tool and will enable the data collection that is required for the quantification of
NFM multiple benefits from an ES perspective achievable. Essentially, this tool, and the variables
identified, will assist in addressing policy and research gaps whereby; NFM measures must be appraised
as a statutory obligation and the multiple benefits are often not extensively researched, resulting in
inconclusive scientific evidence of their wider impacts and benefits. This tool will adopt an “ecosystem
service approach” in selecting variables, a relatively new concept and approach, advocated to provide a
holistic management technique able to comprehensively represent the three pillars of sustainability (social,
economic and environment).
KEY WORDS: Natural flood management, Multiple benefits, Ecosystem services, Riparian vegetation,
Runoff attenuation features.
Predictions by the Intergovernmental Panel on Climate Change (IPCC) and UK Climate Projections
(UKCP09) indicate that the UK will experience increased summer temperatures and increased winter
rainfall events that will become more intense in nature (IPCC, 2007, UK Climate Projections, 2009a, UK
Climate Projections, 2009b). Climate change is likely to increase the number of people at risk of being
flooded from fluvial, pluvial and surface water sources. In order to mitigate the unwanted human,
environmental and economic impacts of climate change, flooding must be managed cost-effectively and
Natural Flood Management in the UK: Developing a Conceptual
Management Tool
Linsey McLean
PhD Student, Heriot-Watt University, Edinburgh.
Dr. Lindsay Beevers
Lecturer, Heriot-Watt University, Edinburgh. Email:
Professor Gareth Pender
Prof. of Environmental Engineering, Heriot-Watt University, Edinburgh.
Dr. Heather Haynes
Senior Lecturer, Heriot-Watt University, Edinburgh. Email:
Dr. Mark Wilkinson,
Catchment Hydrologist, James Hutton Institute, Aberdeen. E-mail:
sustainably to ensure resilience and effective adaptation to future conditions. NFM is theorized and
promoted to be a cost-effective sustainable measure for reducing flood risk and is subsequently explored
in this study.
Natural Flood Management (NFM) has been formally introduced to the UK through the 2007
European (EU) Directive on the Assessment of Management of Flood Risk (2007/60/EC) (Floods
Directive), which has been transposed into UK legislation in the form of the Flood Risk Management
(Scotland) Act 2009 and the Flooding and Water Management Act 2010. These UK laws formally
introduced the requirement for NFM techniques to be fully considered and appraised when managing
flood risk and integrated NFM as a crucial element of sustainable flood management (APS Group
Scotland, 2011). NFM is defined in Scotland as working with or restoring natural flooding processes
with the aim of reducing flood risk and delivering other benefits(Flood Risk Management (Scotland) Act,
2009). There are numerous NFM techniques outlined in Table 1:
Table 1 Natural flood management measures
Despite the statutory requirement for NFM to be considered and advocated when managing flood risk,
policy has essentially promoted NFM when there is lack of evidence to support the theory that natural
processes and features can effectively reduce flood risk at various scales. It is widely indicated that
catchment scale NFM effectiveness remains elusive and further extensive research in flood risk is
required to inform policy. Further to these contentions, insufficient research has been applied to
quantifying the multiple benefits of each of the NFM measures and given the statutory requirement
to appraise shortlisted measures for a specific site, limited data and tools exist to assist and support
this process. NFM multiple benefits could be understood and evaluated by using an ecosystem service
(ES) approach, enabling the benefits of each NFM measure to be examined in relation to the provision of
ES (Frontier Economics Ltd et al., 2013, Iacob et al., 2012). ES are defined as dynamically complex
interacting units at various scales which living organisms interact with one another chemically, physically
or biologically, and with abiotic factors; creating natural processes that enable intricate ecological
balances within one system (TEEB, 2012, Parliamentary Office of Science and Technology (POST),
2007). These ecosystems and their processes provide goods and services that humans benefit from (and
depend on) directly or indirectly: the concept of ecosystem goods and services is synonymous with ES
(POST, 2007). The ES approach is a relatively new concept being advocated as an effective catchment
management perspective when evaluating NFM (Iacob et al., 2012, Barber and Quinn, 2012b, Brauman et
al., 2007).
For the purpose of this study, riparian vegetation and RAFs will be assessed as they each represent
opposite ends of the ES and NFM spectrum and therefore enable the management tool to be tested
effectively. Riparian vegetation for example, is derived as a water quality measure with extensive
literature to indicate their ES provision and multiple benefits, but has recently been advocated as an NFM
measure (despite lack of evidence to support the claim it reduces flood risk). Conversely, RAFs derived
from a hard engineering background and have a good strong evidence base for their flood risk reduction
abilities but limited scientific evidence on their multiple benefits or effects on ES. This study aims to
establish a conceptual management tool, based on literature, which will identify the multiple benefits
of specific NFM measures and the correlating variables suitable to monitor. This paper focusses on
understanding the difference between both NFM techniques and the impact this makes in designing
monitoring strategies, supporting the appraisal of NFM techniques required by UK legislation.
Agricultural land use practices
Bank stabilisation
Riparian vegetation (woodland and buffers)
Erosion control and sediment management
Large woody debris
Runoff attenuation features (RAFs) (using
earth bunds or wooden structures)
Floodplain restoration- reconnection,
woodlands and wetlands
Drain blocking- agricultural and upland
In order to identify the multiple benefits of riparian vegetation and RAFs, evidence gathered will
highlight the potential variables that can be monitored in the field. Further to this review, the ES
associated with these multiple benefits will be identified, as well as the evidence base for the ability of
both NFM measures to reduce flood risk. Based on the findings of the review of literature a conceptual
management tool will be developed illustrating the linkages between NFM multiple benefits and ES. Prior
to conducting the literature search it was required to develop categories for the tool and determine how
these would be linked together. The categories outlined in the framework are shown in table 2.
Table 2 Management tool categories and definitions
Tool Categories
Definitions of categories
Multiple benefits
The specific multiple benefits related to a specific NFM measure.
Measurable variables that can be monitored in the field to establish any changes
that the NFM measure may have on its associated multiple benefits.
ES provided
Identifies the list of specific ES that are provided by the specific NFM measure.
Colour coding of the variables shows the linkages between ES, variables and
multiple benefits.
ES classification
Distinguishes the ES classification of corresponding multiple benefits and
variables in relation to both the Millennium Ecosystem Assessment (MA)
classification (supporting, regulating, provisioning and cultural) and the UK
National Ecosystem Assessment (UKNEA) classification (primary/ intermediate,
final and goods/ benefits).
3.1 Riparian Vegetation Flood Risk Evidence
The riparian zone is an uncultivated strip of vegetated and adjacent to watercourses, which are
considered an ecotone: a habitat where there is an abrupt meeting of two contrasting communities that are
individually homogenous (Stockan et al., 2012, Pert et al., 2010). Riparian vegetation varies from
woodland species to grass and shrub species, all of which have an influence on surface and subsurface
flows by creating storage, slowing flows and attenuating flood peaks (through hydraulic roughness): this
influence varies with density, height, shape, physiology, flexibility, season and succession (Tabacchi et al.,
2000). Table 2 outlines studies that have modelled the impact of riparian vegetation on flood risk and their
key findings. However, there is notably a lack of monitoring based evidence that riparian vegetation,
especially non-woodland species, can reduce flood risk (Lane, 2008), which may be the result of their
origin being from a water quality perspective.
Table 3 Riparian literature findings that demonstrate the ability of riparian vegetation to reduce flood risk.
(Johnson et al.,
Modelling study to investigate
changes in local flood water
storage in a 1 year flood event
and 100 year flood event.
Annual flood event: 15% increase in storage and
Tp reduced by 30 minutes.
100yr RP: 71% increase in storage and Tp
reduced by 140 minutes.
(Anderson et al.,
Modelled four return periods:
2, 10, 50 and 100 year, and
riparian canopy height and
density parameters.
Flood wave propagation occurred between 5 and
20 hours for a 2yr RP and between 7 and 16
hours for a 100yr RP. Wave celerity was more
sensitive to smaller floods. Riparian attenuation
ability (roughness) declines with flood magnitude
and increasing channel size downstream.
3.2 Riparian Vegetation Multiple Benefits
According to Stutter et al. (2012), riparian vegetation buffers (RVBs) and the crucial multiple
functions it carries out are widely researched, but literature is restricted to mostly single riparian functions.
There is now a need for science to address the interdisciplinary multiple function research gap (Stutter et
al., 2012), even more so because the multiple benefits of riparian vegetation need to be fully understood
to ensure effective appraisal as a NFM measure or in terms of managing ES provision. As illustrated by
Table 3, the benefits of RVBs can be categorized into: ecology/ habitat/ biodiversity; hydrology and
hydraulics; pollution control; woody debris; riverbank stabilisation/ erosion control/ sediment trapping;
and socio-economic.
3.3 Runoff Attenuation Feature Flood Risk Evidence
RAFs originate as a hard engineering solution to reducing flood risk that have essentially been
naturalised, by using sustainable natural materials like wood and soil, to become a viable NFM measure.
They have also previously been utilised as a nutrient management features to address diffuse pollution
issues. RAFs are commonly implemented as an “off-line flood storage feature aimed to attenuate
out-of-bank flows during flood events or overland flow (Environment Agency, 2012).
Figure 1 Pilot RAF (Pond 0) and stream (downstream of diversion structure) water level from 5-7th September 2008
flood event (Wilkinson et al., 2010b).
According to a study by Wilkinson et al. (2010b) in the Belford catchment (UK), RAFs demonstrated
their effectiveness by becoming functional when the water level reached ~35cm (Figure 1- the first peak
within the graph) and slowly released the water back to the stream without adversely affecting the
receding limb (Wilkinson et al., 2010b). In the second flood peak event, the RAF is shown to exceed its
capacity and react quicker than the first event due to prior saturation (Wilkinson et al., 2010b). Despite
(upstream RAFs) remaining at capacity for three hours, the travel time to peak is delayed by 15minutes
after RAF construction (Wilkinson et al., 2010b). Nevertheless, the Wilkinson et al. (2010b) demonstrates
the effectiveness and potential to reduce local scale, and catchment scale (Nicholson et al., 2012), flood
risk by using RAFs.
3.4 Runoff Attenuation Feature Multiple Benefits
Table 4 outlines the multiple benefits of RAFs: ecology/ habitat/ biodiversity; hydraulics/ hydrology;
pollution control/ sediment trapping; and socio-economic. Barber and Quinn (2012a) recommend further
research and the development of a methodology to adequately quantify the multiple benefits of RAFs
from an ES perspective.
Proceedings of 2013 IAHR Congress
© 2013 Tsinghua University Press, Beijing
Table 4 Riparian vegetated buffers multiple benefits and measurable variables.
Hydrological functions:
interception, stem flow, infiltration,
evapotranspiration, water storage
and floodplain connection
Hydraulic roughness, turbulence,
flood peak reduction
- Canopy density
- Species physiology
- Vol. rainfall/ time
- Evapotranspiration rates
- Rainfall/ runoff
- Soil moisture
- Slope (channel and hill)
- Geology
- Temp. (soil, water, air)
- Particle size distribution (PSD) of
sediment load (bed and suspended)
- Root system
- Distance from stream
- Soil infiltration rate/ compaction
- Soil structure, type and distribution
- Vol. of biomass
- Groundwater level
- Time to peak
- Base flow
- Peak/ stage/ bank full discharge
- Manning’s n coefficient
- Channel geometry
- Overbank area wetted by flood
- Land use
- Stocking densities
- Crop species, cultivation practices
and timeframes
(Broadmeadow and Nisbet,
2004, Pollen-Bankhead and
Simon, 2010, Rassam et al.,
2006, Anderson et al., 2006,
Gribovszki et al., 2008,
Anderson et al., 2005,
Merritt et al., 2009, Tabacchi
et al., 2000, Ranalli and
Macalady, 2010)
Food source: e.g. inverts
Stream shading & micro-climates
Ecological connectivity
Species diversity (in dominantly
homogenous landscapes)
Habitat for various aquatic and
terrestrial species
- Vegetation/ canopy height
- Canopy cover
- Vegetation density (% bare ground)
- Soil chemistry (pH, N, P, C, S, K,
Ma, Ca & Si)
- Species richness and abundance of
aquatic and terrestrial invertebrates
- Buffer strip age
- Classification of habitat (according
to phase 1 habitat survey)
- Land use
- Fish- population, age structure,
number caught in a recreational
fishing season
- Spatial differences in water
(Tabacchi et al., 2000,
Stutter et al., 2012, Mander
et al., 2005, Stockan et al.,
2012, Gribovszki et al.,
Increase and decrease in flood risk
Attenuate flood peaks
Source and sink for organic and
inorganic debris
Increased N uptake by autotrophs
(in pools)
Hydraulic roughness
- Manning’s n coefficient
- N- (water and sediment)
- Water velocity
- Groundwater level
- Time to peak
- Base flow
- Peak/ stage/ bank full discharge
- Channel geometry & slope (channel
and hill)
- Rainfall/ runoff
- Vol. rainfall/time
- Evapotranspiration rates
- Land use
- Overbank area wetted by flood
(Broadmeadow and Nisbet,
2004, Tabacchi et al., 2000,
Piégay and Gurnell, 1997,
Stutter et al., 2012,
Weigelhofer et al., 2012)
Nutrient Cycling: N, P, C, S &
Maintain DO levels
Filtration of diffuse pollution,
heavy metals & contaminants
(pesticides/ herbicides)
Improve water quality
Reduce sedimentation in channel-
reduced flood risk, turbidity and
mobilisation of P, N and pathogens.
Intercept pollution runoff from
land uses
In addition to Hydraulics/ Hydrology
variables (above):
- P- total, particulate and dissolved
(soil, sediment & water)
- N- total, organic and dissolved (soil,
sediment & water)
- Heavy metals and contaminants
- Fish- population, age structure,
number caught in a recreational
fishing season
- Suspended solids (SS)
- Sediment settling velocity
- PSD of bed and suspended sediment
- Coliform bacteria
- Soil organic carbon (SOC)
- Dissolved organic carbon (DOC)
- Oxygen concentrations
- Water velocity
(Stutter et al., 2012, Stutter
and Richards, 2012, Roberts
et al., 2012, Dorioz et al.,
2006, Hoffmann et al., 2009,
Stutter et al., 2009, Merritt et
al., 2009, Collins et al.,
2009, Rassam et al., 2006,
Krovang et al., 2012,
Mander et al., 2005, Ranalli
and Macalady, 2010)
- Reduces bank erosion
- Reduces sedimentation of channel
and therefore reduces flood risk,
turbidity and mobilisation of P, N
and pathogens
- Effects geomorphological
processes and formations
(meanders/ channel shape/ bars)
- Improves denitrification (more
organic matter (carbon) in
saturated areas)
- Improves water quality- reduces
turbidity, P and N
- Improves soil formation, plant
growth and plant nutrient uptake
- Improves fish habitat
In addition to Hydraulics/ Hydrology
and Pollution Control variables:
- Cross-sectional change
- In-stream bedforms
- Sinuosity
- River migration rates
- Bank material
- Soil formation rate
- Macrophytes: population,
distribution and density.
- Vol. biomass
- Coliform bacteria
- Soil organic carbon (SOC)
- Dissolved organic carbon (DOC)
- Oxygen concentrations
(Stutter et al., 2009,
Broadmeadow and Nisbet,
2004, Collins et al., 2010,
Pollen-Bankhead and Simon,
2010, Krovang et al., 2012,
Merritt et al., 2009, Roberts
et al., 2012, Dorioz et al.,
2006, Stutter and Richards,
2012, Stutter et al., 2012,
Mander et al., 2005)
Aesthetically pleasing
Public/ Educational/ recreational
Biomass/ food/ fuel
- Financial returns (biomass)
- Fish- population, age structure,
number caught in a recreational
fishing season
- No. of fishing permits sold per
season/ no. visitors
- Savings (water treatment/water
(Lovett et al., 2004, Stutter
et al., 2012, Pert et al., 2010)
Table 5 Runoff attenuation feature multiple benefits and measurable variables
Water storage
Groundwater recharge
Disconnection, interception and
attenuation of overland and
out-of-bank flows
Slow infiltration of stored water-
attenuating peak flows.
- Vol. of water storage capacity
- Time to peak
- Peak/ stage/ bank full discharge
- Manning’s n co-efficient
- Slope (channel and hill
slope-DTM or LiDAR)
- Soil type & structure
- Geology
- Residence time (in RAF)
- Vol. rainfall/ time
- Soil infiltration rate & compaction
- Channel geometry
- Overbank area wetted by flood
- Rate of sediment build up behind RAF
- Land use
- Soil moisture/ groundwater level
- Temp. (water)
- Evaporation rate (diurnal and seasonal)
- Hydrological pathways (seasonal)
- Drainage & irrigation connectivity
(Frontier Economics
Ltd et al., 2013,
Barber and Quinn,
2012a, Nicholson et
al., 2012, Owen et
al., 2012, Wilkinson
et al., 2010b,
Wilkinson et al.,
Habitat creation & protection (fish)
Landscape heterogeneity
- Fish species dynamics: age
structure, presence and population
- Number of fish caught (recreationally)
- Sightings of migratory birds
- Population of migratory birds
(Barber and Quinn,
2012a, Morris et al.,
2008, Jonczyk et al.,
Nutrient cycling- N, P, C, S &
pathogens (denitrification &
carbon sequestration)
Filtration of diffuse pollution,
heavy metals & contaminants
(fertilisers/ pesticides/ herbicides/
Mitigates periodic nutrient release
Improved water quality (likely)
- Soil type/structure/ profile/
distribution/ nutrient retention
- Soil moisture & chemistry
(NH4-N, NO3-N, PO4-P, pH, N, P,
C, K, Ma, Si, S and Ca)
- Land use & stock density
- nutrient sources- proximity and
- Hydrological pathways
- Crop species & cultivation practices
- Organic matter
- N and P export coefficient rates from land use
- N and P annual excretion and defecation rates
from livestock
- Fertiliser/ pesticides/ herbicide application-
type, volumes, concentrations, spatial extent,
timing of application
- Temp. (water and soil)
- Macroinvertebrate indicator species
(Frontier Economics
Ltd et al., 2013,
Barber and Quinn,
2012b, Fink and
Mitsch, 2004, Fisher
and Acreman, 2004,
Jonczyk et al., 2008,
Nicholson et al.,
Aesthetic appeal
Re-use of sediment
Reduce costs of the impact of
flooding on local communities.
- Equivalent cost of fertiliser for
sediment re-use
- Cost of flood impacts (when they
- Number of properties at flood risk
- Cost of flood insurance
- Equivalent savings on water treatment due to
improved water quality
No relevant literature
Proceedings of 2013 IAHR Congress
© 2013 Tsinghua University Press, Beijing
Figure 2 Riparian vegetation conceptual NFM-Multiple Benefits-ES management tool. 'S'- supporting services, 'R'
regulating services, 'P' provisioning services, 'C' cultural services, 'I' primary/ intermediate services, 'F' final services,
'£' goods and benefits.
3.5 Discussion
The review of literature indicates there is a larger evidence base for RVBs in relation to their ability
to deliver ES compared to that of RAFs, although, most literature does not explicitly look at “ecosystem
services” but rather the individual benefits it affords (Stutter et al., 2012). There is a notable lack of
evidence to suggest that RVBs can reduce flood risk. Most studies model their impact rather than using
empirical data. Conversely, RAFs do have some literature to support flood risk reduction based on both
empirical and modelling studies. In contrast to RVBs, there is an obvious gap in research for RAF
multiple benefits (Stockan et al., 2012).
In comparing Figure 2 and 3, there are several key points to consider:
RVBs have more multiple benefits than RAFs
The multiple benefits of both techniques cover all the ES classifications
The performance of NFM techniques can be monitored from the perspective of multiple
benefits or ES, which dictates the variables chosen for any study (as does cost and time
Coverage of variables chosen for monitoring are dictated by the range and quantity of ES or
multiple benefits that are desired
The tool highlights which variables relate to which multiple benefits or ES chosen, and can
be used as a reference for when converting between approaches
This highlights the extent of the complexity in considering NFM and its multiple benefits from an
ES perspective. The tool and tables are to date, relatively biased towards assessing only multiple benefits
and excluding a mechanism for additionally (or scoring) the NFM measure’s ability to reduce food risk.
In relation to Section 20 of the Flood Risk Management (Scotland) Act 2009, there is a need to appraise
the “timescale to effectiveness” of any measure. Consequently, further research is required to apply this
conceptual management tool to all NFM measures, as well as integrate and account for timescales, spatial
scales and flood risk effectiveness. Until these can be addressed the tool does not yet fully evaluate NFM
multiple benefits from an ES perspective.
Figure 3 Runoff attenuation conceptual NFM-Multiple Benefits-ES management tool. 'S'- supporting services, 'R'
regulating services, 'P' provisioning services, 'C' cultural services, 'I' primary/ intermediate services, 'F' final services,
'£' goods and benefits
In conclusion, UK flood risk policy and practitioners require more evidence that NFM can
effectively reduce flood risk at various scales. Moreover, quantification of NFM multiple benefits are
urgently needed to enable statutory appraisals of NFM. The push towards an ES approach to catchment
management in the UK is driving the need to understand the overlaps and connections between multiple
benefits and ES. This conceptual management tool sets out the numerous field monitoring variables and
how they can be analysed to quantify the impact of a specific NFM measure in these terms, thereby
identifying similarities and connections between types. This tool is however, is in its infancy and requires
further development to integrate key elements such as: timescales, spatial scales and flood risk mitigation
This study is supported by Heriot-Watt University and James Hutton Institute.
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... With ecosystem services (ES) as a relatively new concept and the lack of quantification of NFM measures in all respects, it is essential for future monitoring of NFM to incorporate a means of data collection that can demonstrate the full range of impacts on ES and multiple benefits. The aim of this paper is to identify suitable variables, using a conceptual tool (CT) developed by McLean et al. (2013), to monitor the impact of an earth bund runoff attenuation feature (RAF) on its associated multiple benefits and ES. Using a site in the Tarland sub-catchment of the River Dee in Aberdeenshire, which is earmarked for RAF implementation, the paper will propose a monitoring strategy to capture the full extent of the RAF impact using the tool. ...
... The classifications are based on those of the Millennium Ecosystem Assessment and the UK National Ecosystem Assessment. As the CT exemplifies RAFs (McLean et al. 2013) this study will apply the tool to the Tarland Burn sub-catchment of the River Dee, Aberdeenshire, as a study test site. This site, earmarked for a RAF to be constructed, offers a rare opportunity to utilise the CT prior to implementation; enabling an examination of its capability to inform a realistic monitoring strategy to quantify changes in multiple benefits and ES. ...
... This paper will demonstrate the use of the CT developed by McLean et al. (2013) on the Tarland Burn sub-catchment in rural Aberdeenshire. The tool will be applied to a study in this catchment that aims to quantify the RAF ability to reduce flood risk and its impact on ES underpinned by sediment, N and P. The tool will be used from a multiple benefits and an ES perspective to identify variables suitable for this study. ...
... This principle of acceptance and mitigation underpins natural flood management (NFM) approaches. Whilst multiple definitions of NFM exist (see Ball et al., 2013;Bracken et al., 2016;McLean et al., 2013), a definition is used herein which combines those from the Scottish Environment Protection Agency (SEPA, 2015) and the Environment Agency (2010): NFM aims to reduce flood risk by protecting, restoring and emulating the natural hydrological and morphological processes, features and characteristics of catchments using environmentally sensitive and beneficial techniques to manage sources and flow pathways of flood waters. ...
... NFM currently lacks a similar, robust empirical evidence base describing the impact of NFM upon flood risk parameters, including before and after impact measurements. Such an evidence base is needed to enhance confidence in implementing NFM measures (Table 1) (Cook et al., 2016;Iacob et al., 2017;McLean et al., 2013;Waylen et al., 2017). The aim of this review is, therefore, to critically review new approaches for NFM progression through a series of evaluations of NFM interventions. ...
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Natural flood management (NFM), or working with natural processes, is a growing flood risk management method in the UK, Europe and worldwide. However, unlike the current dominant technical flood management, it lacks an established evidence base of flood risk parameters. This lack of evidence base can limit the uptake of NFM as a flood management method. This paper critically evaluates examples of NFM and wider relevant literature in order to identify NFM knowledge gaps and suggest how to overcome these. The UK is used as a microcosm of different environments for diverse examples. The sections include: land cover, land management, landscape interactions and trade-offs, evaluating the wider benefits of NFM and, finally, scaling from plot to catchment. This concludes in a suggested framework for a new approach to NFM research, which encompasses spatial scales, interactions and trade-offs of NFM and consistency of reporting results. Widening the NFM empirical evidence base should be seen as an opportunity for a new approach to flood research through exploring new habitats and new flood resilience methods.
... However, this study focuses solely on the variations in infiltration data, and the influence of tree proximity and tree maturity on infiltration-in addition to undertaking statistical testing on such data. Developing an understanding of the influences of tree planting on infiltration, and contextualising these findings in the context of the wider implementation of NFM and existing policy, will aid in the justification and subsequent uptake of NFM methods [15,32]. This will allow for enhanced flood risk reduction both at present, and in the future, considering the predicted impacts of climate change and continued urbanisation [1,[3][4][5]. ...
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Urbanisation and the replacement of previously vegetated areas with impermeable surfaces reduces the lag times of overland flow and increases peak flows to receiving watercourses; the magnitude of this will increase as a result of climate change. Tree planting is gaining momentum as a potential method of natural flood management (NFM) due to its ability to break up soil and increase infiltration and water storage. In this study, a 2.2 km2 clay-textured area in Warwickshire, England, planted with trees every year from 2006 to 2012 was sampled to investigate how infiltration varies dependent on season and tree proximity and maturity. Infiltration data was collected from 10 and 200 cm away from selected sample trees from November 2019 to August 2021 using a Mini Disk infiltrometer (MDI). The results show that mean infiltration is higher at the 10 cm proximity compared with the 200 cm proximity by 75.87% in winter and 25.19% in summer. Further to this, mean 10 cm infiltration is 192% higher in summer compared with winter, and mean 200 cm infiltration is 310% higher in summer compared with winter. There is little evidence to suggest a relationship between infiltration and tree maturity at the study site.
... Despite the praise of NFM to the benefits it creates in reducing flooding, the technique is under intense scrutiny. Mclean et al. (2013), cites how little evidence of the effectiveness of NFM exists, which implies the need for research into the contrasting results from NFM interventions. ...
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Flooding is a global issue with hundreds of flood events occurring annually. An increase in usage of Natural Flood Management has occurred in recent years with the total number of leaky dams on the increase. Leaky dams aim to reduce the surface flow of water both within small gully systems and along the surface. Construction of the leaky dams occurred as a result of previous flood events, most recently in 2015 to mitigate the effect of future flood events. The main aim of this study is to clarify whether leaky dams reduce and regulate the discharge flowing through a gully. Furthermore, exterior influences such as storage pool variation, wetted perimeter and topography is analysed to highlight potential influences of the dams at the site. Results produced from this study show a variety in dam storage pools, with seasonality an influence in affecting how leaky dams reduce the discharge with winter months showing a regulation in discharge. This study examines a small stretch of gully and attempts to provide a framework for future leaky dam projects to provide a means of effective flood reduction for natural flood management schemes in the future.
... The evidence for catchment-scale NFM having an impact on preventing fluvial flooding in downstream, urban areas remains inconclusive (Iacob et al., 2017;McLean et al., 2013). However, three studies in the United Kingdom have amalgamated physical and numerical results at a range of spatial scales from many different catchments (Burgess-Gamble et al., 2017;Dadson et al., 2017;Forbes, Ball, & McLay, 2015). ...
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This study examines whether catchment‐scale natural flood management (NFM) interventions could help to manage water levels in downstream urban watercourses and promote free discharge from surface drainage outfalls. A coupled modelling approach consisting of Dynamic TOPMODEL, HEC‐RAS, and Infoworks ICM models is used to characterise the response from a small Cambridgeshire catchment. Four different NFM scenarios (consisting of in‐channel woody debris and wider catchment afforestation) are defined. The attenuation of catchment response created by these measures is evaluated for an historic event and six different design storms. The consequent moderation of water depths at two downstream drainage outfalls is investigated with respect to maintaining free discharge from a surface drainage system. The case study results show that greatest reductions in the time of outfall inundation from NFM occur during frequent storm events (e.g., up to 5.75 hr during a 5‐year event). These reductions diminish with increasing storm severity but, by slightly desynchronising rural and urban responses, upstream interventions continue to have modest benefit for downstream drainage performance (e.g., preventing system capacity being exceeded during a 100‐year event). These results may interest water companies (increasingly involved in catchment‐scale NFM projects) looking to improve performance of surface water drainage.
... This has particular relevance for England and Wales, where the expected average cost of flood damage is of the order of £1.2 billion per year (Ramsbottom et al., 2012). However, only one study focused on riparian areas and flood management from a modelling perspective (McLean et al., 2013). ...
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The limited understanding of Natural Flood Management (NFM) performance, especially at large hydrological scales, is considered a critical barrier for the further funding and implementation of these nature-based solutions to the increasing international problem of flooding. The publications of the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report and Environment Agency’s National Flood and Coastal Erosion Risk Management Strategy (NFCERMS) for England have shown that extreme weather, including increased likelihood of high magnitude flood events, will occur and will require more novel management methods. This study focused on the ability of co-designed NFM measures to ameliorate downstream fluvial flooding by attenuating catchment response through a highly spatially distributed network of attenuating and roughening measures. Performance was characterised by the ability of NFM to attenuate flood peaks at different spatial scales across a large (187 km2) dendritic catchment, including the lowering of flood peaks and delaying the time-to-peak. Using a coupled modelling methodology and applying it to the upper Stour Valley, Warwickshire-Avon, UK, a rural response to the application of a set of NFM interventions was developed using the hydrodynamic model Flood Modeller Pro and XPSWMM ©. The method demonstrated a means of incorporating local knowledge in a realistic set of NFM schemes, tested to multiple flood risk scenarios (including climate change). Under frequent, smaller design storm events (e.g., Index Flood (QMED) and 3.3% AEP), flood peaks were lowered across all hydrological scales tested (5.8 km2 to 187 km2). As the design flood event severity increases, impact from upstream NFM attenuation on downstream peak response diminished significantly, especially at the largest hydrological scales. However, even at the largest hydrological scale, delays in time-to-peak were noted, increasing the ability of downstream communities to respond and enact flood preparation activities, thus increasing resilience to potential flooding events. While the benefits were limited to large flood events, the modelling indicated that NFM has the potential to reduce downstream flood risk. However, greater integration of observed data to improve model confidence and reduce uncertainty in modelled events is needed, especially the uncertainty associated with using single peaked design storm events from the Flood Estimation Handbook (FEH). This paper proposes a future Before–After Control–Impact (BACI) monitoring programme that could be integrated with models and applied across non-tidally influenced catchments seeking to empirically test the hydrological performance of in-situ NFM.
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Mountain areas are highly exposed to flood risks. The latter are increasing in the context of climate change, urbanization, and land use changes. Non-structural approaches such as nature-based solutions can provide opportunities to reduce the risks of such natural hazards and provide further ecological, social, and economic benefits. However, few non-structural flood mitigation measures are implemented in rural mountain areas so far. The objective of this paper is to investigate if the scientific boundaries limit the implementation of non-structural flood management in rural mountain areas. In the study, we statistically analyzed the knowledge about flood management through a systematic literature review and expert surveys, with a focus on European rural mountain areas. Both methods showed that scientific knowledge is available for decision makers and that nature-based solutions are efficient, cost-effective, multifunctional, and have potential for large-scale implementation.
The evaluation of Natural Flood Management (NFM) has traditionally focused on the ability of interventions to mitigate downstream fluvial flooding by attenuating catchment response. However, the justification for the implementation of NFM projects at a local level is often supported by other benefits provided by such interventions (e.g. improvements to water quality or biodiversity). This study investigates the potential for a further, largely unrecognised, benefit. It is suggested that, by moderating water levels in downstream watercourses, upstream interventions could also help sustain free discharge from drainage outfalls, thereby improving the performance of urban surface drainage systems. A coupled modelling methodology is applied to the upper Calder Valley and the surface drainage in an area of the downstream town of Todmorden. The rural response and subsequent NFM interventions are characterised using hydrological (Dynamic TOPMODEL) and hydraulic (HEC-RAS) models. Several downstream surface drainage systems are then incorporated using an Infoworks ICM model to examine their response to changes in outfall inundation. The results suggest that catchment-scale tree planting and in-channel woody debris create modest benefits for downstream surface drainage systems. Under frequent storm events (e.g. a 1 in 10 year storm), the inundation of low-lying outfalls is completely removed. As storm severity increases (and surface flooding becomes an issue), impact from upstream NFM attenuation on outfall inundation durations diminishes significantly. However, the slight delay in rural response allows more water to escape surface systems, increasing the effective capacity of networks and reducing surface flooding. For instance, outfall inundation during an estimated 20 year event is delayed by 0.5 hours, which results in up to 25% reduction in surface flood volumes. While the benefits are limited in extent, this modelling indicates that NFM can help improve downstream surface drainage performance.
Conference Paper
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The UK climate is projected to get warmer with an increased likelihood of wetter weather and an increased incidence of extreme meteorological events. The risk of inland and coastal flooding is expected to become more severe, though with variable impacts depending on local exposure, vulnerabilities and adaptive capacity. Responding to this challenge will require traditional engineering schemes to protect specific assets but there is an emerging role for natural flood management (NFM) as a means to reduce flood risk while realising multiple co-benefits across the catchment. Here we present a meta-analysis of 20 recent European NFM projects, exploring their flood mitigation performance along with their wider impacts (positive and negative) on ecosystem services, as defined by the UK’s National Ecosystem Assessment. Some measures, such as upland afforestation, perform well in reducing flood risk but have significant impacts on food production and cultural services. Other strategies, including restoring floodplain connectivity or re-meandering have the greatest co-benefits e.g. improved biodiversity, water quality and carbon sequestration, but appear to be less effective in reducing the flood risk. A framework is presented as a decision-support tool, to aid options analysis between alternative NFM schemes within the context of different land management scenarios
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There is currently a dearth of empirical evidence on the performance of most options for mitigating diffuse pollution from agriculture across a representative range of environmental and agricultural conditions. Riparian buffers have, however, received more attention than most mitigation options over the past 20 years. Ranges for positive buffer efficacy were found to be 30-100% for sediment, 30-95% for total phosphorus, 10-100% for total nitrogen, 30-100% for pesticides and 53-100% for faecal indicator organisms. Since many of the experiments underpinning this evidence base were conducted under 'ideal' operating conditions, it is likely that buffer performance in reality will be further hampered by a number of factors such as compaction or the occurrence of concentrated flows. Overall, the evidence base suggests that buffers provide useful short-term benefits, but the longer-term impacts remain questionable owing to risks of pollution swapping. Optimal buffer performance will be site-specific and typically limited in duration, thereby requiring a targeted approach for deployment. Assessing the implications of the reported ranges in buffer performance for implementing a targeted approach remains a key challenge.
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The water quality of our rivers and lakes is a reflection of the landscape over and through which it travels. The UK government, along with all European Union member states, are obliged under the Water Framework Directive (WFD) to aim for good ecological status of fresh water bodies by 2015. In order to evaluate the effectiveness of potential mitigation measures in reducing diffuse water pollution from agriculture at the catchment scale, the Demonstration Test Catchment (DTC) project was developed. The project is jointly funded by Defra, the Environment Agency (EA) and the Welsh Assembly Government (WAG). There are three DTCs across the country: the Eden catchment, Cumbria; the Wensum catchment, Norfolk and the Hampshire Avon catchment. The Eden DTC has established three ~10 km2 focus catchments, chosen to reflect different farming practices, geologies, elevations and hydrological characteristics. Within each focus catchment, two sub-catchments have been selected, one control and one mitigated, in which numerous existing and novel mitigation measures will be tested. It is hoped that the mitigation features will be multi-purpose, having positive effects on pollutant retention, flooding, carbon sequestration, habitat creation and biodiversity. The effectiveness of these measures is assessed through networks of hydro-meteorological and water-quality instrumentation, most of which will provide data in near real time, with sub-hourly time steps.
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Ecosystem services, the benefits that people obtain from ecosystems, are a powerful lens through which to understand human relationships with the environment and to design environmental policy. The explicit inclusion of beneficiaries makes values intrinsic to ecosystem services; whether or not those values are monetized, the ecosystem services framework provides a way to assess trade-offs among alternative scenarios of resource use and land- and seascape change. We provide an overview of the ecosystem functions responsible for producing terrestrial hydrologic services and use this context to lay out a blueprint for a more general ecosystem service assessment. Other ecosystem services are addressed in our discussion of scale and trade-offs. We review valuation and policy tools useful for ecosystem service protection and provide several examples of land management using these tools. Throughout, we highlight avenues for research to advance the ecosystem services framework as an operational basis for policy decisions.
Runoff attenuation features (RAFs) are low-cost, soft-engineered catchment modifications designed to intercept polluted hydrological flow pathways. They are used to slow, store and filter runoff from agricultural land in order to reduce flood risk and improve water quality, specifically by mitigating diffuse water pollution from agriculture. This study focuses on a sub catchment (30 ha) of the Belford Burn catchment (5.7 km2) where the capacity of two RAFs to reduce concentrations of suspended sediment (SS), phosphorus (P) and nitrate (NO 3) in runoff has been investigated. A field bund RAF, designed to intercept overland flow during storm events, has been shown to retain significant volumes of sediment; however, the underlying field drains are still exporting high concentrations of sediment and nutrients, sometimes exceeding 500 mg SS l−1, 1 mg TP l−1 and 40 mg NO 3 l−1. An on-line sediment pond is accumulating sediment during normal flow conditions, but event sampling has revealed a lack of retention of any pollutants during storm events, which has been attributed to remobilisation of previously deposited material. In order to address these problems and improve the quality of the water leaving the sub catchment, a novel multi-stage RAF has been constructed in the ditch network. A low-cost filter trap, using wood chippings, has been installed and will be the focus of on-going monitoring and investigations. The ability to help tackle flooding and pollution by managing runoff flow pathways does have great potential, despite being somewhat difficult to evaluate.
There is evidence to suggest that modern rural land-use management practices have led to increased runoff production at the farm scale. There are concerns that this may have contributed to downstream flooding of towns/villages, especially during intense local storm events. This paper presents an investigation into the potential attenuation of rural runoff through the application of soft-engineered structures upstream of flood-prone settlements, through a demonstration of ongoing initiatives in the Belford catchment, Northumberland (5.7 km2). The soft-engineered features that have been considered in the study include storage ponds, barriers, bunds, and the planting of vegetation and the positioning of woody debris in the riparian zone. The Belford study has been active since November 2007 and is yielding an abundance of good-quality data, including several significant flood events, on how runoff propagates through the small rural catchment and causes flooding of the village, and how flood propagation can be attenuated using Runoff Attenuation Features (RAFs).
Riparian vegetation typically has a great influence on groundwater level and groundwater-sustained stream baseflow. By modifying the well-known method by White [White, W.N., 1932. Method of estimating groundwater supplies based on discharge by plants and evaporation from soil – results of investigation in Escalante Valley, Utah – US Geological Survey. Water Supply Paper 659-A, 1–105] an empirical and hydraulic version of a new technique were developed to calculate evapotranspiration (ET) from groundwater level readings in the riparian zone. The method was tested with hydrometeorological data from the Hidegvíz Valley experimental catchment, located in the Sopron Hills region at the western border of Hungary. ET rates of the proposed method lag behind those of the Penman–Monteith method but otherwise the two estimates compare favorably for the day. At nights, the new technique yields more realistic values than the Penman–Monteith equation. On a daily basis the newly-derived ET rates are typically 50% higher than the ones obtainable with the original White method. Sensitivity analysis showed that the more reliable hydraulic version of our ET estimation technique is most sensitive (i.e., linearly) to the laboratory- and/or slug-test derived values of the saturated hydraulic conductivity and specific yield taken from the riparian zone.
On 5–6th September 2008, prolonged rainfall in the north east of England resulted in flooding in many towns. Belford lies within this region and has a history of flooding, but on this occasion, flooding was minimal. Numerous houses and businesses are at a risk of flooding but traditional flood defence measures are not considered to be cost effective. In the year before the storm, a series of runoff attenuation features had been developed in the Belford catchment (∼6 km2) as part of Farm Integrated Runoff Management plans. Water-level data from the stream and pilot feature indicated the effectiveness of the feature in storing and slowing runoff during the September 2008 storm. These data indicated that the pilot feature held runoff for approximately 8 h. The effect that this had on the travel time of the peak was significant: it increased from 20 to 35 min.