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BHS Eleventh National Symposium, Hydrology for a changing world, Dundee 2012. ISBN: 1903741181© British Hydrological Society

Natural flood management as a climate change adaptation option assessed using an ecosystem services approach

Oana Iacob1,4, John Rowan1,4, Iain Brown2,4 and Chris Ellis3,4

1 Centre for Environmental Change & Human Resilience, University of Dundee, DD14HN, UK2 The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK

3 Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5L, UK4 ClimateXChange, 15 South College Street, Edinburgh, EH8 9AA, UK

*Email: o.iacob@dundee.ac.uk

Introduction

The consequences of global climate change include major hydrological shifts such as rising sea levels, glacial retreat, changed rainfall patterns and increasing frequency of extreme weather events. Within the UK, inland flooding is expected to increase, with direct threats to livelihood and well-being resulting from impacts across multiple socio-economic sectors. European legislation on the assessment and management of flood risk (‘Floods Directive’) encourages natural catchment-based approaches to runoff control and flood generation that go beyond traditional engineering solutions normally directed towards specific asset protection. Integral to this shift in focus is greater attention on sustainable and adaptive flood abatement measures. These are aimed at protecting and restoring natural ecosystem services, and realising multiple co-benefits, whilst providing a socially-acceptable degree of flood protection and minimising social, environmental and economic costs. In many developed countries piecemeal approaches artificially separating land and water management are already giving way to integrated catchment management approaches (Hall and Penning-Rowsell, 2011). Increasing attention is being given to the ways in which natural flood management can reduce flood risk, whilst providing co-benefits at a catchment-scale. Specifically, NFM measures aim to increase the time to peak and the height of the flood wave downstream. NFM measures can also alter aspects of the catchment water balance by promoting infiltration and groundwater storage, enhancing water losses through evapotranspiration and altering hydrological pathways and increasing flow resistance.

In this paper we explore the ways in which ecosystem services might provide a framework to evaluate alternative NFM options and support decision-making by catchment managers. We present a meta-analysis of twenty recent NFM projects and proposals implemented in UK and mainland Europe, having examined both their efficiency in decreasing the flood risk and their impacts (both positive and negative) on different ecosystem service groups.

Methodology and study cases

There is no universally agreed scheme for evaluating ecosystem services, but the Millennium Ecosystem Assessment (MA) framework is a starting point. The UK’s National Ecosystem Assessment (UK NEA) builds on the MA by distinguishing between provisioning, regulating, cultural and supporting services. This provided the first analysis of the UK’s natural environment in terms of trade-offs while aiming for continuous economic prosperity (UK NEA, 2011) and it provides the foundation for the current study. For the present purposes we consider only final and intermediate ecosystem services and not the goods or beneficiaries. The assessment undertaken here acknowledges that several ecosystems (in particular ‘Biodiversity’) fall in more than just one Final Service category; however, the ecosystem services matrix is more closely defined for this study (cf. Table 2). .

Study casesThe case-studies used in the analysis were mainly drawn from Price et al. (2011), the latest review of NFM studies

AbstractThe 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.

doi: 10.7558/bhs.2012.ns26

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developed for SEPA, with added equivalents from the literature (Defra et al., 2010; Johnson, 2007). The categorisation of NFM schemes followed Price et al. (2011), with an additional mixed category where more than one NFM measure was proposed: (a) planting of upland forests and woodland; (b) upland drainage and drain blocking; (c) restoration of wetlands and floodplains; (d) combined measures. The case-study catchments differed greatly in size (see Table 1). Two alternative methods were used to assess the effectiveness of different NFM proposals: (i) hydrologic and hydraulic modelling exercises to assess flood attenuation potential, and (ii) direct monitoring. The variation in scale and lack of consistency in assessment methods presents challenges when evaluating the performance of different NFM measures, but these differences do not substantially affect the qualitative Ecosystem Services analysis undertaken here.

Performance of NFM measures The studies examined present the performance of the NFM measures in different ways: (i) as flood peak reduction for different flood events return periods (e.g. 1, 2, 25, 50, 100 years), (ii) as increase in time to peak parameter or (iii) as a decrease in annual probability of flood risk for the area. Figure 1 shows the flood abatement potential of some of the upland forest options for relatively frequent but small events (i.e. 2 years) contrasted with rarer but larger events (i.e. 50–200 years). For both magnitudes the Pontbren A scheme delivered the greatest flood peak reduction. For large flood events the Trent, Severn, Thames study also showed a reduction in flood peak, though of a lower magnitude than Pontbren A. However the two catchments are of very different size and, when comparing studies, scaling issues are likely to be a confounding factor in the assessment of NFM options, requiring further investigation.

Ecosystem service approach

The Ecosystem Services approach can provide a framework to analyse NFM performance within the wider context of key catchment processes including biodiversity, biogeochemical cycling, water resources, food and timber production as well as recreation and amenity (Figure 2). For this preliminary analysis, the likely impact of the NFM measure was qualitatively scored as positive, neutral or negative, for different ecosystem services (Table 2) alongside a consideration of its impact on flood management. Examples of the decision-making process are provided below. Increasing the coverage of ‘upland forests and woodland’ is a measure resulting in flood peak reduction downstream (e.g. Kamp, Iller and Parrett catchments). Other projects focused alternatively on establishing riparian or floodplain woodland (e.g. Pickering Beck, River Cary). As the percentage of the tree cover increased, the negative effect on ‘Crops’ and ‘Livestock’ gets larger as a result of competition for limited land. Both the Iller and Cary studies proposed to replace the grassland (not the arable land) limiting any trade-off to the ‘Livestock’ ecosystem service. The Trent, Severn and Thames study was considered to have the most significant negative effect on these agrarian ecosystem services, as the measure proposed coverage of large land areas (10 000 km2) with coniferous forest. Although the Pontbren study (Wheater et al., 2010) offered a similar proposal, the effects on ‘Crops’ and ‘Livestock’ services was thought to be lower, since the area of the catchment is smaller (i.e. 4 km2). These comparisons highlight that both the scale of the measure and the size of the area on which the measure is being implemented play a key role when assessing the effects on Ecosystem Services within a broader UK context. Increasing tree cover to control flow regulation and flooding would have significant accompanying effects on hydrology and many inter-related processes. Precipitation

Table 1 General information for the selected studies

No Catchment name and type of NFM scheme Country Area (km2) Approach Reference

Upland forests and woodland

1 River Trent, Severn, Thames England 10000 Modelling (Naden et al., 1996)2 Poyo Spain 380 Modelling (Francés et al., 2008)3 Kamp Austria 622 Modelling (Francés et al., 2008)4 Iller Germany 954 Modelling (Francés et al., 2008)5 Parrett England 1675 Modelling (Park et al., 2006)6 Pontbren Wales 4 Modelling (Wheater et al., 2010)7 Pickering Beck England 66 Modelling (Odoni et al., 2010)8 River Cary England 77 Modelling (Thomas and Nisbet, 2006)

Upland drainage and drain blocking

9 Blacklaw Moss Scotland 0.07 Monitoring (Robertson et al., 1968)10 Llanbrynmair Wales 3 Monitoring (Leeks and Roberts, 1987)11 Coalburn England 1.5 Monitoring (Robinson et al., 1998)12 Nospecifiedarea England 0.2 Modelling (Ballardetal.,2010)13 Ripon (Rivers Laver, Skell andKex Beck) England 120 Modelling (JBA, 2007)

wetlands and floodplains

14 Long Eau, Lincolnshire England - Monitoring (Moss, 2007)15 Quaggy River England - Monitoring (Potter, 2006)16 River Cherwell and its tributary River Ray England - Modelling (Acreman, 1985)17 Sinderland Brook England 2 Monitoring (Defra et al., 2010)

combined measUres

18 River Laver England 79 Modelling (Nisbet and Thomas, 2008)19 Glendey Scotland 2 Modelling (Johnson, 2007)20 Tillicoultry River Scotland - Modelling (Johnson, 2007)

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interception by the tree canopy promotes higher infiltration and groundwater storage, greater evapotranspiration leads to reduced runoff with soil erosion reduced because of root binding. Over time, biogeochemical cycling dynamics will change, promoting greater carbon sequestration, reduced nutrient efflux (subject to woodland species composition) with the potential to significantly augment biodiversity and soil and water quality (Hastie, 2003). The major improvements in these ecosystem services were noted for the studies that propose a significant increase of tree cover over large area.

Studies which addressed actions in the ‘Upland drainage and drain blocking’ category were based both on monitoring and modelling approaches (e.g. Robertson et al., 1968). Upland drainage options were assessed by three studies (e.g. BlacklawMoss, Llanbrynmair and Coalburn). The evidence for potential to regulate the flood flow is mixed. Whilst Robertson et al. (1968) and Robinson et al. (1998) have documented a decrease in the time to flood peak parameter for the Blacklaw Moss and Coalburn studies, Leeks and Roberts (1987) recorded a much peakier runoff response for the Llanbrynmair study after land drainage.

Figure 1 Location of selected NFM studies

Figure 2 NFM performance of upland afforestation for small and large events

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No

Nam

e Ec

osys

tem

serv

ices

Pr

ovis

ioni

ng

Regu

latin

g C

ultu

ral

Supp

ortin

g

Crops

Livestock

Fish

Trees/ Standing Veg.

Peat

Water supply

Climate

Carbon sequestration

Flood

Flow

Disease and pests

Fire

Water quality

Soil quality

Air quality

Science and education Tourism and recreation

Sense of place

History/ Religion

Bio diversity

Soil formation

Nutrient cycling

Water cycling

Oxygen production

Upl

and

fore

sts a

nd w

oodl

and

1 Tr

ent,

Seve

rn&

Tham

ecat

chm

ents

s

2 Po

yo

3 K

amp

4 Ill

er

5 Pa

rret

t

6

Pont

bren

(a)

Pont

bren

(b)

7 Pi

cker

ing

Bec

k

8

Car

y

9

Lave

r

U

plan

d dr

aina

ge a

nd d

rain

blo

ckin

g 10

B

lack

law

Mos

s

11

Ll

anbr

ynm

air

12

Coa

lbur

n

13

B

alla

rd st

udy

14

Rip

on

Wet

land

s and

floo

dpla

ins

15

Linc

olns

hire

16

Q

uagg

y

17

C

herw

ell

18

Sind

erla

nd B

rook

C

ombi

ned

mea

sure

s 19

G

lend

ey, D

evon

20

Ti

llico

ultry

Riv

er

Lege

nd:

Neg

ativ

e ef

fect

--

-

0 +

++

Posi

tive

effe

cts

U

ncle

ar e

vide

nce

Tabl

e 2

Eco

syst

em se

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es e

valu

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the

stud

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Moreover, comparison with the Ecosystem Service framework indicates broad disadvantages. Lowering the water table brings a temporary improvement to the grazing potential of an area, providing benefits for ‘Livestock’ ecosystem services; however, increased permeability leads to erosion and promotes mineralisation (carbon loss) in organic-rich upland soils. Water quality is likely to decline in this situation, with increased colour, nutrient and sediment-losses, leading to negative impacts on aquatic ecosystems locally and downstream. Drain blocking strategies are generally considered to have positive effects on ecosystem services. Both studies discussed here, the study of JBA (2007) and the study of Ballard et al. (2010), recorded a flood reduction. Other ecosystem services were positively affected by this action, with the size of Ripon study (i.e. 120 km2), compared with the other studies (i.e.2 km2), possibly explaining the slightly different magnitude of impact. Although Ballard et al. (2010) assumed no vegetation change in their model, the present analysis explicitly considered the effects of the drain blocking on terrestrial vegetation. With time, drain-blocking may alleviate soil erosion problems. As a soil is rewetted, it holds sediment and prevents erosion into water courses, alongside the drain-blocking materials themselves (Holden et al., 2007). The role of drain-blocking in improving carbon storage and the quality of water is mixed however. While some studies show a significant reduction in pore water DOC and the level of discolouration, others have suggested the method is inefficient (Glatzel et al., 2003; Wallage et al., 2006).Evidence for the efficacy of upland drain blocking remains equivocal, depending on local conditions, grip-drain spacing, and the consequent availability of unsaturated water storage capacity within drained soils (e.g. Robinson, 2006). The restoration of wetlands and floodplains was assessed by four studies. The assessment considers an operational phase, taking into account only the long term impacts and not the disruptions in the river caused by the implementation of the measure. There were similarities among studies in ecosystem service effects. As the River Cherwell study and Sinderland Brook study proposed restoring the river channel through the floodplain, both studies involved only a small land use change. The overall effects on ‘Crops’ and ‘Livestock’ would not be very significant. The proposed measure would provide important benefits to ‘Biodiversity’ and associated cultural services by restoring the catchment to their initial condition. Increasing the capacity of the floodplain to store water will yield a positive effect for ‘Water supply’. The last category to be discussed examined combined NFM measures and their accumulative effects. As this involves a wider range of strategies, including the interactions between them, the benefits to ecosystem services are expected to be high. The River Laver study modelled an increase in riparian and floodplain woodland. As a result, ‘Trees and standing vegetation’, ‘Climate regulation’ and ‘Biodiversity’ would benefit from the implementation of these combined measures. The strategy suggested a landuse change which would have adverse effects for ‘Crops and Livestock’ and all the Cultural Services. The Glendey study investigated the realignment of an artificial water course in a meandering channel and the restoration of the wetland (drain blocking and the planting of tree barriers across the wetland).The scale of the interventions at this site (i.e. 0.0175 km2) are small in relation to the whole catchment (i.e. 2 km2), hence the flood benefits realised are insignificant. The only adverse effects were expected to be on ‘Crops’ and ‘Livestock’ due to land-use change. In the Tilicoutry system (Defra et al., 2010) several measure were being tested, including the restoration of two meanders which would improve habitat (both in-

channel and floodplain connectivity), reduce the need for channel bank maintenance and increase cultural value through aesthetic improvement and greater recreational potential (e.g. angling) as examples of environmental gain. Critically, a key issue relates to how multiple small-scale interventions combine (in terms of numbers, area and locations) to realise cumulative benefits in larger and more complex catchment systems (Fullerton et al., 2010).

Conclusions

Several aspects have been identified as key points when assessing NFM from an ecosystem service perspective. The first one is the scale of the catchment. This differs greatly among studies, varying from 4 – 10 000 km2 (e.g. Pontbren as compared with the Trent, Severn, Thames catchments) within the same NFM category. Scale may potentially influence the performance of the measure to reduce the flood risk and also the changes on accompanying ecosystem services. The ecosystem services evaluation showed that there are greater benefits with NFM implemented at a larger scale. The studies that recorded flood risk reductions and benefits throughout the catchment (e.g. Trent, Severn, Thames) have identified the highest number of adverse effects. Another important aspect of the analysis is the time period considered for the evaluation of NFM strategies. The relationship between the NFM measure and the determined effect is dynamic, and susceptible to change over time. For example, as forest systems mature they have an increasingly strong effect on the environment around them, and their benefit for some of the ecosystem services will increase with time, e.g. carbon storage. The time-table considered for the evaluation must be carefully applied. The study of ecosystem services is increasingly promoted as a cornerstone of effective environmental management, but there remain many methodological challenges to operationalise the approach and fully integrate options analysis into decision-making at both the policy level and at the local level by catchment managers. A systems-based approach, incorporating possible climate futures along with alternative land management scenarios, offers a framework to explicitly include flow and flood regulation as one of multiple ecosystem services and thus better situate NFM within the wider context of climate change adaptation in the UK.

References

Acreman, M. 1985. The effects of afforestation on the flood hydrology of the upper Ettrick valley. Scot.Forestry, 89–99.

Ballard, C., McIntyre, N. and Wheater, H. 2010. Peatland drain blocking: Can it reduce peak flood flows? Proc. BHS Third Int. Symp., Managing Consequences of a Changing Global Environment, Newcastle, 2010. 698–702.

Defra, RSPB, Hedgecott, S. 2010. Working with natural processes to manage flood and coastal erosion risk. Environment Agency, Peterborough. 21–22.

Francés, F., García-Bartual, R., Ortiz, E., Salazar, S., Miralles, J., Blöschl, G., Komma, J., Habereder, C., Bronstert, A. and Blume, T. 2008. Efficiency of non-structural flood mitigation measures: “room for the river” and “retaining water in the landscape”. CRUE Research Report No I-6 London. 172–213.

Fullerton, A., Steel, E., Lange, I. and Caras, Y. 2010. Effects of spatial pattern and economic uncertainties on freshwater habitat restoration planning: A simulation exercise.Restoration Ecol., 18, 354–269.

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Glatzel, S., Kalbitz, K., Dalva, M. and Moore, T. 2003. Dissolved organic matter properties and their relation to carbon dioxide efflux from restored peat bogs. Geoderma 113, 397–411.

Hall, J.W., and Penning-Rowsell, E.C. 2011. Setting the scene for flood risk management. In: Flood risk science and management, Pender, G. and Faulkner, H. (Eds.). Blackwell Publishing Ltd. 2–16.

Hastie, C. 2003. The benefits of urban trees. Warwick District Council, Warwick. 2–4.

Holden, J., Gascoign, M. and Bosanko, N.R., 2007. Erosion and natural revegetation associated with surface land drains in upland peatlands. Earth Surf. Proc. Landforms, 32, 1547–1557.

JBA 2007. Ripon land management project - Final Report. Department for Environment, Food and Rural Affairs. 53pp.

Johnson, R. 2007. Flood Planner: A manual for the natural management of river floods. Report for WWF Scotland, Edinburgh. 32pp.

Leeks, G. and Roberts, G. 1987. The effects of forestry on upland streams – with special reference to water quality and sediment transport. In: Environmental Aspects of Plantation Forestry in Wales, Good, J. (Ed.). Institute of Terrestrial Ecology Symposium, 9–24.

Moss, T. 2007. Institutional drivers and constraints of floodplain restoration in Europe. Int. J. River Basin Manage., 5, 121–130

Naden, P., Crooks, S. and Broadhurst, P. 1996. Impact of climate change and land-use change on the flood response of large catchments. 31st MAFF Conference of River and Coastal Engineers, Keele University, 2.1.1–2.1.16.

Nisbet, T.R. and Thomas, H. 2008. Forest Research Project SLD2316: Restoring floodplain woodland for flood alleviation, Final Report, p. 40.

Odoni, N.A., Nisbet, T.R., Broadmeadow, S.B., Lane, S.N., Huckson, L.V., Pacey, J. and Marrington, S. 2010. Evaluating the effects of riparian woodland and large woody debris dams on peak flows in Pickering Beck, North Yorkshire, p. 29.

Park, J., Cluckie, I. and King, P. 2006. The Parrett Catchment Project (PCP): Technical Report on the Whole Catchment Modelling Project. The University of Nottingham, Nottingham, 69–84.

Potter, K.M. 2006. Where’s the Space for Water? – How Floodplain Restoration Projects Succeed, Master Dissertation for the Department of Civic Design. Liverpool University, Liverpool. 51–69.

Price, D.J., Clowes, J., Sokmener, B. and Donaghey, M. 2011. Development of methodology for assessment required under Section 20. Jacobs Engineering UK Limited. 1.1–2.67

Robertson, R.A., Nicholson, I.A. and Hughes, R. 1968. Runoff studies on a peat catchment. Proc. 2nd International Peat Congress, HMSO, London. 161–166.

Robinson, M., Moore, R., Nisbet, T. and Blackie, J. 1998. From moorland to forest: the Coalburn catchment experiment. Institute of Hydrology Report No 133. Wallingford. 64 pp.

Thomas, H. and Nisbet, T.R. 2006. An assessment of the impact of floodplain woodland on flood flows. Water Environ., 21, 114–126.

Wallage, Z., Holden, J. and McDonald, A. 2006. Drain blocking: an effective treatment for reducing dissolved organic carbon loss and water dicolouration in a drained peatland. Sci. Total Environ., 367, 109–114.

Wheater, H., McIntyre, N., Jackson, B., Marshall, M., Ballard, C., Bulygina, N., Reynolds, B. and Frogbrook, Z. 2010. Chapter 3, Multiscale impacts of land management on flooding. In: Flood risk science and management, Pender, G., Thorne, C. and Cluckie, I. (Eds.). Blackwell Publishing Ltd. 39–59.