3.4 Floodplain management and restoration

please provide general comments to section 3.4 here

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The complexity of floodplain management, with highly dynamic ecosystems and long-term socio-economic pressures, requires holistic approaches where scientific evidence and expert knowledge are operationalised for policy needs (Antrop, et al., 2013). Floodplains originally provided a high variety and quantity of ESs (and a biodiversity hotspot) but in many cases experienced strong human impacts that declined the delivery of ecosystem services. The impact of interventions upstream on the more downstream located regions and finally on the total ESs provided requires in-depth knowledge and understanding of the complex floodplain ecosystems (Scholz, et al., 2012) (See Box. 3.X). It is supposed that floodplains are particularly vulnerable to the impacts of climate change and therefore well-planned floodplain management is more and more required while demand for floodplain ESs are growing (Capon, et al., 2013).

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When remaining active floodplains are compared with floodplains that have been cut off from the inundation regime, the remaining floodplains show a much greater ability to act as flood retention areas, as reservoirs for groundwater, as filters (or sinks) for sediments and dissolved pollutants, as carbon sinks, recreation areas and natural habitats for highly specialised flora and fauna (e.g.(Scholz, et al., 2012)). They are also natural flood protection areas that delay the discharge of flood waves and, thus, contribute to mitigate flood peaks, especially when the floodplains are covered with near-natural forests (see e.g. (Hughes, et al., 2003; Moss, and Monstadt, 2008)).

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Box 3.4           Ecosystem services

Ecosystem services (ESs) can be described as the benefits that people obtain from ecosystems (Millennium Ecosystem Assessment 2005) and can be grouped into provisioning, regulating, cultural and supporting services (figure 3.6). Most ESs refer specifically to the ‘final’ outputs from landscapes, providing benefits for humans and society (Maes, et al., 2012).In a simplified conceptual ecosystems and socio-economic systems are linked by flows of ESs and drivers of change (figure 3.7). Ecosystems are shaped by the interactions of biotic and abiotic environment. Ecosystem functions are the capacity or potential to deliver ESs, where ESs the realised flow (EC 2013f).

As one of the most important ecosystem services of floodplains flood regulation supply addresses the capacity of the ecosystem to decrease flood hazards by reducing the runoff. As such, flood regulation is an ES contributing to human well-being (Millennium Ecosystem Assessment 2005). For the ES flood regulation, there is a spatial link in between downstream areas of a river catchment that are mainly benefitting from increased flood protection, and the headwaters and upstream areas being the flood regulation supplying areas (Syrbe, and Walz, 2012).

Optimizing a balanced supply of multiple ESs can be done by green infrastructure (GI), being an interconnected network of green areas for the conservation of ecosystem functions and providing benefits to society (Schindler, et al., 2014). The European Commission published a communication on GI (EC 2013c) and the concept is also linked to the Habitats Directive (EU 1992, Art. 10) with the aim to overcome landscape fragmentation and the Biodiversity strategy (EC 2011a) with the demand of maintaining and enhancing ecosystems and their services by 2020 by “establishing green infrastructure and restoring at least 15% of degraded ecosystems. The importance of investing in ecosystems, including floodplains as a particular area of interest, is also recognized as a source of economic development for the regional and cohesion policy of the EU (EC 2011b).

To estimate the effect of protecting and restoring floodplains, one needs an overview of the different ESs and their quantity provided by that area. On the European level, this exercise is ongoing for all terrestrial and marine ecosystems (a) in the Mapping and Assessment of Ecosystems and their Services (MAES) process (EC 2013f, 2014e) (see also Box 3.5).

In a study on the Somerset Levels and Moors (SLM) wetlands (Acreman, et al., 2011) the different ESs are looked at individually before combining them as the real added value in terms of management of the area is in the synergies or conflicts between the ESs. Besides mapping the ESs the different ESs also needs to be assessed to value their importance by means of indicators (EC 2014e). This assessment is site specific and, for example, in the SLM wetlands case most ecosystem services are based on the area being wet but with the exceptions of flood storage and methane emissions (Acreman, et al., 2011). The active involvement of an area for flood risk protection needs to consider this, and leads to trade-offs between different land management practices. In addition, climate change may make it difficult to maintain actual or preferred conditions (Acreman, et al., 2009) and the example demonstrates that not all services can be maximized simultaneously (Acreman, et al., 2011).

(a) See http://projects.eionet.europa.eu/eea-ecosystem-assessments/library/draft-ecosystem-map-europe online. Floodplains are not a type of ecosystem but overlap and can be part of almost all ecosystem types and subtypes. In the freshwater pilot, (inland) wetlands were included but these overlap only partly with floodplains (see section 2.3).

Figure 3.6       Basic ecosystem services of rivers and floodplains

Source: (Millennium Ecosystem Assessment 2005)

Figure 3.7       Conceptual framework for ecosystem assessments

Source: (EC 2013f) and (EEA 2015c)

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3.4.1        Protection of floodplains

Remaining floodplains are important to fulfil the goals of different European directives like the WFD, the FD or the BHD (see Chapter 4). The riparian zones are important biological quality components to assess the ecological structure and status. According to FD most countries in Europe have designated flood retention areas which are very often legally protected to manage flood events and to avoid unsuitable land uses. Because of the high biodiversity values, many of these flood retention areas are at the same time overlapping with protected sites for nature conservation, like the Natura 2000 network.

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Floodplains contain a high diversity in habitats and species (section 2.3 and 3.1) and most of the natural or semi-natural floodplain habitats are listed in the annexes of the HD (EU 1992). Floodplain habitats are not only covered in the category of freshwater habitats, but can also be found in the categories of bogs and mires, grasslands and forest. Nearly all natural floodplain forest types are nowadays listed in the Annex 1 of the HD(EU 1992) and are protected at national level. Nevertheless, in most biogeographic regions the conversation status (EU 1992, Art. 17) still remain in unfavourable condition, being classified as “bad” or at least ”inadequate”(EEA 2015d) (Figure 3.8).

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Figure 3.8       Floodplain forest habitats in Natura 2000 Assesment (*)

Note: for EU27 and per biogeographic region; Results of 9 forest type assessments have been aggregated.

Source: Data aggregated from Eionet – ETC/BD 2015: Online report on Article 17 of the Habitats Directive (2001-2006) http://bd.eionet.europa.eu/article17/reports2012/.

(*) Figure to be updated in final version based on most recent data, plus explanation of abbreviations. Conclusions remain.

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Besides restoration of the former floodplains and habitats (see subsection 3.4.2), protection of the valuable areas that are left must be assured and remain a priority as no restoration can reach the level of ESs provided as the intact reference landscape does (Rey Benayas, et al., 2009; Scholz et al., 2012, Schindler, et al., 2014). The interventions in floodplains and the effects on biodiversity lead to the conclusion that there is often a mismatch in spatial and temporal scales between scattered scientific evidence and the holistic approach needed by decision makers (Schindler, et al., 2013). These spatial aspects go beyond areal requirements (minimum area) needed to deliver a certain level of ESs, but also include spatial composition (patterns of different ecosystems) and spatial configuration like buffer strips, connections and corridors (Bastian, et al., 2012). The same goes for the time dimension, where there are minimum time requirements for the generation of a particular ES as well as complex sequences in the utilization of an ES to enhance the benefits and time lags between the supply and demand or use of an ES (Bastian, et al., 2012).

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Where the water storage role of floodplains and wetlands gets increased attention as an ES, ecology-based measures get rarely only positive feedback from different stakeholders (Grygoruk, et al., 2013). Flooding, normally naturally and regularly occurring in lowland floodplains becomes a limiting factor for agricultural activities and an obstacle for economic development. Drainage as a pressure is increasing with broad-scale degradation of the fresh-water dependent ecosystems. The true economic dimension of water storage in floodplains is however more profitable for a broad range of stakeholders and potentially affected people than it appears negative for agriculture (Grygoruk, et al., 2013).

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In economic terms, the benefit of water storage in the floodplain is often compared with the benefit of storage in artificial reservoirs. Although, the total picture need to include other ESs as well, having their own economic value as well as the value of the synergies between ESs. In doing so, the monetary or economic value of water storage on a unit of land cannot be substituted by flood-related losses, but become one element in balanced calculations of whether to drain or keep the floodplain (Grygoruk, et al., 2013). Such an ecologic-economic assessment – extensively studied nowadays (e.g. (Bateman, et al., 2013; Burkhard, et al., 2013; Maes, et al., 2012; Sullivan, 2012)) - is a basic requirement for sustainable development and a necessity for environmental management at country level (Lawton, and Rudd, 2013).

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A sustainable management of floodplains could at least minimize eco-toxicological effects of pollutants by e.g. uptake through plants, restricting agricultural use and by widening the active floodplain areas in terms of connecting rivers to their adjacent floodplains. This is highly important as floodplains fulfil several ecosystem functions and services. Water purification is one of them; floodplains may retain several pollutants and nutrients from river water during inundation events or phases of high groundwater levels (Hoffmann, et al., 2009; Natho, et al., 2013). Consequently, an increase of pollutant and nutrient retention in floodplains supports the efforts undertaken to fulfil the aims of the WFD.

The sum of all inundated floodplains in Germany can retain up to 42 000 tons of nitrogen and 1200 tons of phosphorus per year. This equals a yearly purification service of 500 million Euros, being the avoided costs for water treatment in sewage plants (Natho, 2014; Scholz, et al., 2012).

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3.4.2        Floodplain restoration in Europe

Floodplain restoration refers to the creation of ecosystems that are typical for floodplains, which exhibit a hydrological link between the river and the adjacent land. The term restoration as we use it in this report only refers to rehabilitation or enhancement of the ecological functions of rivers and their floodplains (Moss, et al., 2008). Restoration and rehabilitation of floodplains showed enhanced ESs provided and a consistently increased multifunctionality of the area (Schindler, et al., 2014). Floodplain restoration is an important measure to give more rooms for rivers, especially to reduce flood hazards aiming to prevent them from becoming disasters.

Natural flood plain management requires a specific set of measures to reduce flood risk and improve natural floodplain functioning at the same time. These measures can be aimed at both reducing the flooding probability and minimising the potential damage. Natural flood risk reduction measures contribute to the restoration of the characteristic hydrological and geomorphological dynamics of rivers and floodplains and ecological restoration for biodiversity. Especially in highly and/or long time developed areas, it is (almost) impossible to go back to a complete natural state. Still, natural water retention measures (NWRMs) (see Box 3.5) like artificial wetlands, even on a small scale, help to keep farmland soil out of rivers and reduce river pollution by nutrients (Ockenden, et al., 2014).

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Where structural measures mainly deal with flood control, natural flood risk reduction measures comprise flood control, use and retreat, regulation, financial stimulation and compensation measures (Pichler, et al., 2009). However, the whole discussion has to focus on ESs that are provided and the co-benefits provided by natural flood risk retention measures (EEA and ETC/ICM 2015) rather than on the somewhat arbitrary distinction between structural and non-structural measures or grey and green measures. A ring dike around a floodplain is longer than a straight dike along the river. Nevertheless, the previous is leaving more room for water retention, self-purification, sediment accumulation, recreation, and many other ESs. Case studies in the UK (Pettifer, and Kay, 2012) support the ‘intermediate disturbance hypothesis’; where sites that are frequently and never flooded are less diverse in terms of biodiversity than those that are sometimes disturbed. This calls for sustainable flood risk management approaches with measures that work with natural processes to allow intermediate levels of flooding.

Changes in land use are often needed for the implementation of these measures. Therefore spatial planning and stakeholder involvement are of vital importance when implementing a natural flood defence scheme (Moss, et al., 2008). The protection of existing naturally functioning river and floodplain systems also can be regarded as an important natural flood risk reduction measure.

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Box 3.5           Natural Water Retention Measures

Natural Water Retention Measures (NWRMs) are a nature-based approach to pursue the objectives of water management, providing a variety of co-benefits in terms of biodiversity enhancement, greenhouse gas mitigation, energy saving or rural development opportunities (EC, 2015a). These co-benefits create opportunities to involve different stakeholders and require cooperation between policy areas like agriculture, forestry, energy or tourism but also includes the possibility that no one might be interested in taking the initiative as the benefits are varied and sparsely distributed.

Natural water retention is explicitly mentioned in the EU Floods Directive (EU 2007) and the maximisation of its use forms part specific objectives of the Water Blueprint (EC 2012c). Other restoration measures for natural areas, like re-meandering of natural ponds are (indirectly) recommended by a note on better environmental options for flood risk management (EC 2011d), and seen as a better environmental option and alternative for hard (grey) infrastructure. “Flood risk management should work with nature, rather than against it (EC 2011d). Where the Water Framework Directive (EU 2000) has the water body as a central concept, limited attention is given to riparian zones which might hinder the implementation of NWRMs to its full potential (EC, 2015b). NWRMs call for an integration, not only in between WFD and FD but also nature legislation and all policy fields where water and land planning needs careful coordination (EC, 2015b).

Most of the NWRMs have a long term horizon, where the effectiveness and benefits of a measure only become visible after some time and they need a large spatial scale of implementation, like a catchment to be effective, so one needs to find space on land that is often already serving another purpose (EC, 2015b). This can be challenges or even barriers for implementation, as society can feel less concerned about long-term impacts and benefits that are more uncertain than short term costs (EC 2012b). In addition, the fact that several NWRMs require a commitment for regular management and maintenance can be an additional challenge.

Financing NWRMs can be challenging as there are many beneficiaries and the financing sources used for traditional flood risk management based on infrastructure works are not always available. Even when NWRMs are more cost-efficient than “grey” infrastructure providing the same flood protection, funding for the implementation and maintenance still has to be found (EC, 2015d). In section 4.1, some of the financing sources available for NWRMs are discussed in more detail.

On the other hand, there is a strong evidence base that NWRMs can be effective and cost-beneficial, especially in win-win situations where costs and benefits are distributed amongst several stakeholders (EC, 2015b). Spatial planning activities could provide the appropriate room to bring the different needs and constraints of stakeholders together (Parrod, 2014).

Choosing the right NWRM in connection to one objective is already far from straightforward, and adding multiple objectives makes it even more complicated (EC, 2015c). The mix of NWRMs with other structural and non structural measures will always need to be site-specific and robust to changing conditions, including climate change (Santato, et al., 2013). Many NWRMs are low-regret measures regarding climate change adaptation (Borchers, 2014), yielding benefits even in the absence of climate change and are flexible to be adapted to new insights on a later stage. A single NWRM is unlikely to change significantly the flood risk in a catchment of the status of a water body. Nevertheless, the widespread use of NWRMs can make significant contributions to meet flood risk objectives, water quality objectives and nature objectives, while improving financing possibilities, finding the best adapted solution for the local situation, increasing public acceptance and overcoming concentration on individual policies (EC, 2015c).

For more information, see http://www.nwrm.eu online

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Efficiency and effectiveness of water retention measures

NWRM and other non-structural measures like flood forecasting and early warning are integral part of a modern integrated flood risk management (Pichler, et al., 2009). NWRM and the changes in land use that come with them are important to reach substantial flood risk reductions, but decision makers keep coming back to water managers with the question about their efficiency and effectiveness. Effectiveness, a term also used in the WFD is a result–based term and describes the degree of goal achievement in terms of risk reduction or effects towards risk reduction. Efficiency is a yield-based term and describes how economically an intended risk reduction or an effect towards risk reduction has been achieved. This later one is related to a cost-benefit analysis, and is a key concept in the programme of measures for the floods directive (EEA 2012c; Pichler, et al., 2009)

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In general, the potential additional water storage capacity during floods of NWRMs like microponds or afforestation is rather limited. As smaller and more frequent floods can still have a large contribution to the total risk, the risk reduction capacity of NWRMs can be higher than expected from the hazard reduction (EEA 2012c; Francés, et al., 2008; Pichler, et al., 2009).

When assessing the efficiency and effectiveness of NWRMs, two issues have to be kept in mind: the complexity and the competitiveness. Complexity refers to the fact that NWRMs are not implemented to reach one single goal, e.g. flood protection, but come with a range of benefits. One should not forget that this can impose constraints on some sectors as well, because they perceive that their interests were better served by the former practices than by NWRM (Ungvári, 2014). The competitiveness addresses the issue that NWRMs and nature-based solutions have to deliver comparable sector level results on natural effectiveness, economic efficiency and being able to be implemented.

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Box 3.6           Restoration projects in Europe

During the 1990s interest in river restoration increased all across Europe. Initially restoration was mainly focused on the river channel itself and on aquatic ecology, but since the FLOBAR2 project (Hughes, et al., 2003) and the establishment of a European Centre for River Restoration (ECRR) in 1995 floodplain restoration got increased attention as an essential part of sustainable water management. A RiverWiki-database of the RESTORE project contains almost 1000 river restoration case studies but only a minority of the completed measures is directly related to floodplain restoration; being mainly floodplain reconnections, riparian tree planting, removal of exotic plants as well as wetland and backwater creation.

Also in the NWRM initiative (see Box 3.5) a catalogue with around 125 case studies can be found, including measures focussing on floodplain restoration that mainly can be found under the hydromorphology measures: river wetland and floodplain restoration and management, restoration and reconnection of seasonal streams or oxbow lakes, elimination of riverbank protection, re-naturalisation of polder areas etc.

Sources: http://www.ecrr.org/, https://restorerivers.eu/wiki/, http://www.nwrm.eu/list-of-all-case-studies

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