Natural Water Retention Measures Research Articles

Micro-Catchments, Macro Effects: Natural Water Retention Measures in the Kylldal Catchment, Germany

Floods are among the most devastating and financially burdensome natural disasters in Europe. The combined impact of climate change and land use change is expected to exacerbate and intensify the destructive consequences of river floods. In this study, we analysed the effects of wetland restoration on peak and base flows and on water quality in the Kylldal catchment of the Kyll River in the German Middle Mountains using the Soil and Water Assessment Tool+ (SWAT+). Monthly median daily discharge increases varied between 3% and 33% in the studied (micro)catchments. The higher median flow rates show that discharge peaks were attenuated and distributed over a longer period, making both extreme peak flows and low flows less common. Peak flows tended to decrease, with the largest effects between late fall and early spring when peak flow values decreased by up to 18%. The annual maximum peak flows in each of the three micro-catchments decreased by 12–24% on average. The occurrence of daily average flow rates larger than 1 m3 s−1 was up to 45% lower after wetland restoration. Low flows increased by up to 21% and 13% in the summer and fall, respectively, which suggests that drought risk also decreases after wetland restoration. Average nitrogen exports decreased by 38–50% in the project areas and by 20% at the catchment level. Average phosphorus exports decreased by 52–67% in the project areas and by 25% at the catchment level. The study highlights the potential of wetland restoration for improving hydrological services, mitigating flood risks, and enhancing water quality. Restoring and maintaining freshwater ecosystems and their natural sponge functions is crucial for effectively managing water resources and addressing the challenges posed by climate change and land use changes.

Natural/Small Water Retention Measures: Their Contribution to Ecosystem-Based Concepts

The increasing incidence of droughts and heavy rainfall events is exacerbating conflicts between human and environmental demands for water. However, through providing multiple water-related ecosystem services and benefits simultaneously, Natural/Small Water Retention Measures (NSWRM) can mitigate such competing claims. Thus, they also contribute to the achievement of various Sustainable Development Goals and environmental targets set out in water- and agriculture-related policies of the European Union. In particular, NSWRM provide for the sound management of watersheds, which can significantly contribute to improved water quality and availability—as well as improving the resilience of agriculture and society. This paper demonstrates how NSWRM fit into the framework of ecosystem-based concepts, including Natural Water Retention Measures (NWRM), Green Infrastructure (GI), Sustainable Land Management (SLM), Ecosystem-based Adaptation (EbA), and Nature-based Solutions (NbS). NSWRM, as a distinct concept, bring added value to the other concepts by focussing on easy-to-implement, modestly sized, localised technical solutions to problems associated with water management, sediment, and nutrient loss. Through experience under the EU Horizon 2020 project OPTAIN (“OPtimal strategies to retAIN and re-use water and nutrients in small agricultural catchments across different soil-climatic regions in Europe”), we show what NSWRM are, how they are linked to each of the ecosystem-based concepts, and how they can help add value to these concepts. Fourteen case studies are drawn upon from diverse countries across Europe. As a result of this analysis, we present the potential for the application of NSWRM in the context of these concepts, while helping to identify planning tools, the expertise required, and potential funding mechanisms.

Opportunities and limitations for Nature-Based Solutions in EU policies – Assessed with a focus on ponds and pondscapes

Nature-Based Solutions (NBS) are growing in popularity to mitigate and adapt to climate change, enhance biodiversity, and secure human well-being. However, the emergence of NBS has not generated equal attention for all ecosystems. One such neglected ecosystem are ponds and pondscapes (i.e. groups of ponds in a landscape), which are deteriorating in quality and diminishing in quantity. As the European Union (EU) is regarded as influential in the conceptualisation and operationalisation of NBS, we conducted a qualitative content analysis of 38 EU policies to identify opportunities and limitations for the implementation of ponds and pondscapes as NBS. We focus our analysis on ponds and pondscapes, but their prevalence in different landscapes and their multitude of benefits allows us to also make some inferences about the implications of the EU policy context for NBS at large. We find that EU policies strengthen NBS linked to existing and potential Natura 2000 sites, as well as to ecosystems protected through the EU’s Birds and Habitats Directives and Water Framework Directive. However, if ecosystems fall outside of these already established policies – as is the case with the vast majority of ponds and pondscapes – their implementation as NBS may be hampered. We also find that the EU emphasises natural water retention measures and carbon-rich ecosystems for climate change adaptation and mitigation, but mostly does not explicitly include ponds and pondscapes despite their potential contributions. Other findings are that the EU’s Horizon Europe research policy will likely influence which ecosystems will be used and financed as NBS, while the exact ambition and selection of NBS rests with lower-level authorities or individuals. Therefore, further studies tracing the impact of the supra-national EU policy framework at lower governance levels are vital.

Performance of Sand and Mixed Sand–Biochar Filters for Treatment of Road Runoff Quantity and Quality

Nature-based solutions and similar natural water retention measures to manage urban runoff are often implemented by cities in order to reduce runoff peaks, catch pollutants, and improve sustainability. However, the performance of these stormwater management solutions is relatively rarely assessed in detail prior to their construction, or monitored and evaluated following implementation. The objective of this study was to investigate the field-scale performance of road runoff filters with respect to the management of stormwater quantity and quality. This study synthesizes data from two intensive measurement surveys after the construction of sand and biochar-amended road runoff filters. The filters were able to strongly control the runoff volume and shape of the hydrograph. The long-term retention was about half that of the water inflow, and a hydrographic analysis showed the significant but strong event-size-dependent detention of runoff in both the sand and the sand–biochar filters. The biochar amendment in the filter showed no clear hydrological impact. The pollutant attenuation of the implemented road runoff filters was modest in comparison with that observed under controlled conditions. The impact of the biochar layer on the effluent water quality was observed as the levels of phosphorous, organic carbon, K, Ca and Mg in the sand–biochar filter effluent increased in comparison with the sand filter.

Sustainable Stormwater Management at Urban Expansion Areas of Potential Significant Flood Risk

The Preliminary Flood Risk Assessment (PFRA) for the Greek territory, according to European Directive 2007/60/EC, was completed in 2012 and was revised in 2019. Areas of Potential Significant Flood Risk (APSFR) were defined (and revised) for each River Basin District (RBD). Meanwhile, in 2018, the Flood Risk Management Plans (FRMPs) were approved - by Greek Authorities - for each RBD. In the FRMPs specific measures are proposed for the funding of Stormwater Management (SM) projects that will be designed according to the principles of Sustainable Development (SD), i.e., Best Management Practices (BMPs), Green Infrastructure (GI), Low Impact Development (LID), Urban Natural Water Retention Measures (NWRM) and Sustainable Drainage Systems (SuDS). Within this framework, a preliminary study is drawn up in order to specify some innovative proposals for Sustainable Stormwater Management (SSM) in three areas located into the APSFR of RBD ‘EL11’ (Eastern Macedonia), located in Northern Greece. Two of these areas, Perigiali and Nea Peramos are coastal, while the third one, Doxato, is a continental, plain area. Urban expansion plans are approved for all three cases. The study proposes the implementation of an Innovative Stormwater Management Plan (ISMP) for each area.

The Role of Information and Dissemination Activities in Enhancing People’s Willingness to Implement Natural Water Retention Measures

Under a climate-change scenario, adaptation strategies to pluvial flood risk are crucial in urban and rural areas. Natural water retention measures are particularly helpful to manage runoff water, providing also additional co-benefits to the local population. However, the very limited knowledge of their benefits among citizens hinders their implementation, especially across southern European countries. Therefore, information and dissemination activities aimed at showing the benefits of these measures are particularly important to stimulate implementation by private citizens, although only a few studies have previously investigated their role. This paper considers some demonstrations of natural water retention measures—and the related information and dissemination activities to the local population—in northeastern Italy, explicitly including them as a driver in the Protection Motivation Theory framework. Through a direct survey of 219 households, it aims to quantitatively assess the impact on citizens’ willingness to implement natural water retention measures of the different levels of access to information provision, namely, the role played by active access through participation in the activities; passive access to available information; and no access. The results show that citizens’ willingness to implement the interventions on their properties is positively affected by their active access to information, thus highlighting the importance of high-quality information provision by public and private actors.

Attitudes of administrative decision-makers towards nature-based solutions for flood risk management in Germany

Over the last two decades, alternative and holistic concepts, such as Nature-based Solutions (NbS) were introduced and adopted by policy-makers, including to the field of flood protection, thereby causing a paradigm shift towards flood risk management. The inclusion of natural water retention measures (NWRM) such as dike relocation and floodplain restoration into the German guidelines for flood protection institutionalized the new concepts in Germany. Whereas small scale NbS and the affected population have already been subject to thorough scientific research, large-scale NbS and the decision-makers assigned with the measure’s implementation have yet to be studied. How do administrative decision-makers perceive the new approach and measures? Are there particular attitudes among the decision-makers regarding NbS? Which aspects of implementing large-scale NbS influence possible attitudes? Which hurdles do decision-makers concern for the implementation of the new concepts? This paper investigates these questions on the example of dike relocation and floodplain restoration using Q-methodology with administrative decision-makers of flood protection authorities in the German state of Saxony-Anhalt. The consecutive statistical analysis unveiled three significant viewpoints among the decision-makers. The viewpoints/attitudes were classified as 1. The Convinced, 2. The Concerned and, 3. The Evaluators, defined by varying and individual concerns on the implementation of dike relocation and floodplain restoration. Hereby, this study delivers insights on large-scale NbS as well as on the issues of their implementation.

Experimental Flash Floods Assessment Through Urban Flood Risk Mitigation (UFRM) Model: The Case Study of Ligurian Coastal Cities

Cities are vulnerable to extreme weather events, particularly by considering flash flood risk as a result of even more short-duration intensive rainfall. In the context of climate change, compound flooding due to simultaneous storm surges and increased runoff may further exacerbate the risk in coastal cities, and it is expected to be frequent and severe across several European urban areas. Despite this increasing evidence, the spatial knowledge of the hazardous events/vulnerabilities through modelling scenarios at the urban level is quite unexplored. Moreover, flood-prone areas often do not correspond to the traditional flood risk classification based on predicted return-period. The result that huge impacts (human losses and damages) occur everywhere throughout the city. Consequently, this new challenge requires stormwater flooding mitigation strategies to adapt to cities while mainstreaming urban flood resilience. In this paper, we considered the Urban Flood Risk Mitigation model through the employment of the open-source tool—Integrated Evaluation of Ecosystem Services and Trade-off (InVEST)—developed by the Natural Capital Project, integrated into a GIS environment. The model application in the three urban coastal territory of the Liguria Region (Italy) estimated the amount of runoff due to two extreme rainfall events for each watershed considered. These index calculation results help define examples of Natural Water Retention Measures (NWRM) per land-use type as resilient solutions by addressing site-specific runoff reduction. Local sensitivity analysis was finally conducted to comprehend the input parameter's influence of rain variation on the model.

Assessing multi-scale effects of natural water retention measures on in-stream fine bed material deposits with a modeling cascade

Natural water retention measures (NWRMs) belong to the broad range of nature-based solutions and are receiving increased attention for targeting environmental problems of river catchments as they effectively support the restoration of natural processes and cycles. Challenges involved in NWRMs planning include the development of tools able to project and diagnose the effects at different spatial scales (e.g., catchment or the reach). This paper focuses on NWRMs addressing fine bed material deposits (FBMDs), with the aim of a) assessing factors and scales that control FBMDs; b) simulating the cascading impact of NWRMs on catchment hydrology, sediment loads, reach hydraulics, and FBMD; and c) assessing the effectiveness of NWRMs in targeting FBMDs at different spatial scales (catchment and reach). A modeling cascade was used to propagate the effects. This included a hydrological model (SWAT), a hydraulic model (HEC-RAS), and a spatially distributed Random Forest ensemble to model FBMDs risk for the Aist catchment (650 km2) Austria. Our results show that upstream sediment loads are an important predictor controlling the likelihood of sites to be classified as low risk. The effectiveness of NWRMs in reducing FBMDs is variable and depends on the target risk class. Vegetated filter strips that can trap sediments before they enter into the stream are more effective in increasing the extent of the river network towards natural conditions (5% increase compared to baseline). Sediment retention ponds are effective in reducing the extent of reaches where instream habitats are completely clogged by FBMDs (−8%). Hydromorphological improvements are effective in targeting sites where FBMDs are transported even during mean flow (−10%). A combination of NWRMs could benefit both high-risk as well as low-risk sites. The effectiveness of NWRMs can greatly differ when both reach and catchment diagnostics are analyzed. Thus, multi-scale assessment of the effectiveness can support NWRMs planning by unraveling all the potential benefits and highlighting tradeoffs hidden by analyses limited to a single spatial scale.

Assessment of Green Infrastructure in Riparian Zones Using Copernicus Programme

This article presents an approach to identify Green Infrastructure (GI), its benefits and condition. This information enables environmental agencies to prioritise conservation, management and restoration strategies accordingly. The study focuses on riparian areas due to their potential to supply Ecosystem Services (ES), such as water quality, biodiversity, soil protection and flood or drought risk reduction. Natural Water Retention Measures (NWRM) related to agriculture and forestry are the type of GI considered specifically within these riparian areas. The approach is based on ES condition indicators, defined by the European Environment Agency (EEA) to support the policy targets of the 2020 Biodiversity Strategy. Indicators that can be assessed through remote sensing techniques are used, namely: capacity to provide ecosystem services, proximity to protected areas, greening response and water stress. Specifically, the approach uses and evaluates the potential of freely available products from the Copernicus Land Monitoring Service (CLMS) to monitor GI. Moreover, vegetation and water indices are calculated using data from the Sentinel-2 MSI Level-2A scenes and integrated in the analysis. The approach has been tested in the Italian Po river basin in 2018. Firstly, agriculture and forest NWRM were identified in the riparian areas of the river network. Secondly, the Riparian Zones products from the CLMS local component and the satellite-based indices were linked to the aforementioned ES condition indicators. This led to the development of a pixel-based model that evaluates the identified GI according to: (i) its disposition to provide riparian regulative ES and (ii) its condition in the analysed year. Finally, the model was used to prioritise GI for conservation or restoration initiatives, based on its potential to deliver ES and current condition.

A procedure for designing natural water retention measures in new development areas under hydraulic-hydrologic invariance constraints

AbstractIn recent years, in Italy and elsewhere, regional regulations based on hydraulic-hydrologic invariance (HHI) principles have taken hold, especially for new development areas. Natural water retention measures (NWRMs) are among the most interesting options to provide the storage and infiltration capacities that are needed to achieve the HHI objectives. A procedure for the design of NWRMs in new development areas under HHI constraints is presented and is based on a simple combination of Soil Conservation Service Curve Number (SCS-CN) method for determining rainfall excess and lag-time method for simulating runoff propagation. Three types of NWRMs can be considered: rain barrels, drainage wells and drainage trenches; five types of synthetic hyetographs can be selected and three different approaches for the determination of critical storm duration applied. The results obtained by applying the procedure in a new development area located in northern Italy are illustrated and some general conclusions are drawn. It clearly emerges that practitioners should pay particular attention to the correct determination of design storm duration in order to avoid large underestimations of NWRMs size. Moreover, different combinations of the three NWRMs can provide the required reduction of peak of runoff after the transformation, but it appears that drainage trenches are more effective with respect to harvesting systems in reducing the peak runoff value.

Monitoring Green Infrastructure for Natural Water Retention Using Copernicus Global Land Products

Nature-based solutions are increasingly relevant tools for spatial and environmental planning, climate change adaptation (CCA), and disaster risk reduction (DRR). For this reason, a wide range of institutions, governments, and financial bodies are currently promoting the use of green infrastructure (GI) as an alternative or a complement to traditional grey infrastructure. A considerable amount of research already certifies the benefits and multi-functionality of GI: natural water retention measures (NWRMs), as GIs related specifically to the water sector are also known, are, for instance, a key instrument for the prevention and mitigation of extreme phenomena, such as floods and droughts. However, there are persisting difficulties in locating and identifying GI and one of the most promising solutions to this issue, the use of satellite-based data products, is hampered by a lack of well-grounded knowledge, experiences, and tools. To bridge this gap, we performed a review of the Copernicus Global Land Service (CGLS) products, which consist of freely-available bio-geophysical indices covering the globe at mid-to-low spatial resolutions. Specifically, we focused on vegetation and energy indices, examining previous research works that made use of them and evaluating their current quality, aiming to define their potential for studying GI and especially NWRMs related to agriculture, forest, and hydro-morphology. NWRM benefits are also considered in the analysis, namely: (i) NWRM biophysical impacts (BPs), (ii) ecosystem services delivered by NWRMs (ESs), and (iii) policy objectives (POs) expressed by European Directives that NWRMs can help to achieve. The results of this study are meant to assist GI users in employing CGLS products and ease their decision-making process. Based on previous research experiences and the quality of the currently available versions, this analysis provides useful tools to identify which indices can be used to study several types of NWRMs, assess their benefits, and prioritize the most suitable ones.

Can Land Cover Changes Mitigate Large Floods? A Reflection Based on Partial Least Squares-Path Modeling

Common approaches to large flood management are Natural Water Retention Measures and detention basins. In this study, a Partial Least Squares-Path Model (PLS-PM) was defined to set up a relationship between dam wall heights and biophysical parameters, in critical flood risk zones of continental Portugal. The purpose was to verify if the heights responded to changes in the biophysical variables, and in those cases to forecast landscape changes capable to reduce the heights towards sustainable values (e.g., <8 m). The biophysical parameters comprised a diversity of watershed characteristics, such as land use and geology, surface runoff, climate indicators and the dam heights. The results have shown that terrain slope (w > 0.5), rainfall (w > 0.4) and sedimentary rocks (w > 0.5) are among the most important variables in the model. Changes in these parameters would trigger visible changes in the dam wall height, but they are not easily or rapidly modified by human activity. On the other hand, the parameters forest occupation and runoff coefficient seem to play a less prominent role in the model (w < 0.1), even though they can be significantly modified by human intervention. Consequently, in a scenario of land cover change where forest occupation is increased by 30% and impermeable surfaces are decreased by 30%, interferences in the dam heights were small. These results open a discussion about the feasibility to mitigate large floods using non-structural measures such as reforestation.

Application of Natural Water Retention Measures in Flood Management

Due to climate change, increasingly extreme weather conditions and runoff parameters are leading to the enhancement of flood risk. The increasing probability of fast flowing, high intensity flash floods jeopardize both the residents of small municipalities and the fields of farmers, especially in the downstream areas of mountainous and hilly regions. In many cases the protection of settlements cannot be solved through conventional flood management approaches due to high investment costs and built-in floodplains. The main goal of this article is to analyse the potential of flood risk mitigation with applying natural water retention measures. These additional measures could have a positive effect on the quality and quantity of surface and groundwater. Research results facilitate an even more effective preparation in a way of applying nature based solutions to supplement traditional flood management.

Urban Water Retention Measures

Many cities and urban areas are located in flood plains because land is fertile and flat which is suitable for agriculture and urban development. Rivers provide water supply for domestic, industrial and irrigation uses; they also provide convenient means for navigation, transportation and communication. Cities have large percentage of impervious areas that prevent effective infiltration of rainfall into soil. To have successful flood control and flood risk management, we should consider not only hydraulic and engineering aspects but also socio-economic and environment aspects. Flood management should have involvement of various stakeholders including concerned authorities such as urban planners, civil and water resources engineers, civil disaster defence authorities, health and social services, etc. The best flood mitigation measures from all main points of view – social, economic and environmental are natural water retention measures. Natural water retention measures cover a diversity of measures that are implemented by different sectors or considered in different planning processes dealing with water, food risk management, biodiversity protection, climate change adaptation or urban planning. Some of these measures aim to directly modify the ecosystem, while others focus on changes of practice of economic operators. The paper presents natural water retention measures suitable for application in urban areas.

Realising the potential of natural water retention measures in catchment flood management: trade‐offs and matching interests

Natural water retention measures (NWRM) are a multifunctional form of green infrastructure that can play an important role in catchment‐scale flood risk management. While green infrastructure based on natural processes is increasingly recognised as being complementary to traditional flood control strategies based on grey infrastructure in urban areas, there are a number of outstanding challenges with their widespread uptake. At a catchment scale, it is widely accepted that NWRM in upstream areas based on the concept of ‘keeping the rain where it falls’ can help reduce the risk of downstream flooding by enhancing or restoring natural hydrological processes including interception, evapotranspiration, infiltration, and ponding. However, both the magnitude of flood risk reduction and the institutional structures needed for widespread uptake of NWRM are inadequately understood. Implementing NWRM can involve trade‐offs, especially in agricultural areas. Measures based on drainage management and short rotation forestry may help ‘keep the rain where it falls’ but can result in foregone farm income. To identify situations where the implementation of NWRM may be warranted, an improved understanding of the likely reductions in downstream urban flood risk, the required institutional structures for risk management and transfer, and mutually acceptable farm compensation schemes are all needed.

Current status and restoration options for floodplains along the Danube River

Floodplains are key ecosystems of riverine landscapes and provide a multitude of ecosystem services. In most of the large river systems worldwide, a tremendous reduction of floodplain area has occurred in the last 100years and this loss continues due to pressures such as land use change, river regulation, and dam construction. In the Danube River Basin, the extent of floodplains has been reduced by 68% compared to their pre-regulation area, with the highest losses occurring in the Upper Danube and the lowest in the Danube Delta. In this paper, we illustrate the restoration potential of floodplains along the Danube and its major tributaries. Via two case studies in the Upper and Lower Danube, we demonstrate the effects of restoration measures on the river ecosystem, addressing different drivers, pressures, and opportunities in these regions. The potential area for floodplain restoration based on land use and hydromorphological characteristics amounts to 8102 km2 for the whole Danube River, of which estimated 75% have a high restoration potential. A comparison of floodplain status and options for restoration in the Upper and Lower Danube shows clear differences in drivers and pressures, but certain common options apply in both sections if the local context of stakeholders and societal needs are considered. New approaches to flood protection using natural water retention measures offer increased opportunities for floodplain restoration, but conflicting societal needs and legal frameworks may restrict implementation. Emerging issues such as climate change and invasive non-native species will need careful consideration in future restoration planning to minimize unintended effects and to increase the resilience of floodplains to these and other pressures.

A land-use-based modelling chain to assess the impacts of Natural Water Retention Measures on Europe’s Green Infrastructure

This article details the process of integrating models to answer a specific policy-driven question: ‘What could be the impact of proposed Natural Water Retention Measures (NWRMs) on Europe’s Green Infrastructure (GI)?’ It describes the new Land Use Modelling Platform (LUMP), now enabling a high spatial scale (100-m) and large coverage (pan-European), whereby several sector-specific models contribute to assessing the impact of regional-level policy on a given spatial topic of concern. The configuration (land claims and land allocations modules) and calibration (accessibility and biophysical suitability) of the LUMP are explained. Four NWRM scenarios (riparian areas, afforestation, grassland and baseline scenario) are configured to run the simulations. For the reference: year 2006, the spatial representation of GI is based on land-use features of a refined version of the CORINE Land Cover (CLC), and resumed as connected components made of nodes and links.Mathematical morphological image processing and network graph theory model, available from the free software package GUIDOS (the Joint Research Center of the European Commission), enabled the measurement of the GI connectivity and identified most critical links. Results show that the competition for land claimed by different economic sectors, combined with policy-driven rule-sets for the implementation of different NWRMs, yields very different results for the 2030 land-use projections, and subsequently for the morphology of GI. Three indicators associated with the morphology of GI are computed in order to assess the model outputs for 2030. The indicators are computed to answer the following questions: (1) How is the quantity of GI affected by each of the NWRM, and what proportion of that GI is most valuable? (2) What is the location of the most critical nodes and connectors of GI, and what land-use conversions occur under these? (3) Are the average components getting larger or smaller?Whereas the grassland measure results in the largest net increase of GI, the afforestation measure results in the overall largest number of hectares of key nodes and links within the network. Land conversions occur under the critical GI nodes and links, with a large increase in agricultural areas, especially for the riparian measure under critical nodes and the grassland measure under critical links. Also predominant is the swapping of land from pasture to forest under critical links with the afforestation measure. The riparian measure most increases the average size of GI components, and all three measures contribute to bridging two large components which were divided in the 2006 land-use map, thus increasing the size of the largest component by more than 50%.