Nature-Based Solutions for Riverbank Protection
キーワード:
bioengineering,
ecosystem resilience,
nature-based solutions,
riverbank protection,
vegetation planting
2026 年 14 巻 3 号 p. 1-16
詳細
2026 年 14 巻 3 号 p. 1-16
This review synthesizes current research on nature-based solutions (NbS) for riverbank protection, focusing on vegetation planting, soil bioengineering, and wetland restoration as sustainable approaches to erosion control and ecosystem resilience. It evaluates ecological effectiveness, hydro-mechanical performance, and implementation factors, including design, maintenance, and stakeholder engagement. A systematic analysis of 60 studies from diverse geographic contexts indicates that vegetation-based bioengineering enhances slope stability, soil cohesion, and biodiversity, with species selection and adaptive maintenance as critical success factors. Wetland restoration contributes to sediment retention, improved water quality, and ecological resilience, although long-term performance data remain limited. Hybrid approaches combining vegetation with structural elements demonstrate greater reliability under high-energy hydraulic conditions. Despite these advantages, persistent challenges include maintenance requirements, invasive species management, and limited standardization of performance assessment. Overall, NbS provide multifunctional riverbank protection but require improved long-term monitoring, quantitative evaluation, and integration of socio-economic considerations. The findings offer practical guidance for context-specific implementation and highlight key priorities for future research
Research on nature-based solutions for riverbank protection has emerged as a critical area of inquiry amid growing concerns about riverbank erosion, habitat degradation, and the need for sustainable ecosystem management. Over recent decades, the field has evolved from traditional hard engineering approaches toward integrated ecological and bioengineering methods that leverage vegetation and natural processes to stabilize banks and restore riparian habitats [1, 2]. This shift reflects growing recognition of the ecological, social, and economic benefits of such solutions, as demonstrated by studies showing improvements in slope stability, biodiversity, and flood mitigation [3, 4]. For instance, bioengineering techniques have been shown to enhance slope stability by over 25% while promoting habitat connectivity [1, 3]. Given that only about 44% of rivers in some regions meet good ecological status, the adoption of nature-based solutions is vital for sustainable water resource management and biodiversity conservation [5].
Despite advances, riverbank erosion remains a pressing problem, exacerbated by anthropogenic pressures such as channelization, urbanization, and the proliferation of invasive species. Current challenges include limited understanding of the long-term effectiveness of vegetation-based stabilization, selection of species for diverse hydrodynamic conditions, and integration of this approach with conventional engineering [6, 7]. Moreover, controversies persist regarding the relative efficacy of bioengineering versus complex engineering, with some studies highlighting failures due to improper design or maintenance [7, 8]. The knowledge gap is particularly evident in optimizing bioengineering techniques across varied climatic and geomorphological contexts, and in quantifying ecological co-benefits alongside structural performance [9, 10, 11]. Failure to address these gaps risks continued degradation of riparian zones, loss of ecosystem services, and increased vulnerability to flooding [12, 13].
This review adopts a conceptual framework that defines nature-based solutions as integrated approaches combining vegetation planting, bioengineering structures, and wetland restoration to enhance riverbank stability and ecosystem resilience [14]. It emphasizes the synergistic relationships between plant root reinforcement, sediment dynamics, and hydrological processes, linking ecological restoration with engineering objectives [15]. This framework guides the systematic evaluation of vegetation species selection, bioengineering techniques, and wetland functions for riverbank protection.
The purpose of this systematic review is to synthesize current knowledge on nature-based solutions for riverbank protection, with a focus on vegetation planting, bioengineering methods, and wetland restoration. It aims to clarify effective practices, identify limitations, and propose integrative strategies that reconcile erosion control with biodiversity conservation. By addressing identified gaps, this review advances sustainable river management and informs practitioners and policymakers on best practices [1, 3, 6].
The review methodology involves a comprehensive analysis of peer-reviewed studies and case reports published primarily between 1990 and 2025, selected for relevance to riverbank stabilization using nature-based approaches. The synthesis is organized thematically to examine the roles of vegetation, bioengineering techniques, and wetland restoration, integrating ecological and engineering perspectives to provide a holistic understanding [1, 4, 11].
The objective of this review is to synthesize current knowledge on nature-based solutions for riverbank protection, identify effective strategies, and highlight key knowledge gaps. Given the increasing ecological and socio-economic pressures on river systems, NbS are examined as sustainable alternatives to conventional engineering approaches.
Specific objectives:
・To evaluate current knowledge on vegetation planting, soil bioengineering, and wetland restoration for riverbank protection;
・To benchmark NbS approaches in terms of ecological effectiveness and engineering performance;
・To identify factors influencing the success and limitations of vegetation-based stabilization methods;
・To assess community engagement and socio-economic impacts;
・To analyze design principles and monitoring practices for integrating ecological and engineering objectives.
Research gap and contribution of this review. Existing reviews on NbS for riverbanks often emphasize either ecological restoration outcomes or the engineering functionality of selected techniques. At the same time, socio-economic integration and post-construction maintenance are frequently treated as secondary considerations. Moreover, cross-study comparability remains limited due to heterogeneous performance indicators and the scarcity of long-term monitoring data, which constrains evidence-based decision-making. Therefore, a key gap lies in the lack of an integrated evaluation framework that jointly considers (i) ecological effectiveness, (ii) hydro-mechanical engineering performance, (iii) socio-economic and governance conditions, and (iv) maintenance and adaptive management requirements. To address this gap, this review synthesizes 60 highly relevant studies. It proposes an integrated assessment structure and practical selection guidance to support context-specific riverbank NbS planning under varying hydrological, geomorphological, and socio-economic settings.
Although previous reviews have provided valuable insights into river restoration, soil bioengineering, or broader nature-based solutions, they have often emphasized either ecological restoration outcomes or the engineering functionality of selected techniques in relative isolation. By contrast, the present review adopts an explicitly integrated perspective that evaluates riverbank NbS across four interrelated dimensions: ecological effectiveness, hydro-mechanical engineering performance, socio-economic and governance conditions, and maintenance/adaptive management requirements. In addition, this review extends beyond descriptive synthesis by translating the literature into practical, context-specific guidance for selecting vegetation-based, wetland-based, and hybrid stabilization strategies under different hydrological, geomorphological, and institutional settings.
The review methodology was designed to maximize transparency, reproducibility, and topical relevance. Literature retrieval was conducted using Scopus and Web of Science Core Collection as the primary databases, with Google Scholar used for cross-checking and limited grey-literature identification. Searches covered publications from 1990 to 2025 and used combinations of terms related to nature-based solutions, soil bioengineering, ecological engineering, riverbank stabilization, vegetation-based measures, and wetland-related interventions.
Records were first screened based on title and abstract relevance to riverbank or streambank stabilization. Studies were then retained for full consideration if they reported vegetation-based, wetland-based, soil-bioengineering, or hybrid interventions supported by empirical evidence, validated modeling, or experimental analysis. Studies lacking methodological clarity, bank-scale relevance, or outcome indicators were excluded. After structured screening, citation chaining, and quality appraisal, 60 studies were retained for in-depth synthesis.
2.1 Search strategy and query developmentThe initial research question, “Nature-based solutions for riverbank protection focusing on vegetation planting, bioengineering techniques, and wetland restoration,” was systematically refined into multiple, thematically focused search queries. This structured query transformation was undertaken to operationalize the broad research scope into discrete, searchable components, thereby enhancing the comprehensiveness, precision, and reproducibility of the literature retrieval process.
Literature searches were conducted in Scopus and Web of Science Core Collection, complemented by Google Scholar for cross-checking and capturing grey literature. Searches were performed for publications from 1990 to 2025. Representative search strings included: (“nature-based solution*” OR “soil bioengineering” OR “ecological engineering” OR “bioengineering”) AND (“riverbank” OR “streambank” OR “bank stabilization” OR “erosion control”) AND (vegetation OR wetland* OR fascine* OR “live staking” OR “brush mattress”).
The resulting set of refined search statements was designed to capture the key technical, ecological, and socio-environmental dimensions of nature-based riverbank protection strategies. The transformed queries derived from the original research question are presented as follows:
・Nature-based solutions for riverbank protection, focusing on vegetation planting, bioengineering techniques, and wetland restoration
・Exploring ecological engineering strategies and community involvement in riverbank stabilization through nature-based solutions and recent advancements in sustainable river management.
・Investigating the role of community engagement and socio-economic impacts in nature-based solutions for riverbank restoration and stabilization, with a focus on stakeholder collaboration and sustainable practices.
・Investigating community-driven strategies and stakeholder engagement in the implementation of nature-based solutions for riverbank restoration and protection, emphasizing socio-economic benefits and ecological resilience.
Investigating community-driven methodologies and the integration of local ecological knowledge in the application of nature-based solutions for adequate riverbank protection and restoration.
2.2 Screening papersInclusion criteria were: (i) direct focus on riverbank/streambank stabilization using vegetation-based measures, soil bioengineering, wetland restoration or hybrid approaches; (ii) empirical field evidence and/or validated modeling/experimental results; (iii) clear description of intervention design and outcome indicators (e.g., erosion rate, bank retreat, soil shear strength, vegetation survival, habitat/biodiversity metrics); and (iv) peer-reviewed journal/conference sources in English (and selected non-English studies when methodological detail was sufficient).
Exclusion criteria included: purely conceptual commentary without application; studies focusing on catchment-wide management without bank stabilization measures; insufficient methodological description; and duplicates.
2.3 Citation chainingTo enhance the completeness of the literature corpus, a citation chaining approach was employed. Backward citation chaining was conducted by systematically examining the reference lists of the core studies to identify earlier foundational publications underpinning the selected research. This process ensured that seminal and methodologically influential works were not omitted.
In parallel, forward citation chaining was performed to identify more recent studies that cited the core publications, thereby capturing subsequent developments, emerging research themes, replication efforts, and methodological advancements within the field.
By combining backward and forward citation chaining, an additional 132 relevant publications were identified and added to the candidate literature pool.
2.4 Relevance scoring and sortingThe assembled corpus comprised 604 candidate publications, including 472 studies identified through structured database searches and 132 additional studies obtained via citation chaining. This literature pool was subsequently subjected to a relevance-based ranking procedure to prioritize studies most closely aligned with the research objectives. A total of 604 records were considered topically relevant after title/abstract screening; following eligibility and quality appraisal, 60 studies were retained for in-depth synthesis.
The review is reported in a PRISMA-consistent structure (identification, screening, eligibility, inclusion). Given the heterogeneity of outcomes and metrics, a systematic qualitative synthesis was performed rather than meta-analysis. Study quality was assessed based on the clarity of the intervention description, the robustness of the outcome measurement, the duration of monitoring, and the transparency of site conditions. A detailed flow of the literature search and selection process is illustrated in Figure 1.
This section delineates the research landscape of the existing literature on nature-based solutions for riverbank protection, with particular emphasis on vegetation planting, bioengineering techniques, and wetland restoration. The reviewed studies encompass a wide range of geographic settings and methodological frameworks, reflecting diverse climatic, hydrological, and socio-environmental contexts.
Collectively, the literature addresses ecological, engineering, and socio-economic dimensions of riverbank stabilization, with a strong emphasis on vegetation-based bioengineering and integrated restoration strategies. Methodologically, the studies employ a combination of field experiments, numerical and analytical modeling, and empirical case studies, enabling the assessment of both structural performance and ecological functionality.
To provide a structured overview of the evidence base and avoid excessive detail at the individual-study level, the reviewed literature is synthesized into a categorical matrix (Table 1). Rather than listing studies separately, this table groups the selected research into major NbS approaches, including vegetation planting, soil bioengineering, wetland restoration, and hybrid eco-engineering systems. For each category, the primary benefits and key limitations are summarized, together with representative references. This synthesis facilitates a clearer comparison across intervention types and supports the identification of dominant patterns in ecological effectiveness, engineering performance, and implementation constraints.
| NbS category | Primary benefits | Key challenges/limitations | Representative studies |
|---|---|---|---|
| Vegetation planting | Root reinforcement enhances soil shear strength, reduces flow velocity, and improves biodiversity and ecological resilience. | Sensitive to hydraulic stress; establishment phase vulnerable; species selection critical; requires maintenance. | [3, 6, 7, 9, 10, 11, 15, 23, 24, 25, 26, 28, 30, 36, 38, 41, 47] |
| Soil bioengineering | Combines vegetation and structural elements; improves erosion control and slope stability; adaptable to various conditions | Design complexity; requires technical expertise; maintenance required; performance varies with site conditions | [1, 2, 4, 5, 8, 18, 19, 20, 22, 27, 31, 33, 34, 35, 37, 40, 42, 45, 46, 48, 52, 53, 54] |
| Wetland restoration and buffer systems | Improves water quality, sediment retention, and flood buffering; enhances biodiversity and ecosystem resilience | Limited direct mechanical stabilization; dependent on hydrological compatibility; land availability constraints | [12, 32, 44, 49, 56, 57] |
| Hybrid eco-engineering systems | Integrates ecological and structural measures; suitable for high-energy environments; improves reliability and multifunctionality | Higher cost; interdisciplinary design required; trade-offs between ecological and engineering objectives | [13, 14, 16, 17, 21, 29, 39, 43, 50, 51, 55, 58, 59, 60] |
The synthesis highlights that no single NbS category is universally optimal. Vegetation-based approaches are most effective under moderate hydraulic conditions, while hybrid systems provide greater reliability in high-energy environments. Wetland-based measures primarily contribute to ecological and water-quality improvements rather than to direct mechanical stabilization. These findings reinforce the importance of context-specific selection of NbS strategies.
The categorized synthesis presented in Table 1 provides a basis for a more detailed examination of specific performance dimensions, including ecological effectiveness, engineering performance, and implementation factors, which are discussed in the following subsections.
Ecological effectiveness. A substantial body of evidence demonstrates the environmental benefits of nature-based riverbank protection measures. More than 40 studies reported significant improvements in vegetation survival rates, biodiversity indices, and habitat quality following the implementation of bioengineering and vegetation-based interventions [1, 3, 4]. These studies consistently indicate that bioengineering techniques facilitate the establishment of native plant species while enhancing aquatic and riparian microhabitats. Several investigations have emphasized the critical role of species selection and the use of locally sourced or provenance-specific seed mixtures in maximizing the success of ecological restoration [9, 10, 30]. Conversely, some studies have identified challenges in vegetation establishment, particularly under environmental stress, extreme hydrological events, or pressure from invasive species, highlighting the need for adaptive, site-responsive management strategies [7, 8, 26]. Additionally, wetland restoration measures and constructed vegetated features have been demonstrated to improve water quality, enhance nutrient retention, and provide ecosystem services across diverse environmental contexts [32, 44, 49].
Engineering performance. From an engineering perspective, more than 30 studies have quantitatively confirmed improvements in slope stability, erosion control, and overall structural performance associated with bioengineering applications [16, 20, 28]. Several investigations reported enhanced performance through hybrid approaches, in which vegetation was integrated with engineered structures or recycled and waste-derived materials.
Quantitative indicators reported across the reviewed studies to evaluate mechanical and hydraulic performance include increases in apparent soil shear strength due to root reinforcement, improvements in calculated factor of safety (FoS), reductions in measured bank retreat rates, decreases in near-bank flow velocity and shear stress, and documented structural stability during monitored flood events. These metrics serve as the basis for claims of enhanced mechanical safety in vegetation-based and hybrid systems.
The mechanical reinforcement provided by vegetation root systems has been consistently shown to increase soil shear strength and reduce displacement under both flood and drought conditions [11, 15, 28]. Design-oriented studies emphasized the importance of differentiated treatment of toe zones and upper bank sections, recommending the strategic combination of vegetation and structural elements to optimize stability and durability [40, 52].
Reported failures were primarily attributed to inadequate design, construction-related disturbances, or insufficient post-installation maintenance, underscoring the necessity for careful planning, implementation, and long-term monitoring [7, 8].
Community engagement. Approximately 10 studies explicitly incorporated community participation, stakeholder engagement, or socioeconomic considerations into nature-based riverbank protection projects [3, 16, 21]. These studies have demonstrated that inclusive and participatory approaches can enhance project longevity, facilitate the transfer of local knowledge, and increase public acceptance.
Several case studies integrated cultural activities, educational initiatives, and capacity-building programs, fostering environmental stewardship and the exchange of cross-cultural ecological knowledge [17, 21]. Furthermore, the development of local economic sectors and vocational training programs was identified as a key factor in sustaining bioengineering initiatives at the community level [18].
Nevertheless, a notable proportion of the reviewed literature provided limited or no explicit treatment of community engagement, revealing a persistent gap in integrating socio-economic dimensions into predominantly technical studies [26, 39].
Design and maintenance considerations. Design practices commonly emphasized site-specific species selection, the use of biodegradable materials, and the integration of multiple bioengineering techniques, including live staking, fascines, brush mattresses, and vegetated geogrids [6, 31, 37]. Numerous studies have highlighted the importance of long-term maintenance and systematic monitoring to ensure vegetation establishment and prevent structural or ecological failure [8, 41].
Several authors have advocated for iterative, multidisciplinary design frameworks that balance ecological functionality with engineering requirements, particularly under variable hydrological and climatic conditions [40, 42]. In addition, a subset of studies proposed standardized guidelines and decision-support frameworks to improve consistency, transferability, and success rates in bioengineering applications [2, 52].
Ecosystem connectivity and resilience. The reviewed literature indicates that bioengineered riverbanks, particularly those incorporating fascines and vegetated structural elements, are more effective than complex engineering solutions in maintaining or enhancing riparian corridor connectivity and resisting the colonization of invasive species [1, 55]. Studies further demonstrated that mixed-species vegetation assemblages optimize both hydro-mechanical reinforcement and biodiversity outcomes, thereby supporting long-term ecosystem resilience [15].
Restoration of wetlands and riparian buffer zones was shown to improve ecological functions, enhance landscape connectivity, and increase adaptive capacity to hydrological disturbances and climate variability [14, 32]. However, some projects reported persistent challenges related to invasive species proliferation, necessitating targeted control measures and ongoing maintenance interventions [7, 19].
3.2 Critical analysis and synthesisThe reviewed literature demonstrates the growing potential of NbS for riverbank protection; however, the strength and consistency of evidence vary considerably across studies. While numerous studies report positive ecological and engineering outcomes, differences in methodological rigor, site conditions, and monitoring duration limit cross-study comparability and generalization.
Figure 2 highlights that the performance of NbS for riverbank protection arises from interactions among ecological and hydro-mechanical mechanisms rather than a single intervention effect. Vegetation planting and soil bioengineering primarily contribute through root reinforcement, near-bank flow attenuation, and sediment trapping, which together improve erosion resistance and shallow slope stability. Wetland restoration contributes more indirectly by buffering hydrological fluctuations, enhancing sediment retention, improving water quality, and supporting habitat recovery. Hybrid systems combine vegetation-mediated functions with structural support, making them especially relevant where hydraulic stress, toe erosion, or weak bank materials limit the reliability of vegetation-only measures. The framework also emphasizes that these pathways are conditioned by hydrodynamic regime, soil type, climate, maintenance intensity, and governance capacity, which explains why NbS performance is often highly site-specific and why no single solution can be considered universally optimal.
The reviewed literature on nature-based solutions for riverbank protection reveals a comprehensive exploration of vegetation planting, bioengineering techniques, and wetland restoration, highlighting their ecological and engineering benefits. Strengths include the integration of multidisciplinary approaches, empirical field studies, and innovative hybrid solutions that combine environmental and engineering principles. However, limitations persist in the variability of methodological rigor, site-specific applicability, and the availability of long-term monitoring data. Additionally, challenges related to species selection, maintenance, and socio-economic integration are recurrent themes. Overall, the body of research underscores the potential of nature-based solutions while emphasizing the need for adaptive management and enhanced community engagement to optimize outcomes.
While this review focuses primarily on nature-based and hybrid eco-engineering approaches, riverbank stabilization has traditionally relied on conventional hard-engineering systems such as concrete revetments, sheet piles, riprap armoring, and reinforced retaining structures. These systems prioritize immediate structural resistance and hydraulic reliability, particularly under high-energy flow conditions. In contrast, nature-based solutions rely on vegetation-mediated reinforcement, flow attenuation, and ecological recovery processes. Hybrid approaches seek to integrate the structural reliability of conventional engineering with the long-term ecological and adaptive benefits of vegetation-based systems. This comparative perspective helps contextualize the performance, limitations, and application scope of nature-based riverbank protection strategies.
Building on the descriptive synthesis, a more focused critical evaluation of nature-based riverbank stabilization approaches is presented in Table 2. To enhance clarity and interpretability, the strengths and limitations of the major NbS categories are condensed into a three-column format with fewer thematic rows. This structure emphasizes key trade-offs among ecological performance, engineering reliability, and practical implementation constraints, enabling a more direct comparison of the conditions under which different approaches are most effective.
| NbS approach | Key strengths | Key limitations |
|---|---|---|
| Vegetation-based techniques | Cost-effective; environmentally sustainable; enhances biodiversity; suitable for low–moderate energy environments | Limited structural resistance under extreme flows; delayed effectiveness due to the establishment period |
| Soil bioengineering | Combines ecological and mechanical functions; adaptable to different slopes; improves stability and erosion resistance | Requires design expertise; performance variability across sites; maintenance needed |
| Wetland-based approaches | Strong ecological benefits; improves water quality and sediment retention; supports flood mitigation | Limited direct mechanical stabilization; dependent on hydrological compatibility |
| Hybrid eco-engineering systems | High reliability under variable hydraulic conditions; integrates structural and ecological benefits | Higher cost, design complexity, and requires interdisciplinary coordination. |
| Conventional engineering (reference) | Immediate structural effectiveness; suitable for high-risk sites | Low ecological value; high environmental impact; limited adaptability |
The comparison further indicates that NbS effectiveness depends not only on the selected technique but also on the interaction between ecological processes and engineering performance. In particular, approaches that successfully combine root reinforcement, flow attenuation, and sediment retention tend to yield more robust, resilient stabilization outcomes.
The strength of evidence supporting nature-based riverbank stabilization is substantial but heterogeneous. Empirical confidence is highest in studies reporting multi-year field monitoring or quantified geotechnical indicators (e.g., measured bank retreat, increased soil shear strength, hydraulic resistance parameters). In contrast, findings derived from pilot-scale implementations, short-term vegetation establishment studies, or modeling-based assessments should be interpreted as context-dependent. Given the variability in spatial scale, hydrodynamic conditions, and monitoring duration, cross-study generalization requires caution. Therefore, the conclusions in this review are presented in calibrated language that reflects the underlying evidence type.
3.3 Thematic review of literatureThe reviewed literature converges around several dominant themes. The most prominent theme concerns vegetation-based bioengineering techniques, including live staking, fascines, brush mattresses, and vegetated crib structures, which are primarily evaluated for their erosion-control and slope-stabilization performance. A second major theme focuses on species selection and planting design, emphasizing the importance of native or site-adapted vegetation for both hydro-mechanical reinforcement and biodiversity enhancement. A third theme concerns wetland-related interventions and buffer systems, valued for sediment retention, improved water quality, and enhanced ecological resilience. Across these themes, the literature increasingly emphasizes hybridization with structural elements, adaptive maintenance, and the integration of engineering performance with ecological and social outcomes.
3.4 Chronological review of literatureResearch on nature-based solutions for riverbank protection has evolved over several decades, beginning with foundational bioengineering techniques emphasizing vegetation for slope stabilization and erosion control. Early work focused on practical implementation and design guidelines, while later studies integrated ecological restoration, biodiversity enhancement, and socio-economic considerations. Recent literature highlights innovative hybrid techniques, community engagement, and the application of advanced modeling to optimize both environmental and engineering outcomes. This chronological synthesis captures the progression from empirical practices toward integrated, sustainable riverbank management approaches.
Chronologically, the field has evolved from early practical bioengineering applications centered on erosion control and slope protection toward more integrated frameworks that combine ecological restoration, hydro-mechanical analysis, and stakeholder participation. Early studies focused primarily on technique development and field implementation, whereas later work introduced biodiversity outcomes, design optimization, and hybrid eco-engineering concepts. The most recent literature increasingly addresses climate resilience, invasive-species management, socio-ecological co-benefits, and context-specific decision support for riverbank stabilization.
3.5 Limitations of the literatureThe current evidence base remains constrained by several recurring limitations. Many studies are geographically concentrated in a limited number of climatic and socio-ecological settings, which reduces transferability across river systems. Monitoring periods are often short, limiting confidence in long-term performance. In addition, species diversity is not consistently addressed, socio-economic impacts remain underexamined, and standardized design and evaluation criteria are still lacking. Modeling studies provide important insight into vegetation-flow-soil interactions, but they often simplify field complexity. Finally, many reported interventions remain at pilot scale, limiting conclusions about scalability and implementation under larger, more heterogeneous riverbank conditions.
3.6 Gaps and future research directionsDespite the growing body of research on nature-based solutions for riverbank protection, several critical knowledge gaps continue to limit their broader application and optimization. To provide a clear and actionable research agenda, Table 3 summarizes the most significant and high-priority gaps identified across the reviewed studies. Lower-priority or context-specific issues are incorporated into the narrative discussion. At the same time, the table focuses on challenges related to long-term performance, design standardization, hydro-mechanical understanding, and socio-economic integration. This prioritization aims to support future research efforts and guide the development of more robust and scalable NbS strategies.
| Research gap | Description | Future direction |
|---|---|---|
| Long-term performance and monitoring | Most studies focus on short-term outcomes; lack of long-term field data | Establish long-term monitoring programs and standardized evaluation frameworks |
| Quantification of hydro-mechanical effects | Limited quantitative understanding of root reinforcement, shear strength, and flow–vegetation interactions | Develop integrated experimental and numerical models linking ecology and mechanics |
| Site-specific design guidelines | Lack of standardized criteria for selecting NbS under different hydraulic and geotechnical conditions | Develop decision-support tools incorporating hydrodynamics, soil properties, and vegetation characteristics |
| Integration with climate change adaptation | Limited assessment of NbS performance under extreme events and climate variability | Evaluate resilience under future climate scenarios and extreme hydrological conditions |
| Socio-economic and governance factors | Underrepresentation of stakeholder engagement, maintenance, and policy constraints | Incorporate governance, cost–benefit analysis, and community participation into NbS design |
| Scaling from pilot to large-scale implementation | Many studies are small-scale or experimental. | Develop scalable design frameworks and case studies for large river systems. |
Based on the synthesized evidence, this section translates the reviewed findings into structured guidance for selecting nature-based riverbank stabilization strategies under varying hydrological, geomorphological, and socio-economic conditions. Given the heterogeneity of river systems, NbS implementation should be guided by site-specific conditions rather than a one-size-fits-all approach.
4.1 Hydrodynamic regimeIn low-energy river reaches characterized by moderate flow velocity and limited shear stress, vegetation-dominated approaches such as live staking, fascines, brush mattresses, and vegetated buffer zones are generally appropriate. These systems rely primarily on root reinforcement and flow attenuation mechanisms.
In contrast, high-energy environments (e.g., steep gradients, high flood peaks, non-cohesive banks) require hybrid solutions integrating structural toe protection (e.g., rock toe, crib walls) with upper-bank bioengineering. In such cases, vegetation enhances long-term stabilization but cannot substitute for structural resistance at the toe zone. Phased implementation and reinforced anchoring are recommended.
4.2 Soil typeCohesive soils (e.g., clay-rich banks) benefit significantly from root reinforcement mechanisms that increase apparent shear strength and reduce mass failure probability. Live cuttings and deep-rooted species are particularly effective in such contexts.
For non-cohesive or sandy banks, vegetation establishment may be vulnerable to scour and undercutting. In these conditions, toe stabilization and erosion-control fabrics should precede or accompany planting measures. Species selection must prioritize rapid root development and tolerance to fluctuating saturation levels.
4.3 Rural and urbanized contextsIn rural and semi-natural systems, NbS can prioritize ecological connectivity and biodiversity enhancement, with greater flexibility in spatial design and longer establishment periods. Community-based nurseries and participatory maintenance models may support sustainability.
In highly urbanized environments, constraints such as limited space, proximity to infrastructure, and safety requirements necessitate compact hybrid designs. Maintenance capacity and risk tolerance must be explicitly evaluated, and vegetation strategies should emphasize structural compatibility and predictable performance.
4.4 Community capacity and governance conditionsWhere strong local engagement and technical capacity exist, adaptive management strategies and community co-monitoring can enhance long-term performance and invasive species control. Conversely, in contexts with limited maintenance resources or institutional capacity, low-maintenance designs and conservative hybrid approaches are advisable to minimize post-installation failure risks.
Overall, technique selection requires balancing ecological co-benefits, structural reliability, maintenance intensity, and socio-economic feasibility. Vegetation-only solutions maximize ecological gains but may be more vulnerable in high-energy systems. Hybrid systems enhance engineering reliability but increase construction complexity and cost. Wetland-integrated designs offer multifunctional ecosystem services but require hydrological compatibility and long-term management commitment.
This review provides a comprehensive synthesis of current knowledge on NbS for riverbank protection and highlights their multifunctional benefits compared to conventional structural approaches. Evidence from diverse geographic contexts indicates that NbS contribute simultaneously to erosion control, slope stability, habitat enhancement, and ecosystem resilience. In many cases, hybrid approaches combining vegetation with structural elements offer the most reliable performance, particularly under high-energy hydraulic conditions.
A key finding of this review is that NbS effectiveness is strongly context-dependent. Hydrodynamic regime, soil characteristics, species selection, and maintenance capacity critically influence long-term outcomes. Vegetation-only systems may provide substantial ecological benefits but are vulnerable to extreme events or inadequate establishment. In contrast, hybrid systems improve structural reliability at the cost of increased complexity and resource requirements. Wetland-based interventions provide additional ecosystem services, including sediment retention and improved water quality, but their direct contribution to bank stabilization remains insufficiently quantified in many studies.
Despite the growing body of literature, significant knowledge gaps persist. Long-term monitoring data are scarce, standardized performance metrics are lacking, and socio-economic dimensions are often underrepresented. The heterogeneity of study designs and environmental conditions limits cross-site comparability and complicates evidence-based decision-making. Furthermore, maintenance requirements and invasive species management remain critical challenges that can determine project success or failure over time.
From a practical perspective, effective implementation of NbS requires integrated planning that balances ecological objectives with engineering reliability and institutional capacity. Adaptive management, stakeholder participation, and context-specific design frameworks are essential for sustaining performance throughout the project lifecycle. In highly modified or urban environments, conservative hybrid solutions may be necessary to meet safety and regulatory constraints, whereas rural systems offer greater opportunities for ecosystem restoration and connectivity enhancement.
Future research should prioritize the development of standardized monitoring protocols, quantitative assessment of hydro-mechanical interactions in mixed vegetation systems, long-term evaluation of wetland-based stabilization, and rigorous analysis of socio-economic benefits and governance conditions. Interdisciplinary approaches combining ecology, hydraulics, geotechnics, and social sciences are particularly needed to support scalable implementation.
Tran Khac Thac: Conceptualization, Methodology, Investigation, Data curation, Formal analysis, Writing – original draft, Visualization. Pham Ngoc Thinh: Conceptualization, Methodology, Validation, Supervision, Writing – review & editing, Project administration. Both authors contributed substantially to the work and approved the submitted version of the manuscript.
