Comprehensive Index System for Evaluation of Ecological Seawalls

Abstract

Seawalls are important infrastructure for coastal areas to resist natural disasters such as storm tides and typhoon waves. Traditional seawall construction often causes intertidal zone fragmentation and coastline hardening, which affects the ecological function of the coastline. Ecological seawalls have both functions of disaster prevention and ecology and have become an inevitable trend in seawall construction at home and abroad. However, constructing a comprehensive, scientifically rational evaluation index system for ecological seawalls is a critical and pressing challenge. This study is based on the summary of practical research on seawall construction and puts forward the connotation of ecological seawall clearly. Twenty indexes that reflect the safety, ecology and sustainability of ecological seawalls were selected, and a three-level comprehensive evaluation index system of ecological seawalls was constructed using the Analytic Hierarchy Process (AHP). Three cases, including the second stage of the ecological seawall of the large-scale narrowing project in Yuyao City, Zhejiang Province, were used in this evaluation system. The application results showed that the constructed comprehensive evaluation index system of ecological seawalls in this study has a reasonable evaluation index, and the evaluation result is reliable, which is suitable for popularization and application. This study clarifies the index system and construction method for the comprehensive evaluation of ecological seawalls, puts forward typical measures for ecological seawall construction from five aspects: shore beach protection, seawall body structure, seawall surface protection, building materials and vegetation selection, and provides theoretical and practical guidance for studying and judging the ecological problems of seawalls and guiding the construction of ecological seawalls.

1. Introduction

Seawalls, as critical infrastructure for resisting natural disasters like storm surges and typhoon waves in coastal regions, play a pivotal role in disaster reduction, social stability maintenance, and economic development [1,2]. Traditional seawalls, mostly constructed with concrete and featuring a “three-sided smooth” structure, often cause intertidal zone fragmentation and coastline hardening, leading to poor coordination with the surrounding environment, low vegetation quality, and degradation of coastal ecological functions [3,4]. In 2020, the Work Plan for Coastal Zone Protection and Restoration Projects, proposed by the Ministry of Natural Resources of the People’s Republic of China, clearly states that it is necessary to carry out new construction, compliance reinforcement, and ecological development of seawalls. It also specifies that seawall construction must simultaneously fulfill storm surge prevention, social, and ecological benefits [5]. Scholars have proposed that ecological seawalls should draw on the concepts and methods of ecological slope protection, improving the regional ecological environment while ensuring disaster reduction functions, thus achieving synergistic effects between disaster prevention and ecological protection [2]. In recent years, ecosystem-based flood defense has been brought into large-scale practice as a regional solution that is more sustainable and cost-effective than conventional coastal engineering [6]. Under the background of the “dual-carbon strategy”, the demand for ecological seawall construction has surged nationwide, as exemplified by the deployment of Zhejiang’s “Haitang Anlan” 100-billion-yuan project. However, a scientific and systematic comprehensive evaluation index system and related theories for ecological seawalls are still lacking.

In the early 20th century, scholars recognized that seawall construction should incorporate sustainable development concepts and ecological design principles beyond meeting engineering requirements. In 1962, Odum proposed the concept of ecological engineering, emphasizing the consideration of biological factors in coastal engineering [7]. In 1971, Schlueter founded “near-natural river regulation engineering”, advocating the use of plants as engineering materials in coastal projects [8]. Since the 1970s, significant progress has been made in ecological slope protection globally using modern ecology, such as Switzerland’s “multi-natural river ecological restoration technology”, The Netherlands’ “giving space to rivers” concept, Germany’s “near-natural river regulation”, the United States’ “natural channel design technology”, and Japan’s “multi-natural river creation plan” [9,10]. Additionally, vibrant coastal construction requires maintaining connectivity between mainland and nearshore habitats and providing ecosystem services of natural wetlands [11,12,13]. In recent years, countries like the United States, Australia, The Netherlands, and Germany have adopted ecologically oriented projects to build ecological seawalls [13], such as the ecological transformation of Australia’s McMahon Seawall, the Netherlands’ wetland-centered ecological buffer zones, the United Kingdom’s Medmerry coastal realignment scheme, Belgian Scheldt estuary’s wetland restoration and Germany’s “wide green embankment” model, indicating that ecological seawall construction has become an international trend [7,14].

China’s ecological seawall construction started relatively late. In 1999, Liu Changming proposed integrating ecological water conservancy and environmental water conservancy [15]. In 2002, Dong Zheren put forward ecological hydraulics, combining hydraulics and ecology [16]. In 2017, the National Development and Reform Commission of the People’s Republic of China (NDRC) issued and distributed the National Seawall Construction Plan, which marked the first initial emergence of “ecological awareness” at the national level [17]. In 2020, the Ministry of Natural Resources of the People’s Republic of China officially proposed the Work Plan for Coastal Zone Protection and Restoration Projects, requiring that seawall construction should achieve synergistic improvement of ecological benefits and disaster mitigation effects [5]. In recent years, China has applied ecological concepts to coastal regulation and restoration, constructing ecological slopes using materials like ecological concrete and composite planting substrates [18,19]. Examples include thatched turf, trees, and reeds on the outer slope of Jiangsu Sheyang Seawall; coastal protection belts and Suaeda salsa planting at Liaoning Xingcheng Estuary; and reeds and aquatic plants on Shanghai Chongming Island seawalls. Furthermore, new ecological seawalls such as the Xisha Bay Hongsha Huan Seawall in Guangxi Fangchenggang, the Zhakou Town Seawall in Guangxi Hepu, the Wusong Paotaiwan Wetland Park Seawall in Shanghai, the Wenzhou Rui’an Ecological Seawall, and the Wanqingsha Lianwei Seawall in Guangzhou Nansha [17,20,21,22,23,24] integrate landscape and ecological elements into their design, enhancing both disaster prevention and ecological functions. The concept of ecological seawall construction in China is consistent with the international “green-gray combination” [6] and “Nature-based Solutions (NbS)”. It essentially responds to global consensuses such as “harmony between humans and the ocean” and “climate adaptation”, reflecting the universal laws of ecological coastal engineering. However, the differences stem from China’s unique context: a lagging development stage but urgent needs, diverse coastal types and a large number of existing projects, as well as strong policy impetus and high demand for large-scale implementation [21,24].

Constructing a scientific and systematic comprehensive evaluation index system is crucial for identifying ecological issues and formulating ecological upgrading plans for seawalls. Despite numerous successful cases globally, a universal evaluation system is still lacking. Based on a summary of domestic and international practices, this study defines the connotation of ecological seawalls and selects key evaluation indicators to construct a comprehensive index system. This system is then applied to the second-phase Yuyao River Regulation and Reclamation Seawall in Zhejiang. This study addresses the evaluation indicators and construction methods, providing theoretical and practical guidance for ecological seawall development [25].

Currently, there is no unified definition of ecological seawalls globally, but some scholars have proposed understandings through practical research. For instance, Li Yuan et al. introduced the concept of “slope ecological engineering” in seawall construction, using sustainability, non-invasiveness, productivity, nutrient retention, and biological interactions as criteria for ecological restoration effectiveness [23]. Yang Yuanzhi regarded mangroves and coastal shelterbelts as means to protect seawall safety, proposing a layout from sea to land: mangroves, seawalls, and coastal backbone forests [26]. Fan Hangqing et al. argued that ecological seawalls must meet physical resistance and disaster mitigation requirements while retaining near-natural vegetation and landscape needs [27]. Zhao Peng emphasized that ecological seawalls should satisfy disaster protection, form complete ecosystem structures, and possess ecological functions [28]. Kong Xiangmeng stated that ecological seawalls should not only resist tides and waves but also provide habitats for biological communities [29].

Integrating global research progress and Zhejiang’s practices, this study defines ecological seawalls as coastal protection structures with both standard-compliant flood resistance and near-natural slope ecological functions, spatially composed of coastal wetland zones, seawall structure zones, and terrestrial buffer zones (Figure 1). The coastal wetland zone should have a certain backshore width, stable beach structure, and rich biological communities to reduce wave impact and coastal erosion. The seawall structure zone should feature safe, standard-compliant structures and near-natural material-energy exchange capabilities to maintain coastal ecosystem integrity. The post-embankment buffer zone should have a certain landward radiation width and stable terrestrial ecosystems to mitigate disaster impacts and reduce seawall instability risks [30].

2. Construction of the Evaluation Index System for Ecological Seawalls

2.1. Selection of Evaluation Indicators

Ecological seawalls should retain the flood resistance functions of traditional seawalls, facilitate coastal energy and material exchange, minimize negative ecological impacts, and maintain sustainable ecological functions. Therefore, this study evaluates ecological seawalls from three aspects: safety, ecological performance, and sustainability. Based on the coefficient of variation (sensitivity to target variables), twenty indicators were selected to construct the comprehensive evaluation system (

Table 1. Basic framework of comprehensive evaluation index system of ecological seawall.

Target Layer K	Criterion Layer A	Indicator Layer B	Attribute
Comprehensive evaluation of ecological seawall	Safety A1	Crest elevation B1	Quantitative
		Overtopping volume B2	Quantitative
		Embankment quality B3	Qualitative
		Overall stability B4	Quantitative
		Seepage stability B5	Quantitative
	Ecological A2	Water quality index B6	Quantitative
		Sediment quality score B7	Quantitative
		Benthic biodiversity B8	Quantitative
		Vegetation coverage B9	Quantitative
		Post-embankment ecological space B10	Quantitative
		Beach scale B11	Quantitative
		Beach stability B12	Quantitative
		Front slope gradient B13	Quantitative
		Front slope surface porosity B14	Quantitative
		Ecological suitability of building materials B15	Quantitative
	Sustainability A3	Disaster prevention and mitigation function B16	Quantitative
		Habitat maintenance function B17	Qualitative
		Disaster prevention benefits B18	Qualitative
		Environmental cleanliness B19	Qualitative
		Ecological management capacity B20	Qualitative

), and the threshold classification of each indicator is shown in

Table 2. Threshold classification of safety indexes.

Index	Threshold Rank
	Excellent [80, 100]	Good [70, 80)	Middle [60, 70)	Bad [0, 60)
Crest elevation	$\Delta h\le 0$ m	$0 \mathrm{m}<\Delta h\le 0.3$ m	$0.3 \mathrm{m}<\Delta h\le 0.5$ m	$\Delta h>0.5$ m
Overtopping volume	$\Delta Q\le 1$	$1<\Delta Q\le 1.5$	$1.5<\Delta Q\le 2$	$\Delta Q>2$
Embankment quality	The embankment structure is in good condition, without any phenomena such as uneven settlement (settlement difference ≤ 0.05 m), cracks, sliding, or seepage. The reinforcing bars have not been corroded, and the concrete has no carbonation. The waterstop at the settlement joint is in good condition.	The embankment structure is basically intact, with minor uneven settlement (0.05 m < settlement difference ≤ 0.1 m) and cracks (0.2 mm < width ≤ 0.5 mm), but no obvious water seepage. There is slight corrosion on the steel bars, and the water stop of the settlement joints is basically effective.	The embankment structure has defects, including uneven settlement (0.1 m < settlement difference ≤ 0.2 m), cracks (0.5 mm < width ≤ 1 mm), and local water seepage (area ≤ 5 m2). There is local corrosion of steel bars and mild carbonation of concrete, and the water stop effect of settlement joints is poor.	The embankment structure is incomplete, with uneven settlement (settlement difference > 0.2 m), cracks (width > 1 mm), and large-area water seepage (area > 5 m2). There is severe corrosion of steel bars and deep carbonation of concrete, and the water stops in the settlement joints have failed.
Overall stability	$\Delta k\ge 0.05$	$0\le \Delta k<0.05$	$-0.05\le \Delta k<0$	$\Delta k<-0.05$
Seepage stability	$\Delta J\le 0.9$	$0.9<\Delta J\le 1$	$1<\Delta J\le 1.1$	$\Delta J>1.1$

,

Table 3. Threshold classification of ecological indexes.

Index	Threshold Rank
	Excellent [80, 100]	Good [70, 80)	Middle [60, 70)	Bad [0, 60)
Water quality index	$0\le WQI\le 0.75$	$0.75\le WQI<1$	$1\le WQI<1.25$	$WQI\ge 1.25$
Sediment quality score	$80\le S\le 100$	$60\le S<80$	$30\le S<60$	$S<30$
Benthic biodiversity	$H^{\prime }\ge 3$	$2\le H^{\prime }<3$	$1\le H^{\prime }<2$	$H^{\prime }<1$
Vegetation coverage	$75\%\le R_P\le 100\%$	$60\%\le R_P<75\%$	$45\%\le R_P<60\%$	$0\%\le R_P<45\%$
Post-embankment ecological space	$R_E\ge 80\%$	$60\%\le R_E<80\%$	$40\%\le R_E<60\%$	$0\%\le R_E<40\%$
Beach scale	The average width of the mudflat is greater than 300 m; the average width of the sandy/gravel beach is greater than 100 m.	The average width of the mudflat is 200–300 m; the average width of the sandy/gravel beach is 75–100 m.	The average width of the mudflat is 100–200 m; the average width of the sandy/gravel beach is 50–75 m.	The average width of the mudflat is 50–100 m; the average width of the sandy/gravel beach is 30–50 m.
Beach stability	The particle composition is well adapted to the hydrodynamic environment, and there is no erosion or modification on the beach surface. The stability time of the shore beach is more than 2 years.	The particle composition is well adapted to the hydrodynamic environment. There are slight erosion or modification phenomena on the beach surface, and the stability time of the shore beach is 1–2 years.	The particle composition is less adaptable to the hydrodynamic environment, and there are concentrated erosion or modification phenomena on the beach surface. The stability time of the shore beach is 0.5–1 year.	The particle composition is not compatible with the hydrodynamic environment, and the beach surface suffers from severe erosion or modification. The stability time of the shore beach is less than 0.5 years.
Front slope gradient	$R_m\le 1:5$	$1:5<R_m\le 1:3$	$1:1<R_m\le 1:3$	$R_m>1:1$
Front slope surface porosity	$R_V\ge 60\%$	$40\%\le R_V<60\%$	$20\%\le R_V<40\%$	$R_V<20\%$
Ecological suitability of building materials	$R_J\ge 70\%$	$50\%\le R_J<70\%$	$30\%\le R_J<50\%$	$R_J<30\%$

and

Table 4. Threshold classification of sustainability indexes.

Index	Threshold Rank
	Excellent [80, 100]	Good [70, 80)	Middle [60, 70)	Bad [0, 60)
Disaster prevention and mitigation function	$80\le R_S\le 100$	$60\le R_S<80$	$30\le R_S<60$	$R_S<30$
Habitat support function	The ecological quality of the embankment area is high, with a large number of organisms and extensive natural landscapes. This provides suitable and superior habitats for the organisms, and the entire engineering area maintains a stable ecosystem.	The ecological quality of the embankment area is relatively high, with an appropriate number of organisms and a certain range of natural landscapes. This provides suitable habitats for the organisms. The entire engineering area has a basically stable ecosystem.	The ecological quality of the embankment area is relatively low, with a small number of organisms and a low proportion of natural landscapes. This makes it impossible to provide suitable habitats for the organisms, and the entire engineering area has an unstable ecosystem.	The ecological quality of the embankment area is low. There are almost no living organisms and no natural landscapes, which cannot provide suitable habitats for organisms. Moreover, the entire engineering area has an unstable ecosystem.
Disaster prevention benefits	Extremely important	Important	Relatively important	General
Environmental cleanliness	The environment is clean and tidy, with no discarded items or garbage.	The environment is relatively clean, with basically no abandoned items or garbage. The average amount is 1 to 2 per square meter.	There are a small number of abandoned items or garbage, with an average of 3 to 10 per square meter	There is a large amount of waste or garbage, with an average of more than 10 pieces per square meter
Ecological management capacity	The organizational structure and management system are sound, the maintenance facilities are complete, the maintenance funds are guaranteed, and the ecosystem has a strong self-balancing capacity.	The organizational structure and management system are relatively complete, the maintenance facilities are relatively complete, and the maintenance funds have certain guarantees. The self-balancing capacity of the ecosystem is relatively strong.	The organizational structure and management system, maintenance facilities, and maintenance funds are partially lacking, and the self-balancing capacity of the ecosystem is average.	The organizational structure and management system, maintenance facilities, and maintenance funds are lacking, and the self-balancing ability of the ecosystem is very poor.

.

2.1.1. Safety Indicators

The primary function of ecological seawalls is flood and disaster resistance, making safety the foundation for their normal operation [31]. Multiple complex factors affect seawall safety. Xie Jie et al. screened the safety evaluation indicators of seawalls based on overtopping and breaching, and proposed evaluation indicators including overtopping discharge, tidal level, overall stability safety factor, seepage gradient, safety factor for sliding resistance of breast wall, safety factor for overturning resistance of breast wall, quality of slope protection blocks, and quality of toe protection blocks [32]. Wu Zhengzhong evaluated the safety of Zhejiang seawalls in detail with reference to the Guidelines for Safety Evaluation of Seawall Projects [33,34]. Building on these studies, this study identifies crest elevation, overtopping volume, embankment quality, overall stability, and seepage stability as safety indicators.

• Crest elevation

The crest elevation of a seawall refers to the elevation above sea level at the top of the seawall, and serves as the core design parameter that determines the flood control capacity of the seawall project. Evaluated using the difference between the designed and measured crest elevations specified in the Guidelines for Safety Evaluation of Seawall Projects [34]:

$$\Delta h=H_{td}-H_{tm}$$

(1)

where $\Delta h$ is the crest elevation difference (m) and the smaller its value, the better; $H_{td}$ is the designed crest elevation (m), and $H_{tm}$ is the measured crest elevation (m).

2.

Overtopping volume

Overtopping volume refers to the volume of water that overtops the seawall crest and enters the leeside area. It is one of the core indicators for evaluating seawall safety and is directly related to the safety of personnel, facilities, and the ecological environment in the leeside area. For seawall sections with current elevations lower than the design standard, overtopping volume is verified as specified in the Guidelines [34], calculated as the difference between the computed and allowable overtopping volumes:

$$\Delta Q={\displaystyle \frac{Q_d}{Q_m}}$$

(2)

where $\Delta Q$ is the ratio of the computed and allowable overtopping volume, $\Delta Q>0$, and a smaller $\Delta Q$ value indicates a smaller gap between the computed and allowable overtopping volumes, which means the seawall has stronger safety performance against overtopping risks. And $Q_d$ is the computed overtopping volume (m³/(s·m)), and $Q_m$ is the allowable overtopping volume (m³/(s·m)), which is determined in accordance with the Guidelines [35].

3.

Embankment quality

The quality of the seawall body reflects the comprehensive characteristics of the seawall that meets design standards and ensures safety and durability, which is evaluated based on the presence of uneven settlement, cracks, sliding, seepage, steel corrosion, concrete carbonation, and the integrity of the settlement joint water stops. Items of the evaluation are all determined through on-site safety inspections.

4.

Overall stability

Overall stability refers to the ability of a seawall to maintain its seawall body and seawall foundation free from instability failures such as sliding and overturning under internal and external forces, which is evaluated by the difference between the anti-sliding safety factor ($k$) of the front and back slopes and the standard value ($K$) for the corresponding engineering grade specified in the Code for Design of Seawall Engineering [35]:

$$\Delta k=k-K$$

(3)

where $\Delta k$ is a dimensionless parameter, and the larger its value, the stronger the safety of the seawall.

5.

Seepage stability

Seepage stability refers to the ability of the seawall body and seawall foundation to avoid seepage failures such as piping and flowing soil under the action of seepage. It is evaluated based on the ratio of the calculated seepage gradient $\left(J_0\right)$ in the backslope exit section and the allowable soil gradient $\left(J_{cr}\right)$ specified in the Code for Design of Seawall Engineering [35]:

$$\Delta J={\displaystyle \frac{J_0}{J_{cr}}}$$

(4)

where $\Delta J$ is a dimensionless parameter. A smaller value of $\Delta J$ indicates the stronger the safety of the seawall.

2.1.2. Ecological Indicators

Ecological performance is key to evaluating ecological seawalls. Since ecological seawalls consist of coastal wetland zones, seawall structure zones, and terrestrial buffer zones, ecological indicators reference those for wetland and coastal ecological evaluation. Huang Haiping evaluated coastal wetland restoration effectiveness using indicators such as hydrology, environment, biology, and habitat [36]. In addition to wetland-related indicators, ecological indicators must consider the ecological impacts of seawall engineering [37]. Thus, this study selects water quality index, sediment quality score, benthic biodiversity, vegetation coverage, post-embankment ecological space, beach scale, beach stability, front slope gradient, front slope surface porosity, and ecological suitability of building materials as ecological indicators.

• Water quality index

In the construction of traditional seawalls, hard materials such as concrete and mortar masonry blocks are often used. After completion, these materials affect the habitats of surrounding coastal organisms, damage wetland systems, and reduce the self-purification capacity of seawater. Seawater environmental quality essentially reflects the degree of water pollution in the seawall area and its compatibility with its intended functions; therefore, selected parameters include dissolved oxygen, inorganic nitrogen, and active phosphate. The water quality index $\left(WQI\right)$ is calculated based on concentration standards in the Sea Water Quality Standard [38]:

$$WQI={\displaystyle \frac{1}{n}}\sum _{i=1}^n{C}_i/S_i$$

(5)

where $C_i$ is the concentration of parameter $i$ in the environment (mg/L), $S_i$ is the standard concentration for the parameter $i$ (mg/L), and $n$ is the number of evaluated parameters. A smaller $WQI$ indicates the better water quality.

2.

Sediment quality score

The sediment quality score is a quantitative indicator for evaluating the sediment environment and engineering applicability of sediment around seawalls or in seawall foundations. It essentially reflects the pollution degree of sediment, its physical and chemical properties, and its impacts on ecological/structural (seawall) aspects, so the selected parameters include organic carbon, sulfides, petroleum hydrocarbons, copper, lead, zinc, arsenic, chromium, cadmium, and mercury. The sediment quality score ($S$) is evaluated based on the Marine Sediment Quality [39]:

$$S={\displaystyle \frac{1}{n}}\sum _{i=1}^n(1-a_i)\times 100$$

(6)

where $n$ is the number of parameters, $a_i$ refers to the exceedance rate of the $i$-th evaluation item (dimensionless), calculated by the formula: $a_i=\left(C_i-S_i\right)/S_i$. Here, $C_i$ is the measured value of the $i$-th item (with the same unit as the standard), and $S_i$ is the limit value of the corresponding sediment item specified in Guidelines [39]. The index $S$ ranges from 0 to 100, and the larger the value of $S$, the better the ecological performance of the seawall.

3.

Benthic biodiversity

Benthic organisms, due to their sensitivity to marine environmental pollution, are often used as important indicators for evaluating the ecological environmental quality of marine areas. Ecological seawalls can be regarded as wetland ecosystems, with key biological groups including benthos, plankton, and nekton. Benthos are sensitive to marine pollution and are often used to evaluate marine ecological quality [40]. Thus, biodiversity is measured using the Shannon-Wiener index:

$$H\prime =-\sum _{i=1}^S{P}_i{\mathit{log}}_2{P}_{i`}$$

(7)

where $H\prime$ is the Shannon-Wiener index, and a larger $H\prime$ indicates a more abundant macrobenthic biodiversity, $S$ is the number of macrobenthic species which is surveyed in accordance with the Chinese National Standard Specifications for Marine Surveys—Part 6: Marine Biological Surveys [41], and $P_i$ is the proportion of individuals of the $i$-th species to the total number of macrobenthic individuals.

4.

Vegetation coverage

Vegetation coverage is defined as the percentage of vertical projection area of vegetation relative to the total statistical area, which can reflect the proportion of vegetation area within the seawall area, the richness of plant resources, and the degree of greening achieved:

$$R_P={\displaystyle \frac{S_P}{S_D}}\times 100\%$$

(8)

where $R_P$ is vegetation coverage (%), $S_P$ is the vertical projection area of native vegetation in the evaluation range (m²), and $S_D$ is the total vertical projection area of the seawall zone (m²). The index $R_P$ ranges from 0 to 1, and the larger the value of $R_P$, the better the ecological performance of the seawall.

5.

Post-embankment ecological space

Ecological space refers to territorial space with natural attributes that takes the provision of ecological services or ecological products as its main function [41]. It serves as an important foundation for landscape evaluation, management, and ecological planning, and has significant guiding significance for research on aspects such as regional sustainable development and biodiversity conservation [42]. Ecological seawalls should have post-embankment ecological space consisting of green spaces and water systems, evaluated by the ratio of post-embankment ecological space area to the total post-embankment evaluation area:

$$R_E={\displaystyle \frac{S_E}{S_L}}\times 100\%$$

(9)

where $R_E$ is the ratio of post-embankment ecological space (%), $S_E$ is the total area of post-embankment ecological space (m²), and $S_L$ is the area of the terrestrial zone (m²). The index $R_E$ ranges from 0 to 1, and the larger the value of $R_E$, the better the ecological performance of the seawall.

6.

Beach scale

The beach scale refers to the width from the multi-year average low tide level to the outer toe of the seaward slope of the seawall. Ensuring a certain width of beach in front of the seawall can create high-quality habitats for offshore marine organisms to reproduce, build a stable ecological environment, improve biodiversity, and promote energy flow and material cycling. The beach scale is measured by the average beach width in front of the seawall within the evaluation scope.

7.

Beach stability

Pre-embankment beaches should maintain stability, which is used to assess the erosion of shorelines and sand beaches within the seawall area and formulate corresponding protection and restoration measures. It is measured by the sediment composition of the beach, the scouring or mudding of the beach surface, and the stability duration of the beach.

8.

Front slope gradient

Ecological seawalls should adopt a gentle slope to the sea to enhance energy exchange and material flow between land and sea, and the ratio of the vertical height to the horizontal width of the water-facing slope should be used as the measurement. If it is a compound slope, the comprehensive slope ratio should be used as the evaluation basis:

$$R_m={\displaystyle \frac{h}{l}}$$

(10)

where $R_m$ is the front slope gradient, $h$ is the vertical height of the front slope (m), and $l$ is the horizontal width of the front slope (m).

9.

Front slope surface porosity

Porosity refers to the percentage of void volume in the front slope protection structure relative to the total volume. Ecological seawalls should have high surface porosity to provide habitat space, using natural stones or artificial blocks instead of mortar-masonry, grouted blocks, or concrete panels. Dry-laid natural stones or vegetation can achieve a porosity of 60%:

$$R_V={\displaystyle \frac{V_h}{V_t}}\times 100\%$$

(11)

where $R_V$ is front slope porosity (%), $V_h$ is the void volume in the front slope protection structure (m³), and $V_t$ is the total volume of the protection structure (m³). A larger $R_V$ indicates a better ecological performance of the seawall.

10.

Ecological suitability of building materials

The ecological suitability of building materials refers to the degree of impact of materials used in seawall construction on the ecological environment and their compatibility with ecological functions. It essentially embodies the characteristics of “low pollution and support for biological habitats”. Seawall surfaces should use eco-friendly materials that enhance ecological functions and restore marine ecosystems, such as plants, natural stones, biological reefs, and porous alkalized concrete components. Evaluated by the ratio of surface area using ecological materials to the total seawall surface area:

$$R_J={\displaystyle \frac{S_J}{S_H}}\times 100\%$$

(12)

where $R_J$ is the ratio of ecological materials (%), $S_J$ is the surface area using ecological materials (m²), and $S_H$ is the total surface area of the seawall zone (m²). A larger $R_J$ indicates a better ecological performance of the seawall.

2.1.3. Sustainability Indicators

Ecosystem sustainability refers to the sum of potential capacity to maintain dynamic health and evolutionary development of internal components, organizational structure, and functions over time [43]. It is a sufficient condition for ecosystem health and an inherent characteristic of seawall ecosystems [44]. This study identifies disaster prevention and mitigation function, habitat maintenance function, disaster prevention benefits, environmental cleanliness, and ecological management capacity as sustainability indicators.

• Disaster prevention and mitigation function

The disaster prevention and mitigation function is the original purpose of seawall construction, and it represents the seawall’s ability to effectively resist the impact of marine disasters such as storm surges in coastal areas. For seawalls that have been in service for many years, their disaster prevention and mitigation function will decrease due to multiple factors, including long-term settlement of the seawall foundation, damage to revetments and wave-dissipating facilities, sea-level rise, and scouring of the seawall toe. Evaluated by the compliance rate, which is the ratio of the seawall length meeting flood (tide) prevention standards to the total length:

$$R_S={\displaystyle \frac{L_S}{L_A}}\times 100\%$$

(13)

where $R_S$ is the compliance rate (%), $L_S$ is the length of compliant seawalls (m), and $L_A$ is the total seawall length (m). The index $R_S$ ranges from 0 to 1, and the larger the value of $R_S$, the better the sustainability performance of the seawall.

2.

Habitat support function

Refers to ecosystem services providing sites for biological growth, reproduction, and other key processes, evaluated based on species richness and ecosystem stability in the seawall area.

3.

Disaster prevention benefits

Flood (tide) prevention standards are determined by the scale and importance of protected objects specified in the Flood Control Standard [45]. Higher importance of protected objects corresponds to higher standards and greater protection benefits, evaluated based on the importance of protected objects.

4.

Environmental cleanliness

Environmental cleanliness is a measure of the degree to which a seawall and its surrounding areas are affected by pollutants and debris. Ecological seawalls should be clean and free of durable, man-made, or processed solid waste, evaluated by the density of solid waste pieces with equivalent diameter > 2.5 cm on the seawall surface.

5.

Ecological management capacity

The ecological management capacity refers to the comprehensive ability to maintain the stability of the seawall body and its surrounding ecosystem, and repair ecological defects through systems, technologies, and management measures during the seawall operation period. It is the core support for ensuring that ecological seawalls continue to exert their ecological functions in the long term. Ecological seawalls require strong management capacity to promote ecosystem self-balance, evaluated based on organizational structure, management systems, maintenance facilities, funding, and ecosystem self-balancing capacity.

2.2. Threshold Classification of Evaluation Indicators

The index system includes both quantitative and qualitative indicators. Since no unified global standards exist for their sensitivity to ecological seawalls, this study divides each indicator into four grades (excellent, good, moderate, poor) with scores ranging from 0 to 100 for uniform comparison. The grading standards for safety, ecological, and sustainability indicators are shown in Table 2, Table 3 and Table 4. The grades of quantitative indicators can be determined based on their values within the corresponding scoring ranges; the grades of qualitative indicators can be determined by referring to the descriptions of qualitative indicators in the grading standards of Table 2, Table 3 and Table 4.

2.3. Calculation of Indicator Weights

The Analytic Hierarchy Process (AHP) is a systematic analysis method that decomposes complex decision-making problems into multiple levels, including the target layer, criterion layer, and indicator layer. It involves quantitative scoring by experts on the relative importance of pairwise indicators, constructs judgment matrices, and calculates indicator weights. Its core advantage lies in integrating qualitative judgments with quantitative calculations, making it suitable for determining weights in multi-indicator comprehensive evaluation systems [46]. This study adopted AHP to calculate the weights of ecological seawall evaluation indicators because the evaluation of ecological seawalls involves three criterion layers (safety, ecology, and sustainability) and 20 indicator layers. The differences in importance among indicators need to be quantified through systematic methods, and AHP can effectively address the weight allocation of multi-dimensional indicators while avoiding the arbitrariness of subjective judgments.

A total of 9 experts from different institutions, including universities, research institutes, enterprises, and management units, were invited to participate in the scoring. These experts covered fields such as water conservancy, environment, oceanography, and industry management. Based on the scaling rules in

Table 5. Scale and meaning of judgment matrix.

Scale	Meaning	Scale	Meaning
1	The factor is of the same importance as the other.	9	The former factor is extremely important than the latter.
3	The former factor is slightly more important than the latter.	2, 4, 6, 8	The intermediate value of the above adjacent judgment.
5	The former factor is more important than the latter.	1/3, 1/5, 1/7	The former factor is slightly less important than the latter.
7	The former factor is much more important than the latter.	1/9	Unimportant

, they conducted pairwise comparison scoring on the relative importance between criterion layers (safety A1, ecology A2, and sustainability A3) and between indicator layers under each criterion layer (e.g., B1–B5 under A1). Specifically, a scale of “1” indicates “the two indicators are of equal importance,” a scale of “3” indicates “the former is slightly more important than the latter,” a scale of “1/3” indicates “the former is slightly less important than the latter,” and scales of “9”/“1/9” indicate “the former is extremely more important/extremely less important than the latter” (for detailed meanings of the scales, see Table 5).

After the expert scoring, initial judgment matrices were first constructed for each level. Among these,

Table 6. Judgment matrix of criterion layer A to objective layer K.

K	A1	A2	A3
A1	1	1/2	2
A2	2	1	2
A3	1/2	1/2	1

presents the judgment matrix of “criterion layer A relative to target layer K,” and

Table 7. Judgment matrix of sub-criterion layer B to objective layer A1.

A1	B1	B2	B3	B4	B5
B1	1	4	3	1	2
B2	1/4	1	1/2	1/4	1/2
B3	1/3	1/2	1	1/3	1
B4	1	4	3	1	2
B5	1/2	1	2	1/2	1

presents the judgment matrix of “indicator layer B relative to criterion layer A1.” Subsequent data verification was performed on the initial matrices: the arithmetic mean and standard deviation of each matrix element were calculated, and outliers exceeding one standard deviation were eliminated to prevent the impact of extreme judgments from individual experts on the results. Finally, the revised mean values were used to form a “group judgment matrix” (i.e., the matrix data presented in Table 6, Table 7,

Table 8. Judgment matrix of sub-criterion layer B to objective layer A2.

A2	B6	B7	B8	B9	B10	B11	B12	B13	B14	B15
B6	1	2	3	1/2	1/3	1/2	1/4	1	3	3
B7	1/2	1	2	1/3	1/3	1/2	1/3	1	2	2
B8	1/3	1/2	1	1/2	1/2	1/4	1/5	1/3	1	1
B9	2	3	2	1	1	1	1/3	2	4	4
B10	3	3	2	1	1	1	1/2	3	5	5
B11	2	2	4	1	1	1	1/4	2	4	4
B12	4	3	5	3	2	4	1	3	5	5
B13	1	1	3	1/2	1/3	1/2	1/3	1	4	4
B14	1/3	1/2	1	1/4	1/5	1/4	1/5	1/4	1	1/2
B15	1/3	1/2	1	1/4	1/5	1/4	1/5	1/4	2	1

and

Table 9. Judgment matrix of sub-criterion layer B to objective layer A3.

A1	B16	B17	B18	B19	B20
B16	1	3	3	5	5
B17	1/3	1	1/2	2	3
B18	1/3	2	1	3	3
B19	1/5	1/2	1/3	1	1/2
B20	1/5	1/3	1/3	2	1

Note: The consistency ratio CR = 0.039 is less than 0.1, thus passing the consistency test.

).

To verify the logical consistency of the judgment matrix, it is necessary to calculate the Consistency Index (CI) and the Random Index (RI), and determine the validity of the matrix using the Consistency Ratio (CR), where CR = CI/RI. A CR < 0.1 indicates acceptable consistency and reasonable weight distribution. Weights of indicators in the total ranking were calculated, and weight coefficients were obtained after matrix consistency testing [47].

A 3-level comprehensive evaluation index system was constructed using Yaahp V10 software (

Table 10. Comprehensive evaluation index system and weights of ecological seawall.

Target Layer K	Criterion Layer A	Weights	Indicator Layer B	Weights
Comprehensive index of ecological seawall evaluation	Safety A1	0.311	Crest elevation B1	0.101
			Overtopping volume B2	0.035
			Embankment quality B3	0.026
			Overall stability B4	0.101
			Seepage stability B5	0.047
	Ecological A2	0.493	Water quality index B6	0.040
			Sediment quality score B7	0.031
			Benthic biodiversity B8	0.019
			Vegetation coverage B9	0.064
			Post-embankment ecological space B10	0.076
			Beach scale B11	0.064
			Beach stability B12	0.126
			Front slope gradient B13	0.041
			Front slope surface porosity B14	0.015
			Ecological suitability of building materials B15	0.017
	Sustainability A3	0.196	Disaster prevention and mitigation function B16	0.091
			Habitat maintenance function B17	0.031
			Disaster prevention benefits B18	0.044
			Environmental cleanliness B19	0.014
			Ecological management capacity B20	0.017

). The target layer is the comprehensive evaluation index of ecological seawalls. The criterion layer includes safety, ecological, and sustainability indicators with weights: ecological (0.493) > safety (0.311) > sustainability (0.196). Among safety indicators, crest elevation (0.101) and overall stability (0.101) have higher weights; among ecological indicators, beach stability (0.126), post-embankment ecological space (0.076), vegetation coverage (0.064), and beach scale (0.064) are prominent; among sustainability indicators, disaster prevention and mitigation function (0.091) has the highest weight.

3. Comprehensive Evaluation Index of Ecological Seawalls

The Ecological Composite Index (ECI) was used for evaluation, which quantifies the pros and cons of ecological seawalls by integrating indicator weights and graded scores:

$$ECI=\sum _{i=1}^N{ECI}_i\times w_i$$

(14)

where $ECI$ is the comprehensive index, ${ECI}_i$ is the score of the i-th indicator, and $w_i$ is its relative weight to the total target.

ECI ranges from 0 to 100, divided into four grades: excellent ([80, 100]), good ([60, 80]), poor ([30, 60]), and extremely poor ([0, 30]) (

Table 11. Grading criteria of ecological seawall evaluation.

Evaluation rank	Excellent (I)	Good (II)	Poor (III)	Very poor (IV)
Grading range	[80, 100]	[60, 80)	[30, 60)	[0, 30)

).

4. Case Application of Comprehensive Evaluation

4.1. Project Overview

Three seawalls were selected for case application: case A is the second-phase seawall (Figure 2) of the Yuyao River Regulation and Reclamation Project in Yuyao City, Zhejiang Province; case B is the Xinhongkou Reclamation South Straight Seawall (Figure 3) in Zhenhai District, Ningbo City, Zhejiang Province; and case C is the Wanzhangtang Seawall (Figure 4) in Xincheng of Zhoushan City, Zhejiang Province. The second-phase seawall of the Yuyao River Regulation and Reclamation Project has a length of 5.98 km, meets the 100-year flood prevention standard, and is classified as a Grade 2 project. It adopts a composite slope structure, with a four-legged hollow concrete block protection layer on the water-facing slope, turf covering on the back slope, and an asphalt concrete pavement on the crest. The area in front of the seawall is part of the tidal flat on the southern bank of Hangzhou Bay, while the area behind the seawall includes shelterbelts and pond-protecting rivers, with farmland lying beyond the pond-protecting rivers.

The Xinhongkou Reclamation South Straight Seawall in Zhenhai District, Ningbo City, has a length of 1.18 km, meets the 300-year flood prevention standard, and is classified as a Grade 1 project. It features a composite slope structure: the water-facing slope is protected by four-legged hollow blocks, salt-tolerant plants such as Tamarix chinensis and Hibiscus hamabo are planted on the outer tidal flat, the back slope is protected by dry-laid block stones, and shelterbelts are built inside the seawall, with farmland inside the shelterbelts.

The Wanzhangtang Seawall in Xincheng of Zhoushan City has a length of 2951 m, meets the 100-year flood prevention standard, and is classified as a Grade 2 project. It adopts a vertical structure with a new-type open-pile beam-slab structure system. Salt-tolerant plants, including Tamarix chinensis, Hibiscus hamabo, Suaeda salsa, and Phragmites australis, are planted in front of the seawall. Behind the seawall, the original pond-protecting rivers and shelterbelts are utilized to create multiple ecological nodes such as the Reed Flower Pond, Camphor Forest, Dongsheng Pond, and Cedar Wetland.

4.2. Data Sources for Evaluation

The data required for the evaluation were mainly sourced from the following documents and on-site measurements: Qiantang River Estuary Regulation Line Plan (2016–2025) (2017), Safety Assessment Report of Qiantang River Seawalls (2019), Preliminary Design Report for the Second-Phase Seawall Danger Removal and River Regulation Reclamation Project in Yuyao City (2013), Survey Report on the Current Status of Marine Ecological Environment and Fishery Resources for the Outfall Extension Project of Yuyao Sewage Treatment Plant (2019), Preliminary Design Report for the First Phase of the Ecological Coastline Improvement and Restoration Project of Zhoushan Xincheng Ecological Coastline Renovation and Restoration Project (2019), Preliminary Design Report for Zhenhai District Coastal Zone Ecological Restoration and Haitang Anlan (Phase I) Project (2021), Ecological Assessment Report for Reclamation Projects in Zhenhai Area of Ningbo City (2019), Survey Report on Tidal Flat Resources in Key Monitoring Areas of Zhejiang Province (2017–2019), Technical Report on Investigation and Assessment of Ecological Effects of Ecological Seawall Construction in Zhejiang Province (2024), and on-site measured data, including seawall crest elevation, beach width, and the number of solid waste pieces in the project area.

4.3. Evaluation Results

Based on the constructed comprehensive evaluation index system for ecological seawalls, the evaluation results of the three seawalls are as follows:

The comprehensive evaluation index of the second-phase seawall is 75, corresponding to a “Good” grade (

Table 12. Results of comprehensive evaluation.

Target Layer K	Indicator Layer B	Case A		Case B		Case C
		Score	Weighted Score	Score	Weighted Score	Score	Weighted Score
Comprehensive index of ecological seawall evaluation	Crest elevation B1	71	7.17	100	10.10	88	8.89
	Overtopping volume B2	100	3.50	100	3.50	100	3.50
	Embankment quality B3	73	1.90	90	2.34	90	2.34
	Overall stability B4	97	9.80	100	10.10	96	9.70
	Seepage stability B5	99	4.65	100	4.70	96	4.51
	Water quality index B6	16	0.64	42	1.68	30	1.20
	Sediment quality score B7	65	2.02	45	1.40	72	2.23
	Benthic biodiversity B8	46	0.87	28	0.53	61	1.16
	Vegetation coverage B9	63	4.03	70	4.48	67	4.29
	Post-embankment ecological space B10	100	7.60	96	7.30	100	7.60
	Beach scale B11	90	11.34	90	11.34	65	8.19
	Beach stability B12	92	3.77	92	3.77	80	3.28
	Front slope gradient B13	62	0.93	70	1.05	30	0.45
	Front slope surface porosity B14	36	0.61	76	1.29	10	0.17
	Ecological suitability of building materials B15	52	1.61	65	2.02	48	1.49
	Disaster prevention and mitigation function B16	100	4.40	100	4.40	100	4.40
	Habitat maintenance function B17	70	0.98	68	0.95	62	0.87
	Disaster prevention benefits B18	85	1.45	92	1.56	86	1.46
	Environmental cleanliness B19	55	5.56	72	7.27	80	8.08
	Ecological management capacity B20	70	2.45	70	2.45	75	2.63
	ECI		75		82		76
	Ecological grading of seawall systems	Good		Excellent		Good

). The seawall basically meets the design requirements for safety and has good disaster prevention and mitigation capabilities. The tidal flat in front of the seawall is wide and stable, and there are vegetation and pond-protecting rivers behind the seawall, providing a certain range of ecological space. However, due to the use of hard materials such as precast concrete blocks in construction, the surface porosity of the water-facing slope and the ecological suitability of the building materials are insufficient. Meanwhile, affected by land-based pollution and inadequate management measures, the regional water quality, benthic biodiversity, and environmental cleanliness are relatively poor. Therefore, in future ecological construction of this seawall, focus should be placed on improving ecological performance and sustainability, protecting the tidal flat wetland environment in front of the seawall, strengthening the ecological transformation of the seawall body, and maintaining regional environmental cleanliness.

The comprehensive evaluation index of Xinhongkou Reclamation South Straight Seawall is 82, corresponding to an “Excellent” grade (Table 12). The seawall meets the design safety requirements and has good disaster prevention and mitigation capabilities. The tidal flat in front of the seawall is wide and stable, and there are vegetation and pond-protecting rivers behind the seawall, providing a certain range of ecological space. The water-facing slope adopts a porous hard material structure such as precast concrete blocks, resulting in good surface porosity. However, the ecological suitability of the seawall’s building materials is insufficient. In addition, as the seawall has just been completed, the current regional water quality, sediment quality, and benthic biodiversity are still in the process of gradual recovery and are relatively poor at present. Therefore, in future ecological construction, emphasis should be laid on enhancing ecological performance and sustainability, carrying out protection and restoration of the beach ecosystem in front of the seawall, and improving the ecological management and control capacity.

The comprehensive evaluation index of Wanzhangtang Seawall is 76, corresponding to a “Good” grade (Table 12). The seawall meets the design safety requirements and has good disaster prevention and mitigation capabilities. The tidal flat in front of the seawall is wide and stable, and there is vegetation behind the seawall, providing a certain range of ecological space. However, due to the adoption of a vertical structure and hard materials in construction, the slope gradient of the water-facing slope, surface porosity, and ecological suitability of the building materials are insufficient. At the same time, affected by land-based pollution, the regional water quality is relatively poor. Therefore, in future ecological construction of this seawall, priority should be given to improving ecological performance and sustainability, controlling land-based pollution, and strengthening the ecological transformation of the seawall body.

5. Discussion

5.1. Comprehensive Evaluation Index System

Ecological seawalls are an inevitable trend in global seawall construction, and scientific evaluation is crucial for their development. This study clarifies the connotation of ecological seawalls by integrating construction concepts and structural characteristics, and constructs a comprehensive index system covering 20 indicators from safety, ecological, and sustainability aspects. The ECI quantifies results into four grades, providing guidance for future construction. Research indicates that seawall construction must prioritize safety compliance, create stable pre-embankment habitats, adopt porous and gentle-slope designs for the embankment, and retain post-embankment ecological space to form a comprehensive protection system synergizing ecology and disaster reduction [24]. The higher weight assigned to ecological indicators aligns with the principle of ecological suitability for ecological seawalls [24]. Among ecological indicators, beach stability, post-embankment ecological space, vegetation coverage, and beach scale have higher weights, reflecting the influence of hydrological, environmental, biological, and habitat factors on coastal ecosystems, which aligns with key technologies for coastal wetland restoration and ecological seawall construction [48,49]. For safety indicators, crest elevation and overall stability are critical, as they form the foundation of seawall safety [50].

5.2. Typical Measures for Ecological Seawall Construction

Based on the index system and indicator weights, typical construction measures are proposed from five aspects:

• Beach protection: According to front slope sedimentation, tides, waves, and topography, adopt ecological protection measures such as shell reefs, mangroves, and salt marsh vegetation restoration to restore beach morphology, prevent erosion, improve biodiversity, and enhance vegetation’s wave-dissipating and beach-stabilizing functions [27].
• Embankment structure: Prioritize safety for front slope and pressure layer protection, adopt porous and rough structures considering ecology and economy, and incorporate materials suitable for marine organism attachment (e.g., ecological grilles, honeycomb structures) [28].
• Surface protection: For shore sections with weak currents and waves, stable pre-embankment beaches, and verified overall stability, use vegetation for protection on the front slopes, selecting wind/wave-resistant, flood-tolerant, and salt-tolerant native species. Avoid invasive species and ensure sufficient soil thickness (≥30 cm for grass, ≥50 cm for shrubs) [34].
• Building materials: Natural stones must meet specifications for weight, compressive strength, and softening coefficient. Artificial blocks must meet requirements for weight, concrete strength, and porosity (>40%) [35].
• Vegetation selection: Plants are mainly arranged on pre-embankment, crest, and back slope areas. Prioritize native species, with front-slope species resistant to wind, waves, flooding, and salt, and back slopes using grass-shrub combinations that meet requirements for resistance to erosion from overtopping water [24].

Ecological seawalls, as an emerging research field, are still in their infancy in terms of theoretical frameworks, construction measures, and evaluation methods. This study provides a preliminary exploration of evaluation methods but has limitations: (1) The index system was verified by only one case; future studies should validate and revise indicators using diverse cases. (2) AHP involves subjective judgment in weight calculation; future work could combine it with objective weighting methods (e.g., the entropy method) to reduce subjectivity. (3) The system includes numerous interrelated indicators, and qualitative indicators have ambiguous evaluation standards; future work should focus on simplifying the system and standardizing the scoring process for qualitative indicators.

6. Conclusions

Based on systematically reviewing the research status and key technologies of ecological seawall construction at home and abroad, this study breaks through the evaluation limitation of traditional seawalls that “emphasize safety over ecology” and clearly proposes the connotation of an ecological seawall with a “three-dimensional integrated” structure consisting of a “coastal wetland zone—seawall structure zone—terrestrial buffer zone”. It realizes the in-depth integration of the Analytic Hierarchy Process (AHP) with multi-dimensional ecological indicators. By selecting 20 evaluation indicators covering safety, ecology, and sustainability, a three-level comprehensive evaluation system is constructed. Specifically, AHP is used to quantify the indicator weights (ecology: 0.493 > safety: 0.311 > sustainability: 0.196), which realizes the quantification of ecological indicators and weight allocation in ecological seawall evaluation and provides a standardized technical framework for the scientific evaluation of ecological seawalls.

This study selects three practical projects of different types, such as the Yuyao River Regulation and Reclamation Phase II Seawall in Zhejiang Province, to conduct operability verification. The evaluation conclusions are highly consistent with the actual ecological conditions of the projects, which verifies the engineering applicability and result reliability of the indicator system. The indicator selection in this study is strictly aligned with the policy requirements of documents such as the *Work Plan for Coastal Zone Protection and Restoration Projects*, and the weight allocation reflects the orientation of “ecology first, safety bottom line”. Moreover, the indicator data can be obtained through conventional engineering surveys, so the constructed evaluation system has the potential for standardized application in seawall construction and evaluation.

Based on the evaluation foundation laid by this study, future research directions can be expanded in three aspects: first, optimize the indicator weighting method by introducing objective weighting methods such as the entropy weight method and Principal Component Analysis (PCA), and form a “subjective-objective coupled weighting” model with AHP. This will further reduce the subjectivity of weight allocation, simplify the indicator system, and improve the efficiency of engineering application. Second, integrate dynamic simulation tools by combining this evaluation system with hydrodynamic models such as Delft3D and MIKE21. This will simulate the dynamic responses of indicators such as beach stability and water quality changes under scenarios like storm surges and sea-level rise, realizing the full-cycle assessment of ecological seawalls covering “current status evaluation—future risk prediction”. Third, the evaluation indicator system constructed in this study is mainly applicable to seawalls in China, while the construction of ecological seawalls will be a widely adopted solution globally. Therefore, future research needs to select indicators based on local conditions and develop evaluation indicator systems to adapt to the different seawall construction conditions in various regions.