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Article

Ecological Environment Assessment System in River–Riparian Areas Based on a Protocol for Hydromorphological Quality Evaluation

by
Lan Duo
1,
Martí Sánchez-Juny
1,* and
Ernest Bladé i Castellet
2
1
Flumen Institute, Universitat Politècnica de Catalunya (UPC), 08034 Barcelona, Spain
2
Flumen Institute, Universitat Politècnica de Catalunya (UPC)—Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE), 08034 Barcelona, Spain
*
Author to whom correspondence should be addressed.
Water 2024, 16(21), 3025; https://doi.org/10.3390/w16213025
Submission received: 20 September 2024 / Revised: 18 October 2024 / Accepted: 21 October 2024 / Published: 22 October 2024
Browse Figure
Versions Notes

Abstract

:
This paper aims to propose a method for the evaluation of the hydromorphological quality of a river and its riparian areas using three essential components: morphological characterization, river connectivity, and vegetation coverage. The method has been applied to the Tordera river in Catalonia, Spain. The general goal is to establish a riparian environment assessment tool by proposing parameters for each of the three mentioned aspects. This approach relies on data collection and evaluation with a simple computational procedure for eliminating subjectivity in the weighting and classification of evaluation levels. In the proposed methodology, the weights of the indicators are determined by the Distance Correlation-Based CRITIC (D-CRITIC) method, and the results are integrated using the Coupling Coordination Degree Model (CCDM). The proposed methodology quantifies assessment parameters and analyzes the environmental problems faced by riparian zones and rivers through the parameters and the results of the CCDM and thus can be used as a basis for proposing methods to improve the ecological situation. The results can be used for the enhancement of the coordination between the development of riparian resources and the requirements of ecosystem protection and utilization, and they can be used to promote the healthy development of ecological environments and the effective use of riparian resources.

1. Introduction

Human populations have increasingly placed the ecological integrity of rivers under tremendous pressure, resulting in notable impacts on hydromorphological attributes that are crucial for biodiversity, ecosystem functions, and water quality [1]. A variety of factors, including climate change, river regulation policy updates, and the development of river hydraulic technology, can induce changes in the morphological parameters of a river [2]. It is well-documented that changes in river curvature and cross-sectional dimensions, the construction of human-made riverbeds, and modifications to riverbank structures not only have significant ecological consequences for a river’s aquatic life but also destroy wildlife resources in terrestrial habitats [3,4,5]. Moreover, river regulation can also lead to ecological changes [6,7,8]. For instance, in certain circumstances, the modification of river banks might trigger a response in the natural adjustment of the banks, potentially resulting in an improvement in the ecological environment [2]. In other cases, the construction of roads and railway lines in riparian corridors as well as the construction of river levees to protect the floodplain may result in the degradation of the riparian landscape quality and a reduction in its quantity [9,10]. Additionally, alterations in hydraulic factors and transported substances can lead to changes in the conditions of plant growth in a riparian zone, while the changes in land use in a floodplain area are reflected in the changes in surface roughness, which affect the flood peak discharge and the flood discharge capacity [11]. The encroachment of riparian vegetation into stream channels is one of the most common responses to river regulation, and increased vegetation growth and cover are frequently observed downstream of dams [1]. In order to guarantee flood control and the preservation of the ecosystem, the implementation of two-stage channels has been occasionally proposed as a means of facilitating management of associated problems [12]. Furthermore, these configurations also affect the riparian zones and their extents.
To mitigate the adverse changes in riparian zones caused by human activities, government agencies are committed to implementing protocols and methodologies for the assessment of riparian conditions and monitoring on a regular basis. The processes of hydromorphological assessment utilized by different agencies follow protocols that, while exhibiting certain similarities, include a variety of methodologies adopted in practice [13]. Additionally, these methods, when applied to different types of rivers, such as permanent and intermittent, may vary considerably [14].
Many of these evaluation methods employ a comprehensive approach involving a set of associated attributes, where interval scoring is performed on groups before being aggregated to determine a total score. For example, the Site Assessment and Riparian Evaluation (SARE) method proposed by Fry et al. [15] and used for analyzing and evaluating riparian status includes a range of criteria, such as vegetation cover, channel morphology, erosion, land use, and recreation potential, whereas the Stream Visual Assessment Protocol (SAVP) method [16] relies on riparian landowners to conduct a visual inspection of the physical and biological characteristics of streams and riparian areas. Furthermore, the Qualitat del Bosc de Ribera (QBR) index method [17], which considers the cover of riparian vegetation, the riparian structure, and the complexity, naturality, and degree of river channel alteration, is used in conjunction with biological indicators of water quality to establish the ecological status. The Buffer Zone Inventory and Evaluation Form (BZIEF) [18] is a rapid field reconnaissance tool that assesses riparian conditions by incorporating criteria based on scoring systems developed from a literature review, subsequent peer review, and a pilot field study. Yet another approach by Del Tánago and De Jalón [19] proposes seven attributes to assess the ecological status of riparian zones, including the dimensions and coverage distribution pattern of a riparian corridor, the composition and structure of riparian vegetation, the growth and reproduction status of woody species, and the influence of the artificial factor on river banks and floods. Subsequently, Del Tánago and De Jalón [20] proposed the Riparian Quality Index (RQI) method to quantitatively assess the riparian status by scoring several aspects mentioned above.
In addition to the aforementioned comprehensive assessment methods, there are other novel methods for assessing riparian ecosystems. Macfarlane et al. [21] applied fuzzy systems theory to environmental quality assessment by combining the riparian degradation stressors into a fuzzy inference system to build a drainage network model for assessing riparian status. Furthermore, machine learning techniques have also been employed for the assessment of the quality of riparian habitats. For example, to examine the impact of hydrological changes caused by dam construction on the ecological dynamics of a riparian zone, Pal et al. [10] used the ArcGIS Platform to map the riparian zone and assess the changes in quality by overlaying the intersection of the riparian forest, the wetland, floodplains, and the riparian corridor with topographic cliffs. In recent years, on-site detection of riparian conditions using remote sensing has become more common and is considered to be an efficient and readily available method [22,23]. For instance, the combination of remote sensing with a comprehensive approach facilitates efficiency and accuracy in the assessment [24].
According to Belletti et al. [25], these numerous approaches can be categorized as follows based on their focus and objectives: (1) physical habitat assessment, (2) riparian habitat assessment, (3) morphological assessment, and (4) hydrological regime alteration assessment. In Table 1, examples of each category are listed in order to provide an intuitive comparison of the process of obtaining evaluation results. Practitioners have adopted physical habitat and riparian habitat survey protocols, which consist of two parts: the habitat characterization and the stream quality assessment [2]. For example, these include the On-site Survey, the Overview Survey, the Habitat Quality Assessment (HQA), and the Habitat Modification Score (HMS) [26,27]. The specific operation of these protocols involves an initial selection of a number of cross-sections (usually 10) of the river reach under investigation, situated at equal distances within a certain width. A spot-check is then conducted on these cross-sections before the collection of information pertaining to the substrate and the channel, as well as the riparian zone. Finally, each of these aspects is assessed by using an expert-agreed scoring system to classify the result into several classes [1,28,29,30]. The morphological assessment method differs from the habitat assessment protocol by considering artificial alteration. In some cases, expert judgment is used to assess the outcomes. In other instances, however, each indicator is scored by way of querying the scenarios listed in the description and the definition table. Based on the assigned scores, the final evaluation of the results is then conducted. For example, this is the approach used by the relational system of watercourse hydromorphology auditing (SYRAH-CE) method [13,26] and the Morphological Quality Index (MQI) method [31]. Some methods, such as the methodology for monitoring and assessment of hydromorphological features (HYMO-HR) and the hydromorphological assessment methodology (HYMO-RO) [13], also take into account the assessment of hydrological regime alteration. The evaluation results are derived by checking their performance in specific situations or tasks related to each of the hydromorphological indicators.
For the internal basins of Catalunya, located in the northeast of the Iberian Peninsula, the Catalan Water Agency developed a comprehensive protocol called HIDRI (Protocol d’avaluació de la qualitat HIDromorfologica dels Rius) for the evaluation of the hydromorphological quality of rivers and their riparian areas [32]. The HIDRI protocol is, thus, a hydromorphological quality assessment guide developed by the Catalan Water Agency comprising nine protocols (Table 2) for assessing three aspects: the hydrological flow regime, river continuity, and morphological conditions.
When using the HIDRI protocol in practical assessments [14], the hydrological flow regime assessment employs a distributed rank assessment method, where water withdrawal and environmental flow compliance are quantitatively calculated, scored, and ranked into five categories of bad, poor, moderate, good, and high. Then, using a method similar to a risk assessment matrix, a combined analysis of environmental flow compliance and the water withdrawal degree is performed. Afterward, a quantification of the Index of Hydrological Alteration (IHA) is classified into five levels and combined with the previous results once again to obtain a new set of combined results after considering the following three analyses: the water withdrawal degree, environmental flow compliance, and IHA. Furthermore, the river continuity is determined using the River Connectivity Index method, which calculates the number of impassable barriers per unit of length of the river. The results of this analysis are divided into five classes, as indicated above. Finally, morphological conditions are evaluated similarly to the hydrological flow regime. First, the land use quality and QBR are analyzed and scored, and then a combined analysis is used for both of them. Afterward, the channelization level is calculated and scored, and the final results are obtained by combining these results with the combined result of land use quality and QBR.
The advantage of the HIDRI-protocol-based method, as used in [14], is that it is convenient to implement and allows multiple factors to be aggregated into a single result, which appears to be a more thorough consideration of the evaluation results. However, a notable disadvantage is that distributional considerations may lead to a greater weighting of the factors prioritized for inclusion in the combined analysis, resulting in an accumulation of errors. As for the morphological conditions section, the basis for delineating the riparian buffer in the floodplain land use analysis is less clear. For this, not only the remote sensing method of visual interpretation [33] is used but also the flood information from different return periods and expert criteria.
Thus, the purpose of this paper is to propose a new quantitative evaluation index system based on the HIDRI protocol and to use a comprehensive evaluation method for analyzing the hydromorphological quality of the river and its riparian zone. The advantages of using this method over the HIDRI assessment method are that its integration of the riparian model with the GIS analysis facilitates access to the parameters of the hydromorphological quality assessment, minimizes the influence of subjective assignments, and conveniently achieves the purpose of evaluation. This work provides a practical methodology for quantitatively assessing the hydromorphological quality of riparian zones based on the Catalan Water Agency proposal, and it is used for the assessment of the quality of the riparian zone of the Tordera River, a river with mountainous headwaters that discharges into the Mediterranean Sea on the Catalonian coast.

2. Methodology

The methodology comprises the introduction of a new index system and a comprehensive evaluation method. The comprehensive evaluation method is applied after all of the parameters have been collected. It employs the modified version of the Criteria Importance Through Intercriteria Correlation (CRITIC) method to calculate the weight, including, specifically, the Distance Correlation-Based CRITIC (D-CRITIC) method and the Coupling Coordination Degree Model (CCDM), to assess the level of coupling between the aspects.

2.1. New Index System

The new quantitative evaluation index system for assessing the river and riparian zone environment using parameters based on the HIDRI protocol focuses on the following three aspects: morphological characterization, river connectivity, and vegetation coverage. It is pertinent to note that river continuity in the HIDRI protocol is partially focused on longitudinal connectivity, which emphasizes the uninterrupted movement of the river. However, for the river and the riparian system, connectivity encompasses not only longitudinal but also lateral and vertical connections, which are crucial for the movement of water, sediments, and organisms. Therefore, a series of parameters have been put forth for the purpose of assessing river connectivity. These are used in conjunction with the other two aspects inherent to each protocol in HIDRI, namely, morphological characterization and vegetation coverage. It is also worth noting that as the health of the riparian zone environment is closely linked to the hydrological characteristics of the river, as river flows do not change significantly in the study area, the hydrological parameters that focus on long-term variations are not crucial in the assessment of our case; thus, they were not included.
Table 3 presents the new proposed parameters based on different aspects. The initial step to analyze the hydromorphological quality of the river and its riparian zone involves delineating the extent of the riparian area. This delineation can be based on [34], a methodology that uses the results of two-dimensional hydrodynamic modeling together with a simplified groundwater evolution model. In other previous approaches, the lateral confinement of the evaluation extent is determined by a fixed width. For example, the RHS method, based on a consistent range of land use surveys, determined this width to be 50 m regardless of the river type [35]. The MQI method in the lateral direction is defined by the morphological condition or multiples of the channel width [31]; however, in the comparative evaluation of the MQI and RHAT methods, a width of 120 m was chosen to be the extent limit of the riparian zone [28]. These lateral confinement restricting methods are challenging for users to implement effectively. Instead, a method that takes site-specific conditions into account can offer a more tailored and adaptable solution. Equally important is the fact that dividing the study area from upstream to downstream into a suitable number of multiple assessment units based on the length of the target river reach does not require that the evaluation units are of equal length; rather, the area is spatially partitioned using the Thiessen polygon method, and each assessment unit contains the river and its riparian zone.
The morphological characterization of riparian area is influenced by hydrological, geomorphological, and ecological processes. The riparian area Arp, which is essential for assessing the health of riparian areas, can be obtained through two-dimensional hydraulic riparian modeling delineation [34]; Pant is the proportion of the assessed riparian area that is anthropogenically modified; SI is the sinuosity index calculated as the ratio of the length of the thalweg to the length of the valley; and S0 is the channel elevation gradient. The two factors—SI and S0—represent the degree of tortuousness of the river and the riparian area, and they are calculated at each of the sub-reaches the river is divided into.
The river connectivity is assessed in all three spatial dimensions. In the vertical direction, the changes in groundwater level during a flood event are denoted by Gw. For its obtention, simulations can be performed with the methodology outlined in [34] to determine the groundwater fluctuations at different parts of the riparian zone during a flood event. Vertical connectivity evaluation uses the depth of the water table denoted as Dw. In the horizontal dimension, the proposed parameter F is related to the percentage of the riparian zone in the reach that is inundated or flushed by flooding. It is obtained by multiplying the probability of different return periods (2.5 years, 10 years, 50 years, and 100 years) and the percentage of the riparian area flooded in each of them before calculating the degree of dispersion using the standard deviation. The other parameter, END, represents the channelization level and is acquired directly from the HIDRI protocol. A quantitative value of the channelization level is determined based on the total length of the evaluated water body and the length of the channelized sections weighted by the type of channelization. The applied coefficients of 0.2, 0.5, 0.8, and 1, respectively, are based on the types of artificial structures on the river banks, including levees, gabion breakwaters, walls, and concrete riverbeds, as defined in the HIDRI protocol [32]. This parameter captures the anthropogenic modification of the natural slopes of the river channel. Various types of slopes can affect biological habitats and hydraulic exchange. In the HIDRI protocol, river connectivity is assessed by considering artificial infrastructures that can influence the aquatic biota. Here, B represents the density of crossing structures, such as barriers encountered by aquatic organisms, and is simply calculated as the number of barriers per kilometer. It can be used to assess the longitudinal connectivity.
As regards the vegetation, woody and herbaceous vegetation growing adjacent to the river are particularly important for erosion control, buffering surface runoff to reduce diffuse pollution, and providing vital habitats for the survival of aquatic life. Consequently, it is a key component of riparian ecological health assessments. Area parameters Ab and Abl are used to assess the amount of vegetative cover relative to the bare soil area inside of the natural levee along the river channel.

2.2. Comprehensive Evaluation Method

Comprehensive evaluation problems refer to decision making scenarios where multiple criteria need to be considered to assess and compare the performance or suitability of various alternatives. These problems arise in diverse fields, such as business, engineering, public policy, and environmental management, where decisions are rarely based on a single criterion. Therefore, multi-criteria decision making (MCDM) methods are often used in comprehensive evaluation problems [36]. The MCDM methods are a set of techniques and approaches used to support decision making in situations where multiple—and often conflicting—criteria need to be considered. In MCDM methods, weights play a crucial role in determining the relative importance or significance of different criteria in the decision making process. Weights are assigned to criteria to reflect the decision maker’s preferences and priorities, acknowledging that not all criteria have equal importance. The weight of a criterion represents its contribution to the overall evaluation of alternatives, and the relative importance of each criterion is determined by considering the weights to solve the decision problem [37,38]. Therefore, it is especially important to choose the appropriate weight calculation method [39].
The determination of the weights can be performed using subjective and objective methods. The objective weighting method in MCDM is an approach to determining the weights of criteria based on objective, quantitative information rather than relying solely on subjective judgments from decision makers. This method is employed to enhance the objectivity and transparency of the decision making process by grounding the weights in measurable data and using mathematical calculations to obtain them. It has the advantage of being simple and avoiding the influence of the subjective judgment of decision makers [40,41,42]. In recent years, the entropy weighting method [43], standard deviation methods, and the CRITIC method have been applied as objective weighting methods in many different MCDM problems [44,45,46,47]. The CRITIC method is mostly an applied objective weighting method that can easily be converted into an algorithmic form and is applicable along with other multi-criteria ranking methods [48]. It is designed to address the challenge of deriving criteria weights when there is a lack of precise information or when decision makers find it difficult to assign numerical values to their preferences. On this basis, Krishnan et al. [46] integrated distance correlation into the CRITIC framework as the D-CRITIC method. Distance correlation is a measure of association between two random variables that generalizes the concept of correlation. It assesses the similarity between pairs of observations in a dataset based on their distances in the space defined by the variables. Subsequently, the D-CRITIC method aims to capture not only the linear relationships between criteria but also the nonlinear relationships that traditional correlation measures may fail to discern. This could be particularly relevant in MCDM when criteria interactions are complex and not easily represented by linear correlations. It has been observed that criteria weights produced using the D-CRITIC method are more stable and valid when compared with the CRITIC method.
In using comprehensive evaluation methods, it is common to make an overall evaluation after calculating the weights, but the results are not unique. To evaluate the performance of a system and overcome this the lack of uniqueness of the results, the CCDM can be used. This is because it may help in understanding and considering the interaction and mutual constraints between multiple indicators simultaneously, while also providing an analysis of the coordinated development level as the comprehensive evaluation result. The formula for the multi-subsystem coupling calculation used is as follows [49]:
C = 3 f X · g X · h X 3 f X + g X + h X ;   T =   α · f X + β · g X + γ · h X ;   D = C · T
Here, C is the parameter that quantifies the coupling degree (the greater the value of C, the greater the interaction between the systems), and T is a comprehensive evaluation coefficient obtained by summing up the product of the indexes and their weights. In the present case, f(X), h(X), and g(X) are aspects of morphological characterization, river connectivity, and vegetation coverage, respectively, while α, β, and γ are the contributions of each aspect. Moreover, D represents the coupling coordination degree and is calculated from the coupling degree and the comprehensive evaluation coefficient.
The CCDM has been used to explain the coupling between various category groups and analyze their level of coordinated development [50,51]. These methods are often utilized to study the relationship between socioeconomic and ecological environments, as well as to analyze and demonstrate the current status and driving factors of coordinated development [52,53,54]. For example, Cui et al. [55] used the CCDM to summarize the application of coupled urbanization and ecological environment simulations at different regional scales.
In the present study, the D-CRITIC method is applied to determine the criteria weights of proposed parameters in morphological characterization, river connectivity, and vegetation coverage aspects for evaluation and the CCDM to evaluate the coupling of all parameters, thereby exposing the current state of the riparian zone environment.

3. Results

This section presents the application of the new index system and evaluation method in a reach of the Tordera River in the northeast of Catalunya, Spain. The river length within the study area is 10 km long, ranging from the town of Hostalric upstream to the town of Tordera downstream, where a natural riparian environment has been preserved (Figure 1).

3.1. Parameter Acquisition

The procedure for obtaining the parameters can be summarized in the following three steps. Step 1: the riparian zone delineation is carried out based on a coupled numerical simulation of the river flow using a two-dimensional hydraulic model. The collected data include a high-precision digital terrain model, land use data, soil data, groundwater data, and river discharge data, which are used in an open-source riparian delineation model. Nevertheless, with this delineation method, some riparian areas could be disconnected from the rest due to human-induced changes in land use along river banks, such as urban development and the planting of long-rooted crops. To address this and to generate continuous assessment units, hundreds of random points were generated within the riparian zone, and the α concave hull tool of ArcGIS was used to extract a continuous area covering all of the points [56]. In this case, α is set to 0.05 to obtain the most realistic morphology of the riparian zone.
Step 2: as previously stated, segmenting the river and its riparian zone into multiple units allows for better characterization and analysis of the assessment. The length of the object river was divided into ten sub-reaches, each of which served as an assessment unit (see Figure 1). The assessment unit divisions were obtained using the following steps. First, hundreds of points were randomly generated inside of the river channel polygon using the vector processing tool and divided into ten clusters using the K-means clustering tool by gathering together the random points of each cluster with the closest mean value. Then, the points of the same clusters were assembled, and the centroids were calculated. Afterward, the Thiessen polygons were built to obtain the partition line of the polygons. Finally, the river was divided into sub-reaches based on the partition lines and the riparian area. In this manner, each river channel section and the area associated with the sub-reach served as an assessment unit.
Step 3: GIS statistical tools are applied in each assessment unit to acquire the extent of the riparian zone and the area of artificial infrastructure in order to calculate Arp and Pant. Similarly, Ab and Abl are determined inside of the natural levee along the river channel. Measurement tools can be used to acquire the length of the evaluated length of the river sub-reach and its direct axial length, which can then be used to calculate SI. Additionally, the length of the channelized sections can be determined to calculate END. Elevation can be obtained from the digital terrain model in order to calculate S0. In the context of two-dimensional hydraulic modeling, multi-year average groundwater data are used as input data for riparian zone simulation. Therefore, the Dw of the assessed river sub-reach can be obtained directly in the layer properties function. Once the riparian zone model simulation is complete, new groundwater data can be obtained in the same manner to calculate Gw, the changes between the initial and the final groundwater. In addition, 2.5-, 10-, 50-, and 100-year return periods of floods are used as the input data in the two-dimensional hydraulic riparian model. Therefore, F is calculated by calculating the standard deviation of the ratio of the riparian area to the inundated area under different flood scenarios. The calculation of B is performed using the ratio of the number of barriers and the length of the evaluated length of the river sub-reach.

3.2. Evaluation Result

Each sub-reach was used as a unit of assessment in which the indicators were collected and calculated as explained in Section 3.1. The resulting values are shown in Table 4.
Based on the morphological characterization parameter Arp, it is possible to observe that the riparian area is larger in the middle upper sub-reaches, and the values of SI and S0 indicate that most sub-reaches are straight and flat. Furthermore, there are only two sub-reaches with large curvatures, with SI exceeding 1.2 in a meandering pattern. Additionally, Pant represents the proportion of the anthropogenic modification area in the riparian zones, which varies greatly. Buildings are gathered both upstream and downstream of the selected study reach.
Concerning vegetation coverage parameters, shrub vegetation appears to be more abundant in the lower reaches than in the upper reaches, as indicated by Ab. It is noticeable that Abl starts to increase from sub-reach 5 onward. Due to the increased curvature of the river, bare land is more likely to manifest in the deposited bank.
In terms of river connectivity, the Dw value indicates that groundwater depth in the upstream section is shallow, and it leads to a more significant increase in the groundwater after experiencing a flood event, which can also be seen from Gw. From the value of F, which is related to the proportion of the riparian area inundated by different floods, it can be observed that river sub-reaches 1, 7, and 8 have large differences in the inundated area when different floods occur. Based on the value of END, the results suggest that horizontal river connectivity is also related to the artificial structure on the river margins. Thus, it can be concluded that modifications of the river channel upstream and downstream are relatively large, which leads to a greater impact on biological habitats and hydraulic exchange. Longitudinally, parameter B shows that only sub-reach 5 has a barrier, which is a gauging station.
Table 5 presents the standard deviation, information content, and weight of each parameter as determined using the D-CRITIC method. The normalization process is necessary to standardize the scales of different units into a range between 0 and 1, which can make parameters comparable across different measurement units or scales. In the analysis, Arp, SI, Gw, and Ab are considered to be beneficial criteria, while S0, Dw, F, END, B, Abl, and Pant are considered to be non-beneficial. In terms of conflict measurement, it can be considered that the “distance correlation”—a correlation measure similar to the Pearson correlation coefficient—can reveal the degree of interdependence between the criteria [57,58]. The method assigns lower weights to items with lower levels of conflict, with the lowest weights being 6.86% for Dw and 7.98% for END. The amount of information contained in the criteria can be discussed using contrast intensity [59], and the contrast intensity of each criterion can be seen from the standard deviation results. The distance correlation and standard deviation results were combined to calculate the information content [45]. The higher contrast intensity of the criterion is expected to provide more information. In other words, this item should be given more attention with a higher weight. In terms of standard deviation, Arp has a clear distinction compared with our parameters. Once the weights assigned to each indicator were obtained, the results after obtaining the weight assigned to each indicator revealed that B has the highest weight at 11.16%, followed by Arp at 10.10%.
Table 6 shows the results of using the method of the Coupling Coordination Degree Model. The D-CRITIC weighting method was used to determine the weights (see Table 5), while the coupling coordination method was used to calculate the comprehensive evaluation coefficient T, which provides a perspective on the degree of coupling coordination D. Coupling coordination degrees are usually divided into multiple categories; some are divided by quartiles [60], while others are divided by subjective thresholds of four [61] or five levels [62,63]. However, in this study, coupling coordination degrees are divided into multiple categories by using the uniform distribution method of subdividing into 10 levels from 1 to 10, ranging from extremely dysfunctional to excellent coordination [51,64,65].
As Table 6 shows, from an overall perspective, the level of coupling coordination degree of each sub-reach is generally at a high level of coupling coordination. In the upstream reaches, except for sub-reach 1, the coordination degree is better than in the downstream reaches. In particular, sub-reach 4 has the best coupling coordination degree. The highest comprehensive coordination index represents the highest product of indexes and their weights. The river connectivity aspect accounted for the highest weight. In the case of sub-reach 4, the river connectivity is promising in the vertical, transversal, and longitudinal directions and characterized by high positive parameters and low negative parameters. With the exception of sub-reach 6, all of the sub-reaches within the river reach exhibit a favorable coupling degree, indicating greater system relevance.
The worst sub-reaches are 1 and 6, which are classified as barely maladjusted recession. Sub-reach 1 has the lowest degree of coordination, which means it has the worst degree of consistency between aspect parameters. Furthermore, it has a low degree of mismatch recession, possibly caused by the excessive presence of artificial structures in the riparian zone. Sub-reach 1 has the highest proportion of anthropogenically modified riparian areas and the highest level of channelization, which may affect the physical structure and flow dynamics of the water bodies, which also has significant ecological consequences. Management for improving hydromorphological quality for this sub-reach could include removing unnecessary structures, restoring the hydrological connectivity, and preventing future construction. Sub-reach 6 has the highest proportion of bare land, with relatively little vegetation growing in the overly exposed channel, thus preventing it from being a high-quality riparian habitat. For this sub-reach, restoring native vegetation to stabilize and prevent further erosion and improve the habitat can be considered as a management action. As previous studies have demonstrated, some of the larger morphological changes are caused by extreme flood events, and after such an event, the conditions of dynamic equilibrium are re-established [2]. In addition, the coupling coordination degree for the channel of sub-reach 8 is not as good as that of other sub-reaches, which is because parameters Dw and F in river connectivity are greater than most other river reaches. The water table of this sub-reach is deep, while the groundwater changes during a flood event are low, which represents reduced vertical connectivity. Moreover, the degree of dispersion of the flood disturbance in this sub-reach is greater than that of others. This reveals a notable discrepancy in the lateral extent of the flood limit, indicating that some areas can only be flushed during a great flood. However, the inundation pulse is important to connect the riparian corridor with the river in terms of nutrient exchange, flood plain sedimentation, and survival of the riparian vegetation [4,10]. This also explains why sub-reach 8 is less coupled than the other river reaches in the comprehensive evaluation given the lack of access to the beneficial effects of the flood pulse.

4. Discussion

4.1. Comparison and Validation of the Method

In order to demonstrate the consistency of the method proposed in this paper for the evaluation of the hydromorphological quality, we applied an existing commonly used method—the Morphological Quality Index (MQI) method—in the same river reach. The MQI method integrates remote sensing and field surveys to assess 28 indicators based on a scenario-based scoring system and does not focus on the long-term hydrological regime. To facilitate the comparison of the assessment results, the sub-reaches’ division is maintained, as it is in line with the division requirements of the MQI assessment. The evaluation results are shown in Table 7.
The comparative results reveal a distribution situation with similar quality over the entire river reach. The results of both methods show that the morphological quality of the entire reach is good. Sub-reach 1 exhibits the worst evaluation result, while sub-reach 4 has the best. The trend in quality change is consistent from sub-reach 1 to sub-reach 5. However, there are some differences. The method proposed in this paper considers not only longitudinal and lateral continuity but also vertical hydrological connectivity. From sub-reach 6 to sub-reach 10, the results obtained with this method are less favorable than those of the MQI, which is due to the poor longitudinal hydrological connectivity of this section and the extensive area of bare land in the riparian zone.
In order to further validate the correctness of the output, it was compared with the results of a program that aimed to evaluate the hydromorphological quality of the rivers of the Catalan River Basin District. This work was released by the Department of Territory and Sustainability of the Government of Catalonia in collaboration with the Catalan Water Agency [66]. In it, the ecological state is assessed according to the Water Framework Directive 2000/60/CE and the Hydrological Planning Regulations of the Catalan River Basin District. The hydromorphological quality level is assessed based on three aspects: the hydrological regime, continuity, and morphology. The three aspects are divided into five levels: “Very Good”, “Good”, “Medium”, “Deficient”, and “Bad”. The comprehensive evaluation results are divided into three levels: “Good”, “Fine”, and “Bad”. When all three aspects are “Very Good”, the overall result can be evaluated as “Good”. Because the morphology condition is “Deficient”, the river reach of our study is evaluated as “Fine”. The results presented herewith demonstrate a clear alignment with the authoritative government results.

4.2. Hydromorphological Assessment Aspects

The assessment of the hydromorphological condition of rivers and their surrounding areas is conducted in accordance with a variety of protocols and methodologies across different countries or regions [2,13,26,28,31,67]. These protocols are currently in use for assessing the hydromorphological condition of rivers, with the specific approach taken depending on the prevailing local environmental conditions and the requirements of the relevant policy framework. For example, in the United Kingdom, the River Habitat Survey (RHS) protocol is used as a standardized protocol to assess habitat quality, hydromorphological pressures, and the physical structure and condition of rivers [2]. In Catalonia, northeast Spain, the HIDRI protocol is used to assess the hydromorphological quality of rivers and their riparian areas [14,66]. While these protocols may differ in name and focus, they all assess morphological aspects, such as river morphology and human impacts, hydrological aspects, such as flow regime, flood dynamics, and groundwater interactions, and ecological aspects, such as habitat quality. However, there is often an overlap in the assessment, because the river ecosystem is a complex and interconnected system, and multiple factors working together affect each other.
This manuscript proposes a new method for ecological environmental assessment based on the HIDRI protocol, which focuses on morphological characterization, river connectivity, and vegetation coverage. The proposed method places particular emphasis on other important hydrological considerations, such as the flood regime, river–groundwater exchange processes, and water level fluctuations. The method includes not only the aspects outlined in the HIDRI protocol but also an improved assessment of certain individual aspects, thereby making the results more scientifically based, objectively obtainable, and thus convincing. For example, river continuity in the HIDRI protocol is partially focused on longitudinal connectivity, whereas for the river and riparian system, connectivity includes not only longitudinal but also lateral and vertical connections, which are crucial for the movement of water, sediments, and organisms. Furthermore, river and groundwater flows are also inextricably linked, and their interaction is particularly important in riparian zones. Consequently, when assessing the health of the riparian zone, it is crucial not to neglect the river–groundwater exchange process and its significant influences, and this is achieved using the proposed methodology, which is based on numerical modeling of such a connection.

4.3. Complexity of the Hydromorphological Assessment

The hydromorphological assessment of the river and the riparian area is a complex process due to the interconnected nature of the system, which depends on a variety of factors working together. In conducting an assessment, it is essential to use a comprehensive methodology that takes into account a multitude of interrelated aspects, including but not limited to hydrology, geomorphology, vegetation, and human impact [68].
Based on the summary of the limitations of over 120 hydromorphological assessment methods analyzed in [25], some advantages of the parameter proposed in this paper can be described. With regard to the assessment of hydrological aspects, the majority of methods use IHA as a means of measuring changes in the hydrological regime, which (1) requires large data sets and the use of long-term series and (2) generally does not include the effects of groundwater alteration, which is an important component of river ecosystems. In the assessment of morphological aspects, such as the channel pattern and physical variables, as well as artificial riparian features and historical channel adjustment, the link with groundwater is generally not adequately considered. With this in mind, we have proposed parameters to assess the vertical connectivity of rivers. With regard to vegetation, which is a key factor for habitat assessment, the parameters are in most cases obtained through a site survey, which is usually not of the necessary scale to accurately diagnose and interpret the causes of the morphological changes observed. However, the method proposed in this paper incorporates remote sensing techniques and hydraulic modeling, thereby extending the assessment area beyond that of traditional methods and allowing for a more realistic evaluation of the results.
The integration of hydromorphological assessment results from multiple perspectives is essential for a comprehensive understanding of the river and the riparian system. The application of multi-criteria decision analysis is beneficial in that it evaluates multiple criteria concurrently and considers their interactions. It integrates all aspects and elucidates the influence of each parameter on the overall result [69]. The results of the analysis are usually presented through a scoring method combined with a classification description. Both the expert consensus scoring method and the scenario-based scoring method aggregate the scores, either through simple summation or summation after taking into account the weighting of each aspect. However, it can be reasonably argued that not all aspects contribute equally to the overall health of the system [25]. Furthermore, each individual aspect may have its own assessment errors due to measurement inaccuracies or subjective interpretation, and therefore the error may gradually increase when the scores of a number of aspects are combined [70,71]. The use of weighted scoring can therefore be useful to reduce the overall impact of cumulative errors that are common when scoring multiple aspects [72]. This is achieved by assigning different weights based on the significance of each aspect within the overall assessment, thereby ensuring that the final score is more influenced by the most important factors. Multiple objective weighting methods are generally recommended when there is a need to determine the relative importance of criteria based on quantifiable data. Despite the complexity of these systems, a straightforward categorization, such as “good” or “bad”, is a reasonable approach for the final assessment. This is preferred because it provides a clear answer, especially when an overall view or practical advice is sought. It is a common practice to combine scores or to categorize the results of each aspect before integrating them into a single final score. An alternative approach is to weigh the different assessment parameters and use the Coupling Coordination Degree Model to assess the interactions and the impacts between the aspects [51]. This is achieved by establishing the dynamic correlation and interdependence between the aspects, thus providing the basis for the final assessment.

5. Summary and Conclusions

Based on HIDRI, which is a hydromorphological quality evaluation protocol for the assessment of the ecological status of riparian areas, new indicators for quantitative assessment are proposed for three aspects: morphological characterization, river connectivity, and vegetation coverage. Considering the standard deviation and the distance correlation analysis, the D-CRITIC method is used to obtain the standardized weights of the parameters, which not only provides valid and stable weights and ranks but also ensures the scientific validation of the proposed parameters. Simultaneously, the CCDM is used to evaluate the level of coordinated development and analyze the interactions and impacts among the aspects and to achieve evaluation results that take the dynamic correlation and interdependence between the aspects into account.
The results demonstrate the following. (1) The integration of the riparian model with GIS analysis facilitates access to the parameters of hydromorphological quality evaluation. (2) The combination of the Distance Correlation-Based CRITIC (D-CRITIC) method and the Coupling Coordination Degree Model (CCDM) minimizes the influence of subjective assignments and conveniently achieves the purpose of evaluation. (3) The results of the evaluation are consistent with the actual situation (i.e., the coupling coordination degree is lower in the reaches with higher anthropogenic impacts).
In conclusion, the proposed method significantly enhances the accuracy and comprehensiveness of hydromorphological assessments by integrating advanced hydrological analysis with practical evaluation techniques. It eliminates the operator bias due to subjective assignment of weights and classification of evaluation levels while also avoiding the inclusion of complex calculation procedures for each indicator, which allows environmental or water agencies to easily analyze the problems using the resulting calculations and lay the foundation for further solutions. However, in order to apply the method, although the riparian delineation model is open source and the data used are often readily available, model manipulation and parameter acquisition require basic knowledge of Python and GIS operations.

Author Contributions

Conceptualization, L.D.; methodology, L.D., E.B.i.C. and M.S.-J.; software, L.D.; validation, L.D.; formal analysis, L.D., E.B.i.C. and M.S.-J.; investigation, L.D., E.B.i.C. and M.S.-J.; resources, L.D.; data curation, L.D.; writing—original draft preparation, L.D.; writing—review and editing, L.D., E.B.i.C. and M.S.-J.; visualization, L.D.; supervision, E.B.i.C. and M.S.-J.; project administration, L.D.; funding acquisition, L.D. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Scholarship Fund of China.

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Water 16 03025 g001
Figure 1. Study area location with the results of the riparian area simulation and division into sub-reaches 1 to 10 from upstream to downstream.
Figure 1. Study area location with the results of the riparian area simulation and division into sub-reaches 1 to 10 from upstream to downstream.
Water 16 03025 g001
Table 1. Examples of hydromorphological assessment methods and comparisons.
Table 1. Examples of hydromorphological assessment methods and comparisons.
CategoryMethodFocusResult
Physical habitat assessmentOn-site Survey [27,28]Channels, banks, floodplains, longitudinal profile, bank structure, erosion, substratum typeField-based results, expert-agreed scoring classes
Overview Survey [27,28]Plan view, vegetation, bank stability, migration barriers, river abstractionMapping-based results, expert-agreed scoring classes
Riparian habitat assessmentHabitat Quality Assessment (HQA) [2,19]Substrate, water flow, erosion, sediment characteristics, vegetation types, channel, and riparian zone structureSoftware-based results, expert-agreed scoring classes
Habitat Modification Score (HMS) [2,19]Modification score for habitat qualitySoftware-based results, expert-agreed scoring classes
Morphological assessmentSYRAH-CE [13]Pressures on river water bodies in sediment load, flow, and morphologyExpert judgment scoring classes
Morphological Quality Index (MQI) [31]Geomorphological features, channel artificiality, channel adjustment, continuity, pattern, cross-section, substrate, vegetationScenario-based scoring system
Hydrological regime alteration assessmentHYMO-HR [13]Hydrological regime, river continuity, morphological regime, channel geometry, substrate, vegetation, bank structure, floodplain interactionsScenario-based scoring system
HYMO-RO [13]Hydrological regime, river continuity, longitudinal and lateral connectivity, channel geometry, substrate, bank structure, floodplain interactionsScenario-based scoring system
Table 2. Protocols for the assessment of hydromorphological quality included in HIDRI.
Table 2. Protocols for the assessment of hydromorphological quality included in HIDRI.
AspectsProtocol
Hydrological flow regimeCompliance with Maintenance Flows
Indicators of Hydrologic Alteration (IHA)
River continuityRiver Connectivity Index
Fish Communities
Morphological conditionMorphological Characterization Parameters
Channelization Level of the Riverbed
River Habitat Index (RHI)
Naturalness of Land Uses on Riverbanks
Riparian Forest Quality Index (QBR)
Fluvial Vegetation Index
Table 3. Description of the proposed parameters.
Table 3. Description of the proposed parameters.
AspectsParametersPhysical Meaning
Morphological
Characterization		ArpSimulated riparian area
SISinuosity index, which is the ratio of the length of the thalweg to the length of the valley
S0Channel gradient
PantProportion of the riparian area that is anthropogenically modified
River
Connectivity 		VerticalGwThe mean value of groundwater level changes during a flood event
DwMean value of the initial groundwater depth
TransversalFFlood disturbance
(Sample standard deviation of the product of the proportion of the floodplain area to the riparian area and the probability of occurrence of different floods)
ENDChannelization level
LongitudinalBThe density of structures crossing the river that form a barrier to longitudinal connectivity
Vegetation
Coverage		AbThe area of woody and herbaceous vegetation adjacent to the bush inside of the natural levee along the river channel
AblThe area of bare land inside of the natural levee along the river channel
Table 4. River sub-reach analysis: results by aspect.
Table 4. River sub-reach analysis: results by aspect.
Sub-ReachMorphological CharacterizationRiver ConnectivityVegetation Coverage
Arp
(km2)		SIS0Pant
(%)		Gw
(m)		Dw
(m)		FENDBAb
(km2)		Abl
(km2)
10.2291.0010.00350.490.2812.2230.0580.40000.0390.010
20.5931.0010.00318.281.3063.1480.0280.28800.0620.006
30.5631.0360.0055.081.5643.5710.0260.03100.0500.008
40.4151.0010.0021.701.5493.1390.030000.0440.004
50.5511.5220.0042.091.6743.8660.0230.01010.0410.030
60.5941.3850.0021.161.2893.8950.017000.0420.070
70.2831.0010.00300.984.0910.074000.0850.038
80.2611.0660.0030.190.2724.4530.1080.14200.0760.066
90.4241.0570.0034.120.0523.5750.0440.10400.0700.040
100.2141.0430.0029.230.1953.0800.0400.14900.0620.040
Table 5. D-CRITIC weighting results.
Table 5. D-CRITIC weighting results.
ParametersArpSIS0PantGwDwFENDBAbAbl
Standard deviation0.4110.3550.2780.3070.3990.2840.3100.3440.3160.3520.366
Information content2.1322.0211.8531.8282.0471.4471.7101.6842.3561.9342.093
Weight10.10%9.58%8.78%8.66%9.70%6.86%8.10%7.98%11.16%9.16%9.92%
Table 6. Coupling coordination results.
Table 6. Coupling coordination results.
Sub-ReachMorphological CharacterizationRiver
Connectivity		Vegetation CoverageC *T *D *Level of
Coordination		Coupling Coordination Degree
10.1330.5220.4240.8580.3550.5526Barely maladjusted recession
20.5630.6790.7160.9950.6420.7998Intermediate coupling coordination
30.4890.8380.5600.9730.6530.7978Intermediate coupling coordination
40.6160.8840.5220.9750.7140.8359Good coupling coordination
50.7950.6320.3100.9290.6340.7688Intermediate coupling coordination
60.8720.8220.0310.4900.6940.5836Barely maladjusted recession
70.4620.6600.7600.9790.6030.7688Intermediate coupling coordination
80.4770.4000.4540.9970.4390.6627Primary coupling coordination
90.5640.6050.56910.5830.7638Intermediate coupling coordination
100.4000.6400.4790.9810.5180.7138Intermediate coupling coordination
* C is the value of the coupling degree, T is the comprehensive evaluation coefficient, and D is the coupling coordination degree.
Table 7. Evaluation results comparison.
Table 7. Evaluation results comparison.
Sub-ReachMethod Proposed in This PaperMQI
ScoreClassScoreClass
10.552Barely maladjusted recession0.701Good
20.799Intermediate coupling coordination0.826Good
30.797Intermediate coupling coordination0.847Good
40.835Good coupling coordination0.965High
50.768Intermediate coupling coordination0.813Good
60.583Barely maladjusted recession0.840Good
70.768Intermediate coupling coordination0.958High
80.662Primary coupling coordination0.931High
90.763Intermediate coupling coordination0.868High
100.713Intermediate coupling coordination0.924High
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Duo, L.; Sánchez-Juny, M.; Bladé i Castellet, E. Ecological Environment Assessment System in River–Riparian Areas Based on a Protocol for Hydromorphological Quality Evaluation. Water 2024, 16, 3025. https://doi.org/10.3390/w16213025

AMA Style

Duo L, Sánchez-Juny M, Bladé i Castellet E. Ecological Environment Assessment System in River–Riparian Areas Based on a Protocol for Hydromorphological Quality Evaluation. Water. 2024; 16(21):3025. https://doi.org/10.3390/w16213025

Chicago/Turabian Style

Duo, Lan, Martí Sánchez-Juny, and Ernest Bladé i Castellet. 2024. "Ecological Environment Assessment System in River–Riparian Areas Based on a Protocol for Hydromorphological Quality Evaluation" Water 16, no. 21: 3025. https://doi.org/10.3390/w16213025

APA Style

Duo, L., Sánchez-Juny, M., & Bladé i Castellet, E. (2024). Ecological Environment Assessment System in River–Riparian Areas Based on a Protocol for Hydromorphological Quality Evaluation. Water, 16(21), 3025. https://doi.org/10.3390/w16213025

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