Hydropower Functional Zoning with Crowdsourced Geospatial Data: A Case Study in Sichuan Province

Abstract

Hydro-electric development has received increasing attention due to its characteristics of ecological and environmental protection. In addition, aquatic ecological functional zoning plays a key role in the aquatic ecological management in the basin because of its ecological background and basic unit. However, hydropower function has seldom been considered in aquatic ecological functional zoning. This research proposes a framework for hydropower functional zoning on the aquatic-and-terrestrial-coupled ecosystem function with crowdsourced geospatial data and the spatial-clustering method. Sichuan Province was selected as the research area due to its critical hydroelectric position in China, and it is divided into 53 level 3 zones, 27 level 2 aquatic ecological functional zones, and 17 level 1 ecological functional zones. Focusing on the results of the hydropower functional zoning, the ecological-environmental problem of each zoning and the hydroelectric development in the future are discussed. The soil-erosion area in Sichuan Province did not overlap with the hydroelectric-construction-affected zones. Further, water pollution occurred in construction zones and core affected zones of the Fu River Basin and the Jialing River Basin. In the next 10 years, the middle and upper reaches of the trunk of the Ya-lung River will become key areas for hydropower-engineering projects. This research provides new insight into the development of various regional hydropower projects and the sustainable management of watersheds, which is helpful for the construction of new hydroelectric-energy development.

1. Introduction

Eco-functional zoning based on basins is regarded as one of the most valuable references for watershed management and aquatic-environment protection [1]. Thus, it has a profound impact on aquatic ecological management and environmental control [2]. Considering the fast development process of watershed management in China, studies on the zone administration have made great progress in theoretical and practical areas, including aquatic functional zoning, aquatic-environment functional zoning, aquatic ecological zoning, and aquatic eco-functional zoning. [3]. Ecological and water-environment conditions have always been ignored during aquatic functional zoning. Aquatic-environment functional zoning has provided insufficient consideration of the integrity of an aquatic ecosystem, and aquatic ecological zoning has ignored the influence of various human activities. Most previous studies focused on aquatic ecological zoning [4] and eco-hydrological zoning [5] in China. Aquatic ecological functional zoning could take the impact of natural factors and human activities into full account. Moreover, different ecological functions could be integrated and divided according to the sensitivity characteristics of the human activities in aquatic ecological functional zoning [6,7,8]. Meanwhile, aquatic ecological functional zoning could coordinate aquatic resources, the aquatic environment, and aquatic ecology [2], and it could achieve effective developments and the utilization of local resources. In China, several key basins, including the Liao River [9], the Songhua River [10], the Hai River [11,12,13], Chao Lake [2], and Dian Lake [14], have completed three-level zoning [2,15,16], but hydropower function was seldom considered in those studies.

The research on eco-functional zoning from the perspective of hydropower functions is attractive and valuable. Hydroelectric development is one of the key methods to realize energy conservation and emission-reduction strategies, which can guarantee energy safety [17]. However, the process from the construction to the operation of hydropower engineering may trigger various ecological and environmental effects [18,19,20]. Gwon-soo et al. [21] selected 16 factors that influenced river and bank ecologies in the Daqing Dam of the Jinjiang River Basin in Korea, and graded basins by enforcing an analytic hierarchy process (AHP) based on the ecologies of small river basins and banks. Many studies have assessed the impact of hydroelectric development on river basins, such as the concentrated hydroelectric development in the Mekong River Basin [22] and the Amazon River Basin [23], with different biological and habitat indexes. In fact, the following indexes have been implemented: watershed runoff [24,25], habitat pattern [26,27,28], biological source materials [29], vegetation indexes [30,31], aquatic-population structure [28,32,33], and ecosystem services [19,34]. However, none of the above references could demonstrate the ecological environmental impacts of hydroelectric development on the aquatic eco-functional zoning. Moreover, the data of indexes such as aquatic population and water quality are hard to acquire, which increases the difficulties of quantitative modeling of the ecological environment that influences large-scale hydroelectric development, as well as hydropower functional zoning.

With a focus on data acquisition, we propose a new framework for hydropower functional zoning with crowdsourced geospatial data, which refer to a kind of open geospatial data published by non-professionals voluntarily on the Internet. Open Street Map (OSM) is a representative type of crowdsourcing geospatial data. OSM data are adaptable and quickly updatable, and they are widely applied to a variety of research fields, such as emergency mapping, disaster relief, location services, and so on [35,36,37,38,39]. However, OSM data are not subject to any kind of systematic quality control. The details of OSM data coverage varies across spaces [36]. Therefore, for the subsequent analyses, it is crucial to clean, review, analyze, and assess the various data features in OSM. Ref. [40] showed that the spatial-clustering method could be used to process the point data and evaluate the impact of hydroelectric development in the basin. The point data of hydropower stations provided by OSM was utilized to supply missing data in the study. To increase its accuracy, OSM data were combined with other types of data, including paper reports and geo-logical databases. The hydropower functional zoning was implemented using the aquatic-ecological-zoning theoretical framework and the spatial-clustering results of the assessment of the hydroelectric development.

Sichuan Province is rich in water-energy sources and accommodates 20% of the large hydropower stations in the world. However, ecological problems such as soil erosion and land degradation are continuously threatening ecosystem security. The framework of hydropower functional zoning applied in Sichuan Province could reveal the ecological environmental problems in the hydropower functional zones, which could be helpful to find suggestions for eco-environmental protection in Sichuan Province.

2. Materials and Methods

2.1. Study Area

Sichuan Province (Southwest China, with a total area of 486,900 km²) is located upstream of the Yangtze River (97°21′–108°16′ E, 26°01′–34°23′ N). Sichuan Province has complicated terrain, such as mountainous regions, plateaus, hills, basins, and plains. Furthermore, it crosses over several geomorphic units, such as the Qinghai–Tibet Plateau, the Hengduan Mountains, the Yun-Gui Plateau, the Chengdu Plain, the Qinba Mountains, and the Sichuan Basin [41]. Sichuan Province is rich in water-based energy sources, and the reserves of the local water-energy resources are estimated to reach 143 million kWh, accounting for 21.2% of the national reserves. The technical exploitation amounts to 103 million kWh, accounting for 27.2% of the national total. On top of that, the economic exploitation amounts to 76.112 million kWh, accounting for 31.9% of the national total. Sichuan Province is the largest base of hydroelectric development and the West-to-East Power Transmission Project in China (Figure 1).

2.2. Data Source and Preprocessing

2.2.1. Hydropower-Station Data

In China, hydropower stations with an installed capacity of less than 50,000 kW, 50,000 kW~300,000 kW, and > 300,000 kW are regarded as small-sized, medium-sized, and large-sized, respectively [42]. A total of 4291 hydropower stations are currently located in Sichuan, including 122 medium-sized and large-sized ones. By combining with the various types of crowdsourcing data, such as global dam geological databases [43], OSM data, and hydropower-station planning reports, 255 samples (including 166 medium-sized and large-sized hydropower stations) were selected after data cleaning and review (Figure 2). The relevant information was also provided, including longitudes and latitudes, river basins, engineering states, total installed capacity, annual power output, and normal pool level.

2.2.2. Other Data

The normalized-difference vegetation index (NDVI) was applied with the Medium Resolution Spectral Imager (MERSI) II NVI product of the FengYun-3D satellite, launched by the China Meteorological Administration. The spatial resolution was 250 m and the time resolution was 10 days. In addition, the MERSI-II NVI product generated annual average standard NDVI datasets from 2019 to 2021 after performing waveband operations through projection transformation, mosaicking, and image tailoring. For the digital elevation of the data, ASTER’s Global Digital Elevation Model (GDEM) with a spatial resolution of 30 m was used, which was downloaded from the National Scientific Data Service Platform. As far as the soil-erosion-intensity data are concerned, the basic geological data from 2019 were applied and calculated, with references to Technical Regulations on Water and Soil Conversation Monitoring. The land-use data applied the data with a spatial resolution of 1 km from 2020, and meanwhile, the applied geological-disaster-point data from 2019 were downloaded from the Resource and Environmental Science Data Center, Chinese Academy of Sciences. The runoff data from 2015 were download from a Big Earth Data Platform for Three Poles [44].

2.3. Research Methods

2.3.1. Spatial-Clustering Algorithm

The goal of spatial clustering was to divide data with similar spatial attributes into one class [40]. Getis-Ord Gi* and Moran’s Index are spatial-clustering algorithms that take into account both the spatial relations and the thematic properties.

Moran’s Index is also a global spatial-autocorrelation index that is used to explore the spatial pattern of the study area. The single value was used to reflect the autocorrelation degree of the studied area, and a comparison of the similarity of the observed values at adjacent spatial positions was utilized to measure the global spatial autocorrelation:

$$I=\frac{n\cdot {\displaystyle {\sum }_i^n{w}_{ij}\cdot \left(y_i-\stackrel{-}{y}\right)\left(y_j-\stackrel{-}{y}\right)}}{\left({\displaystyle {\sum }_i^n{\displaystyle {\sum }_j^n{w}_{ij}}}\right)\cdot {\displaystyle {\sum }_i^n{\left(y_i-\stackrel{-}{y}\right)}^2}}$$

(1)

where w_ij denotes a weight matrix of relations among spatial objects. In this work, the basin locations were chosen to construct the spatial-weight matrix. If sub-basin i and sub-basin j are located in the same level 1 sub-basin and adjacent to each other, w_ij = 1; otherwise, w_ij = 0. The value range of Moran’s Index was [−1, 1]. If it is positive, there is a positive correlation between the attribute values of the objects in the spatial relationships. If it is negative, there is a negative correlation between the attribute values. If it is 0, there is no spatial correlation among the attribute values of objects. The p-value and Z-score are calculated from the statistical test. They are statistically significant when the p-value is less than 0.05 and the Z-score is greater than 1.96 (or lower than −1.96).

Getis-Ord Gi* is a local spatial-autocorrelation index, also called the hotspot analysis method. Getis-Ord Gi* is defined as a local spatial-correlation index:

$$G_i\left(d\right)=\frac{{\displaystyle {\sum }_j^n{w}_{ij}\left(d\right)y_j}}{{\displaystyle {\sum }_j^n{y}_j}}$$

(2)

$$U\left(G_i\right)=\frac{G_i-E\left(G_i\right)}{\sqrt{\mathrm{var}\left(G_i\right)}}$$

(3)

When the local Getis-Ord Gi* value is higher than the mathematical expectation and such a difference is statistically significant, a hotspot region is formed.

2.3.2. Zoning System

• Zoning Principle

By considering the impact of hydroelectric development on the ecological environment, eco-functional zoning was implemented in this work in accordance with the common ecological environmental problems in hydropower-engineering development areas in the river basin. Hence, the zoning principle emphasized the coupling relationship between the terrestrial and aquatic ecosystems. Based on the aquatic-ecological-zoning principle [2], the principles of aquatic-and-terrestrial-coupled ecosystem, integral catchment unit, and dominance of human-activity stress should be also observed.

In fact, eco-functional zoning is regarded as a zoning system encompassing a large scale to a small scale. The indexes were selected according to the aquatic-and-terrestrial-coupled ecosystem and the impact of human activities (

Table 1. Zoning index system.

Levels	Scales	Targets	Indexes
Level 1	River basins	Natural geographical condition	Landform, relative-humidity index (temperature and precipitation), runoff
Level 2	Regions	Terrestrial ecosystem	Vegetation coverage
		Human-activity interference	Construction-land-area ratio, Cultivated-land-area ratio
Level 3	Sub-basins	Intensity of hydropower-project development	Reservoir capacity, installed capacity, reservoir quantity

).

2.

Calculation of Zoning Indexes

The geomorphic features were classified according to the geomorphological-classification system of China and were divided based on surface slope, fluctuation height, and altitude of the surface [45]. One of the most crucial indicators for estimating water resources is runoff depth, which is defined as the ratio between the total runoff and the river-basin area [46]. Moreover, the relative-humidity index represents the balance condition between precipitation and evaporation in a certain period, and the index gained comes from the following formula: (precipitation – potential evaporation volume) / (potential evaporation volume). In addition, vegetation coverage refers to the percentage of the vertical projected area of vegetation on the ground in the total regional area, and it is estimated by the vegetation index NDVI based on the dimidiate-pixel model. The value range was [0, 1].

3.

Zoning Unit (Sub-River Basins)

According to the level 3 division standard of the river basin, the following rivers can be found in Sichuan Province: Jinsha River Basin, Ya-lung River Basin, Dadu River Basin, Qingyi River Basin, and Anning River Basin. A total of 92 sub-river basins were further divided by combining them with level 3 river basins. Among them, the largest sub-river-basin area was 19,000 km² and the smallest sub-river-basin area was 422 km² (Figure 3).

4.

Zoning Process

(1) Level 1 zoning. Based on the zoning unit, the results of watershed level 1 zoning are obtained and combined with level 1 indicators of physical and geographical factors.

(2) Level 2 zoning. By overlaying on the level 1 zoning, the results of level 2 zoning are obtained with level 2 indicators of background ecological status and human-activity interference.

(3) Construction of spatial-weight matrix. Considering the connectivity effects of the basins, the spatial-weight matrix of sub-basins can be built.

(4) Aggregation evaluation. The global Moran Index is calculated with the data from hydropower stations (large, medium, and above medium size) and the spatial-weight matrix. The aggregation of hydroelectric development is evaluated with the global Moran Index in the zoning unit.

(5) Impact assessment of hydroelectric development. The hotspot analysis method is used to identify the clustering area of hydroelectric development, and then the distribution results of hydroelectric-development hotspots are obtained. By superimposing the results in hotspots with stations (medium to large), the hydroelectric-development impact can be evaluated in the zoning units and the distribution results of the hydroelectric-development impact assessment can be obtained for the zoning units. The employed evaluation standards are shown in

Table 2. Impact-assessment criteria of hydroelectric development.

Zone	Hydropower Engineering	Hotspot of Hydroelectric Development
Hydropower-engineering construction zone	Positive	Negative
Affected zones of hydroelectric development	Negative	Positive
Core affected zones of hydroelectric development	Positive	Positive

.

(6) Level 3 zoning. By superimposing the distribution results of the hydroelectric-development impact assessment of the zoning units with the level 2 zoning map, a watershed hydropower functional zoning map can be obtained.

The detailed flowchart for hydropower functional zoning is shown in Figure 4.

3. Results

3.1. Assessment of Hydroelectric-Development Intensity

Based on the panel data of sub-river basins where hydropower engineering is located, the hot development zones for large-sized, medium-sized, and larger hydropower stations were summarized by performing spatial-autocorrelation analysis and hotspot analyses, wherein the cumulative effects of reaches were considered. From the extracted outcomes, Moran’s Index was higher than 0 and it passed the significance test (p-value < 0.05), indicating the existence of a highly positive spatial correlation. In other words, the medium-sized and larger hydropower stations showed a positive clustering in terms of quantity (

Table 3. Spatial-autocorrelation test results of the hydropower-station panel data.

Index	Hydropower Stations
	Medium-Sized and Larger	Large-Sized	Medium-Sized
Moran’s Index	0.185246	0.107755	0.144693
Expected Index	−0.006289	−0.006289	−0.00629
Variance	0.002167	0.002159	0.002093
z-score	4.114799	2.454212	3.300263
p-value	0.000039	0.014119	0.000966

).

The hotspot areas of hydroelectric development at three intensities were combined to obtain the core affected zones in Sichuan Province (Figure 5b). Combined with the construction-area distribution of hydropower stations (Figure 5a), Sichuan Province was divided into a hydropower-engineering construction zone, affected zones of hydroelectric development, and core affected zones.

3.2. Hydropower Functional Zoning Results

The various geomorphic types in Sichuan Province include plains, terraces, hilly areas, and mountainous areas. Among them, the mountainous areas occupy the largest area (74%) and are mainly distributed in the southern regions of Qinghai–Tibet Plateau and the southwest Hengduan Mountain region in northwestern Sichuan Province, with an average elevation of 3000–5000 m. Hills, plains, and terraces are the second largest areas (accounting for 12%, 7%, and 7%, respectively). These areas are mainly distributed in basin areas in Eastern Sichuan Province (Figure 6a).

The relative-humidity index represents the spatial-distribution characteristics of climatic differences. Sichuan Province generally belongs to humid and over-humid areas (57% and 41%, respectively), accompanied by local semi-humid or semi-drought areas (2%) (Figure 6b).

Runoff depth, divided into five types based on natural breaks, was also used to characterize water resources (Figure 6c). The distribution of the runoff depth was basically consistent with the landform distribution. The average runoff depth in the western mountainous regions was about 102 mm, whereas it was 710 mm in the eastern basin areas.

By considering the landform, relative humidity, and runoff depth, the distribution of 12 river basins (Figure 3) in Sichuan Province was divided into 17 level 1 ecological functional zones (Figure 6d). In this work, the level 1 ecological functional zones emphasize the aquatic- and terrestrial-ecosystem-coupling relationship and also reflects the characteristics of the river basin in Sichuan Province. The naming of the zones reflects geological and hydrological characteristics. Level 1 ecological functional zones were defined based on the name of the river basin, the location, and landform features, as well as the names and codes of different level 1 ecological functional zones.

The vegetation coverage in 75% of the regions exceeded the value of 0.8. Regions with poor vegetation coverage were mainly distributed in high-altitude regions in the western mountains and in urban areas on the eastern plains (Figure 7a). The percentages of the construction land and the cultivated land were basically consistent with the vegetation coverage. In the western mountains, there were relatively low degrees of agricultural and urban disturbances. The construction land was mainly concentrated in the Chengdu Plain (Figure 7c), and agriculture was mainly concentrated in the eastern hills (Figure 7b).

Based on the level 1 zones and considering the vegetation coverage, the percentage of cultivated land area, and the percentage of farmland area, Sichuan Province was ultimately divided into 27 level 2 ecological functional zones (Figure 7d). Level 2 zoning emphasizes the human–land-coupling relationship. The level 2 ecological functional zones were named “name of level 1 zone,” with the land-use type and the name and code of the different ecological functional zones.

With a focus on the affected zones of hydroelectric-development and hydropower-construction areas, the research area was divided into 53 level 3 aquatic ecological functional zones based on level 2 zoning. The detailed indexes are shown in Figure 8.

3.3. Eco-Environmental Problems in Zoning

3.3.1. Soil Erosion

The hydraulic soil erosion in Sichuan Province was mainly distributed in regions with relatively concentrated agricultural activities or mountainous regions with low vegetation coverage. These regions included construction and non-construction sub-zones in the hilly agricultural Fu River Basin (46% and 41%), core construction sub-zones in the hilly agricultural Jialing River Basin (44%), non-construction sub-zones in the mountainous agricultural Ya-lung River Basin (58%), and construction sub-zones in the mountainous agricultural Yangtze River Basin (42%). Additionally, the total hydraulic-soil-erosion area in some hydropower-construction zones was not large, but the erosion intensity was relatively high, such as construction sub-zones in the mountainous and agricultural Anning River Basin (severe erosion area = 2%, accounting for 1% of the total area of Sichuan Province).

3.3.2. Water Eutrophication

According to the Bulletin on the Second National Survey of Pollution Sources and Ecological Environmental Situations in 2020, emission volumes of pollutants in 10 large river basins in Sichuan Province were acquired (

Table 4. Emission volumes of pollutants and corresponding zoning in 10 large river basins in Sichuan Province.

Basin	Area (km2)	Quantity of Pollutants Discharged (g m−2)				No. of Level 1 Zone
		COD	NH3-N	TN	TP
Yangtze River	97,376	1.911	0.100	0.257	0.027	16, 17
Ya-lung River	107,826	0.299	0.014	0.036	0.004	14, 15
Anning River	11,086	1.606	0.090	0.262	0.018	1
Dadu River	68,002	0.610	0.025	0.072	0.007	2, 3
Qingyi River	12,902	2.503	0.124	0.333	0.039	11
Qu River	45,444	3.534	0.196	0.603	0.051	9, 10
Tuo River	25,510	8.656	0.447	1.313	0.114	13
Fu River	31,985	4.805	0.247	0.647	0.069	4
Jialing River	34,939	3.532	0.175	0.498	0.049	6, 7, 8
Qu River	33,820	5.370	0.257	0.659	0.068	12

). The Tuo River and the Qu River occupied the top two positions in terms of pollutant emissions, which correspond to the non-construction sub-zones in the hilly and urban Tuo River Basin (13-1-1) and the non-construction sub-zones in the hilly agricultural Qu River Basin (12-1-1). Moreover, pollutant emissions in the Fu River Basin and the Jialing River Basin are very high, which correspond to the construction and non-construction sub-zones in the hilly agricultural Fu River Basin (4-1), construction sub-zones in the mountainous agricultural Jialing River Basin (6-1), construction sub-zones in the hilly meadow Jialing River Basin (6-2), and construction sub-zones in the hilly agricultural Jialing River Basin (6-3).

3.4. Hydroelectric-Development Plan in Zoning

According to the 13th Five-Year Plan of Sichuan Province and the completion conditions, the approval of medium-sized hydropower projects has been strictly controlled and small-sized ones have been cancelled. The hydropower-station construction in the Jinsha River, the Ya-lung River, and the Dadu River is still critical (

Table 5. Hydroelectric-development programming and construction in the Jinsha River, Ya-lung River, and Dadu River.

Basin	Planning Installed Capacity (10,000 kw)	No. of Hydropower Stations	No. Built or Under Construction	Percentage Built or Under Construction (%)
Jinsha River	8258	27	18	66.7
Ya-lung River	2883	22	7	31.8
Dadu River	2697	28	21	75.0

). The total area of the built hydropower stations and hydropower stations under construction in the Dadu River was slightly higher than that in the Ya-lung River. Moreover, the total area of the built hydropower stations and hydropower stations under construction in the trunk of the Dadu River was significantly higher compared with that in tributaries. Next, hydropower-engineering construction will shift from the Dadu River to the Ya-lung River and from the lower reaches to the middle and upper reaches. In particular, the middle and upper reaches of the trunk of the Ya-lung River will become essential areas for hydropower-engineering projects in the next 10 years.

4. Discussion

4.1. Framework of Hydropower Functional Zoning

Ouyang et al. [7,12] proposed some valuable and notable studies for Chinese eco-function zones. Currently, ecological regions, ecological sub-regions, and ecological functional regions are divided based on natural conditions. In addition, regional zoning results [47,48] have been afforded more attention for terrestrial ecosystem functions or services based on ecological sensitivity and importance.

Compared with the eco-function zoning method, aquatic ecological-function zoning is a method that aims to maintain the biodiversity and health of an aquatic ecosystem. Gao et al. [2] proposed that the reservoir capacity can be used as level 4 aquatic ecological functional zoning in lake basins, which mainly expresses the spatial-difference characteristics of an aquatic ecological system at the river scale. However, this method ignores the cumulative effect of hydropower development.

In this research, we propose eco-function zoning that emphasizes the coupling of aquatic and terrestrial ecosystems and takes the basin as a unit under the view of hydropower development. The indicators of level 1 and level 2 zoning include landform, climate, soil, vegetation, land use, and social economy. The spatial-aggregation statistical method is used to effectively consider the cumulative eco-environmental impacts among hydropower-development basins in level 3 zoning [40]. As shown in Table 3, the spatial distribution showed a significant clustering in terms of quantity. In addition, it is shown that there were differences in the different hydroelectric-development intensities (

Table 6. Statistics of the different hydroelectric-development intensities.

Hydroelectric-Development Intensity	Hydropower Stations (Unit)	Total Installed Capacity (10,000 kW)
Core affected zones of all hydropower stations	23	1303.85
Affected zones of middle-sized hydropower stations	0	0
Core affected zones of middle-sized hydropower stations	35	632.26
Non-affected zones	17	4599.4
Construction zones	49	1502.43
Affected zones of large-sized hydropower stations	20	1270.8
Core affected zones of large-sized hydropower stations	27	1635.35

). In order to further demonstrate the rationality of the hydropower functional zoning system, a Kruskal–Wallis H test was conducted and it was found that the total installed capacity and number of power stations showed significant differences (p < 0.05) among the seven types of hydroelectric-development intensity. In addition, this hydropower-functional-zoning strategy is not appropriate in situations in which there are few hydropower stations or no significant agglomeration of hydropower development because the framework is based on the quantity and installed capacity of hydropower stations (Table 3).

4.2. Development Suggestions Based on Hydropower Functional Regions

4.2.1. Soil Erosion

Soil erosion has been a prominent problem that threatens the ecological environment of basins in Sichuan Province. Hydropower-engineering development is inevitably accompanied by surface disturbances, which can easily induce soil erosion. Hence, analyzing the distribution and severity of soil erosion based on zoning results can effectively facilitate zone administration and decision-making in river basins. The zones with hydraulic soil erosion mainly belong to regions with either no hydropower stations or with only one. Hence, these regions either suffer no interference or slight interference from hydropower engineering. In future hydropower planning, it is suggested to avoid the construction of hydropower stations in these regions or to pay close attention to the full implementation of water–soil-conservation engineering measures and decrease the disturbances during the construction process.

4.2.2. Water Eutrophication

Hydroelectric development exerts the most direct and significant influence on key biogenic elements, such as C, N, P, and Si. After reservoirs are constructed, due to changes in the hydrological and hydrodynamic conditions, as well as the increased hydraulic retention time, it is easy to cause water bloom or eutrophication in reservoir bays, especially in local areas of high-dam reservoirs with temperature layering [29]. Leve 3 zones contain these non-construction subzones, construction sub-zones, affected zones, and core affected zones of medium-sized hydropower stations in the Fu River Basin and the Jialing River Basin, which deserve close attention to the dynamic monitoring of the water quality during construction or reconstruction activities.

4.2.3. Insufficient Discharge Ecological Flow

The ecological flow is an important index for maintaining the ecological functions of rivers and lakes, and for controlling the development intensity of water resources. It is the important foundation for the overall planning of life, the production of aquatic ecological resources, and the optimization of the allocation of water resources. For example, hydropower avoids discharge ecological flow in the branch ditch of the Moxi River, a tributary of the Dadu River, resulting in a serious water reduction in the Yanzi River and the Bingchuan River. The riverway is almost dried up (Department of Ecology and Environment of Sichuan Province 2021).

Control over the discharge-ecological-flow volume mainly occurs in middle-sized and small-sized hydropower stations, as well as in the affected zones and core affected zones of medium-sized hydropower stations, such as the core affected sub-zone of medium-sized hydropower stations in the middling mountainous forest zone of the major Jialing River Basin (6-1-1), the core affected subzone of medium-sized hydropower stations in the middling mountainous meadow zone of the major Jialing River Basin (6-2-1), and the core affected subzone of medium-sized hydropower stations in the high mountainous forest and urban zone of Min River Basin (9-1-3), the discharge-ecological-flow volume should be systematically examined. The discharge-ecological-flow volume shall be controlled through a pool-level limit of scouring sluice, basic operation discharge, a bottom barrier and slotting, a fixed-gate limit, and other engineering measures.

4.2.4. Aquatic Ecological Influences

Cascade-reservoir construction cuts off the connectivity of rivers, forming the alternative distribution pattern of lacustrine facies in front of the dam and fluvial facies at the tail of the reservoir. Therefore, the natural fluvial facies are shortened and a lake reservoir with a high depth and slow flows is formed in front of the dam. Due to differences in habitat, there are significant discrepancies in the benthonic-animal community and the structure and spatial distributions between the trunk and tributaries of the reservoir. After the cascade reservoirs were constructed, the fish species generally showed a decreasing trend. More specifically, the number of native fishes who prefer riffle and migration-type fishes decreased more than that of other fishes, including Anguilla Japonica, Pseudogyrinocheilus prochilus, and Euchiloglanis kishinouyei Kimura [33]. The fish species decreased the most from Xiluodu to Xiangjiaba after the cascade reservoirs in Jinsha River were constructed. With the operation of reservoirs, this decreasing trend slowed down, and the number of large-sized fish species gradually increased [49]. Therefore, the impact of hydropower-engineering construction and operation on aquatic environments shall be relieved by blocking fish-migration channels and implementing fish-passing technologies, fish reproduction and releasing, and fish habitats (spawning sites, wintering grounds, and feeding grounds). Furthermore, the protection and substitutive habitat, ecological-flow process, and ecologic scheduling in the core affected zones of large-sized hydropower stations and the core affected zones of comprehensive hydropower projects, such as the core affected zones of large-sized hydropower stations in the downstream hilly meadow Dadu River Basin (2-1-1), core affected zones of large-sized hydropower stations in the downstream hilly meadow Ya-lung River Basin (14-1-3), the affected zones of large-sized hydropower stations in the hilly meadow Jinsha River Basin (16-4-3), and so on, should also be taken into account.

5. Conclusions

A new framework for hydropower functional zoning with crowdsourced data was proposed in the research. The spatial-clustering approach was introduced to process the point data and evaluate the impact of hydroelectric development in the basins. The hydropower functional zoning was accomplished based on the assessment results of hydroelectric development. We applied the framework of hydropower functional zoning to Sichuan Province, dividing it into 53 level 3 zones, 27 level 2 aquatic eco-functional zones, and 17 level 1 ecological functional zones. Based on the zoning results, hydroelectric development in the future and the eco-environmental problems and protections in the hydropower functional zones were discussed.

• Soil erosion in Sichuan Province was mainly distributed in regions with concentrated agricultural activities and mountainous regions with relatively low vegetation coverage. These regions mainly belong to non-affected zones and construction zones, which are negligibly affected by hydropower engineering.
• Water pollution occurred in the Fu River Basin and the Jialing River Basin, including construction sub-zones in the hilly agricultural Fu River Basin, construction sub-zones in the mountainous agricultural Jialing River Basin, and construction sub-zones in the hilly meadow Jialing River Basin.
• Hydropower-engineering construction will shift from the Dadu River to the Ya-lung River and from the lower reaches to the middle and upper reaches. In particular, the middle and upper reaches of the trunk of the Ya-lung River will become critical areas for hydropower-engineering projects in the next 10 years.

The new framework for hydropower functional zoning addresses the issue of difficult hydro-data acquisition and provides eco-functional zoning with a new perspective, which is helpful for the development of various regional hydropower projects and the sustainable management of watersheds. In the future, more work should be dedicated to increasing the scenarios for its application, improving the evaluation of hydroelectric development’s rationality, and enriching indicators of hydropower development.