Assessment of riparian vegetation characteristics in Mediterranean headwaters regulated by check dams using multivariate statistical techniques

A framework model to integrate sources and pathways in the assessment of river water pollution

Metal and nutrient pollution, soil erosion, and alterations in climate and hydrology are prevalent issues that impact the water quality of riverine systems. However, integrated approaches to assess and isolate causes and paths of river water pollution are scarce, especially in the case of watersheds impacted by multiple hazardous activities. Therefore, a framework model for investigating the multiple sources of river water pollution was developed. The chosen study area was the Paraopeba River basin located in the Minas Gerais, Brazil. Besides multiple agriculture, industrial, and urban pollution sources, this region was profoundly affected by the rupture of the B1 tailings dam (in January 2019) at the Córrego do Feijão mine, resulting in the release of metal-rich waste. Considering this situation, thirty-nine physicochemical and hydromorphological parameters were examined in the Paraopeba River basin, in the 2019-2023 period. The analysis involved various statistical techniques, including bivariate and multivariate methods such as correlation analysis, principal component analysis, and clustering. The Paraopeba River was mainly impacted by metal contamination resulting from the dam collapse, whereas nutrient contamination, mainly from urban and industrial discharges, predominantly affected its tributaries. Additionally, the elevated concentrations of aluminum, iron, nitrate, and sulfate in both main river and tributaries can be attributed to diffuse and point source pollution. In terms of hydromorphology and soil type, the interaction between woody vegetation and erosion-resistant soils, especially latosols, contributes to the stability of riverbanks in the main river. Meanwhile, in the tributaries, the presence of neosols and sparse vegetation in urbanized areas promoted riverbank erosion potentially amplifying pollution. While the study was conducted in a particular watershed, the findings are based on a methodology that can be applied universally. Hence, the insights on surface water quality from this research can be a valuable resource for researchers studying watersheds with diverse pollution sources.

Effect of topographical features on hydrologically connected riparian landscapes across different land-use patterns in colossal dams and reservoirs

Topographic features impact the riparian landscape, which shapes reservoir ecosystems. We know little about ecological network parameter (ENP) responses to topographical features (riparian width, stream-channel width, slope, and elevation) from three land-use areas (rural, urban, and rural-urban transitional) in larger dams and reservoirs globally. This study used a field-based approach with 305 transects on an inundated area of 58,000 km² inside the Three Gorges Dam Reservoir (TGDR) in China. We discovered that topographical features influenced ENPs differently, involving parameters of plant cover, regeneration, exotics, erosion, habitat, and stressors. As per the Pearson correlation (p < 0.05), riparian width had the most significant effect on transitional ENPs and the least impact on urban ENPs. Riparian width showed the most important influence on the parameters of exotics (with r ≤ -0.44) and erosion (r ≤ 0.56). In contrast, stream-channel widths had the greatest effect on rural ENPs and the least on urban and transitional ENPs. The erosion parameters were the most affected (r ≤ -0.26) by stream width. The slope showed relationships with the fewest ENPs in all three areas and influenced the stress (with a range of -0.51 <r < 0.85) and erosion (r ≤ -0.39) parameters. The impact of elevation was higher in urban areas and was positively correlated with the parameters of plant cover (r ≤ 0.70), erosion (r ≤ 0.58), and habitat (r ≤ 0.69). These results justify the policy emphasis on riparian areas that are managed using the same techniques, which generally ignores their topographical features.

Multiscale spatial analysis of headwater vulnerability in South-Central Chile reveals a high threat due to deforestation and climate change

Headwaters represent an essential component of hydrological, ecological, and socioeconomical systems, by providing constant water streams to the complete basin. However, despite the high importance of headwaters, there is a lack of vulnerability assessments worldwide. Identifying headwaters and their vulnerability in a spatially explicit manner can enable restauration and conservation programs. In this study, we assess the vulnerability of headwaters in South-Central Chile (38.4 to 43.2°S) considering multiple degradation factors related to climate change and land cover change. We analyzed 2292 headwaters, characterizing multiple factors at five spatial scales by using remote sensing data related to Land Use and Cover Change (LUCC), human disturbances, vegetation cover, climate change, potential water demand, and physiography. We then generated an index of vulnerability by integrating all the analyzed variables, which allowed us to map the spatial distribution of headwater vulnerability. Finally, to estimate the main drivers of degradation, we performed a Principal Components Analysis with an Agglomerative Hierarchical Clustering, that allowed us to group headwaters according to the analyzed factors. The largest proportion of most vulnerable headwaters are located in the north of our study area with 48.1 %, 62.1 %, and 28.1 % of headwaters classified as highly vulnerable at 0, 10, and 30 m scale, respectively. The largest proportion of headwaters are affected by Climate Change (63.66 %) and LUCC (23.02 %) on average across all scales. However, we identified three clusters, in which the northern cluster is mainly affected by LUCC, while the Andean and Coastal clusters are mainly affected by climate change. Our results and methods present an informative picture of the current state of headwater vulnerability, identifying spatial patterns and drivers at multiple scales. We believe that the approach developed in this study could be useful for new studies in other zones of the world and can also promote Chilean headwater conservation.

Distribution and management of Fallopia japonica in riparian biotopes in Slovakia and Austria

Globally, invasive species represent a serious threat to biodiversity and to the ecosystem. As an undesirable part of riparian ecosystems, invasive plants form continuous growths on the banks of watercourses. One of the biggest problems at river bank sites is Japanese knotweed, Fallopia japonica (Houtt.) Ronse Decr, which is an extremely invasive and aggressive weed. The topic of the interaction of flow and invasive plant species in shore stands is rich and presents a wide range of possibilities for research. The presented paper brings the results of our studies on the invasions of F. japonica in chosen riparian vegetation sites in Austria and Slovakia from 2011–2020 (36 stands). Our research was aimed at the survey on the changes in the distribution (spread) of F. japonica at the selected river sites; assessment of the impact of the watercourse regime on the spread of F. japonica; monitoring of the population growth dynamics of F. japonica and assessment of possibilities for effective eradication of F. japonica in context of the riparian vegetation management. We used standard techniques of field survey, mapping, flow modeling/simulation, and laboratory experiments. Our research results showed that water streams are not primary invasion starters until there is a flood. As long as flooding does not exceed the critical speed of the water stream, there is no direct damage to the invasive plant. The water body can be a secondary trigger for plant invasion at normal speeds. In addition, F. japonica reproduction ability directly conditions its population dynamic growth. We can report that selective invasion removal adapted to local conditions can be most suitable and beneficial for municipalities.

The impact of ecotourism on ecosystem functioning along main rivers and tributaries: Implications for management and policy changes

Tourism along river basins benefits both tourists and the economy, but its management necessitates trade-offs between nature-based recreation and ecological functioning. Despite ecosystem services being helpful in managing environmental challenges, there are limited data on the impact of tourism activities on ecosystem functioning across different river types globally. This study investigates how people's recreational activities and values affect ecosystem functioning in high-order rivers. The original field data were collected from 308 transects along the main river and tributaries of the Three Gorges Dam Reservoir in China during 2019. Kruskal-Wallis tests (p < 0.01) revealed that the ecosystem functioning indices were significantly higher than the recreational activity and value indices around the rivers and that ecosystem functioning was highest around tributaries. The critical variables of ecotourism activities and ecosystem functioning identified by principal component analysis accounted for 66.49% of the total variance. The Pearson correlation coefficient strengths among tourism and ecosystem functioning parameters were correlated mildly to moderately, but they exhibited positive and negative connections with a range of r = -0.27 to 0.37 (p < 0.05). Furthermore, the distribution patterns of these parameters that were determined by hierarchical cluster analysis were diverse for both the main river and its tributaries. The findings suggest that the development and enforcement of zoning may be necessary for the long-term use of natural resources by all sectors of society. Therefore, it is imperative to raise public awareness and urge governments to adopt more progressive ecotourism policies.

Impacts of Stressors on Riparian Health Indicators in the Upper and Lower Indus River Basins in Pakistan

Riparian zones along rivers and streams provide ecosystem services that may change over time as disturbances increase and deteriorate these buffer zones globally. The effect of stressors on ecosystem services along the rivers in underdeveloped countries is unclear, which impacts the environment directly in the form of riparian health indicators (RHIs). This study fills this gap and measures the impact of stressors on RHIs (parameters of habitat, plant cover, regeneration, exotics, and erosion) in the Indus River basin (IRB) in Pakistan. Data on 11 stressors and 27 RHIs were collected using a field-based approach in 269 transects in the upper and lower Indus basins (UIB and LIB) in 2020 and analyzed using multivariate statistical methods. The Kruskal-Wallis tests (p < 0.05) indicated that RHIs varied significantly under the influence of stressors in the UIB and LIB. However, their highest mean values were found in the UIB. Principal component analysis revealed the key RHIs and stressors, which explained 62.50% and 77.10% of the variance, respectively. The Pearson correlation showed that stressors had greater impacts on RHIs in LIB (with r ranging from -0.42 to 0.56). Our results also showed that stressors affected RHI indices with r ranging from -0.39 to 0.50 (on habitat), -0.36 to 0.46 (on plant cover), -0.34 to 0.35 (on regeneration), -0.34 to 0.56 (on erosion), and -0.42 to 0.23 (on exotics). Furthermore, it was confirmed by the agglomerative hierarchical cluster that indices and sub-indices of RHIs and stressors differ across the UIB and LIB. These findings may serve as guidance for managers of large rivers and ecosystem service providers to minimize the environmental impact of stressors in terms of RHIs.

Nature-based tourism influences ecosystem functioning along waterways: Implications for conservation and management

Nature-based tourism has an influence on ecosystem functioning around watercourses, but this influence lacks scientific evidence. Additionally, strategic and operational management of streams necessitates trade-offs between the recreational activities and values of tourists and riparian zone hospitality services. This paper aims to assist environmentalists and planners by exploring the effects of tourism-based recreational activities on ecosystem functioning along the drawdown zone. The study uses multivariate statistical techniques to delineate the relevant global tourism issues for planners. Kruskal-Wallis tests (p < 0.01) were conducted using quantitative data from 284 transects within the Three Gorges Dam Reservoir in China. The results revealed higher ecosystem function indices than tourism indices. Indicators of tourism contributed both positively and negatively to ecological indicators, with the Pearson correlation coefficients ranging from minor to moderate (r = ̶ 0.24 to 0.38, p < 0.05). Principal component analysis revealed that the critical variables of ecosystem functioning and tourism activities explained 72.26 % of the overall variance. Nevertheless, hierarchical cluster analysis revealed that these indicators responded differently in the upstream, midstream, and downstream sections. Our findings suggest that policymakers should consider the different characteristics of riparian zones in future planning, as doing so will improve both national and global strategic and operational management.

Environmental literacy affects riparian clean production near major waterways and tributaries

Although environmental illiteracy threatens the functioning of landscapes throughout the world, it is frequently ignored. The traditional wisdom assumes that suspicions will evaporate when the public and government authorities are provided with new information. Despite significant efforts to enhance riparian corridor output, limited data are available on the effect of environmental literacy metrics (ELMs) on clean production elements (CPEs) across various streams (e.g., main rivers and tributaries) within impoundments. This study examined such effects within the China Three Gorges Dam Reservoir area (TGDRA) by collecting 336 transects that assessed the breadth of effects on 58,000 km² in 2019. The network visualization revealed 7234 papers published over the last 121 years, each of which focused on themes such as plant cover, regeneration, exotics, erosion, habitat, and stressors. The bar graph showed that the general public lacked understanding of environmental literacy (e.g., knowledge, attitudes, and behavior), which influenced plant cover elements most in tributary zones but had little direct effect on regeneration. Locals' environmental literacy had the greatest impact on CPEs, with Pearson correlation coefficients ranging from -0.69 <r < 0.96 in the main river zones. Moreover, public employees' environmental literacy had a stronger correlation with CPEs (-0.58 <r < 0.83) within the main river regions. Farming systems, exposed soil, dominant grass regeneration, and instream structures, including pollution, were among the most notable CPEs within the TGDRA. According to hierarchical approaches, CPEs and ELMs change substantially across stream types. CPEs and ELMs vary significantly around main rivers and tributaries, requiring efforts to raise the public understanding of the worldwide impacts of stream health on humans.

Modelling Water Flow and Soil Erosion in Mediterranean Headwaters (with or without Check Dams) under Land-Use and Climate Change Scenarios Using SWAT

The use of check dams is a common strategy to reduce soil erosion in the Mediterranean headwaters. However, the effects of these control works on water flow rates and sediment yields have been scarcely investigated under possible scenarios of climate and land-use changes. On this regard, the use of hydrological models, such as SWAT, provide reliable hydrological predictions under variable environmental conditions. To fill this gap, this study has evaluated the effectiveness of check dams on the hydrological response of a forest headwater in Calabria (Southern Italy) in comparison with an unregulated subcatchment with very similar environmental conditions. In this regard, the effects of different combined scenarios of climate change (through three GCMs and two RCPs applied to a time period of the next 80 years) and land use (forest, pasture, and cropland) on water flow rates and sediment yields in the two headwaters were analysed using the SWAT model. The SWAT model was first calibrated in a third headwater with very similar climatic, soil, and land-use conditions, and this verification showed a satisfactory prediction capacity of water flow rate. The water flow rate prediction capacity of the model was satisfactory (coefficients of determination and efficiency of Nash and Sutcliffe equal to 0.71 and 0.67, respectively, and percent bias of 14.9%). No significant differences were detected for the water flow rates and sediment yields between the two subcatchments (with or without check dams) among the different land-use and climate change scenarios. This was linked to the low hydrological response of both headwaters to the forcing actions, which influenced the low effectiveness of the control works. SWAT estimated higher values of both mean and maximum values of water flow rates and sediment yields under RCP2.6 compared with RCP8.5. Both water flow rates and sediment yields were predicted to be very low under all climate and land-use scenarios. The regulated headwater with check dams was predicted to always produce more runoff and erosion compared with the subcatchment without check dams. The increases were predicted to be up to 60% for the maximum flow rate and 30–35% for the sediment yield in forest land use under RCP2.6. Although there was a limitation in this study due to the lack of validation of the erosion data (due to unavailable records of sediment yield), this study demonstrated how the use of check dams in headwater catchments may be not effective for soil conservation purposes several decades after their installation in Mediterranean semiarid areas, where the water flow and erosion rate are limited.

Impacts of riparian width and stream channel width on ecological networks in main waterways and tributaries

Riparian buffer width and stream channel width have different impacts on ecological networks (e.g., plant cover, regeneration, exotics, erosion, habitat, and stressors) and provide various ecosystem services. The protection of riparian zones of increasing widths for higher-order streams and connected tributaries alongside mega-reservoirs and around dams is of great global significance. However, it remains unclear which protection strategies are most effective for such zones. By applying a rapid field-based approach with 326 transects on an inundated area of 58,000 km² within the Three Gorges Dam Reservoir (TGDR) in China, we found that riparian buffer areas were influenced differently by broad-ranging widths. The riparian buffer width of 101.84 ± 72.64 m (mean ± standard deviation) had the greatest impact on the main waterway, whereas the stream channel width of 99.87 ± 97.10 m was most influential in tributaries. The correlation coefficient strengths among ecological and stress parameters (independently) were relatively greater in the main waterway riparian zones; the highest value was r = 0.930 using Pearson correlation (p < 0.05). In contrast, stress parameters revealed substantial and strong relationships with ecological parameters in tributaries, with the highest value being r = 0.551. Riparian width had the strongest influence on buffer vegetation scales, high-impact exotics, and bank stability. In comparison, channel width had the greatest effect on tree roots, dominant tree regeneration, and agricultural farming. These parameters showed distinctive responses in the shapes of indexing in higher-order streams and connected tributaries. These observations confirm the urgent need for research on regional-based extended riparian areas managed by the same administration strategies. Revised guidelines are needed to protect massive dam and reservoir ecosystems from further deterioration.

The effects of sediment traps on instream habitat and macroinvertebrates of mountain streams

Sediment transport in mountain streams can be a major hazard to downstream infrastructure. Consequently, sediment traps are a common feature in many high gradient streams to retain large volumes of sediment and protect settlements from major sediment transport events. Despite the wide application of these instream structures, there is little knowledge regarding the environmental and ecological effects on streams. Here, we investigated the hydromorphological effects of sediment traps on instream habitats and associated macroinvertebrate communities in four impacted and three non-impacted streams in Switzerland. Sediment traps significantly disrupted the sediment regime homogenising grain size percentiles compared to the natural stepwise downstream fining in control streams. This disruption in the sediment regime resulted in finer grain size distributions upstream of the sediment trap, and reduced substrate diversity in the sediment retention basin and just downstream of the trap. The reductions in substrate diversity resulted in an altered macroinvertebrate community composition. Further, the disconnection in sediment transport led to a lack of longitudinal correlation in macroinvertebrate communities. Refugia provision downstream of the sediment trap, and resource availability within the retention basin, were diminished, potentially reducing resilience of macroinvertebrate assemblages to instream disturbances. The effects of sediment traps were most likely localised in three of the four streams with substrate diversity recovering to comparable control values within 8 wetted widths (ca. 50 m) downstream of the trap associated with natural longitudinal fining. In contrast, ecological and environmental effects propagated downstream in one impacted stream with no recovery being evident. Sediment retention basins in the impacted streams provided a local artificially unique habitat of dynamic-braided channels. Our results indicate that sediment traps can significantly disrupt the sediment regime with important consequences for instream ecology and environmental conditions, although these effects can be system specific. Further work is needed to fully understand the effects of sediment traps in mountain streams to assist resource managers in the mitigation and future construction of these structures.

Assessing riparian zone changes under the influence of stress factors in higher-order streams and tributaries: Implications for the management of massive dams and reservoirs

Riparian ecosystem services along higher-order streams and connected tributaries may change over time as disturbances continuously increase, resulting in diverse deterioration of buffer zones. How habitat, plant cover, regeneration, erosion, and exotic parameters (riparian health conditions) change within huge dams and reservoirs worldwide is an unanswered question. We used multivariate statistical techniques to assess changes in riparian health parameters affected by disturbances identified in 304 transects within the Three Gorges Dam Reservoir, China, and associated tributaries. Kruskal-Wallis tests (p < 0.01) revealed high diversity in habitat, plant cover, regeneration, erosion, and overall stream condition. There was also notable variance relating to exotic and pressure parameters. The critical variables of riparian health indicators and stress factors identified by principal component analysis explained 58.40% and 74.6% (in the main waterway) and 53.23% and 71.0% (in the tributaries) of the total variance. Among riparian health indicators, one habitat parameter (riparian vegetation width) in the main waterway and one regeneration parameter (tree size classes) in tributaries contributed greatly, along with other specified parameters. Furthermore, stress factors such as farming systems, land-use types, and pollutant activity variables had the highest impact on these water bodies. In comparison, counting stress factors alone showed more deterioration in the main waterway with a range of (r = -0.527- 0.493), as determined using Pearson correlation (p < 0.05). Furthermore, after indexing, the parameters exhibited weaker coefficient values in tributaries, where exotic correlated negatively with other indexed values. These findings are relevant for managers of massive dam and reservoir ecosystems seeking to mitigate environmental and socioeconomic losses.

Water Infiltration after Prescribed Fire and Soil Mulching with Fern in Mediterranean Forests

Prescribed fire is commonly used to reduce the wildfire risk in Mediterranean forests, but the soil’s hydrological response after fire is contrasting in literature experiences. The mulch treatment can limit the increases in runoff and erosion in the short term after a fire. The use of fern is preferable to straw, due its large availability in forests. However, no experiences of post-fire treatment with fern mulch have been found in the literature and therefore the mulching effectiveness has not been evaluated. This study has measured water infiltration rate (IR) and water repellency (SWR) using a rainfall simulator in three Mediterranean forest stands (pine, oak and chestnut) of Calabria (Southern Italy) after a prescribed fire and mulching treatment with fern in comparison to unburned soil. Prescribed fire reduced water infiltration in all forests in the short term compared to the unburned conditions, and increased SWR in pine and oak forests. These reductions in IR in the time window of disturbance after fire increased the runoff generation capacity in all soils, but had a lower effect on peak flows. However, soil mulching with fern limited the runoff rates and peak flows compared to the burned soils, but this treatment was less effective in pine forest. One year after fire, IR increased in burned soils (treated or not) over time, and SWR disappeared. The effects of mulching have disappeared after some months from fire. The study confirms the usefulness of mulching in broadleaves forest in the short term, in order to control the hydrological effects of prescribed fire in Mediterranean forests. Both post-fire management techniques should be instead adopted with caution in conifer forests.

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

This study has evaluated the runoff and erosion rates in torrents of Southern Italy, two forested headwaters with very similar climatic, hydrological and geomorphological characteristics; in one headwater, 15 check dams were installed in the mid-1950s, while the other is not regulated with engineering works. To this aim, the hydrological variables have been modeled over 15 years after check dam installation using the HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) model coupled to the MUSLE (Modified Universal Soil Loss Equation) equation. The model simulations have shown that check dams have not played a significant role in reducing the surface runoff compared to the unregulated torrent; in both catchments, the well-developed forest cover determined very low runoff coefficients (lower than 0.3%) with a scarce runoff generation capacity. Additionally, the reduction in peak flow due to the check dams was not significant, on average −7.4% compared to the unregulated headwater. Check dams have retained sediments for about 8–10 years after their installation, reducing erosion by about 35%, although soil loss was much lower than the tolerance limit in both catchments. After the sediment retention capacity of the dam sediment wedge was depleted, the sediment yield in the regulated torrent was even higher (by about 20%) compared to the unregulated catchment. Overall, the study has shown that the use of check dams as a catchment management strategy of forested headwaters under semi-arid Mediterranean conditions should be considered with caution, since the structures could be ineffective to reduce water and sediment flows during floods or, in some cases, check dams may increase erosion rates.

The Use of Unmanned Aerial Vehicles (UAVs) for Estimating Soil Volumes Retained by Check Dams after Wildfires in Mediterranean Forests

Check dams act as soil collectors during floods, thus retaining a large amount of sediments. The estimation of the soil volumes stored behind a check dam is a key activity for a proper design of these control works and for evaluation of soil delivery after restoration measures at watershed level. Several topographic techniques have been proposed for this activity, but the sediment wedge mapping tools are complex and time consuming. Conversely, the use of unmanned aerial vehicles (UAVs) has been proposed to support aerophotogrammetric techniques for several survey activities with promising results. However, surveys by UAVs have never applied to calculate the size of the sediment wedge behind check dams that are built in fire-affected watersheds, where soil loss and sediment transport may be high after a wildfire. To fill this gap, this study evaluates the efficiency and efficacy of aerophotogrammetric surveys using UAVs to estimate the volume of the sediments stored behind ten check dams, built as post-fire channel treatment in a forest watershed of Castilla La Mancha (Central Eastern Spain). The results of the aerophotogrammetric technique were compared to traditional topographic surveys using a total station and GNSS/RTK, assumed as reference. The estimation of sediment wedge volume provided by UAVs was more accurate (mean RMSE of 0.432), extensive (density of mapped points of 328 m−2) and quick (two days of fieldwork) compared to surveys using the topographic method (RMSE < 0.04 m, six days of field work and density of mapped points of 0.194 m−2) by the topographic method. The differences in the sediment volume estimated by the two methods were not significant, but the UAV method was more accurate for the larger check dams. Moreover, a significant correlation was observed between the volume estimates provided by the two methods, shown by a coefficient of determination close to 0.98. Overall, these results propose a larger use of the aerial surveys for mapping activities in channels regulated by check dams, such as those built for restoration of fire-affected forest watersheds.

Analyzing the Performances of Water User Associations to Increase the Irrigation Sustainability: An Application of Multivariate Statistics to a Case Study in Italy

Benchmarking techniques are useful and simple tools to analyze the performance of the collective irrigation in the Water User Associations (WUAs) towards an increase in service sustainability. Several benchmarking techniques have been proposed to process and predict performance indicators. Instead, some meaningful statistical techniques based on the distance of data samples, which overcome the limitations of the traditional benchmarking techniques, have never been applied to the collective irrigation sector. This study applies Permutational Multivariate Analysis of Variance (PERMANOVA), Multidimensional Scale Models (MDS), and Distance-Based Linear Models (DISTLM) as benchmarking techniques to evaluate the technical and financial performances of 10 WUAs in Calabria (Southern Italy). These benchmarking techniques revealed that the significant differences in the irrigated areas and financial self-sufficiency of the WUAs, shown by PERMANOVA, depend on the large variability of the remaining performance indicators. Both the MDS and DISTLM demonstrated that a higher number of associated users and larger irrigation service coverage allows an increase in the irrigated areas; this enlargement is facilitated if the water price and the size of the personnel staff decrease. The WUAs’ self-sufficiency is mainly influenced by the number of workers and the maintenance, organization, and management costs, while the impacts of the due service fees and water price are more limited; it is also convenient to increase the number of the associated farmers since this increases the economy of scale and the gross revenues of the irrigation service. Overall, from the analysis carried out for the regional case study, these benchmarking techniques seem to be powerful and easy tools to identify the problems of the irrigation service and help in planning the most suitable policies to improve the sustainability of the collective irrigation at the regional scale.

Evaluating the Effects of Pressure Indicators on Riparian Zone Health Conditions in the Three Gorges Dam Reservoir, China

The possible negative impacts of flow regulation on riparian zone conditions can be observed due to the disruption of the natural flow regime in reservoirs. In spite of considerable literature on the qualitative effects of external disturbances on riparian health indicators (RHIs), quantitative evaluations of such changes induced by pressure are rare in the literature. Our study evaluated the effects of pressure indicators on the RHIs, and the responses of RHIs relevant to the riparian zones of the Three Gorges Dam Reservoir (TGDR), China, by using the field-based approach. This paper is a component of a large project—rapid appraisal of riparian condition for the TGDR, China. The analysis has compared pressures (13 indicators) and RHIs (27 indicators) determined from the transects (259) identified throughout the TGDR (within 15 counties) by categorizing into upstream, midstream, and downstream. By using basic statistical techniques (Kruskal-Wallis tests and Pearson’s correlation), pressure indicators were found to significantly differently influence RHIs for the categorized three sections of the riparian zones of the TGDR. The correlation analysis confirmed that the pressure indicators correlated (range of r = −0.496–0.971) with the RHIs (enlisted as habitat, plant cover, regeneration, erosion, and exotic parameters). Moreover, pressure indicators were found to have a highly significant influence on erosion and habitat parameters, but moderate effects on plant cover, exotic and regeneration parameters. In addition, the highest relative effect of the pressure indicators was detected in the upstream transects, whereas the lowest was in the downstream transects. Agglomerative Hierarchical Cluster analysis also confirmed the substantial dissimilarity in the upstream transects, whereas significant similarities were identified between midstream and downstream transects. These results may be particularly important in the planning stages, to help administrators and planners form better priorities and treatments for reach-scale conservation and restoration of wide-ranging riparian zones.

GIS-Based Site Selection for Check Dams in Watersheds: Considering Geomorphometric and Topo-Hydrological Factors

Check dams are widely used watershed management measures for reducing flood peak discharge and sediment transport, and increasing lag time and groundwater recharge throughout the world. However, identifying the best suitable sites for check dams within the stream networks of various watersheds remains challenging. This study aimed to develop an open-source software with user-friendly interface for screening the stream network possibilities and identifying and guiding the selection of suitable sites for check dams within watersheds. In this developed site selection software (SSS), multi-criteria decision analysis (MCDA) was integrated into geographic information systems (GIS), which allowed for numerous spatial data of the multiple criteria to be relatively simply and visually processed. Different geomorphometric and topo-hydrological factors were considered and accounted for to enhance the SSS identification of the best locations for check dams. The factors included topographic wetness index (TWI), terrain ruggedness index (TRI), topographic position index (TPI), sediment transport index (STI), stream power index (SPI), slope, drainage density (DD), and stream order (SO). The site identification performance of the SSS was assessed using the receiver operating characteristic (ROC) curve method, with results for the case study example of the Poldokhtar watershed in Iran showing excellent performance and identifying 327 potential sites for efficient check dam construction in this watershed. The SSS tool is not site-specific but is rather general, adaptive, and comprehensive, such that it can and should be further applied and tested across different watersheds and parts of the world.

The use of check dams in watershed management projects: Examples from around the world

Check dams are widespread and effective soil and water conservation structures throughout the world. This review paper presents an overview of the use of check dams for soil and water management and runoff control with examples from the literature based on field measurements from four continents. More than 150years of research has reported that check dams are civil engineering landmark structures used all over the world. Among all civil engineering structures, check dams are probably the most emblematic of torrent control works. They were used for centuries, and are located all around the world. Over the past several hundred years, people have increasingly realized the envisioned advantages of check dams such as land development, environmental improvement, agricultural production, enhancement of gully stabilities, and mitigation of intensive flood. The optimum size, location and type had great influences on the efficiency of check dams under watershed management. Moreover, in both the theoretical and practical realms, check dams have been proved to be a useful tool for controlling soil erosion and flooding at a catchment scale. This paper will be helpful for policy makers to extend check dam projects in the whole erosion-prone areas.

Short-term effects of postfire check-dam construction on ephemeral stream vegetation in a semiarid climate of SE Spain

Mediterranean basins and their ecosystems have been traditionally affected by wildfires. After a wildfire, check-dam construction in channels is a widespread practice in semi-arid Mediterranean areas as an emergency action to avoid soil erosion. The ways that these structures affect channels' geomorphological and edaphic characteristics or vegetation dynamics, have been widely studied. In relation to vegetation however, the majority of studies have been conducted in mountain torrents. Our approach focuses on how ephemeral streams' vegetation, is affected locally by check-dam construction in the years following a wildfire. Vegetation and soil samplings were carried out in 17 check dams throughout a semiarid area in SE Spain, which was affected by a wildfire in 2012. Check-dams had a significant influence given the accretion of fine sediments in depositional wedges. This accumulation of fine sediments, organic matter and nutrients resulted in the formation of a suitable environment for ruderal plant development by creating a differentiated community upstream of dams. Check-dam construction also affected species diversity, with slightly higher values for the Shannon and Simpson indexes at those transects directly influenced by the structure.