River Connectivity Research Articles

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

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.

Shifted Flood and Ecology Regimes Due To Channel Bar Greening and Increased Flow Resistance in a Large Dammed River

AbstractDamming profoundly affects downstream flow‐sediment regimes, altering channel bar dynamics and thereby affecting floods and riverine biodiversity. Here, we investigate the response of bars to upstream damming by examining patterns, mechanisms, and impacts in the Middle Yangtze River (∼1,000 km). Over a decade of post‐damming observational data reveal substantial increases in bar revegetation and Leaf Area Index. Shorter flood duration and stable bar size collectively drive bar greening. Consequently, denser vegetation has slowed flow velocity by 17% ± 2% and increased flow resistance by 21% ± 5%, offsetting the water‐level decrease from channel expansion due to scouring and even causing a slight rise in floodwater levels. Furthermore, damming has markedly altered river connectivity, thermal regimes, and solute dynamics, detrimentally affecting fish habitats and aquatic life. These findings, along with refined river stage simulation considering flow‐sediment‐vegetation interactions, facilitate sustainable reservoir operation and river management in big river systems.

Rivers and spatial distance are drivers of genetic diversity in the south American dwarf caiman (Paleosuchus palpebrosus)

AbstractThe distribution of species and the way that lineages are structured are the result of intrinsic historical processes of the species and their relationships with landscape features. Paleosuchus palpebrosus is one of the smallest crocodilians in the world and has a wide geographic distribution in South America, occurring in different habitats. Here, we analyzed mitochondrial cytochrome b sequences of 227 individuals, investigated how elements of landscape heterogeneity impact genetic differentiation, and evaluated the evolutionary and phylogeographic history of the species. Thus, we hypothesized that landscape structures, such as aridity and slope, should act as resistance surfaces to population connectivity, while rivers could mediate the dispersion of the species as a conductor of the gene flow. The analyses recovered three main lineages of P. palpebrosus. While most of the observed genetic variation was explained by geographic resistance distance, river connectivity had a smaller contribution for the observed variation. We also found a recent history with limited genetic divergence throughout the wide distribution of the species. Our findings highlight the main drivers for the evolutionary history of the species and how landscape features can shape the diversification, especially if we consider rivers as a facilitator of gene flow.

Fish community dynamics following the low-head dam removal and newly installed fish passage in a headstream tributary of Jinsha River, Southwest China

Low-head dams and small hydropower developments are widely distributed in global rivers because of their high cost-efficiency and smooth implementation. However, these installations have great ecological impacts on native fish communities due to the loss of longitudinal river connectivity. Although dam removal and fishway construction are effective measures to mitigate river fragmentation, research on their effects on fish communities remains limited to date. In this study, we investigated fish community dynamics in a mountainous tributary of the Jinsha River–Heishui River following dam removal, fishway construction, and fishway renovation. Our fish sampling data from 2018 to 2023 yielded 6137 fish belonging to 25 species, 12 families, and 3 orders. The native fish community predominantly represented the typical fish fauna of the Qinghai-Tibetan Plateau, primarily including the genus Schizothorax and the families Sisoridae and Nemacheilidae. Representative fish species in the Heishui River demonstrate notable adaptations to cold water, high altitude, and rapid flow environments. After removing the Laomuhe Dam, upstream fish abundance increased sharply, but species richness slightly decreased in the short term. Fishway construction significantly enhanced species richness and abundance and reduced the difference between the upstream and downstream fish communities from the Songxin Dam. However, the subsequent fishway renovation altered the dominance of fish species, with marginal changes in community structure and abundance. Variations in fish community dynamics in the river channel and fishway structure can be attributed to differences in ecological guilds (e.g., flow preference and thermal regime) and environmental factors (e.g., flow discharge, water temperature, and water depth). The present study provides insight into the significance of mitigation measures for the impact of dams on mountainous rivers in southwest China through ecological assessment and guides for decision-making in the conservation and restoration of specific fish communities.

Use of long-term underwater camera surveillance to assess the effects of the largest Amazonian hydroelectric dam on fish communities

The increase in the construction of mega dams in tropical basins is considered a threat to freshwater fish diversity. Although difficult to detect in conventional monitoring programs, rheophilic species and those reliant on shallow habitats comprise a large proportion of fish diversity in tropical basins and are among the most sensitive species to hydropower impacts. We used Baited Remote Underwater Video (BRUV), an innovative, non-invasive sampling technique, to record the impacts caused by Belo Monte, the third largest hydropower project in the world, on fishes inhabiting fast waters in the Xingu River. BRUV were set in a river stretch of ~ 240 km for 7 years, 2 before and 5 after the Belo Monte operation. We explored the spatial and temporal variation in fish diversity (α, β, and γ) and abundance (MaxN) using generalized additive models. We also investigated the variation of environmental variables and tested how much information we gained by including them in the diversity and abundance models. Belo Monte altered the flow regime, water characteristics, and fishery yield in the Xingu, resulting in changes in the fish community structure. Temporally, we observed sharp declines in α diversity and abundance, far exceeding those from a previous study conducted with more conventional sampling methods (i.e., catch-based) in the region. γ-diversity was also significantly reduced, but we observed a non-expected increase in β diversity over time. The latter may be associated with a reduction in river connectivity and an increase in environmental heterogeneity among river sectors. Unexpected signs of recovery in diversity metrics were observed in the last years of monitoring, which may be associated with the maintenance of flow levels higher than those previously planned. These results showed that BRUV can be a useful and sensitive tool to monitor the impacts of dams and other enterprises on fish fauna from clear-water rivers. Moreover, this study enhances our comprehension of the temporal variations in freshwater fish diversity metrics and discusses the prevalent assumption that a linear continuum in fish-structure damage associated with dam impoundments may exhibit temporal non-linearity.

Analysis of changes in river connectivity during the urbanization process: a case study of the southeastern plain of Yinzhou, China.

Affected by human activities, the naturally occurring river network in the southeastern plain of Yinzhou has gradually evolved into a natural-artificial composite water system, and changes in river connectivity due to changes in river network systems have caused water security problems, including urban flooding. To clarify the river connectivity change and its relationship with the urbanization process, this paper discusses an evaluation method for river connectivity based on complex networks and cellular automata (CA) from the perspective of complex systems, quantitatively analyzes the spatial-temporal characteristics of the structural and functional river connectivity in the study area during the 1990s-2020s, and reveals the impact of river nodes and chains on the connectivity level under the disturbance of natural or human factors. The results contained the following revelations: ① River connectivity showed a decreasing trend in the initial and rapid development stages of urbanization from the 1990s to the 2010s and a limited increasing trend in the optimization and upgrading stages from the 2010s to the 2020s. ② River network degradation and ongoing connectivity decline are found in the northeastern part of the study area. The highest river connectivity exists in Dongqianhukaifaqu. ③ The number of river nodes and chains should be maintained at approximately 80% for normal river connectivity. The nodes of high degree in the inflow area are listed in the key protection areas. ④ Changes in river connectivity are significantly correlated with the urbanization process. Changes in the functional connectivity level affect the magnitude of a flood. This study provides a theoretical basis for river network connectivity improvement and flood prevention in plain areas.

Enhancing the natural absorbing capacity of rivers to restore their resilience

Abstract Resilience, which can also be described as absorbing capacity, describes the amount of change that a system can undergo in response to disturbance and maintain a characteristic, self-sustaining regime of functions, processes, or sets of feedback loops. Rivers exhibit varying levels of resilience, but the net effect of industrialized anthropogenic alteration has been to suppress river resilience. As changing climate alters the inputs to rivers and human modification alters the morphology and connectivity of rivers, restoration increasingly considers how to enhance resilience. Characteristics that underpin river absorbing capacity include natural regimes, connectivity, physical and ecological integrity, and heterogeneity. River management emphasizing channel stabilization and homogenization has reduced river absorbing capacity. We propose that the paths to restoring rivers include defining relevant measures of absorbing capacity and understanding the scales of restoration and the sociopolitical elements of river restoration. We provide a conceptual framing for choosing measures that could be used to assess river absorbing capacity.

Molecular identification of Nemacheilus sp. from Bangka Island, Indonesia Based on the Cytochrome C oxidase Subunit I (COI) Gene

Abstract Nemacheilus is a genus of stone loaches native to Asia. There are 13 species of the genus Nemacheilus that can be found in western Indonesia, from 44 species that exist in Asia. During our expedition to Bangka Island, which took place between the 20th and the 25th of January 2023, we discovered 15 live specimens of Nemacheilus sp. These specimens were collected using a fish trap in the Bencah River, Bangka Island, Indonesia. We identified Nemacheilus sp based molecular analysis by using the DNA Barcoding method based on the Cytochrome C oxidase Subunit I (COI) gene. DNA barcoding is a solution to provide accurate, fast, and automatable identification of species and species discovery. Based aon the COI gene, Nemacheilus sp. Nemacheilus from Bangka Island is genetically closest to Nemacheilus pfeifferae, which is found in Sumatra. Sumatra and Bangka Island have a history of river connection before the maximum glacial phase II. However, based on the similarity of DNA base pairs, these two species are only 90% similar. This indicates that the genetic difference between these two species is 10%, which is far below the threshold for what is considered to be an identical species, which is under 3%. Therefore, we hypothesize that the Nemacheilus that was found on the island of Bangka is not the species known as Nemacheilus pfeifferae, but rather another species. Since the data for this other species are not yet available in Genbank, we are referring to it as Nemacheilus sp. Bangka for the time being.

Linking watershed formation with the phylogenetic distribution of a soil microscopic fungus in Yunnan Province, China

BackgroundPhylogeographic studies have gained prominence in linking past geological events to the distribution patterns of biodiversity, primarily in mountainous regions. However, such studies often focus on plant taxa, neglecting the intricate biogeographical patterns of microbes, particularly soil microbial communities. This article explores the spatial distribution of the nematode-trapping fungus Arthrobotrys oligospora, a widespread microorganism, in a tectonically active region at the southeastern edge of the Qinghai-Tibetan Plateau. By analysing the genetic variation of this fungus alongside the historical structure of major river watersheds, we sought to uncover potential connections between the two. Our study involved sampling 149 strains from 116 sites across six major watersheds in the region.ResultsThe resulting haplotype network revealed five distinct clusters, each corresponding closely to a specific watershed. These clusters exhibited high haplotype diversity and low nucleotide diversity, supporting the notion of watershed-based segregation. Further analysis of haplotypes shared across watersheds provided evidence for three proposed past river connections. In particular, we found numerous shared haplotypes between the Yangtze and Mekong basins, as well as between the Yangtze and the Red basins. Evidence for a Irrawaddy-Salween-Red and a Yangtze-Pearl-Red river connections were also portrayed in our mapping exercise.ConclusionsThese findings emphasize the crucial role of historical geomorphological events in shaping the biogeography of microbial biodiversity, alongside contemporary biotic and abiotic factors. Watershed perimeters emerged as effective predictors of such patterns, suggesting their suitability as analytical units for regional-scale studies. Our study also demonstrates the potential of microorganisms and phylogeographic approaches to complement traditional geological analyses, providing a more comprehensive understanding of past landscape structure and its evolution.

Quantitative Assessment and Regulation of Passage and Entrance Attraction Efficiency of Vertical-Slot Fishway on Heishuihe River in Southwest China.

Fish passage facilities are essential for restoring river connectivity and protecting ecosystems, effectively balancing economic and ecological benefits. Systematic and comprehensive monitoring, assessment, and optimized management are therefore crucial. This study quantitatively evaluated the entire upstream migration process of fish from the downstream river to the entrance and exit of the fishway and investigated the upstream movement patterns of fish under various environmental factors. A total of 19 fish species were monitored in the Heishuihe River downstream of the dam, with 15 species reaching the fishway entrance and 12 species successfully passing through it. The entrance attraction and passage rates of the vertical-slot fishway at the Songxin hydropower station were 15.7% and 40.42%, respectively. The best upstream performance was observed in May, with fish demonstrating better upstream timing and speed during nighttime compared to daytime. Specifically, the highest entrance attraction efficiency was recorded at a flow rate of 6-7 m3/s and a temperature of 19-20 °C, while the optimal passage efficiency was observed at a flow rate of 0-0.5 m3/s and a temperature of 17-20 °C. Additionally, a multifactorial Cox proportional hazards regression model was constructed to identify key factors influencing the probability of fishway entrance attraction and successful passage. The model elucidated the impact patterns of these key factors on fish upstream migration, ultimately generating an alignment diagram for prediction and control. This study provides a theoretical foundation and data support for developing optimized operational schedules for fishways. The findings offer a more comprehensive and systematic approach for monitoring and evaluating fish passage facilities, serving as a scientific basis for ecological restoration and fish conservation in this region and similar areas.

Modeling the risk of aquatic species invasion spread through boater movements and river connections.

Aquatic invasive species (AIS) are one of the greatest threats to the functioning of aquatic ecosystems worldwide. Once an invasive species has been introduced to a new region, many governments develop management strategies to reduce further spread. Nevertheless, managing AIS in a new region is challenging because of the vast areas that need protection and limited resources. Spatial heterogeneity in invasion risk is driven by environmental suitability and propagule pressure, which can be used to prioritize locations for surveillance and intervention activities. To better understand invasion risk across aquatic landscapes, we developed a simulation model to estimate the likelihood of a waterbody becoming invaded with an AIS. The model included waterbodies connected via a multilayer network that included boater movements and hydrological connections. In a case study of Minnesota, we used zebra mussels (Dreissena polymorpha) and starry stonewort (Nitellopsis obtusa) as model species. We simulated the impacts of management scenarios developed by stakeholders and created a decision-support tool available through an online application provided as part of the AIS Explorer dashboard. Our baseline model revealed that 89% of new zebra mussel invasions and 84% of new starry stonewort invasions occurred through boater movements, establishing it as a primary pathway of spread and offering insights beyond risk estimates generated by traditional environmental suitability models alone. Our results highlight the critical role of interventions applied to boater movements to reduce AIS dispersal.

Assessing the Impacts of Reservoirs on Riverine Dissolved Organic Matter: Insights From the Largest Reservoir in the Pearl River

AbstractExtensive reservoir construction has fragmented more than 70% of the world's rivers, significantly impacting river connectivity and carbon cycling. However, the response of riverine dissolved organic matter (DOM) to reservoir influence and its potential downstream effects remains unclear. In this study, we employed multiple analytical techniques, including Fourier transform ion cyclotron resonance mass spectrometry, radiocarbon dating, and environmental factor analysis, to investigate the dynamic changes in DOM and its controlling factors under different hydrological management regimes in the LongTan Reservoir, the largest reservoir in the Pearl River, which is the second largest river in China by water discharge. Our results indicate that the molecular diversity of riverine DOM is reduced in the reservoir. Oxygen‐rich and heteroatomic compounds, such as those containing nitrogen, sulfur, and phosphorus, are preferentially removed through enhanced photo‐ and biodegradation processes in the reservoir, particularly during the storage period. This leads to DOM that is enriched with oxygen‐poor compounds and shows a biodegraded Δ14C value downstream. This study highlights that the composition of riverine DOM is significantly altered by the reservoir, but these effects could potentially be mitigated by optimizing the outlet location.

Investigating the influence of weirs and small dams on coarse sediment connectivity in low-energy rivers: A case study of the orne and vire rivers in Normandy, France

The removal of weirs has become emblematic of efforts to restore the good ecological status of rivers in France (Water Framework Directive -WFD- in 2006; the French Eel national management plan in 2007); however, it is increasingly facing opposition for the recreational and cultural considerations it brings (Germaine and Lespez, 2017). Previous studies have highlighted that bedload can pass through or over these weirs, although they acknowledged the difficulty in applying their conclusions to all geographic contexts. In this context, we aimed to determine the influence of these structures on the bedload connectivity in low-energy, highly human modified rivers. In this way, the objective of this study is threefold: generate knowledge about the mobility of a potential bedload in low-energy, highly anthropized contexts, better understand the influence of weirs and dams on these bedlaod dynamics, and identify the associated morphological changes. We monitored the bedload fraction of the Orne and Vire rivers (France) for 4 years using 848 pebbles equipped with passive transponders injected upstream of 2 dams and 4 weirs of different size and 2 reference sites where a weir or dam had been removed. While tracers' mobility was low (∼3–5 m yr−1 for T < 2 yrs), it was highly influenced by the presence of transverse structure (shorter distances and frequency of mobilization), even small ones. After 4 years of monitoring, no tracers crossed any of the weirs. This reduction in mobility was also due to decrease of shear stress within the reservoir as well as the physical barrier created by the weir. This interruption in bedload continuity resulted in a downstream coarsening of bed material downstream of the weirs but not at sites that had been restored for several years. Ultimately, the results of this study contribute to the scientific debate by focusing on two river reaches that have been greatly influenced by human activities for centuries.

Subsurface flow pathway and hydrochemistry of a geographically isolated depression wetland in the Serra Geral Diabase Formation, São Paulo State, Brazil

Connectivity among water bodies is crucial for hydrological and ecological processes and fundamental for water management. Hydrochemistry and potentiometric studies on an isolated wetland allow to assess landscape influence, flow pathways, and subsurface connection. This study focuses on an isolated wetland over diabase on a topographic depression, with no visible river connection, and aims to determine the influence of rainfall and landscape on water composition and investigate subsurface flow toward the Santa Gertrudes stream. Water levels were monitored, and samples were collected from four wells during wet and dry seasons. Physical and chemical water parameters were measured, and ion concentrations determined. Pearson’s correlations highlighted codependence between physical and chemical parameters and ions and Piper’s diagram classified water composition. Six potentiometric maps were generated using interpolated hydraulic loads from monitoring campaigns. The findings show fluctuations in water level (0.11 to 0.93 m during wet periods and 1.25 to 1.79 m during dry periods), indicating rainwater directly affects water availability. Water composition was categorized as Sodium Bicarbonate and electrical conductivity values (greater than 100 µS/cm) may indicate that upstream wells are retaining salts from the surrounding crops. Strong positive correlation between sodium, bicarbonate and carbonate, and sulfate with electrical conductivity suggests simultaneous release of ions due to rock and soil mineral alteration. Potentiometric data reinforce the hypothesis of a subsurface connection between the studied area and the Santa Gertrudes stream. Future studies could benefit from expanding the monitoring network to include more GIWs and applying additional methods, such as isotope tracers.

Global and local behaviour of brown trout (Salmo trutta, L.) and chub (Squalius cephalus, L.) inside a laboratory vertical slot fishway model

Fish passes are commonly installed to partially reinstate river connectivity for fish species. They are designed according to the hydrological context and the biological features of the target species. Vertical slot fishways (VSF) still need a design optimization for small fish species, potentially relying on a better knowledge of fish behaviour inside the pools. This work studied the behaviour of two common fish species in France rivers: brown trout (Salmo trutta L.) and chub (Squalius cephalus L.) while passing through a VSF model. Fish movements were recorded by video tracking and analyzed following two steps: (i) global fish passages and (ii) fish behaviour inside one pool (trajectories, use of resting zones, movement patterns, position, and orientation before a successful upstream move). The mean total efficiencies (i.e. number of individuals that managed to pass and stay upstream over the total number of individuals studied) were 23.6 and 35.7% for trout and chub, respectively. Two behaviours were observed: direct passages in the upstream pool and passages with stops in one or more “resting” zones. Direct passages induced short transit times (several seconds) while a resting behaviour induced longer times (up to several minutes). A preferential resting zone, where flow conditions were the least constraining, was highlighted. Finally, the distance of fish from the slot was identified as a key parameter to ensure a successful passage. These results highlight the importance of the presence of resting zones and their hydraulic conditions for small fish passage success in VSF.

Thermotactic behaviour in lacustrine and riverine forms of Salmo trutta and its relevance to an emerging parasitic disease (PKD) in the wake of climate change

The thermotactic response of brown trout (Salmo trutta) was examined with the goal to investigate potential effects of the emerging temperature-dependent fatal trout disease PKD (proliferative kidney disease). First the differences in cold-water preferences of two forms of brown trout, lacustrine (migratory) and riverine, were determined. Second, it was studied whether this preference was changed in fish infected with PKD. The experiment involved a one-week habituation period at 14 °C in a two-chamber runway followed by a week of 3 °C temperature difference between the two runways. The fish could freely move between lanes via an opening at the end where food was provided. The temperature manipulation was repeated twice, and there were 3 trials per experimental group. All fish developed a clear spatial preference in the test. Lacustrine trout demonstrated a preference for warmer water, while riverine trout preferred cooler water. This may increase the risk to PKD in the lacustrine form. Most strikingly, riverine trout experimentally exposed to Tetracapsuloides bryosalmonae, the parasite that causes PKD, demonstrated stronger cold-seeking behaviour than control fish. Cold seeking behaviour suggests the occurrence of a disease-induced behavioural chill response, which may play an important role in disease recovery. This demonstrates the significance of protecting river connectivity and cold-water sanctuaries as management strategies for preserving salmonid populations in a warming climate.

Recreational fishing in the lower basin of the Santa Cruz river(Patagonia, Argentina) in the face of damming scenarios

The Steelhead ecotype (Oncorhynchus mykiss) and chinook salmon (Oncorhynchus tshawytscha) have promoted a recreational fishery in the Santa Cruz river, the last large free flowing river of Patagonia. However, two dams are being built upstream in the middle course, potentially affecting the life cycle of these anadromous salmonids. The study describes the dynamics of the recreational fishing of the Santa Cruz river around Piedrabuena city and anglers perceptions, discussing its trends according to possible river connectivity scenarios. The fishery was assessed through a monthly year-round field sampling from April 2018 to April 2019, developing instantaneous angler counts, discriminating fishing methods, effort, and catch per unit effort; also, in situ interviews were used to collect information on anglers’ motivations and perceptions. In addition, information on fishing tournaments was used. Three fishing zones (FZ) were identified near Piedrabuena city: FZ-1, located downstream where anglers used baited hook and line to catch the native marine Patagonian blenny (Eleginops maclovinus); FZ-2, located in the town where baited hook and line, spinning, and fly-cast are used to catch Patagonian blenny and salmonids; FZ-3 located upstream the town, where fishing effort was mainly directed to salmonids employing spinning and fly-cast. Fishing effort showed a seasonal pa�ern with high values from March to May and September to October, agreeing with Steelhead and Chinook salmon runs, respectively. The most relevant motivations for anglers were nonoriented catch variables. Anglers preferred the capture of salmonids over native species, considering dams to be a major threat to fishery. Although a postdamming scenario could allow the adult salmonids to migrate upstream, the current reproduction grounds of Steelhead will be flooded, and juveniles and adults of both species will be hindered in their downstream migration to sea. These aspects seem to seriously compromise the future of these unique fisheries.

Spatial heterogeneity of the effects of river network patterns on water quality in highly urbanized city

River water quality deterioration is a serious problem in urban water environments. River network patterns affect water quality by influencing the flow, mixing, and other processes of water bodies. However, the effects of urban river network patterns on water quality remain poorly understood, thereby hindering the urban planning and management decision-making process. In this study, the geographically weighted regression (GWR) model was used to explore the spatial heterogeneity of the relationship between river network pattern and water quality. The results showed that the river network has a complex structure, high connectivity, and relatively even distribution and morphology. Important river structure indicators affecting water quality included the water surface ratio (Wp) and multifractal features (∆α, ∆f) while important river connectivity indicators included circuitry (α) and network connectivity (γ). River structure has a more complex effect on water quality than connectivity. This study recommends that the Wp should be increased in agricultural areas and appropriately reduced in urban built-up areas, and the number of river segments and nodes should be controlled within a rational configuration. Our study provides key insights for evaluating and optimizing the river network patterns to improve water quality of urban rivers. In the future, the land use intensity, hydrological processes, and human activities should be coupled with the river network pattern to deepen our understanding of urban river environment.

Identification, Mapping and Solutions for Drought Management in Kaliori District, Rembang Regency, Indonesia

Rembang Regency is one of the regencies in Central Java that often experiences drought. Based on the results of the mapping of drought-prone areas for 2020 carried out by the Rembang Regency government, there are 63 villages spread across 14 sub-districts, 18,885 families are recorded as experiencing drought. Kaliori District is one of the sub-districts in Rembang Regency that is experiencing drought, this sub-district consists of 23 villages and is directly adjacent to the north of Java Sea. The purpose of this research is to be able to do a mapping for planning sustainable drought solutions, obtain quantitative data on drought and stages of drought management. The stages of the research carried out were site surveys and interviews related to drought in the Kaliori area. Prior to the Focus Group Discussion (FGD), a questionnaire was prepared. This research was conducted through joint FGD with all village heads in Kaliori District regarding water drought in Rembang. Based on the FGD and the statistical analysis results, it was found that 70% of Kaliori District experienced drought. When there is a drought, generally villages in Kaliori sub-district use water from water tanks and some use wells of poor quality and having a salty taste. The majority of villages in Kaliori Sub-district experienced a drought that lasted for 4-5 months of a year. Several parties involved in dealing with drought in Kaliori Sub-district included PAMSIMAS, Karang Taruna, Banser, Paguyuban, and P3A. Some solutions proposed are river connection, estuary river gate, and reservoir optimation.

Towards transient connectivity of river networks during rainfall events: Insight from hydrological observation and functional data analysis

River connectivity, which is critical for river networks to perform their functions, is deteriorating in highly urbanized areas. While it is well known about the structural and functional connectivity of river networks using traditional indicators, much less is known about the process connectivity and its influence factor. To this end, we propose a new approach based on hydrological observations and functional data analysis that has the advantage of capturing transient changes in process connectivity and responses to rainfall events. Applying the method to a typical river-dense plain in China, the results show that 1) the highest and the lowest values of process connectivity were concentrated in 0.6–0.95 and 0.04–0.61 during 2015–2020, respectively. The average values of process connectivity were lower in 2015, 2016, and 2020 with 0.49, 0.44, and 0.46, respectively, and higher in 2017 to 2019 with 0.52, 0.57, and 0.58, respectively. 2) There is a significant negative correlation between rainfall intensity and process connectivity, especially when heavy rainfall occurs. Under the same rainfall intensity, the process connectivity was weaker in the river network with lower structural connectivity, lower overflow capacity of main streams, strong concentration of rivers, more sluices and larger unit areas. 3) The main influencing factors on process connectivity were structural connectivity and rainfall, with contributions of 34.67% and 22.67%, respectively. Following closely are unit features and human regulation, contributing 14.07% and 12.61% to process connectivity, respectively. 4) Structural connectivity and unit features are the primary factors influencing process connectivity during low-intensity rainfall events. During high-intensity rainfall events, rainfall and unit features become the predominant factors affecting process connectivity. Our results provide a new insight for quantifying process connectivity in the plain and are expected to support the study of the changing mechanism of hydrological connectivity.