Hydropeaking has become a global issue because of extensive hydropower dam construction worldwide. Yet, its ecological impacts on riverine ecosystems are not well studied. We explored the effects of ...hydropeaking on riverine plants, based on data from a ~300 km reach downstream of the world's largest hydropower dam, the Three Gorges Dam. We tested three hypotheses relating to hydropeaking impacts on species elevational distributions, assemblage structure and species-specific biomass patterns by generalized linear mixed modelling and joint species distribution modelling. We found that, first, hydropeaking greatly shaped species elevational ranges, leading to expansions of herbs to high elevations and shifting species dominance at low elevations. Secondly, we detected contrasting effects of hydropeaking on assemblage-level characteristics of herbs. The inundation induced by hydropeaking had strong effects on assemblage composition and biomass allocation, where more biomass was allocated to belowground part. Hydropeaking blurred the species richness-biomass relationship, although it had little effect on species richness or plot-level biomass. Thirdly, hydropeaking induced inundation was the most important covariate driving species biomass patterns of riverine plants, although complex species-specific effects were identified, and random effects were often large in fitted models. We concluded that hydropeaking likely acted as a major driver of plant community assembly in rivers with a hydropower dam. Conservation and restoration of riverine plants can benefit from the inclusion of water level management in operational schemes of hydropower dams, especially during the early life history stages.
Display omitted
•Hydropeaking drove plant species distribution, assemblage structure and species richness-biomass relationship.•Hydropeaking generated complex species-specific effects on plant biomass patterns.•Hydropeaking is likely a major driver of plant community assembly in hydropeaking-affected rivers.
Understanding the relationship between a dam's size and its ecological effects is important for prioritization of river restoration efforts based on dam removal. Although much is known about the ...effects of large storage dams, this information may not be applicable to small dams, which represent the vast majority of dams being considered for removal. To better understand how dam effects vary with size, we conducted a multidisciplinary study of the downstream effect of dams on a range of ecological characteristics including geomorphology, water chemistry, periphyton, riparian vegetation, benthic macroinvertebrates, and fish. We related dam size variables to the downstream–upstream fractional difference in measured ecological characteristics for 16 dams in the mid‐Atlantic region ranging from 0.9 to 57 m high, with hydraulic residence times (HRTs) ranging from 30 min to 1.5 years. For a range of physical attributes, larger dams had larger effects. For example, the water surface width below dams was greater below large dams. By contrast, there was no effect of dam size on sediment grain size, though the fraction of fine‐grained bed material was lower below dams independently of dam size. Larger dams tended to reduce water quality more, with decreased downstream dissolved oxygen and increased temperature. Larger dams decreased inorganic nutrients (N, P, Si), but increased particulate nutrients (N, P) in downstream reaches. Aquatic organisms tended to have greater dissimilarity in species composition below larger dams (for fish and periphyton), lower taxonomic diversity (for macroinvertebrates), and greater pollution tolerance (for periphyton and macroinvertebrates). Plants responded differently below large and small dams, with fewer invasive species below large dams, but more below small dams. Overall, these results demonstrate that larger dams have much greater impact on the ecosystem components we measured, and hence their removal has the greatest potential for restoring river ecosystems.
•A potential failure of a large dam could lead to substantial downstream damage.•Dam failure event is simulated using a 1D HD model for piping and overtopping case.•The dam-break flow is routed to ...the downstream using well calibrated 2D HD model.•Flood hazard maps are developed to evaluate human, vehicle and structural stability.•Flood risk maps are developed by combining the hazard, vulnerability and exposure.
The large dam at the upstream of the densely populated city required due attention on its failure due to catastrophic consequences in the downstream area. The densely populated city of Surat, India, is situated 100 km downstream of the large Ukai Dam having a storage capacity of 7414.2 Mm3. The potential failure of the Ukai Dam could lead to substantial damage in and around Surat city, underscoring the necessity for dam-break flood modelling and associated risks for emergency action plans. In the current study, the Ukai Dam failure is simulated to derive the dam-break flood hydrographs by integrating an empirical dam breach equation with a hydrodynamic model for piping as well as overtopping conditions. The simulations for different (36 Nos.) scenarios by considering the effects of reservoir level, inflow with an early peak, and erosion of the earthen embankment indicates the sensitivity of the considered breach parameters on the outflow hydrograph. The peak discharge resulting from the Ukai Dam failure at full reservoir level (FRL), highest flood level (HFL), and 1 m overtopping are 4.6, 5.0, and 7.5 times higher than the maximum observed flood recorded after the construction of the Ukai Dam. The effect of dam-break flood wave propagation in the lower Tapi River and Surat city is evaluated using the well-calibrated 2D HD model. The dam-break flood simulation, corresponding risk assessment revealed that the maximum area of the city, including existing critical infrastructure, was flooded with water depths more than 1.2 m. Nearly 50 % of the considered area is exposed to significant flood hazards, exhibiting threats to people, vehicles, and building safety. The socio-economic vulnerability and exposure analysis for the wards and villages within Surat Urban Development Authority (SUDA) administrative boundary revealed that, 30 % and 22 % area is under high to very vulnerable and exposure category. Ultimately, it leads to nearly 25 % area under SUDA is under high-risk category. The developed inundation, hazard, and risk maps will be useful to local and disaster management authorities to develop plans for response to recovery practices, emergency action plans (EAPs), and prioritize the wards and villages during the flood mitigation with scarce resources.
One of the interesting directions of complexity theory is the investigation of the synchronization of mechanical behavior of large-scale systems by weak forcing, which is one of manifestations of ...nonlinearity/complexity of a system. The effect of periodic weak mechanical or electromagnetic forcing leading to synchronization was studied on the laboratory load-spring system as well as on a big dam's strain data. Due to synchronization, the phase space structure of the forced system strongly depends on the weak forcing intensity-determinism show itself in the recurrence of definite states of the forced system. The nonlinear dynamics of tilts/strains/seismicity near grand dams reflect both the complexity of the mentioned time series, connected with the natural agents (regional and local geodynamics), which were presented even before dam erection, as well as the effects of the water level (WL) variation in the reservoir, which is a quasi-periodic forcing superimposed on the natural geodynamic background. Both these effects are documented by the almost half-century of observations at the large Enguri Dam. The obtained data on the dynamics of strain/seismicity near a large dam can be used for the assessment of the possible risks, connected with the abrupt change of routine dynamics of construction.
Arid ecohydrology relies on sporadic rainfall and flooding to sustain linear river oases, crucial for supporting flora and fauna during the long dry season and drought years. Growing water demands ...have led to large reservoir constructions, severely impacting the fragile arid ecosystems. We analyse the hydro-geomorphological impacts of the large Neckartal Dam (completed in 2019) on the Fish River oasis based on existing dams, regional studies, field surveys, hydrological data, and modelling. The Neckartal Dam, along with three smaller dams, impounds 80 % of the desert oasis basin (1235 Mm3, 55,870 km2), exceeding the average annual runoff threefold. A gradient of dam-induced changes was identified, varying with distance from the dam wall. Immediate downstream, hydromorphological impacts include channel narrowing (⁓15 %) and reduce mean annual sediment yield (⁓20 %). Also, water distribution losses create chronic low flows, favour for invasive flora and fauna to spread, significantly disrupting the pristine nature of the desert ecosystem. This phenomenon has been observed over a 70 km stretch below the Hardap Dam. This situation is irreversible, as the invasive flora can withstand even large floods. As the distance increases, the dam suppresses low to moderate annual floods and prolongs droughts from months to years or even decades. Based on our flood routing model, only the largest floods (recurrence interval, RI >25 years) can exceed the dam storage, continue downstream, transport sediment and maintain the pool-bar morphology along 245 km of the oasis. The lack of significant flows between major floods means that sediment from smaller, lower arid basins accumulates in the Fish River valley, filling pools and further reducing water availability during dry periods. The Neckartal Dam's impact assessment demonstrates potential changes in arid river systems globally.
As a key component of global change, dam‐induced sediment reduction occurs in large rivers worldwide, which has profound implications on the fluvial systems. However, the systematic change of ...suspended sediment concentration (SSC) and its dynamic processes are not well known. We summarize typical SSC changes and propose a new sediment modeling framework for heavily dammed fluvial systems with the Changjiang (Yangtze River) as a background. We find that the fluvial SSC has declined by an order of magnitude, i.e., from ∼1.0 to ∼0.1 kg/m3, and even to ∼0.01 kg/m3 locally. The SSC distribution pattern along the mainstream has changed remarkably, with the sediment source/sink being partially reversed. Downstream of the Three Gorges Dam, the SSC recovery capacity gradually decreases with the sediment erosion quantity accumulated over time, and the SSC contribution rate of a linked large lake (Dongting) will change from negative (ca. −39%) to positive (ca. 17%), in the coming decades.
Plain Language Summary
Suspended sediment plays a key role in fluvial nutrient transport and aquatic ecological processes. Globally river damming has led to sediment discharge reduction to the sea, yet the systematic riverine concentration (SSC) changes and their mechanisms remain poorly understood. Herein, we propose a new modeling framework for reproducing and forecasting suspended sediment processes for dammed fluvial systems with the Changjiang as a reference. Results show a sediment source/sink reverse, downstream recovery capacity decrease and a change in river‐lake relationship under severe SSC decline. These findings offer essential guidelines for river management subject to super reservoirs, which have been built (e.g, the Three Gorges Reservoir) or planned in large rivers, such as the Congo and Amazon River.
Key Points
Suspended sediment concentration of the Changjiang River has decreased by an order of magnitude in recent 3 decades from ∼1.0 to ∼0.1 kg/m3
Sediment source/sink reverse partially and downstream recovery capacity decrease exponentially under the reservoir operation
Predicted by a new sediment modeling framework, the river‐lake relationship in the fluvial system will change considerably in 2030s
The paper offers a geographical interpretation of the evolving technical, political, and economic intricacy of large dams. It incorporates existing hydropolitical scholarship and the notion of the ...Chinese Water Machine to reframe dams as assemblages built by specific political, financial and technical processes in particular socioenvironmental regions. The paper examines the continuity of hydropolitical relationships through a genealogical inquiry into the formulation and materialisation of Ghana's three dams: the Akosombo and Kpong dams built during the Cold War, backed by Western lenders and engineering companies; and the Bui dam commissioned in the 2010s, with support from China. Based on fieldwork in Ghana and China, as well as documentary evidence, the paper argues that the thinking, planning and building of dams interconnect the host regime and external techno-financial actors with their floating political-economic interests, but in a durable way. Sometimes, even if little concrete is actually poured, the symbolic power of dams endures, transforms, and at certain times and places expands, through events and discourses of national and international interest groups pursuing their own purposes, albeit with the replacement of influential individuals and powerful institutions, and regardless of the involvement of Western, Chinese and/or other actors. Ruptures exist but do not necessarily break the continuity of dam assemblages. The emergence of an opposition assemblage that battles against dams is a more recent complexity.
Large dams and their removal can profoundly affect riparian ecosystems by altering flow and sediment regimes, hydrochory, and landform dynamics, yet few studies have documented these effects on ...downstream plant communities. Ecological theory and empirical results suggest that by altering disturbance regimes, reducing hydrochory, and shifting communities to later successional stages, dams reduce downstream plant diversity. Dam removal could reverse these processes, but the release of large volumes of sediment could have unexpected, transient effects. Two large dams were removed on the Elwha River in Washington State, USA, from 2011 to 2014, representing an unprecedented opportunity to study large dam removal effects on riparian plant communities. Our research objectives were to determine: (1) whether the Elwha River dams were associated with lower downstream plant diversity and altered species composition across riparian landforms pre‐dam removal, and (2) whether dam removal has begun to restore downstream diversity and composition. To address these objectives, we compared plant species richness and community composition in river segments above, below, and between the two dams. Plant communities were sampled twice before (2005 and 2010) and four times after (2013, 2014, 2016, and 2017) the start of dam removal, with 2013 and 2014 sampled while the upstream dam removal was ongoing. Prior to dam removal, native species richness was 41% lower below dams compared with the upstream segment; 6 years after dam removal began, it increased ~31% between the dams, whereas nonnative species richness and cover were not apparently affected by dams or their removal. Deposition caused by large volumes of released reservoir sediment had mixed effects on native species richness (increased on floodplains, decreased elsewhere) in the lowest river segment. Plant community composition was also different downstream from dams compared with the upstream reference, and has changed in downstream floodplains and bars since dam removal. In the long term, we expect that diversity will continue to increase in downstream river segments. Our results provide evidence that (1) large dams reduce downstream native plant diversity, (2) dam removal may restore it, and (3) given the natural dynamics of riparian vegetation, long‐term, multiyear before‐and‐after monitoring is essential for understanding dam removal effects.
The extraction of large dam candidate regions is critical for broad-scale efforts to rapidly detect large-area dams. The framework proposed in this paper attempts to combine random forest ...classification models and spatial analysis methods with large dam candidate area extraction methods for large-scale areas. First, we studied the combination of optical, microwave, texture, and topographic features of the dam and constructed a multisource remote sensing and topographic feature vector of the dam. Secondly, we constructed random forest classifiers in different study areas and evaluate their performance. Then we explored the geographic characteristics of the dams and their relationships with other features. Finally, we introduced the spatial analysis method to constrain the large dam candidate area. The proposed framework was tested in a total area of 968,533 km
2
in five countries and achieved promising results, which constrained the candidate area to less than 1.06% of the total area. We calculated the completeness rate of large dams using the multi-source dam datasets. The framework achieved a completeness rate of more than 97.62%. Our results show that the entire framework is reliable for automated and fast large dam candidate area acquisition based on data from open remote sensing products.
Display omitted
•Partitioning methods provided insights into reservoir exotic species distribution.•Reservoir flooding has a high independent effect on exotic species richness.•Exotic invasion was ...significantly associated with landscape variables.•A landscape approach to conservation of regulated riparian ecosystems is needed.
Riparian zones of regulated rivers are susceptible to species invasion due to a variety of anthropogenic disturbances. Adjacent land use and landscape patterns may be significant drivers in this process in conjunction with direct effects of flow regulation. Understanding different influences on invasion is necessary for regional landscape management. Here we explored the effects of local and adjacent landscape factors on exotic vegetation distribution along the Pengxi River controlled by the Three Gorges Dam. Vegetation data were collected in 5×1m quadrats along transect lines perpendicular to the riverbank between 172m and 178m elevation. A total of 21 exotic herbs were found, accounting for 11.3% of all identified taxa. There was greater exotic species richness below 175m zone directly affected by reservoir flooding. Variation partitioning indicated that landscape structure played a more important role in explaining the degree of invasion than did local variables. As expected, the landscape subgroup “landscape composition” appeared to be more influential than “landscape configuration”. Hierarchical partitioning showed that overall invasion increased with increasing adjacent agricultural land uses and flooding presence, but decreased with greater distance to human impacts. Given that re-regulation of the reservoir flow regime is unlikely at this time, we support a landscape approach to riparian vegetation management, where the nature and impacts of the surrounding landscape matrix, and the particular composition and forms of land use and human activity should be considered. Suggestions include establishing buffer reserves, reclaiming abandoned agricultural land, and stricter urban greening regulations.
