Are hydropower dams and sand mining responsible for hydrological change in the Red river (Asia)?

Hydropower generation, flood control and dam cascades: A national assessment for Vietnam

Changes in meander patterns of the Red River in northeast Texas from 1860 to 1980 were identified from various maps, aerial photographs, and fieldwork by a 430-km stretch from the Denison Dam on Lake Texoma downstream to Texarkana. Denison Dam closure in 1943 resulted in increased daily base flow and substantially reduced frequency and intensity of flood peaks. The Red River responded to the closing of the dam by increasing width, depth, meander wavelength, amplitude, radius of curvature, and channel length. Changing only discharge and sediment load downstream from the dam reveals a geologically instantaneous fluvial response to the dam closure. Qualitative prediction of these recent changes on the Red River is generally confirmed by empirical studies in the literature. Three ancient meander patterns preserved on the Holocene Red River flood plain record a different hydrologic regimen in which well-sorted, clay-rich sediment was transported in a paleoriver having low wavelength, amplitude, width, and depth with high sinuosity. Bankfull discharge is estimated to have been quite low. Archeological remains suggest these features formed 5,000 ± 1,000 years ago. In perspective, the isolated hydrologic changes that occurred as a result of the closure of the Denison Dam are minute by comparison to the climate-related changes the Red River has undergone over the last 5,000 years. End_of_Article - Last_Page 1424------------

Abstract. Regarding to the important environmental issues, eco-balance and eco-system should be discussed using long period data analysing and visible result of study. These visible results will be materials for construction of geo-design of the river basin. Both hydrological changes and surface changes of the Mekong delta was analysed with new data using hydrologic model with visible mapping in this study. The Mekong River delta, the third largest delta in the world, is presently shifting from growing to shrinking with its ecosystem and environment seriously degraded. These environmental changes are due to several factors such as 1)ill-planned water management schemes including hydropower dams in the river basin, 2) sediment starvation, 3) increased nutrient inflows, in combination with other human activities including infrastructural extension, riverbed mining, delta subsidence, degradation of coastal mangrove belt, and gaps in governance in the whole Mekong basin under the climate change and sea level rise. Both scientific and management communities have suggested that the rate of Mekong delta shrinking will increase markedly this century. The paper compiled new data and mapping together with recent key studies implying that much of the degradation in the Vietnamese Mekong delta is due to recent human activities, particularly hydropower dams in the entire Mekong river basin.By comparison with period before 1990s when there were no large dams, the natural regime here has changed with the annual sediment load to the delta having decreased by 50–60%, the flood discharges have also decreased, the hydrological seasonal regime has shifted as most of the Mekong River water is now trapped in these large dams, and the salinity intrusion into the delta now occurs earlier by 20–30 days. Further, the river bed is on the average deeper by 0.14 m, to which riverbed mining also contributes. There has been a recent increase of erosion of river banks at 400 locations and coasts. The 66% of all of foreshore is now eroding, and the rate of these events is accelerating with time. If all the proposed mainstream hydropower dams in the Lower Mekong Basin have been built, then the Vietnamese Mekong delta with its ecosystems and about 18 million people face critical issues of sustainability. This presentation also focused on some remedial conceptual solutions that may decrease, but not eliminate, the negative impacts of these dams for the Vietnamese Mekong delta. Non-engineering solutions have the highest propriety, but engineering solutions are needed for protecting eroded coastal foreshore, river bank erosion and the fragile mangrove belt. Toward to realization of SDG’s in this study region, the integrated management system of the river basin would be desired.

Climate change is predicted to drive various changes in hydrology that can translate into risks for river ecosystems and for those who manage rivers, such as for hydropower. Here we use the WWF Water Risk Filter (WRF) and geospatial analysis to screen hydropower projects, both existing (2488 dams) and projected (3700 dams), for a variety of risks at a global scale, focusing on biodiversity risks, hydrological risks (water scarcity and flooding), and how those hydrological risks may shift with climate change, based on three scenarios. Approximately 26% of existing hydropower dams and 23% of projected dams are within river basins that currently have medium to very high risk of water scarcity; 32% and 20% of the existing and projected dams, respectively, are projected to have increased risk by 2050 due to climate change. For flood risk, 75% of existing dams and 83% of projected dams are within river basins with medium to very high risk, and the proportion of hydropower dams in basins with the highest levels of flood risk is projected to increase by nearly twenty times (e.g., from 2% to 36% of dams). In addition, a large proportion of existing (76%) and projected hydropower dams (93%) are located in river basins with high or very high freshwater biodiversity importance. This is a high-level screening, intended to elucidate broad patterns of risk to increase awareness, highlight trends, and guide more detailed studies.

Abstract. The Red River is a typical example of the Southeast Asian rivers, which has been strongly affected by human activities. This paper analyses the change of total suspended sediment (TSS) load of the Red River from 1960 to 2015 in which numerous new dams in both China and Vietnam have been constructed. A strong decrease of TSS load of the whole Red River (from 79±26×106 t yr−1 in 1960s to 6±1×106 t yr−1 in 2010s) allocated to the dam impoundments in spite of population and deforestation increase. Base on the experimental equation describing the relationship between TSS and total organic nitrogen (TON) concentrations, and on the available data of TSS concentration and river discharge, the longterm TON concentrations and fluxes were calculated for the three tributaries and the whole Red River. The annual average of TON concentrations spatially varied from 0.41 to 3.19 mg L−1, averaging 0.98 mg L−1 for the whole period; the lowest was found for the Da River where the new dams have been impounded. The highest TON concentrations and fluxes occurred in the wet season in relationship with the highest sediment loads and river discharges. The riverine TON fluxes transferred to estuary significantly decreased from 141×103±38×103 t yr−1 (equivalent to 902±247 kg km−2 yr−1) in 1960s to 32×103±5×103 t yr−1 (equivalent to 207±35 kg km−2 yr−1) in 2010s. The TSS flux decrease has driven a clear reduction of associated elements like nitrogen, which let to hypothesis a change in biogeochemical processes in the coastal zone.

A spatio-temporal analysis of rice production in Tonle Sap floodplains in response to changing hydrology and climate

Hydropower dam projects in the Lower Mekong Basin are part of long-term and interactive land and water transformations, displacement, and violence. Within these ongoing processes, dams represent intense and adverse episodes of disruption that escalate nature-society transformations. Drawing on research at Cambodia's Lower Sesan 2 Hydropower Dam (LS2 Dam), we examine how such episodes of nature-society rupture catalyze new waves of frontier-making and mobility that further intensify land and resource struggles. 1 In this ethnically diverse landscape, the abrupt hydrological changes caused by the LS2 Dam have escalated land struggles among various ethnic groups, especially migrants intent on claiming land and water resources, and Indigenous/minority groups displaced by the dam. We show how historical relations with land and socio-political marginalization by the state have produced differentiated opportunities, risks, and frictions among the four main ethnic groups present in this landscape: Indigenous Bunong, Lao, Cham, and Khmer. The LS2 Dam case shows how nature-society rupture reifies frontier dynamics by disrupting existing land/water relations, which precipitates in-migration, new resource claims, and associated conflict along ethnic lines.

Background and aims – Biomonitoring is an important tool for assessing river water quality, but is not routinely applied in tropical rivers. Marked hydrological changes can occur between wet and dry season conditions in the tropics. Thus, a prerequisite for ecological assessment is that the influence of ‘natural’ hydrological change on biota can be distinguished from variability driven by water quality parameters of interest. Here we aimed to (a) assess seasonal changes in water quality, diatoms and algal assemblages from river phytoplankton and artificial substrates through the dry-wet season transition (February–July 2018) in the Red River close to Hanoi and (b) evaluate the potential for microscopic counts and high-performance liquid chromatography (HPLC) analysis of chlorophyll and carotenoid pigments for biomonitoring in large tropical rivers.
 Methods – River water (phytoplankton) and biofilms grown on artificial glass substrates were sampled monthly through the dry (February–April) to wet (May–August) season transition and analysed via microscopic and HPLC techniques.
 Key results – All phototrophic communities shifted markedly between the dry and wet seasons. Phytoplankton concentrations were low (c. thousands of cells/mL) and declined as the wet season progressed. The dominant phytoplankton taxa were centric diatoms (Aulacoseira granulata and Aulacoseira distans) and chlorophytes (Scenedesmus and Pediastrum spp.), with chlorophytes becoming more dominant in the wet season. Biofilm diatoms were dominated by Melosira varians, and areal densities declined in the wet season when fast-growing pioneer diatom taxa (e.g. Achnanthidium minutissimum, Planothidium lanceolatum) and non-degraded Chlorophyll a concentrations increased, suggesting active phytobenthos growth in response to scour damage. Otherwise, a-phorbins were very abundant in river seston and biofilms indicating in situ Chlorophyll a degradation which may be typical of tropical river environments. The very large range of total suspended solids (reaching > 120 mg/L) and turbidity appears to be a key driver of photoautotrophs through control of light availability.
 Conclusions – Hydrological change and associated turbidity conditions exceed nutrient influences on photoautotrophs at inter-seasonal scales in this part of the Red River. Inter-seasonal differences might be a useful measure for biomonitoring to help track how changes in suspended solids, a major water quality issue in tropical rivers, interact with other variables of interest.

Lake Turkana, major Omo River developments, associated hydrological cycle change and consequent lake physical and ecological change

In order to reveal the influence of hydropower development on river ecology, we selected a number of research sites, including a natural channel (NC), a channel reservoir (CR), and a channel below the dam (CB) of a certain dam-type hydropower station on the Red River in China. We used the Ecopath model to analyze the differences in structures and energy characteristics of the three ecosystems. As indicated from the results, the energy flow in the three ecosystems of NC, CR, and CB mainly flows between trophic levels I and IV, and the overall transfer efficiencies of the three ecosystems are characterized by CR

Hundreds of hydropower dam projects, of all sizes, have been initiated in Yunnan Province, China, since the late 1990s. This paper frames hydropower‐driven resource reallocations as resource grabs that combine aspects of land, water and green‐grabbing, investigating how two dams built along the Red River have impacted local communities and how corporate and governmental stakeholders have viewed local livelihood changes and considered compensation mechanisms. This research documents how hydropower expansion triggers changes in both land and water availability, in turn depriving riverside communities of a wide range of intersecting livelihood benefits. Villagers were compensated for some losses, but in ways that failed to address how impacts accumulated over time and how hydrologic changes would impact overall livelihood activities. Financial compensation and specific environmental and modernisation agendas legitimised resource reallocations together with the provincial, national and global development campaigns driving them. Considering how different actors experience, frame and address the impacts of hydropower development through a resource‐grabbing lens elucidates the compartmentalised approaches of distant hydropower actors as well as scholars. This study answers recent calls to mobilise the scholarship on resource‐grabbing in the service of shedding light on the socio‐political projects driving resource reallocations and their livelihood impacts.

Environmental pressures on livelihood transformation in the Vietnamese Mekong Delta: Implications and adaptive pathways.

The Mekong River–Tonle Sap Lake interaction system plays a vital role in supporting livelihoods in the region through the reverse flow phenomenon. During the flood season, a substantial volume of water flows from the Mekong mainstream into the Tonle Sap Lake floodplain, which is then gradually drained during the dry season to provide additional water to the Vietnamese Delta. This interaction is critical for fisheries and agriculture, benefiting approximately 20 million residents across the Tonle Sap Lake and Mekong Delta regions.However, since 2010, extensive dam construction in the upper Mekong River and local sand mining activities have significantly altered the flow regime, weakening the interaction in two key aspects: the duration of reverse flow and the volume of nutrient-sediment water entering the lake. Utilizing an integrated modeling framework comprising hydrodynamic and hydrological models, this study found that while the Tonle Sap Lake system demonstrated resilience to climate change between 2010 and 2024, the influence of human interventions has been profound.Our results indicate that the average annual reverse flow volume, which was approximately 43 km³ during the historical period (1980–2000), has declined by about 25% to an average of 30 km³ in recent years. Additionally, the duration of the reverse flow has shortened by approximately 20 days. These changes underscore the dominant role of anthropogenic stressors in disrupting the Mekong River–Tonle Sap Lake system.To sustain this critical interaction, urgent measures are needed to regulate local sand mining and foster transboundary collaboration with upstream states regarding dam operations and future reservoir construction. Such actions are essential to maintaining flow regimes that approximate natural conditions and securing the livelihoods of millions in the region.

<p>Deltas are home to 4.5% of the global population and support a range of ecosystem services that are vital to lives and livelihoods. As low-lying regions, deltas are also amongst the most vulnerable areas to the threat climate change and relative sea-level rise, which are being exacerbated by ongoing local resource exploitation. Anthropogenic activities such as riverine sand mining, construction of flood embankments, deforestation and changes of land use and hydropower dams are disrupting the natural evolution of deltaic systems, with many of the world’s large deltas now being sediment starved. This is important because changes of the sediment flux into large deltas can have implications for the evolution of the morphology of delta bifurcations and their function at routing water and sediment seaward. This can amplify flood hazard and risk for riparian communities and intensify processes such as bank erosion, presenting hazards to human lives and exacerbating land loss. The present study focuses on the Chaktomuk junction at the apex of the Mekong delta, connecting the Mekong with the Tonle Sap Lake and the downstream delta. The junction is important as it provides the connection between the Mekong and the largest freshwater lake in Southeast Asia and because of the proximity of the junction to the rapidly expanding urban centre of Phnom Penh. We present a combined 2D hydrodynamic and sediment transport model for the Chaktomuk junction, constructed and based on high-resolution bathymetric data obtained with multibeam echosounders. A series of established sediment transport equations are adopted and tested through a sensitivity analysis to identify the most appropriate sediment transport solver for the model, which is then validated against field observations. The model was forced with a series of scenario combinations including changes of water and sediment flux and rates of sand mining. Simulation runs are presented that project the future evolution of the apex of the Mekong delta, including changes in bifurcation morphology, water and sediment routing seaward through delta distributary channels and changes in water and sediment exchanges between the Mekong and the Tonle Sap. The implications of these future trajectories will be discussed in terms of the sustainability of the delta to future change.</p>

Changing sediment budget of the Mekong: Cumulative threats and management strategies for a large river basin