Changes Of River Course Research Articles

Evaluation of the high-energy flood of mid-July 2021 as a morphologic driver in the anthropogenically developed Ahr Valley, Germany, in interaction with infrastructures

BackgroundThis study explores morphologic changes in the Ahr River, Germany, caused by the high-energy flood in mid-July 2021. This study aims to assess the flood's significance as a morphological driver using the Lateral Mobility Index (LMI), as well as the impact of infrastructure on morphodynamics in terms of the formation of mud deposits and stagnant water pools, considering three focus areas of about 1 to 5 km river length. The three focus areas cover differences in the valley morphology as well as near natural and anthropogenically affected sections.ResultsThe LMI is derived from orthophotos from 1998 to 2022, and based on the surface area of the old and the new channel. It describes the sum of new and abandoned channel area in relation to the previous channel area. For the 2021 high-energy event, an increased LMI suggests an increasing change in river course and morphology. Post-flood, the LMI in focus areas 1 (furthest upstream, LMI of 1.5) and 3 (at the Rhine confluence, LMI of 3.2) surpasses the historic LMI by a factor of about 3. Focus area 3 exhibits the highest activity, while focus area 2 (LMI between 0.25 and 0.70) the lowest. The area of mud deposits and stagnant water pools increased immediately after the flood, especially in focus area 3. Over the following months, initial post-flood mud deposits not only washed away but also rebuilt to some degree later on.ConclusionsThe LMI enabled to quantitatively identify a rare and significant morphological disruption in the Ahr River’s lateral development in three focus areas, and thus, serves as additional proof that the flood of mid-July 2021 was a high-energy event impacting the local river geomorphology. Infrastructure impacted the formation of mud deposits and stagnant water zones during and after the flood, with additional influence from factors such as driftwood and valley width. The data suggested a phase of resuspension of sediments after the flood, likely due to cleanup and ad hoc river management, highlighting the need for continued river monitoring.

Fish biodiversity and their conservation measures in the Mathabhanga river, Chuadanga, Bangladesh

The study was concerned to determine the present status of the fish biodiversity in the Mathabhanga river, Chuadanga and its conversation measures based on the questionnaire interview with 40 fishers, focus group discussion with river bank community members and cross check interview with key informants. A field study was conducted for a period of four months from December, 2021 to March, 2022 to assess the fish biodiversity in the Mathabhanga river, investigate the existing fishing practices and also to identify proper management strategies for the conservation of fish biodiversity in the river. The results revealed that three categories of fishers were engaged in the Mathabhanga river namely, professional fishers (45.0%), seasonal fishers (37.5%) and subsistence fishers (17.5%). Shannon-Weaver diversity (H) and Margalef’s richness (D) values revealed that diversity and richness of fish species were the highest in March (H = 2.99, D = 4.45), followed by February (H = 2.96, D = 3.69) and January (H = 2.63, D = 3.15), while the lowest values were obtained in December (H = 2.60, D = 2.80). The Pielou’s evenness (e) values were found to be slightly varied with the variations of total number of species, being the highest in December (e = 0.94) and the lowest in January (e = 0.91). Different types of fishing gears like seine net, gill net, cast net, hook and line, and traps were found to be operated to catch fish by the fishers during this survey. A total of 26 fish species were identified in the catches of the Mathabhanga river. According to the survey, indiscriminate and overexploitation were found to be responsible for almost 40% loss, and pollution and siltation caused about 25% loss of ecosystem. Around 20% and 15% loss of ecosystem were caused by habitat destruction and changes of river course, respectively. As a result, the water quality was deteriorating day by day, and the availability of fish species and other aquatic biodiversity were decreasing gradually. During the survey, almost 16 fish species was found at a risk to be endangered. The specific conservation measures including community based fisheries management, establishment of sanctuary, control of pollution, maintenance of fishing gears and the implementation of fisheries act should need to be made for the sustainable utilization and conversation of fish biodiversity in the Mathabhanga river.

The Response of the Rivers of NW Greece to Late Quaternary Neotectonics, as Interpreted from Detrital Petrology

The modern drainage systems of the fold and thrust belt of the external Hellenide orogen of NW Greece are principally orogen-parallel. Late Quaternary changes in river courses have resulted from neotectonic deformation associated with the Katouna–Stamna fault and with footwall uplift in developing transverse grabens. This study assesses the impact of neotectonic deformation on river patterns and basin deposition. River sands show differences in modal abundance and varietal geochemistry of heavy minerals and fine sand lithic clasts, determined by scanning electron microscope, that allow identification of past river supply to raised fluvial terrace and beach deposits. In the past 200 ka, footwall uplift south of developing grabens at Lake Trichonis and the Amvrakikos Gulf promoted orogen-transverse flow, diverting the Arachthos-Louros rivers to the west, causing reversal of drainage to the north in the lower reach of the Acheloos River. A raised terrace gravel south of Preveza records the southwestward flow of a large paleo-Arachthos river, confirmed by sand petrology in beaches farther south on the Echinadon Sea coast. The use of varietal heavy minerals and lithic clasts is a rapid and powerful tool for tracking tectonically-induced changes in river patterns.

Floods, aridity and rivers: An environmental history of pargana Mandalghat in eighteenth-century Bengal

This essay interrogates the role of rivers and the water they provided in the context of the agricultural economy of colonial Bengal; it provides a minute analysis of the impact of excess flow or floods at the pargana or locality level and documents the destruction of crops, drowning of cattle, loss of seeds and overall devastation to habitation. Riverine water played an important role in the formation of soil in the country, and, therefore, its supply affected the agricultural economy. The augmentation of the delta through soil formation was a geologic process that was gradual and slow, while changes in river courses could be sudden and violent. This essay constructs a narrative around riverine activities including responses to flooding situations, navigability of rivers and the interventions of the early colonial state in Bengal in the second half of the eighteenth century. Focusing on the specific impact of flooding in the locality of pargana Mandalghat, this essay demonstrates that the study of floods can reveal the manner in which agricultural decline affected pockets of habitation within the Bengal delta.

EVALUATION OF RIVER COURSE CHANGE DETECTION USING REMOTE SENSING & GIS

The Brahmaputra is one of the largest alluvial rivers in the world characterized by frequent bank erosion leading to channel pattern changes and shifting of bank lines. This study was aimed at quantifying the changes of river course along the Brahmaputra for a period of different years and months. A course of about 56 kms has been studied using an integrated approach of Remote Sensing and GIS. The channel configuration of the Brahmaputra has been mapped for a period (1985-2018) using USGS and Landsat 8 OLI/TIRS C1 Level 2 satellite image respectively. The analysis of satellite data has provided not only channel configuration of the river system but also significant facts about the changes in river morphology, stability of the river banks and changes in the main channel.

Climate‐Change Controls on River Delta Avulsion Location and Frequency

AbstractCoastal rivers that build deltas undergo repeated avulsion events—that is, abrupt changes in river course—which we need to understand to predict land building and flood hazards in coastal landscapes. Climate change can impact water discharge, flood frequency, sediment supply, and sea level, all of which could impact avulsion location and frequency. Here we present results from quasi‐2D morphodynamic simulations of repeated delta‐lobe construction and avulsion to explore how avulsion location and frequency are affected by changes in relative sea level, sediment supply, and flood regime. Model results indicate that relative sea‐level rise drives more frequent avulsions that occur at a distance from the shoreline set by backwater hydrodynamics. Reducing the sediment supply relative to transport capacity has little impact on deltaic avulsions, because, despite incision in the upstream trunk channel, deltas can still aggrade as a result of progradation. However, increasing the sediment supply relative to transport capacity can shift avulsions upstream of the backwater zone because aggradation in the trunk channel outpaces progradation‐induced delta aggradation. Increasing frequency of overbank floods causes less frequent avulsions because floods scour the riverbed within the backwater zone, slowing net aggradation rates. Results provide a framework to assess upstream and downstream controls on avulsion patterns over glacial‐interglacial cycles, and the impact of land use and anthropogenic climate change on deltas.

Suspended sediment load prediction using long short-term memory neural network

Rivers carry suspended sediments along with their flow. These sediments deposit at different places depending on the discharge and course of the river. However, the deposition of these sediments impacts environmental health, agricultural activities, and portable water sources. Deposition of suspended sediments reduces the flow area, thus affecting the movement of aquatic lives and ultimately leading to the change of river course. Thus, the data of suspended sediments and their variation is crucial information for various authorities. Various authorities require the forecasted data of suspended sediments in the river to operate various hydraulic structures properly. Usually, the prediction of suspended sediment concentration (SSC) is challenging due to various factors, including site-related data, site-related modelling, lack of multiple observed factors used for prediction, and pattern complexity.Therefore, to address previous problems, this study proposes a Long Short Term Memory model to predict suspended sediments in Malaysia's Johor River utilizing only one observed factor, including discharge data. The data was collected for the period of 1988–1998. Four different models were tested, in this study, for the prediction of suspended sediments, which are: ElasticNet Linear Regression (L.R.), Multi-Layer Perceptron (MLP) neural network, Extreme Gradient Boosting, and Long Short-Term Memory. Predictions were analysed based on four different scenarios such as daily, weekly, 10-daily, and monthly. Performance evaluation stated that Long Short-Term Memory outperformed other models with the regression values of 92.01%, 96.56%, 96.71%, and 99.45% daily, weekly, 10-days, and monthly scenarios, respectively.

Modeling long-term delta dynamics reveals persistent geometric river avulsion locations

River deltas grow through repeated stacking of sedimentary lobes, the location and size of which are determined by channel avulsions (relatively sudden changes in river course). We use a model coupling fluvial and coastal processes to explore avulsion dynamics under a range of wave energies and sea-level-rise rates and find that the primary control on avulsion location and delta lobe size in our model is the critical superelevation ratio (SER), the amount of channel aggradation relative to the surrounding floodplain that is required to trigger an avulsion. The preferred avulsion location arises because of geometric constraints – a preferential avulsion node occurs at the break in floodplain slope that develops as the river progrades and/or sea level rises. This concavity develops in our model because the river profile aggrades and erodes via linear diffusion, whereas the diffusion of the floodplain topography is limited to episodic crevasse splays. These results are in contrast to recent modeling work, which was motivated by laboratory experiments and assumes a union between river channel and floodplain aggradation rates, and where avulsion nodes are driven by backwater hydrodynamics. The preferred avulsion length in our model scales well with laboratory, field, and model results without including hydrodynamic backwater effects. This work suggests an alternative mechanism to explain avulsion locations on deltas where floodplain topography aggrades and/or diffuses more slowly than the river channel profile, and it points to the need to elucidate river channel and floodplain connectivity over large space and time scales, and how the connectivity varies from one type of delta to another.

Dynamic flood topographies in the Terai region of Nepal

AbstractFlood hazard maps used to inform and build resilience in remote communities in the Terai region of southern Nepal are based on outdated and static digital elevation models (DEMs), which do not reflect dynamic river configuration or hydrology. Episodic changes in river course, sediment dynamics, and the distribution of flow down large bifurcation nodes can modify the extent of flooding in this region, but these processes are rarely considered in flood hazard assessment. Here, we develop a 2D hydrodynamic flood model of the Karnali River in the Terai region of west Nepal. A number of scenarios are tested examining different DEMs, variable bed elevations to simulate bed aggradation and incision, and updating bed elevations at a large bifurcation node to reflect field observations. By changing the age of the DEM used in the model, a 9.5% increase in inundation extent was observed for a 20‐year flood discharge. Reducing horizontal DEM resolution alone resulted in a <1% change. Uniformly varying the bed elevation led to a 36% change in inundation extent. Finally, changes in bed elevation at the main bifurcation to reflect observed conditions resulted in the diversion of the majority of flow into the west branch, consistent with measured discharge ratios between the two branches, and a 32% change in inundation extent. Although the total flood inundation area was reduced (−4%), there was increased inundation along the west bank. Our results suggest that regular field measurements of bed elevation and updated DEMs following large sediment‐generating events, and at topographically sensitive areas such as large river bifurcations, could help improve model inputs in future flood prediction models. This is particularly important following flood events carrying large sediment loads out of mountainous regions that could promote bed aggradation and channel switching across densely populated alluvial river systems and floodplains further downstream. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Accelerated river avulsion frequency on lowland deltas due to sea-level rise

Sea-level rise, subsidence, and reduced fluvial sediment supply are causing river deltas to drown worldwide, affecting ecosystems and billions of people. Abrupt changes in river course, called avulsions, naturally nourish sinking land with sediment; however, they also create catastrophic flood hazards. Existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea-level rise, hampering the ability to forecast delta response to global climate change. Here, we combined theory, numerical modeling, and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self-formed lobes that scale with backwater hydrodynamics. Results show that avulsion frequency is controlled by the competition between relative sea-level rise and sediment supply that drives lobe progradation. We find that most large deltas are experiencing sufficiently low progradation rates such that relative sea-level rise enhances aggradation rates-accelerating avulsion frequency and associated hazards compared to preindustrial conditions. Some deltas may face even greater risk; if relative sea-level rise significantly outpaces sediment supply, then avulsion frequency is maximized, delta plains drown, and avulsion locations shift inland, posing new hazards to upstream communities. Results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land; however, there is a threshold beyond which coastal land will be lost, and mitigation efforts should shift upstream.

EVOLUTION ANALYSIS OF WATERCOURSE AND SHOALS OF THE XUNJIANG RIVER IN WUZHOU BASED ON TIME-SERIES REMOTE SENSING DATA

Abstract. Wuzhou reach of Xunjiang River is the most valuable waterway in Guangxi. The research on the evolution of Xunjiang River in Wuzhou is of great practical significance in the aspects of river regulation and water conservancy construction. Based on Landsat images of normal water level in 1997, 2001, 2005, 2009, 2014 and 2018, this paper firstly conducts a quantitative analysis of evolution of the watercourse and shoals in Wuzhou section of Xunjiang River through using RS and GIS. Then the relationships between the changes of river course and sandbars of the research area and the annual rainfall and vegetation coverage of the upstream region are analyzed to determine the causes of the changes of watercourse and shoals of Xunjiang River in Wuzhou. The results show that the riverway contracted with a contraction amount of about 9.93 km2 from 1997 to 2005, and the expansion volume of sandbars was about 12.21 km2. From 2005 to 2014, the watercourse approximately expanded 12.33 km2, and the shoals shrank about 12.49 km2. From 2014 to 2018, the river course was a contraction trend, reducing about 1.57 km2 in area; the sandbars showed an expanding trend, with an expanding amount of about 0.82 km2. The changes of river channel and shoals are mainly influenced by the incoming water and silt from the upper reaches and are related to the annual rainfall and vegetation coverage of the upstream area. The correlation coefficient between watercourse area and upstream annual rainfall is 0.26, and that between riverway area and upstream vegetation coverage is 0.78. However, the correlations between the area of shoals and the annual rainfall and vegetation coverage of the upstream region are contrary to that of the river channel. The correlation coefficients between the area of shoals and the annual rainfall and vegetation coverage of the upstream district are −0.28 and −0.83 respectively.

The Impact of Land Use Land Cover on the Flood Plain of Bhagirathi River, Purba Bardhaman District, West Bengal, India

Aims: Human interference is the most important factor to change the LULC pattern over the earth surface. Land cover means to the physical parameters and land use means the cultural components. The present study associated with the changes in land uses a land cover pattern for the simultaneous changes of geomorphic features as well as the changes in the course of the river. This work is mainly going to summarize the changing behavior of land use land cover areas of a river bank in several decades.
 Place and duration of the Study: The research area traced in between 24°00’00’’N to 23°16’15’’N and 88°12’00’’E to 88°28’00’’E, which is situated in the eastern part of Purba Bardhaman District, West Bengal.
 Methodology: Entire study made by GIS techniques through the uses of topographical sheet (SOI-1960, Scale 1:50,000) and Satellite data (2002, 2008 & 2016). Through the help of superimposition technique the changes of river course have been identified which is directly affecting the LULC pattern of the entire flood plain.
 Result: The study reveals that the entire area changes their LULC pattern which reflects the entire flood plain.
 Conclusion: Due to the high interference of human physical elements as well as water bodies, sand bar, fallow lands are being decreased in past decades, whereas settlement patches are continuously growing up. It means for the necessity of human livelihood human always have been modifying the land in different ways.

Environmental change in a modified catchment downstream of a gold mine, Solomon Islands

Solomon Islands is rapidly developing its natural resource exploitation sector, but data needed to assess consequent environmental impacts are scarce. We assessed catchments surrounding the Gold Ridge gold mine (Guadalcanal, Solomon Islands) and found that extensive changes in river course, and water and sediment quality have occurred downstream of the gold mine since its development. Sediment run-off from exposed areas associated with the mine pit has increased, elevating turbidity (up to 2450 NTU) and metal and arsenic levels, with levels of the latter being up to 0.141 mg/L in surface waters and 265 mg/kg in sediments. An overfull, inoperative tailings storage facility associated with the currently inactive gold mine with fluctuating arsenic levels (up to 0.087 mg/L in the water; 377 mg/kg in the sediment) presents an ongoing threat to the environment. Arsenic, due to its toxicity, appears to be the greatest threat, with sediment and water guideline levels in rivers exceeded 10-fold and exceeded nearly 20-fold in the tailings dam sediments. Despite elevated metal and arsenic content in the area, no toxic inorganic arsenic was found to have bioaccumulated in locally harvested food. In summary, the natural environment surrounding the Gold Ridge mine has been modified substantially and requires an ongoing monitoring program to ensure the ecosystem services of food and water for the local communities continue to be safe. This study informs not only the local area but also provides a microcosm of the broader global challenges facing the regulation of extractive industries in proximity to subsistence communities.

River channel segmentation in polarimetric SAR images: Watershed transform combined with average contrast maximisation

This publication presents a computer method allowing river channels to be segmented based on SAR polarimetric images. Solutions have been proposed which are based on a morphological approach using the watershed segmentation and combining regions by maximising the average contrast. The image processing methods were developed so that their computational complexity is as low as possible, which is of particular importance in analysing high resolution SAR/polarimetric SAR images, where it has a measurable impact on the total segmentation time. What is more, compared to the existing solutions known from the literature review: (1) in the proposed approach, there is no need to execute further steps necessary to eliminate objects (i.e. background components) located outside the river channel from the image as a result of the segmentation carried out, (2) there is no need to sample the entire image and carry out a pixel–wise classification to prepare the segmentation process. If the steps listed in items (1) – (2) are performed, they can, unfortunately, extend the segmentation time. The experiments completed on images acquired from the ALOS PALSAR satellite for different regions of the world have shown a high quality of the segmentations carried out and a high computational efficiency compared to state–of–the art methods. Consequently, the proposed method can be used as a useful tool for monitoring changes in river courses and adopted in expert and intelligent systems used for analysing remote sensing data.

Morphometric Analysis of Kakoi River Watershed for Study of Neotectonic Activity Using Geospatial Technology

Morphometric analysis is defined as the quantitative measurement of landscape shape. Morphometric studies of a watershed helps the researcher to compare different landform and calculate the geomorphic indices that may be useful for identifying a particular characteristic such as the level of neotectonic activity in a watershed. The present study has been carried out in Kakoi River Watershed which is a part of Lower Subansiri River Basin in Assam. The study area is geo-dynamically unstable region characterized by active faults, continuing crustal movements and complicated structural region which fall under the seismic zone V of India. In recent century, the Lower Suabsiri River Basin has gone tremendous morphological changes due to active tectonics activities. After the Assam Earthquake of 1950, some of the rivers like Subansiri and its tributaries Dirgha, Kadam and Kakoi suddenly changed their channels giving birth to new channels. The present study is to examine the neotectonic domains and the changes of river course. The geomorphic indices such as Hypsometric Integral (HI), Elongation ratio (Re), Asymmetry Factor (AF), Stream-length Gradient Index (SI), Mountain Front Sinuosity (Mfs), Basin shape index (Bs), Ratio of Valley floor width to Valley Height (Vf) and Channel sinuosity (S) etc. have been studied from remote sensing data. The results shows that the study area is under active tectonic area based on Vf (0.301), Rl (0.461), Bs (3.6), Sl (165.73) and other parameters such as S (1.38) and Mfs (2.02) indicated as moderate active tectonic region. Utilization of geospatial technology and remote sensing data in the present study becomes more reliable and helpful in analyzing, monitoring and understanding the landform changes in a watershed.

Effect of Degraded Ecosystem on Fish Biodiversity in the Old Brahmaputra River, Bangladesh and Its Conservation Measures

The study was conducted about the ecosystem-based approach on fisheries management of the Old Brahmaputra River in Mymensingh region, Bangladesh. The primary area for the study was in the Old Brahmaputra River adjacent to the Bangladesh Agricultural University, Mymensingh. This research focused on the identification of proper management strategies for the conservation of fish biodiversity. There are degraded ecosystems and declining biodiversity have found during the study. According to the survey, fishing pressure and overexploitation were responsible for almost 42%, and water pollution caused about 35% loss of fish biodiversity. Around 17% and 10% loss of fish biodiversity were caused by Change of river course, and the habitat degradation respectively within the study area. These have been created a great impact on river ecology and surrounding river conditions. As a result, the water quality is deteriorating day by day and the availability of fish species and other aquatic biodiversity is decreasing gradually. During the survey, 19 species were also found at a risk of being endangered. This study identified possible ways to achieve a rich fish biodiversity in the Old Brahmaputra River with social, economic and environmental aspects. The specific recommendations are included community-based fisheries management, establishment of sanctuary, control of pollution, maintenance of fishing gears and the implementation of the fish act for the conservation of fish biodiversity of the Old Brahmaputra River.

Clinicopathological Study of Thyroid Swellings with Some Emphasis on Geographical and Community Distribution: A Hospital Based Analysis

Introduction: Thyroid swellings/goiter are still prevalent in north east part of India. Apart from its sub-Himalayan location the areas along the river Brahmaputra suffer from flooding every year and there is also frequent changing of river course, thought to be another reason for iodine depletion in soil of this region(3).
 Aim: To determine the incidence of thyroid swellings and distribution among different sections of society and geographical areas, and to evaluate the role of FNAC in the diagnosis and management and find out its accuracy by comparing with histopathology.
 Materials and methods: In the present study, total 212 patients with thyroid swellings attending department of ENT of a state medical college during the period from January 2013 to December 2015 and undergone FNAC at department of Pathology were taken into consideration.
 Results: Out of 212 cases major fraction (52.83%) were hailed from areas along the Brahmaputra river followed by patients (33.96%) from tea gardens and adjacent areas. Patients belonging to tribal communities constituted 45.28%, whereas patients from tea workers section of society formed the second majority (34.9%). Female male ratio of cases was 5:1. Majority of patients were from 21-40 years age group with mean age of 37.2 years. Cytology results of 212 cases showed colloid goiter 73.58%, adenomatous goiter 8.49%, thyroiditis 9.9%, hurthle cell neoplasm 1.41%, follicular neoplasm 4.24%, papillary carcinoma 1.41%, papillary carcinoma of follicular variant 0.47% and medullary carcinoma in 0.47% cases. Histopathology was possible in 65 cases and compared with FNAC results with accuracy rate of 89.23%.
 Conclusion: Frequent flooding and changes of river course may be one of the reasons for high prevalence of thyroid swellings and goiter along the Brahmaputra valley apart from its sub-Himalayan location. Consumption polluted drinking water and goitergenous food stuffs may be another reason of high incidence. FNAC is an easy, rapid, reliable, less invasive, low cost technique for diagnosis of thyroid swellings.

Development of Channel Characteristics during Post-Avulsion Period-A Case Study on a Part of Torsa River, West Bengal

Avulsion in any river course is the change of the system in a complex manner where river has to readjust it through different behavioral responses. Channel shifting in recent time on piedmont part of Sub-Himalayan West Bengal is high flood discharge induced while river captures an old course and neo-tectonic reasons are underneath. In the last decade one of the biggest changes in river courses in West Bengal occurred when Torsa River left its actual course and captured one of its old course called Bura Torsa or Sil Torsa (eastern branch) below Hasimara Railway Bridge in Jalpaiguri district (now Alipurduar district). Abandonment of former course, readjustment into the new course and development of new floodplain are the consequent actions. Development of present channel and plan form characteristics are controlled by few natural factors like vegetation, physiography, discharge, sediment load etc. Geomorphic characteristics of Torsa River are accompanied with development of gravel and sand bars, formation of swamps within the braid plain while high discharge induced by intensive rainfall associated with high suspended load are the major hydrological characteristics. In recent time braiding intensity as well as average width of the floodplains and width of the active corridor of Sil Torsa has increased. Distinctions among phases of channel development of the newer part within the stretch downstream of bifurcation are quite clear.

Transboundary impact assessment of Indian dams: a case study of Chenab River Basin in perspective of Indus Water Treaty

Several transboundary rivers are being shared in South Asia by neighbouring states within a certain framework. A comparative analysis of the Indus Water Treaty has been carried out with other South Asian water treaties while suggesting measures to enhance mutual cooperation over shared rivers between India and Pakistan. With a specific focus on Chenab River, transboundary impact assessments of Indian dams have been carried out keeping in view the aspects of quantity, quality and temporal change in river course. A decreasing trend and significant fluctuation in river discharge was observed with an average decrease of 0.5 billion (109) cubic metres per year in annual inflow. In terms of water quality, pH (7.90 to 8.06), nitrates and other parameters were found within permissible limits. Total coliform (34 to 280 no/100 ml) and faecal coliform (21 to 193 no/100 ml) values were higher than permissible limits in three streams, whereas Escherichia coli was found +ve in only the Jummu Tawi River. Water was found unsuitable for drinking while suitable for agriculture and aquatic life. Temporal analysis shows significant change in river course over a span of 40 years. As a result of impact assessment evolving threats and their remedial measures have been suggested.

Multi-hazard scenarios and consequences in Beichuan, China: The first five years after the 2008 Wenchuan earthquake

Risk assessment for engineering construction, public safety and city planning must answer three questions: (1) What can go wrong? (2) What is the likelihood that it will go wrong? (3) What are the consequences if it goes wrong? All the three questions are difficult to answer. Often “unexpected” hazard scenarios arising from cascading effects lead to disastrous consequences because such hazards are not prepared for. During the Wenchuan earthquake in 2008 and in the subsequent five years, the Beichuan town in northern Sichuan experienced extraordinary hazards, which impacted upon every corner of the town. A systematic study of such hazard scenarios would provide the required evidence for properly answering the aforementioned questions. This paper starts with an overview of the disaster chain in the Beichuan town triggered by the Wenchuan earthquake. It then describes seven episodes of hazards in the town and the extremely severe consequences of these hazards. The hazards included a strong earthquake, multiple large landslides, dam-breaching floods, large-scale debris flows, severe sedimentation, change of river course, and flooding/scouring. The interactions among these hazards are discussed. Finally, a protocol for identifying geohazards triggered by a strong earthquake is suggested. The protocol emphasizes hazard interactions and the concept of the hazard lifecycle, and helps enhance the engineering geological practices.