Assessment of Dam-Induced Changes in Ecogeomorphological Behaviour and Fluvial Functionality in the Damodar River, West Bengal, India

Anthropogenic interventions in the form of dams and barrages often alter the fluvial functionality and ecogeomorphological (geomorphology, hydrology, and ecology) behaviour of the river systems. The present work examines the environmental flow, channel metamorphosis, and fluvial functionality of Damodar River in the context of Damodar Valley Corporation (DVC) dams and development. The structural (dams, barrages, weirs, etc.) and non-structural (urban-industrial and agricultural disposal with effluents, sand mining, etc.) interventions hinder the ecological functionality of the river. This study portrays that the eco-geomorphological behaviour and fluvial functionality of the river have changed due to flow alteration and diversion by dams and barrages and due to the urban-industrial and agricultural growth in the basin area. These changes have affected riverine ecological integrity. The ecological functionality level of this study area ranges from 85 to 181 i.e. poor to good-fair. The ecological functionality level in sample channel sections (i.e., immediate upstream and downstream of Durgapur Barrage) is poor, and the value ranges from 61 to 100 due to the hydrological impact of the barrage and the Durgapur urban-industrial belt. This assessment work would help to restore the fluvial environment for humans as well as riverine biota.

In-stream habitat availability for river dolphins in response to flow: Use of ecological integrity to manage river flows

Population decline and extinction risk of river dolphins are primarily associated with flow alteration. Previous studies predominantly highlighted maintenance of adequate flow for low water seasons when habitats contract and the risk of local extinction escalates. Although river dolphins are sensitive to reduction in river flow, no studies quantify the relationships between flow and ecology of river dolphins to mitigate the potential adverse impacts of flow alteration. We quantify the relationships between flow and the ecology of river cetaceans concerning Ganges River dolphins (GRD; Platanista gangetica gangetica) usable area availability (AWS) for the low water season at wider flows (50–575 m3/s) at finer spatial and temporal scales. This study reveals that distribution of area usable to GRD is highly regulated by the adequate flow and river attributes (velocity and depth) interactions that likely offer energetically efficient modes of locomotion to GRD, suggesting the hydro-physical environment as a major determinant of river dolphin distribution and abundance. Flow and AWS relationships indicate that the flow during the dry season negatively contributed to AWS, whereas that of pre-monsoon maximized the AWS, suggesting that modifying flow regimes does alter in-stream habitats at varying spatial scales and may influence life-history strategies. Substantial fragmentation in suitable pool availability and loss of longitudinal connectivity exhibited by dry season flow suggested a higher risk of adverse biological effects during the dry season, which may reduce population viability by reducing survivorship and reproduction failure. Owing to river dolphins’ dependence on the attribute of freshwater flow, they can be expected to be more affected by flow regulations as interactive effects. Considering the seasonal effects and changes in the availability of usable areas by flow alteration, adopting effective habitat retention plans by water-based development projects appears critical to avoid further ecological risks in aquatic species conservation. Identifying priority riverscapes for river cetaceans and prioritizing investment opportunities is an essential first step towards effective riverine cetacean conservation.

Hydrological alteration: the missing dimension of water in wastewater treatment plants. The case of the Manzanares River in Madrid (Spain)

The effects of the discharge of wastewater treatment plants (WWTP) on the status of rivers have most commonly been focused on water quality. A very limited number of works have characterised the ability of treatment plants to modify flow patterns in the receiving rivers. This paper presents a methodology for the assessment of the hydrologic alteration caused by WWTP discharges, over a two-fold sequence. The first phase comprises the application of indicators derived from accessible data and informative of the capacity of treatment plants to produce significant flow alterations. The second phase, which may only be carried out when flow data in the receiving river is available, is based on the indicators of hydrologic alteration provided by the free software IAHRIS (6 indicators) and IHA (2 indicators), and on a new indicator proposed in this paper to obtain information of flow alteration at seasonal and monthly time scales. The procedure suggested in this work is applied to the Manzanares River (Central Spain), allowing the quantification of the flow alteration generated by the 12 WWTP which give service to Madrid city (3.8 million inhabitants): Large increases of annual water volumes (from 108 hm3 to 410 hm3); at a monthly scale (increase from 246% to 1516%); variability in flow decreases in wet years by up to 47% and increases in dry years by up to 380%; seasonal patterns is altered within an altered regime. Results of the analysis show: (i) the ability of the proposed methodology to characterise the modification of flow patterns due to WWTP discharges; (ii) the importance of assessing such changes when evaluating the environmental impact of treatment plants; (iii) the importance of designing preventive and mitigation measures which maintain the ecological integrity of river ecosystems in the receiving channels.

The Fate of Stationary Tools for Environmental Flow Determination in a Context of Climate Change

Environmental flows (eflows) refer to the amount of water required to sustain aquatic ecosystems. In its formal definition, three flow characteristics need to be minimally maintained: quantity, timing and quality. This overview paper highlights the challenges of some of the current methods used for eflow determination in the context of an evolving climate. As hydrological methods remain popular, they are first analyzed by describing some of the potential caveats associated with their usage when flow time series are non-stationarity. The timing of low-flow events will likely change within a season but will also likely shift in seasonality in some regions. Flow quality is a multi-faceted concept. It is proposed that a first simple step to partly incorporate flow quality in future analyses is to include the water temperature as a covariate. Finally, holistic approaches are also critically revisited, and simple modifications to the Ecological Limits of Flow Alteration (ELOHA) framework are proposed.

Linking Altered Flow Regimes to Biological Condition: an Example Using Benthic Macroinvertebrates in Small Streams of the Chesapeake Bay Watershed

Regionally scaled assessments of hydrologic alteration for small streams and its effects on freshwater taxa are often inhibited by a low number of stream gages. To overcome this limitation, we paired modeled estimates of hydrologic alteration to a benthic macroinvertebrate index of biotic integrity data for 4522 stream reaches across the Chesapeake Bay watershed. Using separate random-forest models, we predicted flow status (inflated, diminished, or indeterminant) for 12 published hydrologic metrics (HMs) that characterize the main components of flow regimes. We used these models to predict each HM status for each stream reach in the watershed, and linked predictions to macroinvertebrate condition samples collected from streams with drainage areas less than 200 km2. Flow alteration was calculated as the number of HMs with inflated or diminished status and ranged from 0 (no HM inflated or diminished) to 12 (all 12 HMs inflated or diminished). When focused solely on the stream condition and flow-alteration relationship, degraded macroinvertebrate condition was, depending on the number of HMs used, 3.8–4.7 times more likely in a flow-altered site; this likelihood was over twofold higher in the urban-focused dataset (8.7–10.8), and was never significant in the agriculture-focused dataset. Logistic regression analysis using the entire dataset showed for every unit increase in flow-alteration intensity, the odds of a degraded condition increased 3.7%. Our results provide an indication of whether altered streamflow is a possible driver of degraded biological conditions, information that could help managers prioritize management actions and lead to more effective restoration efforts.

Mapping potential impacts of dams and reservoirs in South America

<p>We present a continental-scale evaluation of the distribution of dams and reservoirs in South America. This analysis is relevant to estimate potential impacts on water supply and flow alteration. A combined total of 808 of the largest dams across the continent, which can store about 1,003 cubic kilometres of water, were evaluated. We divided the area of study into 27 hydrological regions and for each region we determined necessary inputs to assess the potential impacts of dams and reservoirs such as: total area, mean annual runoff, total storage volume, population, or equipped area for irrigation. Although the storage capacity of the reservoirs represents around 10% of the region's total mean annual runoff, the potential impacts for flow alteration differ considerably between hydrological regions because dams and reservoirs are not evenly distributed in South America. Whilst in some hydrological regions in the north, including the Amazon river, water storage from reservoirs represents less than 5% of their mean annual runoff, some hydrological regions in the south of the continent can store the equivalent of 2 to 3 years of their mean annual runoff. The region with the highest potential for hydrological impacts is the Rio Colorado basin in Argentina, where storage from reservoirs can be almost 3.5 times the region’s mean annual runoff. The observed variations in water storage can be explained by the diversity in hydrology and water demands of the different hydrological regions of the continent. For example, water storage for hydropower purposes represents about 85% of the total water storage in the continent. Also, the highest number of dams exclusively allocated for hydropower production are located in the east of the continent in Argentina and Brazil. The hydrological region with the highest ratio of water storage is “La Plata” in the southeast of the continent with approximately 35% of the total water storage of the continent.  In addition, almost 70% of dams are located in humid or sub-humid areas. In average, the dams in the continent can store 9,700 m<sup>3</sup> of water per person and 161,000 m<sup>3</sup> of water per hectare equipped for irrigation. The regions with the highest concentration of dams are Venezuela and the eastern region of Brazil, while the regions with the least number of dams per area are found in the northeast of Brazil and the south of the continent. These ratios may be useful to understand the potential effects of dams and reservoirs on a regional and continental scale, considering that development plans in several countries include many new dams across the continent. With this study, we expect to provide valuable insights to researchers and water resource managers about the current and future potential impacts of dams and reservoirs in South America.</p>

LOADING AND STRUCTURAL RESPONSE OF DEVELOPED SHORELINES UNDER WAVES, SURGE, AND TSUNAMI OVERLAND FLOW HAZARDS

Inundation from storms like Hurricanes Katrina and Sandy, and the 2011 East Japan tsunami, have caused catastrophic damage to coastal communities. Prediction of surge, wave, and tsunami flow transformation over the built and natural environment is essential in determining survival and failure of near-coast structures. However, unlike earthquake and wind hazards, overland flow event loading and damage often vary strongly at a parcel scale in built-up coastal regions due to the influence of nearby structures and vegetation on hydrodynamic transformation. Additionally, overland flow hydrodynamics and loading are presently treated using a variety of simplified methods (e.g. bare earth method) which introduce significant uncertainty and/or bias. This study describes an extensive series of large-scale experiments to create a comprehensive dataset of detailed hydrodynamics and forces on an array of coastal structures (representing buildings of a community on a barrier island) subject to the variability of storm waves, surge, and tsunami, incorporating the effect of overland flow, 3D flow alteration due to near-structure shielding, vegetation, waterborne debris, and building damage.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EDLiEK6b64E