196,192 research outputs found
Guidance on Environmental Flows - Integrating E-flow Science with Fluvial Geomorphology to Maintain Ecosystem Services
No full textFluvial systems provide a wide range of necessary services for human society to thrive on. These are the so-called ecosystem services: food, drinking water, natural flood mitigation, energy and so forth. Such services are linked to an appropriate level of functionality of fluvial processes, which can be accounted for in terms of ecological objectives. These ecological objectives in watercourses can be reached only if appropriate flow and sediment regimes and related quality of channel morphology are guaranteed. The establishment and maintenance of such flow regimes, namely environmental flows (e-flows), is therefore an essential element in preserving riverine ecosystems and the services they provide, and should be included as a constraint in water resource assessment and in national legislative frameworks. It is well established that e-flows refer to the typical seasonal and interannual variability of the natural flow regime, and not only to the minimum amount of water (low flows) to be maintained in a river. In addition to this pure hydrological assessment of natural flow variability, there is also the necessity to link e-flow definition to the related hydromorphological processes and local ecological objectives of a river. This guidance therefore presents a methodology (based on knowledge and literature on river system processes) to consider hydrological and morphological aspects in defining e-flows for environmental river management. The report has been produced within the context of an agreement between the WMO Commission for Hydrology and the Italian National Institute for Environmental Protection and Research (ISPRA), to cooperate in the implementation of activities related to managing river flows and maintaining services offered to human society and ecosystems. The research can be contextualized inside the implementation of the WMO Hydrology and Water Resources programme
Habitat modeling in high gradient streams: the meso-scale approach and application
No full textThe study aims to set out a new methodology for habitat modeling in high gradient streams. The methodology is based on the meso-scale approach of the MesoHABSIM simulation system and can support the definition and assessment of environmental flow and habitat restoration measures. Data coming from 40 study sites located within the mountainous areas of the Valle d'Aosta, Piemonte and Liguria regions (NW Italy) are used in the analysis. To adapt MesoHABSIM to high gradient streams, we first modified the data collection strategy to address the challenging conditions of surveys by using GIS and mobile mapping techniques. Secondly, we built the habitat suitability models at a regional scale to enable their transferability among different streams with different morphologies. Thirdly, due to the absence of stream gauges in headwaters, we proposed a possible way to simulate flow time series and, therefore, generate habitat time series. The resulting method is evaluated in terms of time expenditure for field data collection and habitat modeling potentials, and it represents a specific improvement of the MesoHABSIM system for habitat modelling in high gradient streams, where other commonly used methodologies can be unsuitable. Through its application in several study sites, the proposed methodology adapts well to high gradient streams and allows: (1) definition of fish habitat requirements for many streams simultaneously, (2) modeling of habitat variation over a range of discharges, and (3) determination of environmental standards for mountainous watercourses
Improving the aerodynamic performance of a cycloidal rotor through active compliant morphing
No full textCycloidal rotors are a novel form of propulsion system that can be adapted to various forms of transport such as air and marine vehicles, with a geometrical design differing significantly from the conventional screw propeller. Research on cycloidal rotor design began in the early 1930s and has developed throughout the years to the point where such devices now operate as propulsion systems for various aerospace applications such as micro air vehicles, unmanned air vehicles and compound helicopters. The majority of research conducted on the cycloidal rotor’s aerodynamic performance have not assessed mitigating the dynamic stall effect, which can have a negative impact on the rotor performance when the blades operate in the rotor retreating side. A solution has been proposed to mitigate the dynamic stall effect through employment of active, compliant leading-edge morphing. A review of the current state of the art in this area is presented. A two-dimensional, implicit unsteady numerical analysis was conducted using the commercial computational fluid dynamics software package STAR CCM+, on a two-bladed cycloidal rotor. An overset mesh technique, otherwise known as a chimera mesh, was used to apply complex transient motions to the simulations. Active, compliant leading-edge morphing is applied to an oscillating NACA 0015 aerofoil to attempt to mitigate the dynamic stall whilst maintaining the positive dynamic lift coefficient (Cl) contributions. It was verified that by applying a pulsed input leading-edge rotational morphing schedule, the leading-edge vortex does not fully form and the large flow separation is prevented. Further work in this investigation will focus on coupling the active, leading-edge motion to the cycloidal rotor model with the aim to maximise aerodynamic performance
An Integrated Methodology to Study Riparian Vegetation Dynamics: From Field Data to Impact Modeling
No full textAbstract Riparian environments are highly dynamic ecosystems that support biodiversity and numerous services and that are conditioned by anthropogenic activities and climate change. In this work, we propose an integrated methodology that combines different research approaches—field studies and numerical and analytical modeling—in order to calibrate an ecohydrological stochastic model for riparian vegetation. The model yields vegetation biomass statistics and requires hydrological, topographical, and biological data as input. The biological parameters, namely, the carrying capacity and the flood‐related decay rate, are the target of the calibration as they are related to intrinsic features of vegetation and site‐specific environmental conditions. The calibration is here performed for two bars located within the riparian zone of the Cinca River (Spain). According to our results, the flood‐related decay rate has a spatial dependence that reflects the zonation of different plant species over the study site. The carrying capacity depends on the depth of the phreatic surface, and it is adequately described by a right‐skewed curve. The calibrated model well reproduces the actual biogeography of the Cinca riparian zone. The overall percentage absolute difference between the real and the computed biomass amounts to 9.3% and 3.3% for the two bars. The model is further used to predict the future evolution of riparian vegetation in a climate‐change scenario. The results show that the change of hydrological regime forecast by future climate projections may induce dramatic reduction of vegetation biomass and strongly modify the Cinca riparian biogeography
A numerical investigation into the aerodynamic characteristics and aeroelastic stability of a footbridge
No full textThe results of a numerical investigation into the aerodynamic characteristics and aeroelastic stability of a proposed footbridge across a highway in the north of England are presented. The longer than usual span, along with the unusual nature of the pedestrian barriers, indicated that the deck configuration was likely to be beyond the reliable limits of the British design code BD 49/01. The calculations were performed using the discrete vortex method, DIVEX, developed at the Universities of Glasgow and Strathclyde. DIVEX has been successfully validated on a wide range of problems, including the aeroelastic response of bridge deck sections. In particular, the investigation focussed on the effects of non-standard pedestrian barriers on the structural integrity of the bridge. The proposed deck configuration incorporated a barrier comprised of angled flat plates, and the bridge was found to be unstable at low wind speeds with the plates having a strong turning effect on the flow at the leading edge of the deck. These effects are highlighted in both a static and dynamic analysis of the bridge deck, along with modifications to the design that aim to improve the aeroelastic stability of the deck. Proper orthogonal decomposition (POD) was also used to investigate the unsteady pressure field on the upper surface of the static bridge deck. The results of the flutter investigation and the POD analysis highlight the strong influence of the pedestrian barriers on the overall aerodynamic characteristics and aeroelastic stability of the bridge
Base cartography for land and water management in Sub-Saharan Africa
No full textBase cartography at proper scale for land and water management is rarely available in Least Developed Countries (LDCs). Despite the massive presence of international cooperation programs and projects carried out in various LDCs, a low budget is usually allocated for base data retrieval, which could be helpful for a wide range of on-site actions. A food security project in Burkina Faso, aiming at increasing the agricultural production through supporting farmers' unions, is herein used as a case study. In this framework update cartography at large scale was needed in order to plan Soil and Water Conservation (SWC) interventions at catchment scale. However, best existing official maps, dated 1984, were at 1:50.000 scale, which is a highly coarse detail level to intervene at large scales. Data at higher resolution were available at the national cartographic institute, obtained from aerial surveys performed in the last decade. Aerial imagery allowed then to perform feature extraction over the areas of interest, thus updating the existing cartography and making it suitable for land and water management plannin
The Influence of Soil Characteristics in Low Flows Regionalization
No full textProblem statement: For the purpose of low flows regionalization, relevant issue for water resources management like environmental flows requirements definition, this study focused on the controls on the seasonal and spatial variability of q95 (i.e., the specific discharge that was exceeded on 95% of all the time) with particular reference to the role of soil characteristics, that, like soil infiltration rate, aquifers recharge, evapotranspiration and topography, usually play a relevant role in low flows seasonality and occurrence within a river. Approach: Piemonte and Valle d'Aosta Regions (North-Western Italy) were the investigated study area (30,027 km2) where 41 catchments were analyzed with the aim of robust regression models enabling the transfer of hydrological information from gauged to un-gauged sites. Results: The regionalization method consisted of multiple regression models between low flows and catchment characteristics. Twenty-five catchment descriptors were used, checking their relative influence with the multi-regressive procedure and a special attention was devoted to the selection of significant soil characteristics in the regionalization process. Seasonality indices were used to classify catchments into two sub-regions and separate multiple regressions was performed by checking the prediction performance with cross-validation. Also a global regression was fitted out but it yielded a lower performance. In the study domain land use, topography and Thornthwaite moisture index demonstrated to be the most significant variables in order to represent relationships between catchment soil characteristics and low flows regime. Conclusion/Recommendations: Results obtained in this study were comparable with other regionalization studies carried out in Austria and Switzerland. The interpretation of the identified regression models provided, at local scale, new tools for water management and environmental flows requirements and, from a wider point of view, useful insights into the general comprehension of low flows processes
M. Habitat time series analysis to develop flow management criteria in rivers affected by hydropeaking.
No full textHydropeaking induced by storage hydropower plants can modify the natural flow regime at different time scales, with severe impacts on the biodiversity of the downstream river ecosystems. In this research, a case study on the Noce River (NE Italy) is presented, where habitat simulation models and habitat time series were used to compare restoration scenarios and develop flow management criteria. Habitat time series analyses are based on the assumption that habitat events occurring rarely in nature create stress to aquatic fauna and shape the community. The identification of habitat stressor thresholds (HST) provided a means of quantitatively comparing different flow magnitude scenarios as well as duration and frequency of events. Results indicate that (i) the proposed flow management plan should nullify the rare habitat stress events to support the recovery of existing fish populations and (ii) HST can be used to identify flow release strategies in rivers affected by hydropeaking
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