Browsing by Author "Pacheco, A."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- Applicability of sediment transport models to evaluate medium term evolution of tidal inlet systemsPublication . Pacheco, A.; Williams, J. J.; Ferreira, Óscar; Garel, Erwan; Reynolds, S.This paper derives local formulae to estimate bed roughness and suspended transport and present a method to calculate net sediment transport at tidal inlet systems, combining field data and a range of well established empirical formulations. To accomplish this, measurements spanning a spring-tidal cycle of mean water levels, waves, near-bed flow turbulence and bed forms were obtained from the Ancão Inlet, Ria Formosa lagoon system, Portugal. High-resolution hydrodynamic data were gathered using acoustic equipments and by measuring sediment properties (grain-size diameter and bed form dimensions) under fair-weather conditions. The results compared favourably with available direct and indirect field observations of sediment transport rates. The approach appears to be robust and widely applicable and so can be applied to the same conditions in any tidal inlet system. This is of particular importance when attempting to understand sediment transport at inlet mouths, and has practical applications in a range of coastal engineering and coastal management areas concerned with navigation safety, coastal erosion, ecosystem health and water quality. The study discusses the applicability of the method on evaluating system flushing capacity, giving important insights on multiple inlet evolution, particularly with regard to their persistence through time. The methodological framework can be applied to assess the long-term stability of single- and multiple-inlet systems, provided that estimates of sediment storage at ebb-tidal deltas are available and sediment transport estimates during storm events are statistically considered.
- A coastal management program for channels located in backbarrier systemsPublication . Pacheco, A.; Carrasco, A. Rita; Vila-Concejo, A.; Ferreira, Óscar; Dias, J. A.Management of the interactions between social/economic interests and the coastal environment requires practical, interdisciplinary assessment techniques. Backbarrier systems are critical natural resources that provide both economic and social benefits. Activities such as aquaculture, fishing, shipping and port activities, sediment mining, salt extraction, and tourism all take place in these ecosystems but are often not compatible with each other. Therefore, a program to manage such a system must congregate many different types of activities and stakeholders with potentially conflicting interests. In this paper, we develop a proposed coastal management program (CMP), based on the driving-pressure-state-impact-response (DPSIR) framework and the integrated coastal management (ICM) cycle, for the management of channels located in backbarrier systems subject to dredging operations. The conceptual model involves the application of regional sediment management (RSM) actions and is applied to a case study, Faro Channel, located in the Ria Formosa backbarrier system in Algarve, Portugal. The CMP provides results on the interactivity between scientists, stakeholders, and decision-makers, by defining and clarifying the economic and environmental aspects of decision-making processes through the utilisation and measurement of local coastal indicators. The proposed CMP proved to be a useful tool in the definition of coastal management initiatives for channels inside backbarrier systems, since it identified management problems and allowed management solutions to be formulated. The CMP could be used within a broader ICM program but would also be effective when used on its own.
- Hydrodynamic changes imposed by tidal energy converters on extracting energy on a real case scenarioPublication . Pacheco, A.; Ferreira, ÓscarThe development on tidal turbine technology is ongoing with focus on several aspects, including hydrodynamics, operation and environment. Before considering an area for exploitation, tidal energy resource assessments in pre-feasibility energy extraction areas must include the relevant characteristics of the device to be used. The present paper uses the momentum source approach to represent a floatable tidal energy converter (TECs) in a coastal hydro-morphodynamic model and to perform model simulations utilising different TEC array schernes by quantifying the aggregated drag coefficient of the device array. Simulations for one-month periods with nested models were performed to evaluate the hydrodynamic impacts of energy extraction using as output parameters the reduction in velocity and water-level variation differences against a no-extraction scenario. The case study focuses on representing the deployment of floatable E35 Evopod TECs in Sanda Sound (South Kintyre, Argyll, Scotland). The range in power output values from the simulations clearly reflects the importance of choosing the location of the array, as slight changes in the location (of <1 km) can approximately double the potential power output. However, the doubling of the installed capacity of TECs doubles the mean velocity deficit and water level differences in the area surrounding the extraction point. These differences are amplified by a maximum factor of 4 during peak flood/ebb during spring tides. In the simulations, the drag coefficient is set to be constant, which represents a fixed operational state of the turbine, and is a limitation of coastal models of this type that cannot presently be solved. Nevertheless, the nesting of models with different resolutions, as presented in this paper, makes it possible to achieve continuous improvements in the accuracy of the quantification of momentum loss by representing turbine characteristics close to the scale of the turbine. (C) 2016 Elsevier Ltd. All rights reserved.
- On a new method to design solar photovoltaic systems in renewable energy communities: The case of Culatra Island (Ria Formosa, Portugal)Publication . Ewart, M.; Santos, J.; Pacheco, A.; Monteiro, Jânio; Sequeira, ClaudiaIslands must reach sustainable lifestyles by improving resources management and by getting accustomed to renewable energy sources. Culatra, a small Portuguese island, is actively increasing renewable energy penetration into local processes in order to be the first 100% sustainable Portuguese territory by 2030. Based on the electric consumption of Culatra, the objective of the present study is to project a photovoltaic unit composed of several sub-fields, each with a distinct orientation, in order to increase the self-consumption ratio while at the same time reducing the surplus of energy production, assessed by the self-sufficiency ratio criteria, resulting in a lower levelised cost of energy of the power system. To achieve this, MATLAB's implementation of a genetic algorithm was used to find the optimised set of orientations for a given load profile. The results indicate that it is possible to optimise the photovoltaic plant to reach a more continuous electricity generation through daytime, reducing the storage needs and increasing the value of photovoltaic systems. The method can be extended to other locations or demand curves, assisting on comparing different energy management strategies, and their respective advantages and disadvantages.
- Thresholds for morphological changes on an exposed sandy beach as a function of wave heightPublication . Almeida, L. P.; Ferreira, Óscar; Pacheco, A.A sandy beach in the south of Portugal (Faro beach, Ria Formosa) was surveyed from the dune crest seaward to 15 m depth 20 times over a period of 26 months.Wave time-series between surveys were analysed to obtain relationships between wave height and vertical profile variations and to define wave thresholds for important morphological changes. Results show that the active zone of the profile lies between 5 m above and 10·4 m below mean sea level, and that there are clear cross-shore differences in the vertical variability of the profile. Based on the pattern of vertical variability, the profile was divided into four cross-shore sectors: A (berm), 20–80 m from the profile origin; B (sub-tidal terrace), 80–170 m; C (long-shore bar), 170–360 m; and D, 360–700 m. The relationship between the modulus of the maximum vertical change in each sector and the 99th percentile of significant wave height between surveys was always significant. Calculated thresholds for significant wave height generating important morphological changes were 2·3 m in sector A, 3·2 m in sectors B and C, and 4·1 m in sector D.