COMPUTATION OF OPTIMUM WATER COURSE FLOW VELOCITY FOR THE SUSTAINABLE OPERATION OF A FISH REFUGE LATERALLY TO THE FLOW

Στην εργασία πραγματοποιήθηκαν εργαστηριακές μετρήσεις και ανάπτυξη μαθηματικών μοντέλων κυκλοφορίας και μεταφοράς συντηρητικού αιωρήματος για τον υπολογισμό της βέλτιστης ταχύτητας ροής υδατορεύματος για τη βιώσιμη λειτουργία ιχθυοδεξαμενής παράπλευρα της ροής, όπως εμφανίζεται στο ποτάμιο περιβάλλον με τις φυσικές ή τεχνητές δεξαμενές ιχθυοπληθυσμών παράπλευρα στην ροή του κύριου ρεύματος. Τα αποτελέσματα δείχνουν ότι όσον αφορά την παγίδευση αιωρουμένων στην ιχθυοδεξαμενή η καλύτερη περίπτωση (μικρότερη παγίδευση) είναι αυτή στην οποία η ταχύτητα του κυρίου ρεύματος είναι περίπου 0.30 m/s, η οποία βρίσκεται σε συμφωνία με την βέλτιστη ταχύτητα συνθηκών διαβίωσης των ψαριών.In this study the development of mathematical models of hydrodynamic circulation and matter transport and laboratory measurements for the computation of optimum watercourse flow velocity for the sustainable operation of a natural or artificial fish refuge laterally to the main riverine low were held. Concerning the trapping of the suspended particles in the fish reservoir, the results show, that the best case (with the minor trapping) corresponds to flow velocity of the main stream approximately 0.30 m/s, which is in very good agreement with the optimal living conditions of the fishes

Modelling of Environmental Parameters of a Harbor Basin in a Coastal Zone with a Seawall

Long straight seawalls along the coastal front are quite common, especially in cases of coastal cities. In this study in the middle of a coastal zone, a harbor basin in the form of an orthogonal area recessed to the waterfront is considered. A mole of variable length and position offers protection from waves. The renewal time of the waters and the self-purification capacity of the harbor under the influence of alongshore coastal currents of different intensity were examined. The effect of technical partial closing of the harbor’s entrance to the water renewal rate is examined in the present research. More specifically, the study was based on the use of a two dimensional, depth averaged hydrodynamic model which describes the water circulation along the coastal zone. For the solution of the equations of mass and momentum conservation, the method of finite differences was used. The adjustment and the validation of the reliability of the numerical model at a laboratory level were conducted in a recent research based on the use of PIV measurements which ensured a very good agreement between numerical and experimental results

Mathematical modelling of cohesive sediment transport in coastal basins. Application to Thermaikos Gulf

The aim of the present thesis is the study of cohesive sediment transport-incoastal basins, based on the development and application of a 3-dimensional mathematicalmodel. The necessary hydrodynamic data for the application of the sedimenttransport model are obtained from an existing, well documented and evaluated, hydrodynamicmodel. The transport model is based on the Tracer Method (Lagrange-Monte Carlo Method)Στόχος της εργασίας αυτής είναι η μελέτη της μεταφοράς συνεκτικών φερτώνυλών σε παράκτιες λεκάνες με τη βοήθεια ανάπτυξης και εφαρμογής ενός τρισδιάστατουμαθηματικού ομοιώματος. Τα απαραίτητα υδροδυναμικά δεδομένα για το μοντέλομεταφοράς λαμβάνονται από ένα υδροδυναμικό μοντέλο το οποίο έχει ήδη εφαρμοστείμε επιτυχία στο παρελθόν. Το μοντέλο μεταφοράς βασίζεται στη μέθοδο τουιχνηλάτη (μέθοδος Lagrange σε συνδυασμό με τη δειγματοληψία -Monte CarloMethod)

Turbulent Simulation of the Flow around Different Positions of Mussel Shocks

This study presents the results of laboratory experiments that were performed to simulate the positions of mussel shocks which were selected aiming at the optimization of the quality of mussels’ production in mussel farming areas. The mussel shocks were studied in natural scale. Velocity measurements were taken upstream of two successive mussel shocks and for different positions in relation to the central axis of the channel and different distances between the shocks for three different mean velocities. Based on the results of several numbers of experiments, the main conclusion of this study was that the position and the distance between the mussel shocks play a significant role to the quality of mussels’ production in mussel farming areas. This is due to the fact that the different distances between the mussel shocks influence the velocities and the eddies around them

Modelling studies on the processes that influence matter transfer on the Gulf of Thermaikos (NW Aegean Sea)

The development and application of a three-dimensional hydrodynamic and sediment transport model for the Gulf of Thermaikos, in the Northwestern Aegean Sea is presented. The processes that control the transfer of river-borne waters and fine-grained sediments are examined. These processes are: the overall basin circulation, the wind-driven flow, the buoyancy-driven flow that is associated with river plume dynamics and the sedimentation processes (flocculation, settling, deposition and erosion). We perform individual experiments, where only some of the processes are included, in order to study the different components of the transport mechanism separately. We also perform comprehensive experiments, where all processes are taken into account. It is found that a large percentage of the suspended particulate matter is deposited on the seabed of the Thermaikos Gulf and mainly near the river discharge sites. Although the sedimentation processes are of primary importance, the transport rates and pathways are greatly affected by the hydrodynamic processes that control circulation. Furthermore, the basin topography has a considerable impact on the transport, as the main rivers discharge near the narrow basin head and near areas of strong coastline curvature that act as sediment trapping zones

Experimental Study of the Effects of Heating or Cooling on the Water Surface in an Open Channel

In the present study, the effects of heating or cooling of the water surface in an open channel were investigated experimentally. The experiments were performed in a horizontal open channel, which was filled with water, to study the temperature and density fields of water, when a part of the surface receives or loses energy (heating or cooling). Initially, the effect of the water surface heating was investigated. The intensity of the thermal radiation was adjusted with the help of a dimmer and the produced velocities were measured in a two-dimensional field with the help of a camera and a dye (rhodamine). This method determined the range of flow velocities at different times in selected areas. This field will be time-varying until thermal equilibrium is reached and the flow becomes steady. The effect of the water surface cooling was then investigated in a similar way. The flow field in this case remains variable until the refrigerant load (ice columns) is finished. A waterproof digital pin thermometer was used to measure the temperature field and water density was measured by a densimeter. The results showed that the flow velocities developed by heating are much lower than those developed by cooling

Modelling of Environmental Parameters of a Harbor Basin in a Coastal Zone with a Seawall

Long straight seawalls along the coastal front are quite common, especially in cases of coastal cities. In this study in the middle of a coastal zone, a harbor basin in the form of an orthogonal area recessed to the waterfront is considered. A mole of variable length and position offers protection from waves. The renewal time of the waters and the self-purification capacity of the harbor under the influence of alongshore coastal currents of different intensity were examined. The effect of technical partial closing of the harbor’s entrance to the water renewal rate is examined in the present research. More specifically, the study was based on the use of a two dimensional, depth averaged hydrodynamic model which describes the water circulation along the coastal zone. For the solution of the equations of mass and momentum conservation, the method of finite differences was used. The adjustment and the validation of the reliability of the numerical model at a laboratory level were conducted in a recent research based on the use of PIV measurements which ensured a very good agreement between numerical and experimental results

Aspects of Mussel-Farming Activity in Chalastra, Thermaikos Gulf, Greece: An Effort to Untie a Management Gordian Knot

Small-scale mussel farming in the coastal area of Chalastra (Thermaikos Gulf, Greece) has faced major problems during the last decade due to environmental limitations and to institutional constraints imposed by the absence of local planning and development policies. The aim of our work was to demonstrate crucial aspects of implementing the Systems Approach Framework (SAF) in the area, and more specifically to explain: (a) the key parts of a bioeconomic model that constitutes the basis of a draft management tool, (b) the results of several investigative scenarios examined through the management tool, and (c) the stakeholders' feedback through the participative procedures. The goal was to evaluate the effects of the SAF implementation on the communication between scientists, policy makers, and local stakeholders. The scenarios refer to alternative farming techniques and different environmental conditions, and examine the effects of institutional deficiencies in qualitative and quantitative ways, regarding the sustainability of the activity. The selection of the scenarios was directed from the need to provide a dialogue platform between the conflicting stakeholders. The results clearly demonstrate the effects of mussel-farming techniques on mussel production, as well as the impacts of environmental conditions, human decisions, and institutional choices on the regional (and individual) economic welfare. In the bottom line, the value of the SAF is demonstrated through the apprehension of the policy issue, its impacts, and the alternative management perspectives, as well as through the establishment of a multidimensional collaboration group for the area, which is essential for the further development of the management tool and the implementation of an integrated management policy