جستجوی مقالات مرتبط با کلیدواژه "جزر و مد" در نشریات گروه "جغرافیا"

General circulation of Persian Gulf has a cyclonic pattern that affected by tide, wind stress and thermohaline force. Although tidal force is very effective in values of current speed, but thermohaline force is dominant in long time because tidal forcing has a short period and returning nature. Tide and density parameters are important in navigating and shipping, especially when ships approaching the shore and shallow water to determine the drainage of them. In this study using the Mike model based on the three-dimensional solution of the Navier Stokes equations, assumption of incompressibility, Boussinesq aproximation, and hydrostatic pressure, Persian Gulf circulation modelled. After model stability, the effects of tidal force on horizontal and vertical distribution of density were investigated. Results show that forcing of tide caused current direction be regular and without tidal force, wind stress dominates on isopycnal and turbulent pattern forms in sea surface layer especially in cool season. Also, with the elimination of the tide effect, the velocity of current is reduced to 75% and the water density is increased to 1-2 kg/m3. Density profile show that the Persian Gulf is a baroclinic environment and it is stronger in cool season relative to warm season. The impact of forces is not the same in different regions of the Persian Gulf, so that the effects on the change in density in the Strait of Hormuz are more perceptible and moving inward to the Gulf, the intensity of its effect is reduced.

As one of the largest ports in southern Iran,MahshahrPort faces the risk of seawater intrusion from Mahshahr estuary. Mahshahr and Mousa estuary form an 86 kilometerwaterway. Midday mixed tide is dominant throughout this waterway. Moving towards the vertex of the estuary, this dominance of the midday tidebecomes much more evident. Considering an average depth of 38.4 m, midday tidal wave of M2 with an approximate wavelength of 860 km can be reinforced in this waterway. Grounding of boats and otherammunitions in the basin of Mahshahr port (betweenMajidiyeh garrison and the Persian Gulf) was one of the most important issues during the Imposed War.Mahshahrestuary is the only possible way to access the Persian Gulf fromImam Khomeini port and Majidiyehnaval garrison. From a military perspective,Mahshahrestuary has a special feature that can be considered as a strategic factor and used in various types of active and passive defense. In spite of the shallowness of its internal parts,it is considered to be a safe haven for small vesselsin times of crisis and air attacks. Sometimes, it is critical to use these estuaries and their navigable waterways as the main route for transportation of military weapons, medical aid, and rescue services. Crisis managers and urban planners need an appropriate plan based on risk map of the study areato reduce the risk of tidal process. However, zoning tidal process and mapping its risk are not enough by their own: a useful system needs toidentify sensitive and vulnerable pointsto increase the efficiency of tide risk zoning.

Seeking to reduce the risk of tidal process,the present study determinesmaximum level of development in areas covered during high tides usingHecgeoras software. In order to achieve the goals, hydrographic data of the substrate was used along with information and statistics received from high accuracy hydrometric stations. This zonesurrounds an area of around 944 hectares. Field visits indicate thatduring tidal process, soil conditions in the study area hampers sending emergency aids using land routes.Considering the conditions and structures inMahshahr estuary and the tide zone in the study area, investigating geology of the study area seems necessary.

Considering the soil conditions in the study area, the highest level of soil flooding was observed during high tide. This increasessoil adhesion, affects water intrusion, and hampers sending aids. Critical areas in danger of water intrusion from the estuary (such as Mahshahr gas reservoirs and Majidieh military garrison) were identified in the present study. Moreover, results were investigated and land visits were performed to present accurate and reliable results. Land visits were carried out during 2016-2017 winter and 2017 summer in order to achieve better and more accurate results based on the climatic changes. Investigating the recorded level of water in the study area shows up to 3-metervariation in the water level of Mahshahr estuary. Necessary decisions regardingthe use of different types of vessels, and passive/active defenses can be made in accordance with water level fluctuations and specified times for each water level. During local visits performed for quantitative analysis of results, soil type and its role in passive defense were also discussed.

Field studies and observations in the study area indicated that 1) dominant soil type of the region is a highly adhesive type with a high clay content; 2) during tide time, soil flooding results in increased adhesion of soil and practically hampers movements of ammunition; 3) In summer and winter, water level changes repeatedly and thus, necessary measures shall be considered for military programs in accordance with the time in which water fluctuations occur. Although the depth of water in the study area is significant, it should be noted that Mahshahr estuary finally reaches an urban area, and thus can be used for military actions. In fact, mapping tide zone is a very effective method for reducing the risk of tidal process in coastal areas.

Maritime territories and quasi-territories are, in fact, continuation of territories underwater,formedbased on rules and principles governing political systems,international law and international relationsin maritime environment.Place making, territoriality, delimitation and demarcation of territories in the seas are performed based on geographical factors (particularly physical geography). As one of many different physical geographic factors, tideplays a decisive role in maritime delimitation and territoriality. It is considered as the basis upon which boundaries of different maritime territories and quasi-territories in different countriesare demarcated and delimited and formalnautical maps are drawn. Each country of the worldapplies a different basisfor determining low water lineand thisresults in many issues and challenges in maritime territoriality. Meanwhile, sea level has risen due toclimate changesand is expected to increase in the future. Thiswill also affect the above mentioned phenomenon, and may cause serious challenges for demarcation of the existing boundaries. Thus, the present study employs a descriptive-analytical method toinvestigate the role and significance of tides in maritime delimitation andanalyze the impact of sea levelrise on delimitationand maritime territoriality process. 

The present study is an applied research following a descriptive-analytical method. Related data was collected through library and internet-based methods and the research follows a qualitative method of analysis. Moreover, GIS and mathematical map calculator known as the “Raster Calculator” were used to draw the maps required for therise of sea levels. Based on the existing scenarios and their average values,the present study considers a two-meter rise for the sea level rise by the end of the 21st century. 

Tideis the most significant factor based on which baselines are drawn. Setting low water line as a fixed basisused for delimitation of maritime territories and quasi-territories is only possible ifcoastline is stabilized at one level or in other words at a definite plate during tide. This function is carried out by the tidal datum. Datum is the reference level based on which all depths andcorresponding elevations are plotted. Therefore, tides play a significant role in determining the Law of the Sea. On flat coastlines, baseline is determined based on the low water line. On dented and jagged beaches, the base points are also determined according to the same phenomenon. Moreover, some features such as the low–tide elevations and islands are also identified based on the datum used. Selection of low water line (as opposed to high water line) leads outer limits of the territorial sea and consequently other areas toward the sea. This will expandmaritime area under sovereignty and jurisdiction of different countries. The country which uses a lower datum will expand its marine sovereignty and jurisdiction. In Persian sources, terms such as the lowest tide line have been used mistakenly as a translation for the term “Low Water line” stipulated in Article 5 of the 1982 Convention. This is while lowest tide is only one type of low water lines, and though this concept plays the most important role in maritime territoriality, no clear reference has been mentioned for datum in the 1982 Convention. The convention stipulates thatdatum used in the official nautical charts published by different states is the tidal datum based on which normal baseline must be defined. Although the International Hydrographic Organization has proposed the lowest astronomical tide as the basis for determining the datum, there is a major difference between states in this regard and they use a variety of tidal base lines. However, coastal countries usually prefer to use the lowest datum. It seems that sea level rise, as the most important phenomenon resulting from climate change, has significant impacts on tides and boundaries delimitated based on tides. This is because low water line may retreat due to sea level rise, and as a result base points upon which baselines are drawn, along with marine territories and quasi-territories might also move closer to the land. However, states which have based their datum on higher averages oflow water will encounter fewer challenges caused by the retreating baseline compared to those that have selected the lowest low water line. However, evaluating a two-meter rise in sea level by the end of the 21st century shows that in different coastal regions of the world,the impact of sea level rise on low water line is not balanced and similar. Thus, given the spatial-geographical variations, only flat regions of the world will encounter submersion of coastlines and retreating low-water line.

Results indicate that sea level rise has dramatically changed tides and will challenge Political Geography of the Sea. However, a two-meter sea levelrise will severely affect tides in areas facing coastal retreat, and since normal baselines are drawn based on this geographic factor, a retreat in those baseline should also be expected. In case ofstraight baselines, if base points immerse due to two-meter rise in sea level, these lines will also retreat. Yet, this largely dependson the datum considered for drawing the baselines. On the other hand, the approach used bydifferent states, especially in areas in which maritime boundaries have been delimited, shows that low-water line drawn onformal maps is more referable than the actual low-water line and, therefore, maps can play a stabilizing role as the most important geographic instrumentin the future.

As fluctuations of ocean and sea levels on coasts especially on coastal shapes and also process of morphogenesis of it, study of these fluctuations and its causes is needed. Level fluctuations can be divided to short-term and long-term. Waves derived from wind, pressure from metrological elements and temperature are short-term elements and surface winds are most important among others on temporary sea level. Water level changes in Hormuz strait area has been studied based on the data obtained from Bandar Abbass station during 1990-1998 periods. The length of Persian Gulf as a branch of The Indian Ocean is about 990 km, its maximum width is about 330 km (at Hormuz strait about 60 km) and its depth is about 100 m. The Persian Gulf is connected to Oman Sea via Hormuz strait.Materials and MethodsIn the present study, first of all, correlations between atmospheric elements such as pressure, temperature and the density of wind energy (independent variables) with sea level changes are studied by drawing the graphs and then linear regression graphs of pressure and temperature and the density of wind energy (seasonal) with sea level changes for a 9-year period (1990-1998) and their correlation coefficient are calculated. Furthermore, wind energy calculated using empirical relationships in the area and equation of sea level changes prediction has beenobtained for the coast of this region.Results and discussionSea level changes: the results of the present study show that sea level changes can be divided into two types in the coast of this region. Temporary changes lasting from a few hours to several days and permanent changes that is seasonal and may last for several months. Air pressure changes: air pressure changes at sea level is inversely related to the water level changes in this region that means that with decreasing air pressure at sea level, water level increases and vice versa (pressureinversion effect). Using data from meteorological stations and tidal station in the region, it is distinguished that there is a strong negative correlation (-0.83) between air pressure and sea level.Effects of air temperature: air temperature has two contrastive and seasonal effects on water level. There is a strong positive correlation (0. 812) between air temperature and sea level in Bandar Abbass. In summer, air temperature increase due to seawater heating causes reduction in seawater volume, increasing salinity and density of seawater as well as increasing the volume and reduction in seawater density due to volume expansionof seawater. In winter, air temperature decrease due to seawater temperature reduction causes reduction in seawater volume, increasing the density of surface waters due to volume contraction of seawater. Effects of wind characteristics: it is distinguished that wind velocity and consequently wind power is low in the Spring based on average of wind velocity and wind power graphs in different months of the year. In summer, the power and velocity of wind increase and in autumn the increasing status will continue and in the winter they reach to a peak. In general, whenever the wind velocity was high, the wind power increased too. By studying the simultaneous wind velocity variations, the density of wind energy with sea level changes in this region, it is distinguished that sea level coming up by the start of wind (landward) and reaches to a peak and sea level retard with wind velocity decrease and come back to its former level.ConclusionIt would be concluded that there is significant correlations between temperature and pressure with sea level fluctuations and these fluctuations are seasonal. With maximum value in summer and minimum in spring and winter. When the wind starts to blow, sea levels swells and reach to maximum.An average of correlation coefficient for Bandar Abbass station was 0.733 that showed the relation between wind velocity and sea level fluctuations; these fluctuations will influence on erosion process into delta in coastal

There are many estuaries on the Oman Sea and the Persian Gulf but Tang estuary is one of incomparable with its shape and occurrence course which is located in the east part of Tang port on Mokran coast of Iran. The geomorphology phenomena around this estuary is one of incomparable with its shape and occurrence course which is located in the east part of Tang port on Mokran coast of Iran. The geomorphology phenomena around this estuary concerning to geomorphology are so important and some conditional geomorphic like "Toumboloy of Tang" are unique.Recognition of morphologic situations of the region of case study either its shape and circumstances or genesis and appearance are most important and has positive effects in making basic installation and improve hunting and fishing industry in the region.In this article it will be tried recognizing phenomea and important geomorphologic conditions based on field experiences and objective observations in the region because the studied sources and accomplished works are so little.