شبيه‎سازي ديناميك امواج و انتقال ماسه در سواحل درياي خزر (محدوده خليج گرگان)

Simulation of Waves Dynamics and Sand Transport in the Caspian Sea (Area of Gorgan Bay)

ماسه‎هاي ساحلي، عموماً منشا رودخانه‎اي داشته و تحت تاثير ديناميك امواج و حركات آب دريا، در طول خط ساحلي توزيع مي‎شوند. رودخانه‎هاي سفيدرود، هراز، بابلرود، تجن و گرگانرود، سهم عمده‎اي در تدارك رسوب به درياي خزر در سواحل خزر جنوبي دارند. منطقه مورد مطالعه در اين پژوهش، بخش جنوب شرق درياي خزر، در محدوده خليج گرگان با بيش از 60 كيلومتر طول است. هدف از اين پژوهش بررسي راستاي امواج غالب و نحوه توليد جريان در امتداد ساحل است كه درنهايت بر توزيع ذرات ماسه در طول خط ساحلي موثر است. براي دست‎يابي به اين هدف، از داده‎هاي باد امواج و نيز نقشه‎هاي توپوگرافي و عمق‎سنجي كه ابزار و داده‎هاي اصلي پژوهش به‎شمار مي‎روند، استفاده شده است. با بهره‎مندي از داده‎هاي باد و امواج، به‎ترتيب گلبادها و گل‎موج‎هاي محدوده پژوهش ترسيم و با توجه به راستا و فراواني امواج، مدل‎سازي امواج در نرم‎افزار مايك 21 انجام شد. در ادامه، داده‎هاي امواج براي توليد مدل جريان‎هاي موازي ساحل در منطقه شكست مورد استفاده قرار گرفتند و درنهايت، مدل‎سازي انتقال ماسه در خط ساحلي تجزيه‎وتحليل شد. نتايج نشان مي‎دهد كه راستاي غالب امواج از جهات شمال غرب، موجب توزيع و جابه‎جايي ماسه‎ها به‎سمت شرق شده است. توسعه و عريض‎شدن زبانه ماسه‎اي ميانكاله به‎سمت شرق و ايجاد خليج گرگان در پشت زبانه ماسه‎اي مذكور با برايند توليد و توزيع رسوب در راستاي غرب به شرق، در مدل نرم‎افزاري مايك 21 برازش نشان مي‎دهد.

Introduction The study area are located in 53°23 to 54° 5 E and 36°47 to 36°55 N in south of Caspian sea. The study area encompasses Sand spit called Miankaleh peninsula in Gorgan province, between Caspian sea and Gorgan Bay, a narrow strip with approximate length 65 KM and variable width between1/2 to 3/6 KM with Semi-closed basin Gorgan Bay with average length and average width of 60 to 12 KM. Due to the relationship between Gorgan Bay from the Caspian Sea, Sea wave energy is available in the form weak. Gorgan Bay area most affected by internal basin processes by rivers of Garehsou and Gorganrood that According to a deposition rate is very prominent and obvious The role of the Gorganrood river near the mouth of the of Gorgan Bay. Methodology This study is based on an analytical method. during this study has been Analysis of sediment transport with field observations and sampling of coastal sand with data from synoptic stations of Gorgan and waverecorder Amir Abad Port. Beginning, demarcation and location of the watershed area is characterized by using topographic maps with 1/250000& 1/50000 scale. The data used in this study, are were data from waves (Waverecorder Amir Abad 2009-2012) with speed and direction of wind daily from synoptic stations of Gorgan (2000-2008). Then with the correction process and information Processing Was drew Windrose and Waverose during the yaers. The next step in MIKE21 Software is modelling by Models of Spectral Wind-Wave, Sea Hydrodynamic, Sand Transportation. To determine the diameter of the particles, one of the input data in Sand transport model, 5 numbers of sand samples collected along the coastline and transferred to the laboratory is done classification of sand particles using Shaker and the results were analyzed in software Gradistat. Finally, Using data and their modeling in MIKE21 Software were Simulate the behavior of waves and ocean currents in order to analysis of transport sand along the shoreline. Results and Discussion Software analysis of selected samples indicate that The most Sand spit Created of Gorgan Bay is composed of fine sand and this Show low waves strength in The transport of coarse sand after the surf of the coastal zone along of sand spit. Modelling of Spectral Wind-Wave shows the average of waves of the West that reduced wave height the waves are inclined toward the north line with waves reaching the regional surf and low bed depth. Then did Simulation sand transport in shallow waters close to the coastline of the Gorgan Bay using Modelling of Spectral Wind-Wave & Sea Hydrodynamic. Modelling of sand transport shows significant changes in bedload waters near the coastline. Deep area in the sea not much change in bed load and remains unchanged Positive or negative approximately. but is allocated near the coastline, Removal and move of sand more of their. The rate of change on the sea bed in terms of meters in day implies the removal of coastal sand in shallow waters by coastal currents, waves and rivers. The rate of deep water tends towards the positive numbers that is showes the accumulation of sand in the direction perpendicular to the shoreline in deep water. Simulation sand transport rate in the direction perpendicular to the shoreline shows that Changes is very high within the shallow waters of the coastal seabed that is associated with Daily scale by changing the pattern of the bed profile. As regards to positive change sediment transport will be more along the sand spit, this Explain the evolution of sand spit with Sediment moving West to East in Long time. Conclusion The results of the modeling software MIKE 21, Indicate the general trend of sand transport to the East. Although due to a fundamental change in the direction of the dominant waves Sectors East and North East is seen tend to drift of sediments towards the West at some days of the year. Sediment transported to the shoreline under the prevailing west and northwest winds and waves moves in terms of particle size, with the current move, creep or suspension in surfzone of Coastline in all seasons. Due to the curvature of the coastline and with Considering the angle of approach of the waves along the coast, only the waves of the shoreline angle of 35 degrees and further, can participate in the production process and the growing waves. In autumn and early winter waves are dominant along the North East and East Due to the dominance of the Siberian high-pressure And entry a cold, dry winds from the North East. Except for the period, in other cases, are important the dominant wave direction of West, North West and North. High frequency waves from the West and Northwest to the northeast Waves is created coastal currents along the coast in the West to the East and is facilitates Predominant movement of sediment along the shoreline toward the East. Growth of sand spit the Miankaleh peninsula from Estuaries of Nekarood river toward of the East implies the above argument. Maximum wave heights is Close the mouth of the Gulf of Gorgan in the southeast corner of the Caspian Sea to 0/4 meters. Waves with low high, with Coastal currents along the West to the East, Approached the mouth of the bay cannot to drift Sandy sediment inward Gorgan Bay. Narrow mouth of the bay with slash and backslash of Continuous wave, Cause of creating change is in top of Miankaleh sand spit to the NNE that Corresponded with general cuurent in south of Caspian sea.