پهنه بندی ریسک جزر و مدی خور ماهشهر با استفاده از gis

بندر ماهشهر یکی از بزرگترین بنادر جنوب کشور است که در معرض خطرات ناشی از پیشروی آب دریا از طریق خور ماهشهر قرار دارد. به منظور کاهش ریسک فرآیند جزر و مدی، مدیران بحران و طراحان شهری نیازمند یک طرح مناسب بر اساس نقشه پهنه‌‌بندی خطر در منطقه مورد مطالعه هستند. به هرحال نقشه پهنه‌‌بندی ریسک ناشی از فرآیند جزر و مدی به تنهایی کافی نیست؛ یک سیستم مفید به منظور افزایش کارایی نتایج ریسک ناشی از جزر و مد نیازمند مشخص کردن نقاط حساس و آسیب‌‌پذیر است. در این تحقیق، جهت کاهش ریسک فرآیند جزر و مدی به کمک نرم افزار hecgeoras حداکثر گسترش پهنه تحت پوشش در زمان مد مشخص شد. به منظور نیل به اهداف مورد نظر از داده‌‌های هیدروگرافی بستر و آمارواطلاعات ایستگاه‌‌ های هیدرومتری با دقت بالا استفاده شد. این پهنه مساحتی در حدود 944 هکتار را احاطه می‌کند که با توجه به شرایط خاک ‌شناسی منطقه که طی بازدیدهای صحرایی مشاهده شد، عملاً در هنگام فرآیند مد و در زمان بروز حوادث، کمک رسانی زمینی به دلیل چسبندگی بالای خاک منطقه مورد مطالعه، مختل می‌‌شود. با توجه به شرایط خاک شناسی منطقه، غرقاب شدن خاک منطقه باعث افزایش حالت چسبندگی خاک و به نوبه خود عاملی مضاعف در هنگام پیشروی آب دریا در کمک ‌رسانی‌‌ها خواهد بود. در این مطالعه مناطق حساس در معرض آسیب پیشروی آب، شناسایی و معرفی گردید. همچنین با بررسی نتایج و بازدیدهای زمینی، صحت نتایج بدست آمده با قطعیت بیشتری ارائه شد. بدین منظور در دو فصل زمستان 1395 و تابستان 1396 اقدام به بازدیدهای زمینی صورت گرفت تا با توجه به تغییرات اقلیمی نتایج بهتر و دقیق‌تری حاصل شود. در واقع تهیه نقشه پهنه جزر و مدی در مناطق ساحلی، برای کاهش ریسک فرآیند جزر و مدی بسیار موثر و مفید است.

Zoning tide risk in Mahshahr estuary using GIS

Extended Abstract Introduction 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.  Materials & Methods 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.  Results & Discussion 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 20162017 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 3metervariation 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.  Conclusion 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.