ارتباط بافت رسوبات و توسعه یافتگی خندق‌ها در سطح مخروط‌افکنه‌های جنوبی البرز شرقی (گرمسار سید آباد)

قطر ذرات رسوبات سطحی با فرایندهای غالب موثر در توسعه یافتگی و مورفولوژی سطحی لندفرمها ارتباط تنگاتنگی دارد. این پژوهش به ارتباط بافت رسوبات و توسعه یافتگی خندق های واقع در دشت سرهای جنوبی البرز شرقی به روش تحلیل آماری و با اندازه گیری قطر ذرات در چهار سایت مطالعاتی حدفاصل گرمسارسیدآباد پرداخته است. سایت ها با توجه به تفاوت ها و تشابهات مورفولوژی سطحی بر روی تصاویر و بازدیدهای میدانی انتخاب شده اند. نمونه های برداشت شده از بخش های ابتدایی، میانی، انتهایی و دیوارهگالی ها در آزمایشگاه توزین و پس از الک، نتایج توسط نرم افزار gradistat در قالب نمودارها و جداول استخراج و تحلیل شده اند. علاوه بر این، با برداشت 800 نمونه از باکس های 5 در 5 متری، شاخص پهن شدگی و مورفومتری آنها محاسبه شد. نتایج حاصله نشان می دهند که بافت سطحی رسوبات چند منشایی بوده و بیانگر تفاوت فرایندهای موثر در طی زمان هستند( در سایت 1 و 2 و 4، سنگفرش قلوه سنگی با نام قلوه سنگ ماسه ای است به جز سایت 3، که ماسه قلوه سنگی است. سایت یک و چهار، دو منشایی محاسبه شدند. سایت 2، سه منشایی و سایت 3، تک منشا.) کج شدگی زیاد، جورشدگی ضعیف و کشیدگی متفاوت بیانگر آن است که نوع و اندازه رسوب سطحی و عمقی گالی ها نتوانسته در همه سایت ها به طور کامل در توسعه یافتگی آنها موثر باشد. شاید در سایت 4، توسعه یافتگی گلی ها را فقط به عامل قطر رسوب منطقه و در سایت 2، عدم توسعه یافتگی گالی ها را بتوان به این عامل نسبت داد ولی در دو سایت دیگر یعنی سایت 1 و 3، به هیچ عنوان نمی توان توسعه یافتگی گالی ها را تنها به بافت و قطر رسوب منطقه نسبت داد بنابر این با توجه به تکتونیک فعال در منطقه عوامل تغییر سطح اساس بیش از خصوصیات فیزیکی رسوبات در این مسئله تاثیر گذار بوده اند.

Investigating the relation between sediments texture and gullies development in plains in the southern part of eastern Alborz using statistical analysis method (Case study: GarmsarSeyyed Abad)

Surface sediment’s particles diameter is closely related to dominant processes of developing surface morphology of landforms. This study investigates the relation between sediments texture and gullies development in southern plains of eastern Alborz using statistical analysis and measuring the particles’ diameter in four pilots in GarmsarSeyyed Abad, Iran. The pilot sites were selected based on differences and similarities of surface morphology using satellite imageries and field studies. Samples were collected from bottom, middle, and upper part of gullies. After measuring the weight and doing sieve analysis of representative samples, the results were analyzed using GRADISTAT software in the form of graphs and tables. In addition the morphometric index was measured collecting 800 samples from 5*5 m boxes. The results showed that the surface sediments are derived from multiple sources which indicates the difference of effective processes over time (sites 1, 2 and 4, covered by gravel pavement called sandy gravel, sited 3 covered by gravely sand. Site 1 and 4 are derived from two sources, site 2 is three sources, and site 3 is single source). Poorly sorted sediments indicate that the size and type of gully’s surface and deep sediments have not been able to fully affect on gullies development in all sites. Therefore, gullies development is not only related to sediments texture and diameter, but also consideration of more important factors such as tectonics processes is required in these sites.Keywords: Garmsar, Granulometry, Morphometry, Gully erosion.IntroductionGully erosion is one of the important and threatening factors of environmental resources balance and its sustainability. This type of erosion not only limited to abnormal changes in landscape, land degradation, soil loss, impossibility agricultural activities, and economic utilization of natural resources, but also will lead to increase flood hazards, sedimentation of farmlands and make them unsuitable. In most cases, gullies are considered as environmental and surface change indicators, which are of great importance due to their rapid development. Sometimes, gully development is so quick that can be controlled by any means.MethodologyThis research has been carried out in several steps: (a) at first, after data collection, digital images processing, and preparation of different maps using different softwares, the scope of the study area was divided into 4 sites. The sites were selected based on differences and similarities of surface morphology on satellite images and field studies. Total number of gullies is 35 in these sites, which one gully was selected and considered in each site. The analysis method is mainly based on comparing effective variables and analyzing their relationships. Sediment data collected during field studies were used to determine the percentage of soil particles (morphometry) in gullies. In this regard, three samples were taken from the bottom, middle, and upper sides across gullies’ length in each site. In order to investigate gullies’ depth changes, three samples were taken from each gully’s wall beginning 25%, middle 50%, and ending 75%. Totally, 24 samples were taken and put in special pockets with given title and number, which transferred to laboratory.Results and discussionSite 1: It consists of two sources of well sorted sediments, with sandy gravel texture, finegrained, and much stretched particles.Site 2: It consists of three sources of sediments with moderate sorting, sandy gravel texture, very finegrained, and much stretched particles.Site 3: It consists of one source of poorly sorted sediments, with gravely sand texture, finegrained, and moderate stretched particles.Site 4: It consists of two sources of poorly sorted sediments, with sandy gravel texture, very finegrained, and stretched particles.Site 1 and 4 have two modes, such as site 1 has more coarsegrained sediments in surface layer and mixed sediments in subsurface layer. Site 4 also includes coarsegrained sediments in surface layer and finegrained sediments in subsurface layer. On site 2, sediments are clearly derived from two different basins: a) a small and close basin with mediumsized sediments, and b) a large and far basin with very coarsegrained sediments. Finegrained sediments can also be seen under the above two layers, which refers to availability of third mode in this site. As seen in the area, site 3 consists of very finegrained pebbles, which derived from one source. All of these differences and inconsistencies in sorting, skewness, and kurtosis can be related to irregular, dispersed, energetic, and low energy flows during different periods on the lower playa, and the effect of tectonics and crosssectional or permanent upliftig, which have been seen in many different sites of the region.ConclusionThe type and size of surface and deep sedimentation of gullies have not been able to fully affect on gullies development in all sites. Perhaps, the sediment diameter of the region is the only reason of gully development in site 4, and nondevelopment of it in site 2.  In sites 1 and 3, gully development can not only be depended on sediment’s texture and diameter of the region, but also some of other more important factors including tectonics should also be considered in these sites in further researches.