برآورد زمان و سرعت جابجایی رواناب ها در سطوح شیب دار نواحی کوهستانی مطالعه موردی : حوضه آبریز اوجان چای

نوع مقاله: مقاله پژوهشی

نویسندگان

دانشگاه تبریز

چکیده

جریان رواناب ها در سطوح شیب دارعلت اصلی آشفتگی دامنه ها و تولید رسوب برای رودخانه ها هستند.هرچه سرعت جابجایی رواناب ها بیشتر و زمان تمرکز آنها کمتر باشد،نشان دهنده حساسیت سطوح برای سایش بیشتر توسط آب های جاری است.با بررسی زمان تمرکز و سرعت رواناب ها در سطوح شیب دار می توان پتانسیل ایجاد سیلاب ها و رسوب زایی دامنه ها را مورد بررسی قرار داد .حوضه اوجان چای که در دامنه های شرقی کوهستان سهند قرارگرفته است ،دارای دامنه هایی است که سطح آنها توسط آبکندهای متعددی بریده شده و یکی از رسوب زاترین زیرحوضه های آجی چای محسوب می شود. در این مقاله برای برآورد زمان تمرکز رواناب سطحی در سطوح دامنه های حوضه اوجان چای ،سطح حوضه بر حسب محدوده های جمع آوری به بیش از 140 زیرحوضه کوچک تقسیم بندی شده و تمامی محاسبات با    استفاده از داده های برگرفته از ویژگی های این زیرحوضه ها صورت گرفته است.در این محاسبات،بخشی از اطلاعات از نقشه های رقومی گرفته شده و بخشی از داده های مورد نیاز از بررسی ها و سنجش های میدانی بدست آمده است .برای برآورد زمان تمرکز و سرعت جابجایی رواناب ها در سطح این زیرحوضه از روابط مختلفی استفاده شده است(Tc1,Tc,Tti,Tt,Tl1,V1,V,.. )که درآنها متغیرهای بارش ،شیب،نوع آبراهه ها و...دخیل داده شده است.نتایج حاصل از بکارگیری این روابط در حوضه اوجان چای نشان می دهدکه میزان تمرکز رواناب ها در آبراهه ها در بخش های شمالی و جنوبی حوضه که شیب دامنه ها زیاد است بالامی باشد.نتایج بررسی ها حاکی از این است که سرعت جابجایی رواناب ها با توجه به نوع متغیرهایی مورد بررسی مانند،شیب ،نوع بارش ،نوع سازندهای سطحی و نوع آبراهه ها در بخش های مختلف حوضه مورد مطالعه ،بسیار متفاوت است .

کلیدواژه‌ها


عنوان مقاله [English]

The Time and Runoff velocity Estimation on slopes of Ojan Chay watershed

نویسندگان [English]

  • maryam bayati
  • fariba karami
چکیده [English]

The runoff response from arid and semi-arid catchments is a problem that is difficult to approach and is not satisfactorily nswered yet. One of the reasons is that runoff events in dry regions are rare, and difficult to observe and to monitor. Another reason is the fact that overland flow, which plays a crucial role in dry watersheds, is difficult and complicated to quantify Channel incision is part of  denudation,  drainge -network development and landscape evolution. The causes of river channel are numerous. It is generally agreed that runoff generation in drylands is caused by infiltration excess or Hortonian overland flow. Partial area contribution and variably contributing areas are a phenomenon in drylands as well The focuses on time factors is very important in practical study and its bring in modeling is fundamental. Slope erosion by runoff  can be investigating in related to time scale . Disturbance  of  slope surface by runoff can be  explanation in during time. When  flow water on slope is faster and  time concentration is short ,surface  potential for erosion is very high. In this conditions is shaping liner erosion  forms  on slopes, such as ,  Ravin , Gully and Rill. In these slopes also is occurred flash flood . Ojhan  Chay  catchament located in the eastern slopes of  Sahand   mountain .Load sediments is very high in this catchement .The purpose of this paper  therefore is measurement of runoff concentration time and is estimated  flow velocity on slopes.
 
Study area
  Ojan Chay  catchament is one sub-basin  that located on  eastern slopes of  Shand  mountain .This basin is located  at  37° 54'  N to 37° 44 ' and from 46° 50' to 46° 31'.Ochan  River is one reach of  Achy Chay that it at western site adjacent to Saaied Abad Sub-basin, and at eastern site is adjacent to other sub-basin. Ojan basin is experience intensive  liner  erosion  and  all forms of liner erosion is created  on  foot and sharp slope .Geology and lithology of this basin is  various .Sediment and Igneous rocks formed base of this basin. Thickness of these rocks is high .Diorit ,Volcano sediments  ,Ash ,Igenberits  are sample  of  these  rocks in Ojan basin. Miocence  sediment rocks are contained of Marl-Gyps  and Sandstone. Quaternery sediments as trase and alluvial fans  is  in  northern site of basin. This formation is made of lay ,clay and sand . 
Material and Methods
   In order to estimation  of  runoff  time  concentration on  slope  surface  in  Ojan Chay  basin ,is  divided to 140 parts and all accounts is made  in  these parts . Many data  is obtained  from  these sub-basin properties .Some data is obtained from  digit maps and others data is obtained from field studies.In this paper, we focused on time concentration estimation by used of Tc1,Tti  and Tc. Tci ,Tti and Tc is defined in terms of  channel Lengths ,storm and slope .Where l is channel length ,S is slope ,p is storm  and  n  is  Maning Index. We  used in Tl1 , maning index table .  Velocity of flow is estimated by used of V1, V,Tt,T1,... V1,V are defined in term of  slope ,channel length,storm ,k (is constant that related to flow type ).The results are show that on maps .
Results and Discussion
   Surface flow that on slope is concentrating and is flowing  in single channel ,have very high power for erosion .When surface material are suitable to erosion ,is created liner erosion forms ,such as ,Rill,Gully ,...,on slope by flow . River Ojan  have very high bar load in water .All parts of these sediments are due to slope erosion by rill and gully erosion on slope and footslopes. Ojan Basin is a mountainous basin ,for this reason ,slope factor play main role in erosion .Central  and northwestern site of Ojan slope is high because  erosion in these sites is intensive . In study area  time concentration is related to many factors .slope ,length of channel ,storm are affects factors on slope erosion. In this study these factors is considered .The results of investigation on time concentration show that rate of time concentration is high  in central   and northwestern site of Ojan slope.In this site surface of slope is disturbance by rills and gullies .In these  areas  lengths of channel is short ,such as , rills. Water flow due to shower is moving quick. Basins these single channel are not big and these shapes are  round that water is flow into channel that is located  at foot slope.    Investigation  on velocity of runoff in Ojan (by  V1) show that flow  velocity is under 10 second in all parts of basin .In this method ,channel length play very important role in velocity  of  flow on slope ,therefore  short rills is made on slope . Velocity of flow is quick on slope that rills is created .              
Conclusion
  Runoff on slope is creating  initial channels and then is disturbance surface and delivered sediment to foot slope channels. Sensitiveness of surfaces for intensive erosion is high when flow velocity is high and time concentration is low. In these  slope we can seen vary forms of liner erosion ,such as ,rills, gullies,....Also in these slope is experience flash floods. Some parts of rain water is not influences into soils ,because many parts of water is reduced to runoff. Investigation is suggested that surface materials and topographical factors are suitable to liner erosion ,short channels are made by concentrated water . Channels have high depth in foot slope in Ojan Chay. At upslope  area of basin is not vast. Length of channel have short in these site. Due to , time  concentration is short .When area at upslope is vast , rill is not created ,but gully is created ,in foot slopes. In  these condition ,slopes is gentle and velocity of flow is slow. Bcause  area is vast and therefore amount of water is high ,gullies big and deep.  

کلیدواژه‌ها [English]

  • Time concentration
  • runoff
  • Channel
  • Ojan Chay Basin