Journal of Spatial Analysis Environmental Hazards
تحلیل فضایی مخاطرات محیطی
Journal of Spatial Analysis Environmental Hazards
Literature & Humanities
http://jsaeh.khu.ac.ir
1
admin
2423-7892
2588-5146
10.61186/jsaeh
fa
jalali
1400
12
1
gregorian
2022
3
1
8
4
online
1
fulltext
fa
تحلیل خطر فرسایش کناره رود با روش BEHI ، مطالعه موردی: رودخانه سجادرود، استان مازندران
Streambank erosion hazard analysis by BEHI method, case study: Sajadroud stream, Mazandaran province
تخصصي
Special
پژوهشي
Research
فرسایش کناره رود یک فرایند طبیعی و پیچیده است و تخمین فرسایش پذیری کناره رود با مشکلاتی همراه است. در این تحقیق، شاخص خطر فرسایش کناره رود (<span dir="LTR">BEHI</span>) و روش <span dir="LTR">BEHI</span> اصلاح شده، در امتداد بخشی از رودخانه سجادرود در استان مازندران مورد بررسی قرار گرفت. شاخصهای مختلف <span dir="LTR">BEHI</span> اصلی شامل نسبت ارتفاع کناره به ارتفاع لبالبی، عمق ریشه، تراکم ریشه، زاویه کناره، حفاظت کناره، ترکیب رسوبات کرانه و لایهبندی آنها در 4 بازه و 36 سایت مورد اندازهگیری قرار گرفتند. 92 درصد سایتهای مورد مطالعه در طبقات فرسایشی زیاد و خیلی زیاد قرار گرفتند. روش <span dir="LTR">BEHI</span> اصلاح شده نسبت به <span dir="LTR">BEHI</span> اصلی برآورد بالاتری (اغراق آمیز) داشته است. امتیاز کل دو روش <span dir="LTR">BEHI</span> با ضریب همبستگی 0.21 نشان دهنده ارتباط ضعیف بین نتایج این دو روش است. ضرایب رگرسیونی شاخصهای <span dir="LTR">BEHI</span> نشان میدهد که حفاظت کناره و نسبت ارتفاع کناره به ارتفاع لبالبی بیشترین تاثیر را در فرسایشپذیری کناره رود داشتهاند. در بازههای مورد مطالعه که رودخانه فروسایی شده است (تیپ <span dir="LTR">A</span>) به علت افزایش ابعاد کانال و ظرفیت انتقال جریان، رسوبات درشتتر به عنوان عامل حفاظتی در پای کناره عمل نموده و فرسایشپذیری کناره در دبی لبالبی کاهش مییابد. اما طی جریانهای سیلابی با دوره بازگشت طولانیتر فرسایشپذیری به علت ارتفاع زیاد کناره، عمق و تراکم کم ریشه و رسوبات منفصل آبرفتی افزایش مییابد.
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Streambank erosion hazard analysis by BEHI method, case study: Sajadroud stream, Mazandaran province</span></span></b></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Extended Abstract</span></span></span></b></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Introduction</span></span></span></b></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">River bank erosion is a complex natural process and plays an important role in the dynamic equilibrium of the river. The amount of river bank erosion affects the river plan, cross section and dimensions of the river and is the main factor controlling channel migration and the evolution of the river planform. This research was conducted with two main objectives, which are: 1. River bank erosion susceptibility analysis in incised rivers in mountainous areas, 2. Comparison of river bank erodibility with two methods original BEHI and modified BEHI.</span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Method</span></span></span></b></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">In this study, Bank Erosion Hazard Index (BEHI) and the modified BEHI method along a part of Sajadrood Stream in Mazandaran province have been investigated. The original BEHI (Rosgen, 1996, 2001) evaluates the river bank erosion field measurements. In this method, several parameters are measured, including bank height, Bankfull height, bank angle, root depth, root density, surface protection, bank material structure and stratification. From this parameters, the bank angle and height, root depth can be measured, but indicators such as plant root density and surface protection are visually estimated as a percentage. The score of each index varies from 1 to 10. The total scores of all indicators are classified into 6 groups: very low, low, medium, high, very high and extreme.</span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Newton and Drenten (2015) Based on the modified BEHI proposed a protocol for estimating the river bank erosion. In this protocol, the lengths of similar riverbanks are first defined as a uniform section of bank. These uniform sections can be identified due to differences in bank slope, differences in bank material and a break in vegetation. The characteristics of uniform sections are then evaluated in a pre-screening questionnaire consisting of six questions. If the answer to two or more questions is "yes", there is a high probability of erosion and the BEHI evaluation will be performed. Otherwise, the measurement will not be taken because the erosion is low or very low.</span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Result and discussion</span></span></span></b></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">The study area was divided into four reaches and 36 sites were surveyed. These river reaches have a deep bed (incised), high slope, low sinuosity, low width to depth ratio and predominant cobble sediments in the bed. They are in type A3 according to the Rosgen River classification. The height of the banks of the stream is high and its average is 2.6 meters with a minimum and a maximum of 0.4 to 9.7 meters. The average height of bankfull was 0.44 meters and varied from 0.15 to 0.85 meters. Hence, the ratio of bank height to bankfull height has been high. The root depth of plants was low and their average was 0.34 meters. Root density of plants was also low and averaged 5.7% The stream bank angle is measured from 31 to 90 degrees and an average of 51degree. The percentage of surface protection varied between 25 and 65% and averaged 42%. From a total of 36 sites, 8% are in the medium group, 39% in the high erosion category, 45% in the very high erosion group and 8% in the extreme erosion category.</span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Among the various variables, the β coefficients of the surface protection index and the ratio of bank height to bankfull height were -0.62 and 0.51, respectively. To evaluate the modified BEHI method, all reaches were first examined according to the pre-screening table and more than two "yes" answers were confirmed for each reach. In the modified BEHI method, 26 out of 36 sites were in the erosion group. But in the original BEHI method, 16 sites are in a very high class. The total score of the studied sites was evaluated by two BEHI methods with Pearson correlation coefficients, which obtained a coefficient of 0.21 and shows a relatively low correlation.</span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Conclusion</span></span></span></b></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Sajadrood stream has high and steep banks due to the incision created in the channel bed. The deposition of large boulders at the toe of the streambank has caused its protection and the flood currents of bankfull are not able to carry this piece of rock. Under these conditions, calculating the ratio of bank height to bankfull height cannot indicate the erodibility of the streambank in the bankfull stage. Nevertheless, the erodible potential of the bank for larger flood currents is confirmed. Comparison of the original BEHI with the modified BEHI showed that the modified method has an overestimate than the original BEHI.</span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><span style="font-size:8.0pt"><span style="line-height:115%"><span style="font-family:"Times New Roman",serif"></span></span></span></span></span></span><br>
<span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Key word:</span></span></span></b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times=""> river bank erosion, BEHI, Sajadroud, Mazandaran</span></span></span></span></span></span><br>
فرسایش کناره رود, BEHI, سجادرود, مازندران
river bank erosion, BEHI, Sajadroud, Mazandaran
27
40
http://jsaeh.khu.ac.ir/browse.php?a_code=A-10-1146-1&slc_lang=fa&sid=1
Reza
Esmaili
رضا
اسماعیلی
r.esmaili@umz.ac.ir
100319475328460010609
100319475328460010609
Yes
University of Mazandaran
دانشگاه مازندران
fatemeh
abedini zadeh
فاطمه
عابدینی زاده
re_esmaili@yahoo.com
100319475328460010610
100319475328460010610
No
دانشگاه مازندران