Comparison and Evaluation of NBS and BEHI Models’ Results in Bank Erosion of Hashtrood Qaranqoo Chai River

Document Type : مقاله پژوهشی


Shahid Beheshti University


1. Introduction
River bank erosion has an important role in the instability and damage to agricultural lands and facilities around the rivers and it is a significant source of sediment in fluvial systems. The river bank protection against the erosion is considered as one of the main objectives of river improvement in sustainable development of water resources. The erosion of the river banks is causing damage to agricultural land, damage to structures such as bridges and roads, widening of stream channel and environmental issues considerably. Bank erosion is a major cause of non-point pollution of water resources and increased sediment load in many rivers. Not only increasing banks erosion does increase the sediment load but it also causes river instability and changing flow and channel pattern. Thus, during the recent decades, sediment load and river banks have been created a large concern in the world and the large sums have been spent to stabilize banks. Hence, river bank erosion and channel changes are social, environmental and economic issues that often cause irreparable damage to people and infrastructure in the river banks.
2. Material and Methods
Qaranqoo chai catchment (upstream of Sahand dam) is located on the southwestern of Hashtrood city (located in 37° 43 to 37° 20 northern latitude and 46 58 to 46 28eastern longitude). The catchment is located on the east Azerbaijan province.In this reach, we used Bank Erosion Hazard Index (BEHI) and Near-Bank Stress (NBS) to predict annual bank erosion in QaranqooChai River. Therefore, nine cross-sections were selected and some parameters were measured for BEHI, parameters such as bank full width, average bank full height, root depth, root density, bank angle, surface protection, and bank material and stratification bank were measured. Bank full height is the distance from bank toe to bank full stage elevation. Bank height divided by bank full height gives a bank-height ratio. Rooting depth is measured from the top of the bank to the bottom of vegetal rooting. Rooting depth is then divided by bank height to get root-depth ratio. The weighted root density calculation begins with a visual estimate of root mass, per unit volume of soil. Bank angle is the angle of the bank face along the elevation plane of the bank. Surface protection is estimated as the percent of bank covered by vegetation, woody debris, boulders or manmade materials. An open bank face has 0% protection while a fully vegetated bank has 100% surface protection. Bank material may affect a bank’s susceptibility to erosion. If bank material is medium or large cobble, ten points are subtracted from the total BEHI score. Five to ten points are added for gravel, a mix of gravel and small cobble, or a mix of gravel and sand. Sand, or a predominantly sand mixture requires the addition of ten points. No adjustment is made for cohesive silt or clay bank material. Banks of bedrock or boulder are always scored as to be very low. Indeed BEHI incorporates bank variables that are factors in entrainment, surface erosion and mass erosion. These variables are bank–height ratio, root–depth ratio, weighted root density, bank angle and surface protection. Variables have empirical values that are in turn, converted to index values and summed for a total BEHI score. Scores are adjusted by bank material and bank material stratification. BEHI scores are then categorized by erosion potentials. A greater score indicates greater erodibility.
2- NBS: Near-Bank Stress (NBS) assessment is important in predicting erosion so that it is associated with energy distribution in channel cross-section spatially stream banks and this disproportionate distribution of flow energy can lead to bank erosion. In NBS method, two levels were used (level 2 and level 5).Ratio of radius curvature to bankfull width (Rc/Wbkf), ratio of near-bank maximum depth to bankfull mean depth (dnb/dbkf).
3. Results and Discussion
According to NBS method and level2, the erosion ranged from moderate to extreme in all of cross-sections except the cross-section 7 (low). Also according to level 5, the erosion was very low in the cross-section one and was extreme in the cross-section two and was low to moderate in the other cross-sections. The results of BEHI method showed that both of right and left banks have erosion so that the erosion risk was moderate to very high in all of the right banks of the cross-sections and was only very low in the cross-section 4 and also the erosion risk of the left banks have been estimated to be very low to extreme in the cross-sections.
4. Conclusion
According to the results of both models, in general erosion in the period under study is the important factor at sediment production in QaranqooChai river and bank erosion risk. Also, both methods used to analyze and evaluate this type of erosion show that in general, due to the exacerbation of the hydraulic stress on the external side the amount and risk of erosion for the outer sides of the arches in the area of the meandering river pattern is more than the opposite side.
Similarly, the degree of risk of erosion is reduced on both sides of the banks in the middle section of the studied reach. In the last section of the studied reach, the risk of erosion is increased by both models. This study showed that the river pattern, vegetation, and marginal materials play a crucial role in maintaining the bank stability in this area. Based on field observations, the results of the model of the Bank Erosion Hazard Index (BEHI) in the QaranqooChai River is more consistent with reality.


اسماعیلی، رضا؛ حسین زاده، محمد مهدی ؛ اقبالی، رضا؛ 1392. اثرات برداشت شن و ماسه بر ویژگی‌های ژئومورفیکی رودخانه لاویج رود، استان مازندران. جغرافیا و مخاطرات محیطی، شماره ششم، صص 70-57.
اصغری سراسکانرود، صیاد؛ زینالی، بتول؛ ۱۳۹۲. بررسی مقاومت ذرات رسوبی در برابر فرسایش رودخانه سراسکندچای هشترود با استفاده از روش‌های ریاضی. پژوهش‌های فرسایش محیطی. شماره ۱۲. صص ۳۰-۴۲.
حسین زاده، محمد مهدی؛ خالقی، سمیه؛ واحدی فر، فراز؛ رستمی، میلاد؛ 1395. برآورد فرسایش کناره‌ای در رودخانه قرانقوچای هشترود با استفاده از مدل راسگن. چهارمین همایش ملی انجمن ایرانی ژئومورفولوژی، تهران.
حسین زاده، محمد مهدی؛ صدوق، حسن؛ متش بیرانوند، سعیده؛ اسماعیلی، رضا؛ 1396. بررسی پایداری رسوبات بستر رودخانه لاویج با استفاده از روش تنش برشی بحرانی و دبی بحرانی. پژوهش‌های دانش زمین. شماره 29. صص86-75.
خالقی، سمیه؛ ملکانی، لیلا؛ 1394. برآورد فرسایش کرانه رودخانه لیقوان چای با استفاده از شاخص تنش برشی نزدیک کرانه راسگن. چاپ در مجموعه مقالات کنگره بین المللی جغرافیا و توسعه پایدار، تهران، صص
کرم، امیر؛ لایقی، صدیقه؛ 1393. طبقه‌بندی هیدروژئومورفولوژیکی رودخانه جاجرود با مدل روزگن. پژوهش‌های ژئومورفولوژی کمی. شماره3. صص.142-130.
یمانی، مجتبی؛ حسین زاده، محمد مهدی؛ 1381. بررسی تغییرات الگوی رودخانه تالار در جلگه ساحلی دریای مازندران. مجله پژوهش‌های جغرافیایی. شماره 43. صص 109-122.
A study of bank erosion rates within selected reaches of the housatonicriver. (2009). Stantec Consulting, 30 Park Drive, Topsham, England. ME 04086.
Coryat, M. (2014). Analysis of the bank assessment for non-point source consequences of sediment (BANCS) approach for the prediction of stream bank stability and erosion along Stony Clove Creek in the Catskills (Unpublished master’s thesis) Syracuse University, New York.
David, L., & Rosgen, P.H. (2001). A stream channel stability assessment methodology. Colorado: Wildland Hydrology Books, Fort Collins.
Genet, M., Stokes, A., Salin, F., Mickovski, S. B., Fourcaud, T., … Beek, R. V. (2005). The influence of cellulose content on tensile strength in tree roots. Plant and Soil, 278, 1-9.
Gregory, K.J. (2006). The human role in changing river channels. Journal of Geomorphology, 79, 172-191.
Gurnell, A. (1997).The hydrological and geomorphological significance of forested floodplains. Global Ecology and Biogeography Letters, 6, 219-229.
Kang, R.S. (2007). Effects of urbanization on channel morphology of three streams in the Central Redbed Plains of Oklahoma (Unpublished doctoral dissertation). Faculty of the Graduate College, Oklahoma State University.
Krishna, G. G., Pal, S., & Mukhopadhyay, S. (2016). Validation of BANCS model for assessing stream bank erosion hazard potential (SBEHP) in Bakreshwar river of Rarh region, Eastern India. Modeling Earth Systems and Environment, 95(2), 1-15.
Kwan, H., & Swanson, S. (2014). The prediction of annual stream bank erosion for Sequoia National Forest, California.Journalof the American Water Resources Association, 50(6), 1439–1447.
Lawler, D. M. (1995). The impact of scale on the processes of channel-side sediment supply: Aconceptual model. Effects of Scale on Interpretation and Management of Sediment and Water Quality, 226, 175-184.
Moret, S.L. (2001). Predicting channel stability in Colorado Mountain streams using hydrobiogeomorphic and land use data: A cost-sensitive machine learning approach to modeling rapid assessment protocols (unpublished doctoral dissertation). Oregon State University, Corvallis, Oregon.
Pollen, N. (2007). Temporal and spatial variability in root reinforcement of streambanks: Accounting for soil shear strength and moisture. Catena, 69,197-205.
Rosgen stream classification technique _Supplemental Materials. (2007). National Engineering Handbook. U.S. 210–VI–NEH, Part 654.
Rosgen, D.L. (1996). Applied river morphology. Wildland Hydrology, Pagosa Springs, Colorado.
Rosgen, D.L. (2006). Watershed assessment of river stability and sediment supply (WARSSS). Colorado: Wildland Hydrology Books, Fort Collins.
Rosgen, D.L. (2008). River stability field guide. Colorado: Wildland Hydrology, Fort Collins.
Sass, C. K., & Keane, T. D. (2012). Application of Rosgen’s BANCS model for NE Kansas and the development of predictive streambank erosion curves. Journal of the American water Resources Association, 48(4), 774-787.
Schumm, S.A. (1973) geomorphic thresholds and complex response of drainage systems. In M. Morisawa (Ed.), Fluvial geomorphology (pp.299-310). New York: Publications of Geomorphology, State University of New York, Binghamton,.
Thorne, C. R. (1990). Vegetation and erosion: Processes and environments. Chi Chester: John Wiley & Sons Ltd.
Wynn, T. M., & Mostaghimi, S. (2006). The effects of vegetation and soil type on streambank erosion, Southwestern Virginia, USA. Journal of the American Water Resources Association, 42(1), 69-82.