بررسی آزمایشگاهی اثر پارامترهای هیدرولیکی بر ظرفیت انتقال رسوب در کانال مرکب با شیب جانبی سیلابدشت

در این تحقیق اثر دانه بندی و تغییرات پارامترهای هیدرولیکی در مقطع سیلابی مرکب (با دشت سیلابی یک طرف کانال اصلی) بررسی شد. دو مدل آزمایشگاهی مقطع مرکب با مدل اول شیب دیواره جانبی سیلاب دشت صفر و در مدل دوم مقدار برابر با50 درصد در نظر گرفته شد. همچنین با هدف بررسی تاثیر شیب طولی بر شستن رسوبات بستر رودخانه، شیب طولی در سه گام0.002، 0.004 و0.006 تغییر داده شد. با هدف بررسی تاثیر قطر متوسط رسوبات بر روند آبشستگی، در طول آزمایش ها از رسوبات ماسه ای با قطر0.9 و 3 میلی متر استفاده شد. با مقایسه تغییرات پارامترهای هیدرولیکی(سرعت، تنش برشی، نسبت عمق کانال اصلی به عمق سیلاب دشت، دبی و عدد فرود) با تغییر دانه بندی رسوب نتایج نشان داد با کاهش اندازه دانه بندی و در شیب عرضی صفر، میزان پارامترهای هیدرولیکی افزایش یافته است. نتایج نشان داد، افزایش شیب طولی و عرضی تاثیر زیادی بر افزایش حجم رسوبات شسته شده در طول کانال دارند و با افزایش این شیب‌های طولی و عرضی در کانال، میزان حجم انتقال رسوبات بیشتری اتفاق می افتد. با بررسی تغییرات تنش برشی و توان جریان واحد در مقابل ظرفیت انتقال رسوب نتایج نشان داد که با افزایش شیب طولی و در شیب عرضی 0.5 ظرفیت انتقال رسوب افزایش یافته است.

laboratory study of effect of hydraulic parameters on sediment transport capacity in a compound channel with lateral floodplain slope

introductionstudy the soil erosion process, sediment transport capacity plays a vital role in the physical description of soil erosion processes. in recent years, researchers examining the sediment transport capacity under different laboratory conditions have shown that hydrodynamic parameters, especially shear stress and unit stream power have a significant effect on sediment transport capacity. the results of researchers’ studies show that this assumption is not correct(martin et al., 1991). increasing the transverse slope of the plain flood changes the transition stress between the flow through the main channel and the floodplain. the presentation of a method for estimating the weight of sediments discharged from the channel was investigated (karamisheva et al., 2005). despite the studies, the effects of sediment size on sediment transport are still not well understood and considering that previous studies have been done in direct channel, the effect of longitudinal slope and transverse slope change by changing sediment particle size in composite channel is investigated and not well understood. it should be noted that various parameters affect the hydrodynamic conditions of river floodplains. therefore, recognizing and investigating the factors affecting this case is of special importance in hydraulic science. one of the influential factors in the hydraulic and hydrodynamic conditions of floodplains is the lateral slope of floodplains. however, qualitative and quantitative study of the parameter requires the presentation of appropriate laboratory research methods. in this study, by aiming at the effect of lateral slope of floodplain on hydraulic and hydrodynamic conditions of flow, as well as the effect of granulation and hydraulic parameters on the amount of sediment output, an experimental design was presented to investigate this parameter. shear stress varies in longitudinal and transverse slopes.methodologythe experiments were performed in a laboratory compound channel 12 meters long, 30 centimeters wide and 0.5 meters high. flow field analysis and velocity vectors upstream of the overflow were performed using measured adv 3d speedometer data. in this study, to show the overflow flow conditions on the deposition status behind the overflow wall, the horizontal velocity in the grid drawn in a section of the channel was used. during the experiments, tools embedded at the end of the channel were used to change the longitudinal slope of the channel. it should be noted that slopes of 0.002, 0.004 and 0.006 were used to change the slope.q = flow rate (liters per second); ho = water depth in the canal (meters), hs = sediment height (meters); hf = height of plain flood; b = plain flood width (meters), so = longitudinal slope of the canal (no dimension); sc = transverse slope of the channel (without dimension), w = width of the main channel (meters); v = flow rate (meters per second); γ = weight mass of fluid (newton per cubic meter); μ = water dynamic viscosity (pascal-s); σ = fluid surface tension (newtons per meter); ρ = fluid density (kg / m3); g = acceleration of the earth’s gravity (meters per square second); b = total channel width (meters); vs = sediment volume of the channel (cubic meters) and d50 = average particle diameter (mm). in the above parameters in relation to dimensional analysis and puckingham theorem, some parameters can be omitted from the above parameters. for example, because the water thickness on the floodplain is large enough, surface tensile forces can be avoided. also considering that the transverse slope and the length slope are dimensionless parameters. they can be taken out of calculations and introduced as a dimensionless number. to simplify dimensional analysis, it is better not to consider this parameter. with these interpretations it can be stated that:   results and discussionas the shear stress increases at different longitudinal and transverse slopes, the sediment transport capacity increases. these findings indicate that the slope has a positive effect on shear stress. the results show that the transverse slope has a significant effect on the increase and change of shear stress with sediment transfer capacity and in the transverse slope of 0.5 and in different longitudinal slopes, increase in sediment transfer capacity is more and washed sediment increased (fig.1). sediment transport capacity measured with the unit stream power has changed in different slopes (fig.2). with increasing depth of flow in main channel to depth of flow in floodplain, more sediment is removed from the flume and the least amount of sediment washed is when the longitudinal slope is equal to 0.002, transverse slope zero, and median particle diameter is 3mm, occurring in discharge of 1.6 l/s (fig.3).  as the froude number increases, the amount of sediment output will increase more when the size of the sediment particle decreases.        conclusionsin this study, the effect of grain size and hydraulic parameters on sediment transport in two hydraulic models with longitudinal slopes of 2,4 and 6 per thousand and transvers slopes of zero and 0.5 were investigated. the results showed that with increasing the longitudinal slope, at zero transverse slope, with decreasing particle size, the amount of output sediment would increase. most leached sediment in zero transverse slope and longitudinal slope 0.006 has occurred. further studies are needed considering the large particle size range and transverse slopes with greater range of variation.