Manning Roughness Coefficient Research Articles

Effects of vegetation stem coverage on the hydraulic characteristics and on-wall and jet flow proportions at the gully head

Vegetation in the upstream area played a critical role in influencing runoff processes and subsequent headcut erosion at the gully head. However, it remains unclear how the vegetation stem coverage affects the hydraulic parameters and the on-wall and jet flow characteristics at the gully head. A simulation flow scouring experiment was performed to explore the influences of the vegetation stem coverage (5 levels) on the hydraulic parameters and on-wall and jet flow proportions at the gully head under inflow discharges ranging from 3.6–9.6 m3 h−1. The results indicated that the runoff in the upstream area occurred in the supercritical turbulent flow regime, and its velocity decreased while the Manning roughness coefficient and Darcy–Weisbach coefficient increased with increasing vegetation stem diameter. The runoff velocity at the gully brink decreased with increasing vegetation stem diameter and increased as a linear function of the inflow discharge (R2 = 0.849–0.997). With increasing vegetation stem diameter, the proportion of on-wall flow increased, and the proportion of jet flow decreased. The on-wall and jet flow proportions ranged from 7% to 92% and 8% to 93%, respectively, under inflow discharges from 3.6–9.6 m3 h−1, thereby attaining the highest correlation with the runoff velocity, Reynolds number, and runoff kinetic energy and following a significant logarithmic function. The vegetation stem influences the hydraulic parameters of the upstream area and gully head and thus influences the on-wall/jet flow proportion. This study could help elucidate the effect of vegetation on the hydraulic mechanism of headcut erosion and provide a theoretical foundation for improving gully headcut erosion models.

Robustness of storm water management model parameter sets for dry and wet hydroclimatic conditions

The Storm Water Management Model (SWMM) is an urban watershed model for simulating urban runoff quantity and quality. Although SWMM has been widely used, little to no research has explored the effect of fitting the same SWMM dataset to multiple hydrologic conditions. This paper assesses the impact of best-fit parameter estimates on the hydrologic responses of dry and wet hydroclimatic conditions, evaluates parameter uncertainty, and identifies the physical processes that govern parameter changes during dry and wet conditions. We compared the ability of SWMM to predict flows when independently calibrated to a dry and a wet year, respectively, using an automatic calibration program for SWMM, OSTRICH-SWMM (Optimization Software Toolkit for Research Involving Computational Heuristics). The model developed using SWMM calibrated to a wet year performed better during the model assessment period. The best fit estimates of SWMM parameters differed significantly between dry and wet years. For instance, Manning's roughness coefficient for overland flow was higher in a dry year, as less runoff meant less flow depth on surfaces. Some parameters, e.g., % effective imperviousness, exhibited an expanded posterior probability distribution, increasing the uncertainty of the parameter estimate. However, other parameters, such as Manning's roughness coefficient for streams were the least sensitive and well-defined as the width of their posterior distribution only spanned a relatively narrow range which did not change drastically between the two cases. The robust assessment conducted in this study demonstrated that the hydrologic behavior of SWMM was different between models developed and calibrated for dry and wet hydroclimatic conditions. The different optimal parameter values suggest that although the processes and mechanisms driving hydrologic processes in dry and wet years are similar, their magnitude differs greatly. This study highlights that precipitation patterns affect the selection of optimal parameter values and the water budgets differed markedly between dry and wet years, as expected. The results of this study can assist urban watershed planners in selecting the most appropriate model to use for prediction purposes or when there is a paucity of data available for model calibration. This study recommends changing SWMM model parameters on an annual basis when projecting the effects of new conditions outside of current experience (i.e., land use and climate change) on urban runoff quantity and quality.

Investigating the Relationship between the Manning Coefficients (n) of a Perforated Subsurface Stormwater Drainage Pipe and the Hydraulic Parameters

Subsurface perforated pipes drain infiltrated stormwater runoff while attenuating the peak flow. The Manning roughness coefficient (n) was identified as a fundamental parameter for estimating roughness in various subsurface channels. Hence, in this work, the performance of a six-row non-staggered sand-slot perforated pipe as a sample of the subsurface drainage is investigated experimentally in a laboratory flume at Universiti Sains Malaysia (USM) aimed at determining the Manning roughness coefficients (n) of the pipe and assessing the relationship between the Manning’s n and the hydraulic parameters of the simulated runoff flow under the conditions of the tailgate channel being opened fully (GFO) and partially (GPO), as well as the pipe having longitudinal slopes of 1:750 and 1:1000. Water is pumped into the flume at a maximum discharge rate of 35 L/s, and the velocity and depth of the flow are measured at nine points along the inner parts of the pipe. Based on the calculated Reynolds numbers ranging from 38,252 to 64,801 for both GFO and GPO conditions, it is determined that most of the flow in the perforated pipe is turbulent, and the calculated flow discharges and velocities from the outlets under GFO are higher than the flow and velocity rates under GPO with similar pipe slopes of 1:750 and 1:1000. The Manning coefficients are calculated at nine points along the pipe and range from 0.004 to 0.009. Based on the ranges of the calculated Manning’s n, an inverse linear relationships between the Manning coefficients and the flow velocity under GFO and GPO conditions are observed with the R2 of 0.975 and 0.966, as well as 0.819 and 0.992 resulting from predicting the values of flow velocities with the equations v = ((0.01440 − n)/0.009175), v = ((0.01330 − n)/0.00890), v = ((0.02007 − n)/0.01814), and v = ((0.01702 − n)/0.01456) with pipe slopes of 1:750 and 1:1000, respectively. It is concluded that since the roughness coefficient (Manning’s n) of the pipe increases, it is able to reduce the flow velocity in the pipe, resulting in a lower peak of flow and the ability to control the quantity of storm water in the subsurface urban drainages.

Manning's roughness coefficient in a truncated triangular open-channel flow section

Abstract In uniform flows, Manning's roughness coefficient n plays an important role in the calculation of the normal depth in the open channels. When calculating uniform flows in open conduits and channels, Manning's coefficient is arbitrarily chosen. This arbitrary choice is not physically justified because the coefficient n must be determined according to the parameters that influence the flow, particularly the normal depth sought. In this paper, a new method is presented to compute Manning's coefficient in a truncated triangular channel section. In the first step, the study proposes to establish the general relationship that allows computing Manning's coefficient in this type of channel. The relationship is presented in dimensionless terms, giving it a character of general validity, including the dimensionless Manning's resistance coefficient, denoted as N. The latter is shown to depend on the aspect ratio of the wetted area, the side slope of the channel, the relative roughness and the modified Reynolds number, which is physically justified since flow resistance is closely related to flow depth. In the second step, the rough model method is proposed to express Manning's coefficient when the horizontal dimension of the channel is not a given data of the problem.

Numerical Modeling of Flow Pattern at a Right-angled River Bend Using CCHE2D Model

In this study, the CCHE2D model is used to analyse the flow pattern in a meander reach of the Gomati River. The finite volume method is used by the numerical model to solve the depth-averaged two-dimensional equations with 𝑘−𝜀turbulence closure. The numerical findings were compared with field data for two different flow rates in order to calibrate the CCHE2D model using various Manning's roughness coefficients. The results show that for the minimum and maximum discharges, a smaller Manning's roughness factor (0.015≥𝑛≥0.025)is more favorableto a higher Manning's roughness factor(0.030≤𝑛≤0.040). The results of the numerical model demonstrated that fluctuations in hydraulic parameters including shear stress, velocity, flow depth, and Froude number in the river bend are greatly influenced by the existence of centrifugal force and helical cells. The linear relationship between velocity and shear stress is presented across the whole study reach, as indicated by the R-squareand linear correlation coefficient (r) components. The results of the model show that the flow field within the river bend can be accurately simulated by the computational model.

The effect of building arrangement on the flow characteristics in meandering compound channels

Due to the fact that most of the cities and villages are built on the banks of the rivers, the hydraulic characteristics of water flow always undergo changes during floods, so it is necessary to study the interaction of the flood flows of meandering compound channel in these areas. In this paper, the effect of building arrangement on the flow characteristics in meandering compound channels was investigated by using laboratory models. For this purpose, a smooth floodplain (without building) and three different types of building arrangement on the floodplain including structural obstacles perpendicular and parallel to the floodplain flow and checkered structural obstacles have been used. The tests have been conducted at three relative depths of 0.29, 0.39 and 0.49 and the corresponding discharges. All experiments were performed under a quasi-uniform and fully developed flow condition. The measurement data were recorded at different sections along the meandering main channel. Stage-discharge curves, Manning's n, velocity distribution, boundary shear stress and Darcy-Weisbach friction factor are determined over 12 test runs. The results of this research show that the arrangement of buildings has a great effect on the longitudinal velocity of the main channel. At a relative depth of 0.49, in a meandering compound channel with the arrangement of structural obstacles perpendicular to the floodplain flow, the dimensionless longitudinal velocity of the main channel compared to the smooth floodplain increases by 113%, but with the arrangement of structural obstacles parallel to the floodplain flow, the dimensionless longitudinal velocity increases by 27%. Also, the building arrangement is effective in reducing the discharge capacity of the meandering compound channel, so that in a building density of 18.5%, structural obstacles perpendicular to the floodplain flow reduce the discharge capacity of the channel by 50% compared to the smooth floodplain. In the channel with structural obstacles arranged perpendicular to the floodplain flow, Manning's roughness coefficient increases sharply with increasing the relative depth, but in the channel with the structural obstacles parallel to the floodplain flow, Manning's roughness coefficient decreases with increasing the relative depth. In the channel with the arrangement of structural obstacles perpendicular to the floodplain flow, the bed shear stress of the main channel is higher than the other building arrangements, so that at the relative depth of 0.49, the average maximum bed shear stress in all sections increases by 42% compared to the smooth floodplain.

Study the Affecting Factors on Free overfall Flow and Bed Roughness in Semi-Circular Channels by Artificial Neural Network

One of the significant problems facing the water resource engineer is calculating the coefficient of roughness for subsequent design calculations of the discharge amount of a channel or river. In this study, experiments were conducted in a semi-circular, straight channel to investigate the factors affecting bed roughness and flow discharge using Artificial Neural Network (ANN). For this purpose, three semi-circular channel models with free overfall were constructed and installed in a 6-meter-long laboratory flume. The length of these models was 2.50 m with three different diameters (D= 150, 187, and 237mm) and three bed slopes (S=0.004, 0.008, and 0.012). Three sand particle sizes (ds) were used for each semi-circular channel to roughen the bed. The results showed that the Manning roughness coefficient obtained using a rough bed surface was higher than the channel with a smooth bed surface. Also, the results revealed that the Manning roughness coefficient and the Froude number were inversely related. (ANN) analysis showed a good agreement between the experimental and predicted results of flow and roughness. The bring depth (yb) had an 85.8% impact percentage on the free overfall discharge for semi-circular channels, while the bottom slope (S) had only 1.1%.

Estimation of Segment-Averaged Geometric-Hydraulic Relationships as a Function of Depth in Natural Rivers Using Inverse Modeling

This article presents a novel method to identify geometric-hydraulic relationships–in terms of mathematical formulas—in the form of segment-averaged outputs and a function of depth in rivers. There are several methods for determining geometric-hydraulic relationships in rivers, including flow area, wetted perimeter, and the flow top width. Direct field surveying and using aerial and satellite sensor instruments are the most prevalent. The model presented here, however, is based on the inverse solution of the Saint-Venant equations without costly field-surveyed river geometry data. The relationships mentioned earlier can be easily used in various hydraulic models, such as flood routing, sediment transport, pollutant transport, and so on. Moreover, this method requires the lowest number of parameters as the input of the inverse model because by minimizing the corresponding objective function, the desired parameters are estimated in the whole studied segment. The proposed inverse model is validated using hypothetical and real test cases. In one of the test cases—as the most comprehensive and practical test case—the application of the presented inverse model was validated in a river network. The Manning roughness coefficient and geometric-hydraulic relationships for different segments were simultaneously estimated at an acceptable level of accuracy and computational costs in this river network. Ultimately, the real and identified geometric-hydraulic relationships are compared for each test case, and statistical indexes are demonstrated. Overall, the results and statistical indexes indicate that the model is more successful and also cheaper than costly conventional methods.

Effect of effluent and magnetized effluent on Manning roughness coefficient in furrow irrigation

Due to the water crisis, wastewater utilization is an effective way to meet the water needs of plants and also reduce environmental pollution. In order to know the effect of treated and magnetic wastewater on Manning roughness coefficient, a study was conducted in the form of randomized complete blocks with three irrigation treatments with "wastewater outlet", "magnetic effluent" and "normal water" in four replications. Statistical analysis on the relative changes of the roughness coefficient in the design did not show a significant difference. At the same time, a decreasing trend was observed during the irrigation season in the roughness coefficient, which was expected due to the smoothing of the flow path and the effect of organic matter of the effluent on the bed. The magnetic field was not affected by the magnetism. Manning roughness values with more irrigation with effluent and magnetic effluent, in most cases had a decreasing trend, but due to the use of water, an increasing trend was observed in them. However, the increase in normal water treatment could not be analyzed according to the information of this project. There was no statistically significant difference between the treatments of the project.

Vegetation affects gully headcut erosion processes by regulating runoff hydrodynamics in the Loess tableland region

Vegetation plays an important role in gully headcut erosion processes. However, it is still unclear how vegetation in the upstream area affects gully headcut erosion processes by changing the hydraulics. A series of in situ inflow scouring experiments were conducted on bare land plots and vegetation plots (including the upstream area, headwall, and gully bed) planted with Bothriochloa ischaemum (BI), Agropyron cristatum (AC), and Medicago sativa (MS) with clustered stems and Artemisia gmelinii (AG) with erect stems to investigate the influence of vegetation on the hydrodynamic parameters involved in gully headcut erosion processes. The results showed that, compared with bare land, vegetation increased the Manning roughness coefficient (n) and Darcy–Weisbach friction factor (f) in the upstream area by 0.2–2.5 times and 0.9–9.6 times, respectively, but reduced the runoff velocity in the upstream area and gully brink. However, the jet flow velocity at entry into the plunge pool increased rapidly after passing through the gully head. The influence of vegetation with clustered stems on roughness and runoff velocity was greater than that of vegetation with branched stems. At 3.6 m3/h inflow discharge, vegetation can increase the runoff shear stress of the upstream area. The energy consumption of the gully head, upstream area, and gully bed accounted for 74 to 76 %, 19 to 21 %, and 4 to 7 % of the total energy consumption, respectively. The four vegetation treatments reduced the gully headcut soil loss by 31 to 81 %, among which MS exhibited the highest reduction. The soil loss rate was positively correlated with the jet flow velocity and its kinetic energy, and the correlation was the best (R2 of 0.934 and 0.935, respectively, P < 0.01), presenting a logarithmic trend. These results are helpful to deepen the understanding of the roles of vegetation in regulating runoff hydraulic action during gully headcut erosion.

Dynamic Roughness Modeling of Seasonal Vegetation Effect: Case Study of the Nanakita River

Hydraulic models of rivers are essential for vulnerability assessment in disaster management. This study simulates the 2019 Typhoon Hagibis at the Nanakita River using a dynamic roughness model. The model estimates the roughness of the river on a pixel level from the relationship between the Manning roughness coefficient and the degree of submergence of vegetation. This degree is defined as the ratio of water depth to plant height. After validating the model, the effect of vegetation on the water level in different seasons from April 2020 to March 2021 was assessed. The vegetation area and height were obtained on a pixel level using unmanned aerial vehicle photogrammetry. The dynamic roughness model showed that the water level profile increased by 7.03% on average. The seasonal effect of vegetation was observed, revealing a strong correlation between variations in the vegetation conditions and water level profile. This approach may help mitigate flood damage by indicating the factors that can increase the risk of flooding.

Accelerating Tsunami Modeling for Evacuation Studies through Modification of the Manning Roughness Values

The role of the Manning roughness coefficient in modifying a tsunami time series of flow depth inundation was studied in Iquique, Chile, using a single synthetic earthquake scenario. A high-resolution digital surface model was used as a reference configuration, and several bare land models using constant roughness were tested with different grid resolutions. As previously reported, increasing the Manning n value beyond the standard values is essential to reproduce mean statistics such as the inundated area extent and maximum flow depth. The arrival time showed to be less sensitive to changes in the Manning n value, at least in terms of the magnitude of the error. However, increasing the Manning n value too much leads to a critical change in the characteristics of the flow, which departs from its bore-like structure to a more gradual and persistent inundation. It was found that it is possible to find a Manning n value that resembles most features of the reference flow using less resolution in the numerical grids. This allows us to speed up inundation tsunami modeling, which could be useful when multiple inundation simulations are required.

Hydrodynamic characteristics of grass swale runoff in Guanzhong area of Loess Plateau, Northwest China.

Grass swale has been widely used in sponge city construction, which can effectively improve the urban ecological environment. To explore the regulation mechanism of runoff in grass swale, runoff scouring experiment was carried out to study the hydrodynamic characteristics of runoff and the distribution of cross-section velocity under the combined conditions of five slopes (1%, 2%, 3%, 4%, 5%) and five scour flows (20, 30, 40, 50, 60 L·min-1). With the increases of flow rate and slope, flow velocity, Reynolds number and Froude number all increased gradually, while the Manning roughness coefficient and Darcy-Weisbach friction coefficient decreased gradually. The velocity (V) could be expressed as a power function V=0.3387Q0.555S0.6601 of flow rate (Q) and slope (S). The variation ranges of Reynolds number and Froude number were 1160.95-6596.82 and 0.17-1.21, respectively. The runoff flow patterns were all turbulent. The flow pattern was greatly affected by the slope. When flow rate and slope were small, they had great influence on friction coefficient. Under the experimental conditions, the Darcy-Weisbach friction coefficient was negatively correlated with Reynolds number. The velocity distribution of cross-section showed symmetrical distribution on both sides of the center. The maximum velocity point was located at the center of water surface. With the increases of flow rate and slope, the velocity contours of cross section gradually became dense and the gradient of the velocity change increased. Our results provide a theoretical basis for the design, application and hydraulic calculation of grass swale in the construction of sponge cities in loess areas, and reveal the runoff regulation mechanism by analyzing the hydraulic characteristics of grass swale runoff.

Unsteady flow analysis using hydrological and hydraulic models for real-time flood forecasting in the Vamsadhara river basin

Abstract The river Vamsadhara runs through the states of Andhra Pradesh (AP) and Odisha along a stretch of coastline that is prone to cyclonic storms. Riverine flow, along with cyclonic gales, is a crucial issue for most of India's coastal districts. As a result, a developed flood forecasting model is required to mitigate the danger of flooding to a certain level. For evaluating maximum water depth and inundation of flood plains induced by storms under existing and future land use circumstances, hydrological and hydraulic models are more prominently studied. The current work employs hydrological and hydrodynamic models to simulate a real flood inundation model for unsteady flow conditions. The technique involves the processing of the digital elevation models (DEM) to generate flood hydrographs that serve as boundary conditions for the reaches. In the present analysis, Manning's roughness coefficient is used as a sensitive parameter. Calibration and validation of extreme flood events that occurred in 2006, 2010, and 2013 using observed water levels yielded good results, with model performances of 0.79, 0.68, and 0.84, respectively. The findings of the generated depth, velocity, and flood extent maps are presented. These maps can be used to plan for flood disasters and long-term watershed management.

An experimental study of the hydrodynamics and contaminant transport in a Y‐shaped confluence with flexible submerged vegetation

AbstractVegetation greatly affects the flow characteristics and contaminant transport in river confluences. In this study, the flow characteristics and contaminant transport in the non‐vegetated/vegetated Y‐shaped confluence were explored systematically through a series of experiments. A total of 10 scenarios were designed to answer the three main research questions: what is the difference between the flow characteristics and contaminant transport in (1) asymmetrical and Y‐shaped confluences; (2) non‐vegetated/vegetated Y‐shaped confluences; (3) vegetated Y‐shaped confluences with different confluence ratios? The experimental results revealed that vegetation remarkably changes the internal flow structure in Y‐shaped confluences. Briefly, the velocity profile can be divided into three vertical layers within the vegetated system, but it remains nearly constant in the non‐vegetated channel. Vegetation changes the circulation location and reduces the intensity of the secondary current, weakening the strength of contaminant mixing. However, the turbulent kinetic energy within the vegetated system is larger than that in the non‐vegetated case, and it peaks at the top of the vegetation canopy. Under different confluence ratio cases, the overall fluctuation of the longitudinal dispersion coefficients along the cross‐sections in the mainstream was similar but increasing the confluence ratio causes the circulation to appear to advance and enhances its intensity. In addition, the vegetation density (200 item/m2) in this study render the manning roughness coefficient at 0.068, which is larger than that under lower vegetation density cases. The outcomes from this study are helpful for both environmental and river management applications.

Evaluation of effective parameters of Manning roughness coefficients in HDPE culverts via kernel-based approaches

Abstract The prediction of Manning coefficients plays a prominent role in the estimation of head losses along culvert systems. Although the Manning coefficient is treated as a constant, previous studies showed the dependency of this coefficient on several parameters. This study aims to evaluate the effective parameters of the Manning roughness coefficient using intelligence approaches such as Gaussian process regression (GPR) and support vector machines (SVM), in which the input variables were considered as dimensionless and dimensional. In addition to the enhanced efficiency of the SVM approach compared to the GPR approach in model development with dimensionless input variables, the accuracy of model A(I) with input parameters of Fr (Froude) and y/D (the ratio of water depth to culvert diameter) and performance criteria of correlation coefficient (R) = 0.738, determination coefficient (DC) = 0.0962, root mean square errors (RMSE) = 0.0015 and R = 0.818, DC = 0.993 and RMSE = 0.0006 for GPR and SVM approaches were the highest. Thus, for the second category, a model with an input parameter of discharge (Q), hydraulic radius (RH), and culvert's slope (S0) showed good efficiency in predicting the Manning coefficient, in which the performance criteria of GPR and SVM approaches were (R = 0.719, DC = 0.949, RMSE = 0.0013) and (R = 0.742, DC = 0.991, RMSE = 0.007), respectively. Furthermore, developed OAT (one-at-a-time) sensitivity analysis revealed that relative depth y/D and Q are the most important parameters in the prediction of the Manning coefficient for models with dimensionless and dimensional input variables, respectively.

Effects of Bed Materials to Flow Characteristics on Open Channel and Gradually Varied Flow Simulation Using Genetic Algorithm (GA)

Determination of accurate roughness coefficient was realized necessary for hydraulic parameters estimation in open channel flow. For the purpose this study was planned to carry out on experimental basis in hydraulic laboratory hall of campus itself. In this study, a combination between experimental and numerical models study were carried out to investigate the influence of bed roughness on flow characteristics. Experiments were conducted on six bed materials (Sand, Gravel, Cement plaster, Grass, Formica and cast iron (original bed of channel)) in three conditions. Firstly the discharge was varied at same tail water level. Secondly the depths were varied for same discharge and thirdly the depths were measured for different discharges for each bed material Results were analyzed and were graphically presented .The Manning roughness coefficient was estimated for each bed material using the experimental and discharge optimization technique. The percentages of errors between the observed and predicted were reported. Since the channel represents compound case having glass wall and different bed material, the roughness coefficient of each bed materials were predicted by optimization on genetic algorithm to the lotter’s modified equation in which the exponent alpha value varies from 1.28 to 1.76 The shear stress distribution was examined by first and second approximation theory on smooth rectangular channel on Knight et al (1984) model. It was compared with the experimental average shear stress and was found the first approximation theory over estimated to the experimental value whereas second approximation result was within the average relative error of 1.61% for bed. Side wall/bed stress ration was found of 0.61. Similarly gradually varied flow was simulated in python using optimal value of roughness coefficient.

Assessment of the Rehabilitation of Watercourses (Study Case)

The goal of this study is to assess the rehabilitation of Bahr Awlad Mohamed canal.The canal was rehabilitated by installing lining trapezoidal cross-sections. Before and after the rehabilitation process, a field investigation, hydraulic and hydrographic measurements, and a mathematical model (Sobek – 1D) were conducted. According to the findings, the canal's rehabilitation improved average water velocity from 0.18 m/s to 0.32 m/s, the average Manning roughness coefficient from 0.065 m-1/3s to 0.020 m-1/3s, the water surface slope from 17 and 50 cm/km to 2 and 6 cm/km, the average areas of cross-sections reduced from 3.37 m2 to 3.07 m2, the average water width was reduced from 5.84 m to 4.83 m, the water losses were decreased by approximately 27.31 % from the canal's inlet discharge. Additionally, the water level fulfilled the requirements for water distribution, the canal banks were restored and widened, the hydraulic efficiency of the study canal was improved, alleviating downstream farmers' concerns and conserving water that could be utilized for irrigation, and saving time and maintenance cost. Finally, canal rehabilitation necessitates periodic maintenance, appropriate maintenance equipment, and a strategy of canal preservation. In addition, other canals in Egypt must be improved to determine the irrigation network's water-saving potential.

A Two-Level Optimization of the Manning Roughness Coefficient Method Based on the Modification of USDA-NRCS Method for Basin Irrigation Evaluation

A Two-Level Optimization of the Manning Roughness Coefficient Method Based on the Modification of USDA-NRCS Method for Basin Irrigation Evaluation

Flow resistance and velocity distribution in a smooth triangular channel

Abstract This study investigates the flow resistance and velocity distribution in a smooth triangular channel under varying slope conditions in a laboratory environment. For this purpose, two triangular cross-sectional shaped channels with 30° and 45° sidewall slopes were made. In various hydraulic conditions, bed slopes were carried out at different flow discharges and channels. The results have been used to test the stage-discharge curve, Manning roughness coefficient, n, the Darcy-Weisbach friction factor, f, and flow velocity profiles. By increasing the channel bed slope and flow discharge, the water surface fluctuation increased simultaneously. The fluctuation of flow surface profile in the triangular cross section (TCS) at 45° is more than in TCS 30° cases. The stage-discharge rating curve has less curvature with increasing channel bed slope. The Darcy-Weisbach f obtained from TCS 30° is higher than for TCS 45°, which means that TCS 30° has more resistance against flowing water passing through the channel than the 45° cross-section. Examination of the velocity contours shows that the maximum velocity occurred in the 30° triangular cross-section. Practical-sound findings from this research might be helpful for hydraulic engineers to design cost-effective open channels and other similar hydraulic structures.