A new formula for predicting movable bed roughness coefficient in the Middle Yangtze River

2021 ◽  
pp. 030913332110662
Author(s):  
Xin Liu ◽  
Junqiang Xia ◽  
Meirong Zhou ◽  
Shanshan Deng ◽  
Zhiwei Li
Keyword(s):  
Yangtze River ◽  
Iterative Solution ◽  
Flood Routing ◽  
Sand Wave ◽  
Roughness Coefficient ◽  
Cross Sectional ◽  
Channel Boundary ◽  
Bed Roughness ◽  
New Formula ◽  
Movable Bed

Computing movable bed roughness plays an important role in the modeling of flood routing and bed deformation, and the magnitude of movable bed roughness is closely associated with complex bedform configurations that change with the sand wave motion. The motion of sand wave is dependent on the incoming flow and sediment conditions and channel boundary. After the operation of the Three Gorges Project, the flow and sediment regime changed remarkably in the Middle Yangtze River (MYR), followed by significant channel adjustments. A dramatic decrease in sediment concentration caused continuous channel degradation and significant variations in cross-sectional profiles of the MYR. These adjustments in the channel boundary influence the motion of sand wave, which can further affect the magnitude of movable bed roughness. A new formula for predicting the movable bed roughness coefficient is developed, which can be expressed by a power function of both Froude number and relative water depth. The proposed formula was first calibrated using 1266 datasets of measurements at five hydrometric stations in the MYR during 2001–2012. A back-calculation process shows that the roughness coefficients calculated by the proposed formula agree well with the observations, with the determination coefficient being equal to 0.88. The proposed formula was further verified using 651 datasets of measurements at these hydrometric stations during 2013–2017. Furthermore, four common roughness formulas selected from the literature were tested for comparison. The results indicate that the calculation accuracy of the proposed formula is significantly higher than that of the previous formulas, and the Manning roughness coefficients predicted by the proposed formula have the errors less than ±30% for 96% of the datasets. Therefore, the new bed roughness predictor proposed in this study can accurately calculate the roughness coefficients straightforwardly without iterative solution and graphical interpolation, and the parameters required in the roughness predictor are easily obtained from the hydrometric observations.

scholarly journals Experimental Investigations of Interactions between Sand Wave Movements, Flow Structure, and Individual Aquatic Plants in Natural Rivers: A Case Study of Potamogeton Pectinatus L.

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1166 ◽  
Author(s):  
Łukasz Przyborowski ◽  
Anna Łoboda ◽  
Robert Bialik
Keyword(s):  
Flow Velocity ◽  
Three Dimensional ◽  
Potamogeton Pectinatus ◽  
Sand Wave ◽  
Experimental Investigations ◽  
Cross Sectional ◽  
Bending Tests ◽  
Long Duration ◽  
Elevation Changes

Long-duration measurements were performed in two sandy bed rivers, and three-dimensional (3D) flow velocity and bottom elevation changes were measured in a vegetated area and in a clear region of a river. Detailed flow velocity profiles downstream and upstream of a single specimen of Potamogeton pectinatus L. were obtained and the bed morphology was assessed. Potamogeton plants gathered from each river were subjected to tensile and bending tests. The results show that the existence of the plants was influenced by both bottom and flow conditions, as the plants were located where water velocity was lower by 12% to 16% in comparison to clear region. The characteristics of the flow and sand forms depended on the cross-sectional arrangement of the river, e.g., dunes were approximately four times higher in the middle of the river than in vegetated regions near the bank. Furthermore, the studied hydrophytes were too sparse to affect water flow and had no discernible impact on the sand forms’ movements. The turbulent kinetic energy downstream of a single plant was reduced by approximately 25%. Additionally, the plants’ biomechanical characteristics and morphology were found to have adjusted to match the river conditions.

A Modified Chezy Formula for One-Dimensional Unsteady Frictional Resistance in Open Channel Flow

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Junwei Zhou ◽  
Weimin Bao ◽  
Geoffrey R. Tick ◽  
Hamed Moftakhari ◽  
Yu Li ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Frictional Resistance ◽  
Mitigation Strategies ◽  
Flood Routing ◽  
Flood Events ◽  
Complex Flow ◽  
Cross Sectional ◽  
Friction Resistance ◽  
Flow Unsteadiness ◽  
Better Than

Abstract It has been observed in literature that for unsteady flow conditions the one-to-one relationships between flow depth, cross-sectional averaged velocity, and frictional resistance as determined from steady uniform flow cases may not be appropriate for these more complex flow systems. Thus, a general friction resistance formula needs to be modified through the addition of new descriptive terms to account for flow unsteadiness, in order to eliminate errors due to uniform and steady-flow assumptions. An extended Chezy formula incorporating both time and space partial derivatives of hydraulic parameters was developed using dimensional analysis to investigate the relationship between flow unsteadiness and friction resistance. Results show that the proposed formula performs better than the traditional Chezy formula for simulating real hydrograph cases whereby both formula coefficients are individually identified for each flood event and coefficients are predetermined using other flood events as calibration cases. Although the extended Chezy formula as well as the original Chezy formula perform worse with the increasing degree of flow unsteadiness, its results are less dramatically affected by unsteadiness intensity, thereby improving estimations of flood routing. As a result, it tends to perform much better than traditional Chezy formula for severe flood events. Under more complex conditions whereby peak flooding events may occur predominantly under unsteady flow, the extended Chezy model may provide as a valuable tool for researchers, practitioners, and water managers for assessing and predicting impacts for flooding and for the development of more appropriate mitigation strategies and more accurate risk assessments.

scholarly journals Modeling total resistance and form resistance of movable bed channels via experimental data and a kernel-based approach

2020 ◽  
Vol 22 (3) ◽  
pp. 528-540
Author(s):  
Seyed Mahdi Saghebian ◽  
Kiyoumars Roushangar ◽  
V. S. Ozgur Kirca ◽  
Roghayeh Ghasempour
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Laboratory Data ◽  
Gaussian Process Regression ◽  
Roughness Coefficient ◽  
Alluvial Channels ◽  
Sediment Characteristics ◽  
Modeling Process ◽  
The Impact ◽  
Movable Bed

Abstract An accurate prediction of roughness coefficient in alluvial channels is of substantial importance for river management. In this study, the total and form resistance in alluvial channels with dune bedform were assessed using experimental data. First, the data of experiments carried out at the Hydraulic Laboratory of University of Tabriz was used to investigate the impact of hydraulic and sediment parameters on roughness coefficient. Then, these data were combined with other laboratory data, and the total and bedform resistance were modeled via a Gaussian Process Regression (GPR) approach. For models, developing different input combinations were considered based on flow and sediment characteristics. The obtained results from the experiments showed that the Reynolds number has a better correlation with flow resistance in comparison with other hydraulic parameters. It was found that the roughness variations due to bedform are almost between 40 and 80% of the total roughness coefficient. Also, the obtained results proved the capability of the GPR method in the modeling process. It was found that the model which took the advantages of both flow and sediment characteristics performed better compared to the other models. The sensitivity analysis results showed that the Reynolds number has the most significant impact in the prediction process.

scholarly journals Analysis of Sedimentation for The Optimization of Lempake Dam Operations for Flood Control for The City of Samarinda, Province of East Kalimantan

2021 ◽  
Vol 004 (01) ◽  
pp. 010-021
Author(s):  
Sandi Erryanto ◽  
Ussy Andawayanti ◽  
Ery Suhartanto
Keyword(s):  
Flood Control ◽  
Flood Routing ◽  
Raw Water ◽  
Reservoir Operations ◽  
Cross Sectional ◽  
East Kalimantan ◽  
Safe Limit ◽  
Normal Water ◽  
The City ◽  
Mapping Program

The Lempake Dam currently functions as a dam that provides raw water for irrigation and clean water, besides its indirect functioning as the only flood control dam in the Karangmumus sub-watershed. Current conditions indicate that the Lempake Reservoir has experienced decreased capacity from year to year. At the normal water level, the reservoir capacity of Lempake Reservoir in 2013 was 0.76 million m3 and in 2018 was 0.39 million m3. Therefore, efforts are needed to control reservoir sedimentation and reservoir operations to allow the Lempake Dam to continue to function as a flood control reservoir. This study was carried out by analyzing the volume of sedimentation in the reservoir using the ArcGIS program and analyzing the flood hydrograph at the site by flood routing at the Pasar Segiri River, optimizing reservoir operations, and mapping flood inundation using the RAS Mapping program (HEC-RAS). The results showed that the storage volume in 2020 is predicted to be 0.241 million m3 with an annual sediment rate of 0.074 million m3. From the flood routing analysis and optimization of reservoir operations, the cross-sectional capacity of the river in Pasar Segiri (safe limit elevation +3.30 m) is insufficient for a flood discharge of a return period of more than 2 years (more than 222.14 m3/sec) for Scenario 1, and of more than 5 years (more than 320.48 m3/sec) for Scenario 2

scholarly journals Flow Resistance in Lowland Rivers Impacted with Distributed Aquatic Vegetation

2021 ◽  
Author(s):  
Saeid Okhravi ◽  
Radoslav Schügerl ◽  
Yvetta Velísková
Keyword(s):  
Cross Sections ◽  
Flow Resistance ◽  
Aquatic Vegetation ◽  
Roughness Coefficient ◽  
Sources Of Resistance ◽  
Lowland Rivers ◽  
Lowland Streams ◽  
Resistance Factors ◽  
Seasonal Flow ◽  
Bed Roughness

Abstract The study addresses the research concern that the employment of fixed value for bed roughness coefficient in lowland rivers (mostly ‌sand-bed rivers) is deemed practically questionable in the presence of a mobile bed and time-dependent changes in vegetation patches. To address this issue, we set up 45 cross-sections in four lowland streams to investigate seasonal flow resistance values within a year. The results first revealed that the significant sources of boundary resistance in lowland rivers with lower regime flow are bed forms and aquatic vegetation. Then, the study uses flow discharge as an influential variable reflecting the impacts of the above-mentioned sources of resistance to flow. The studied approach ended up with two new flow resistance predictors which simply connect dimensionless unit discharge with flow resistance factors, Darcy-Weisbach (f) and Manning (n) coefficients. A comparison between the computed and measured flow resistance values indicates that 87-89% of data sets were within the ±20% error bands. The flow resistance predictors are also verified against large independent sets of field and flume data. The obtained predictions using the developed predictors may overestimate flow resistance factors to about 40% for other lowland rivers. From a different view of this research, the findings on seasonal variation of vegetation abundance hint at the augmentation in flow resistance values, both f, and n, in low summer flows when the vegetation covers river bed and side banks. The highest amount of flow resistance was observed during the summer period, July-August.

scholarly journals Bankfull discharge estimation for Fishpot Creek

2020 ◽  
Vol 2 (5) ◽  
pp. 74-91
Author(s):  
Farhad Sakhaee
Keyword(s):  
Laser Scanning ◽  
Roughness Coefficient ◽  
3D Laser Scanning ◽  
Stream Channel ◽  
Cross Sectional ◽  
Bankfull Discharge ◽  
Data Points ◽  
The Cross ◽  
Sectional Shape ◽  
Discharge Estimation

Abstract: Fishpot Creek has been investigated and bankfull discharge was calculated based on the collected data points obtained from 3D laser scanning of the stream. This report consists of two major parts. One is the 3D scanning and analysis the results, other part includes sampling of both bed and bank materials. In the first part, essential parameters of roughness coefficient based on Cowan’s method were calculated as well as calculating the cross-sectional area and wetted perimeter based on the profile obtained from stream channel scanning.  Leica Scan Station HDS 3000 scanner was used to visualize the cross-sectional shape of the stream based on a high-density scan technology and finally applied to the manning’s equation to calculate the bankfull discharge. for sampling part both bed and bank materials were analyzed in lab, mechanical sieve test performed to investigate the gradation of bed and banks materials within the study area.

scholarly journals Effect of Roughness on Discharge

2013 ◽  
Vol 4 (3) ◽  
pp. 29-33 ◽  
Author(s):  
T.W. Lau ◽  
N.R. Afshar
Keyword(s):  
Grain Size ◽  
Flow Rate ◽  
Roughness Coefficient ◽  
Coefficient Increase ◽  
Different Types ◽  
Channel Slope ◽  
Experimental Works ◽  
Bed Roughness ◽  
Material Grain Size ◽  
Effect Of Surface

These Water resource projects and hydraulic engineering works have been developing rapidly throughout the world, thus prediction of water roughness coefficient is becoming an importance criteria for the designs of hydraulic related structure like open channel, and dam structure. The purposes of this research are to determine the effect of roughness on discharge and study on the factors that affect roughness coefficient. The roughness coefficient for this study is expressed in terms of Manning’s n. Experimental works were carried out to study the effect of roughness by using flumes (8m x 0.3m x 0.4m) with different types of roughened bed such as 2mm grain size plate and 5mm grain size plate. The experiments were being tested with various flow rates for slope equal to 1:300, 1:600 and 1:900 to determine the effect of slope on roughness coefficient. The results of the experimental study were presented and shown that the effect of surface roughness, material grain size, channel slope, and Manning’s roughness coefficient on flow rate. For the range of conditions tested, the discharge was found to be decreased as roughness coefficient increase. From the experiments, it shows smoother surface is having lower roughness coefficient and less retarding effect on the water flow, higher flow rate is produced. As conclusion, flow rate and roughness coefficient were influenced by bed roughness and slope.

scholarly journals Analysis of the Flow Performance of the Complex Cross-Section Module to Reduce the Sedimentation in a Combined Sewer Pipe

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3291
Author(s):  
Hyon Wook Ji ◽  
Sung Soo Yoo ◽  
Dan Daehyun Koo ◽  
Jeong-Hee Kang
Keyword(s):  
Flow Velocity ◽  
Cross Section ◽  
Roughness Coefficient ◽  
Cross Sectional ◽  
Complex Cross ◽  
Complex Cross Section ◽  
Combined Sewer ◽  
Manning's Equation ◽  
Manning’S Equation ◽  
Rainy Days

The difference in the amount of stormwater and sewage in a combined sewer system is significantly large in areas where heavy rainfall is concentrated. This leads to a low water level and slow flow velocity inside the pipes, which causes sedimentation and odor on non-rainy days. A complex cross-section module increases the flow velocity by creating a small waterway inside the pipe for sewage to flow on non-rainy days. While considering Manning’s equation, we applied the principle where the flow velocity is proportional to two-thirds of the power of the hydraulic radius. The flow velocity of a circular pipe with a diameter of 450 mm and the corresponding complex cross-section module was analyzed by applying Manning’s equation and numerical modeling to show the effects of the complex cross-section module. The tractive force was compared based on a lab-scale experiment. When all conditions were identical except for the cross-sectional shape, the average flow velocity of the complex cross-section module was 14% higher while the size of the transported sand grains was up to 0.5 mm larger. This increase in flow velocity can be even higher if the roughness coefficient of aging pipes can be decreased.

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