• Water Engineering Research
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• v.6 no.3
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• pp.113-122
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• 2005

Periphyton is known to be one of major primary producers for river ecosystem. While the growth of periphyton usually observed on the stone surface in gravel river, the large growth of periphyton is sometimes seen even in sand river with relatively small river discharge. In the present study, field observations and numerical simulations were performed to investigate the growth of periphyton in sand river. In the field observation, the growth of periphyton on fixed sand bed was measured weekly. The results of the field observations show that the large growth of periphyton occurs in sand river until the bed material sands have not moved. An integrated numerical simulation model is presented to describe the growth of periphyton at observed river reach, and a series of numerical simulations were performed to study the effect of river discharge on growth of periphyton in the sand river. The results of the numerical simulations show that the net primary production of periphyton decreases with the river discharge. These results suggest that the reduction of river discharge at ordinary water stage strongly affects the primary productivity of periphyton even in sand river.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.149-149
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• 2018

Prediction on initial motion of sediment is crucial to evaluate sediment transport and channel stability. The condition of incipient movement of sediment is characterized by bed shear stress, which is generated from force of moving water against the bed of the channel, and by critical shear stress, which depends on force resisting motion of sediment due to the submerged weight of the grains. When the bed shear stress exceeds the critical shear stress, sediment particles begin rolling and sliding at isolated and random locations. In Mountain River, debris flow frequently occurs due to heavy rainfall and can lead some natural stones from mountain slope into the bed river. This phenomenon could add additional forces to sediment transport system in the bed of river and also affect or change direction and magnitude of sediment movement. In this paper, evaluations on incipient motion of uniform coarse gravel under falling spheres impacts using small scale flume channel were conducted. The drag force of falling spheres due to water flow and length movement of falling spheres were investigated. The experiments were carried out in flume channel made by glass wall and steel floor with 12 m long, 0.6 m wide, and 0.6 m deep. The bed slopes were selected with the range from 0.7% to 1.5%. The thickness of granular layer was at least 3 times of diameter of granular particle to meet grain placement condition. The sphere diameters were chosen to be 4cm, 6 cm, 8 cm, 10 cm. The spheres were fallen in to the bed channel for critical condition and under critical condition of motion particle. Based on the experimental results, the Shields curve of particles Reynold number and dimensionless critical shear stress were plotted. The relationship between with drag force and the length movement of spheres were plotted. The pathways of the bed material Under the impact of spheres falling were analyzed.

• Magazine of the Korean Society of Agricultural Engineers
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• v.22 no.4
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• pp.96-107
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• 1980

This study is carried out to estimate the rate of sediment transportation both to measure the amount of suspended and bedload sediment that moves on or near the river bed and passes through the cross section of a river in unit time, with suspended and bed load samplers used for the Milyang river and to determine the most satisfactory and convenient formula of some formulas for sediment discharge by comparing the measured rate with the calculated rate. The results of this study are summarized as follows; 1) The interrelationship (1) between the total discharge and the total sediment discharge (2) between discharge and suspended sediment load and (3) between discharge and bed load in the Milyang river are (1) i) 4$\leq$Q$\leq$100 C.M.S. Qr=0. 00272 Q0.70 (kg/sec) ii) 150$\leq$Q$\leq$800 C.M.S. Qr=0. 4807 Q0.46 (kg/sec) (2) Qs~=0. 07576 Q1.02 (kg/sec) (3) QB=0. 00957 Q0.44 (kg/sec) 2) The rate of suspended sediment load to total sediment discharge is found to be about; 99%. The suspended load is shown to be almost wash load which consists of silt and clay. 3) The relation between the total discharge and the suspended sediment load that are measured at three medium and small rivers in Korea is Qs=0. 13831 Q0.97 (kg/sec) 4) Brown's formula is determined to be the most convenient formula for application and comparison with observed data obtained for the Milyang river.

• Water for future
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• v.18 no.4
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• pp.327-333
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• 1985

The flow pattern of the nearshore current generated around the breached breakwaters and river-mouth was simulated by numerical model in the case of the inclined incident wave without river discharge when the detached breakwaters were installed at the river-mouth area for the protection against the blockade of the river-mouth. The validity of the numerical model was testified y comparision with the results obtained through the hydraulic model test at the fixed bed. The deformation of the topographic features around the river-mouth and the detached breakwaters was examined through the three-dimensional hydraulic model test at the movable bed. The usefulness of the detached breakwater work for the protection against the blockade of the river-mouth was identified by the experimental results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.1-7
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• 2012

Quasi-two dimensional numerical model (GSTARS) was applied to determine the optimal sediment discharge formula for simulating the sedimentologic characteristics of Hyeongsan river. The field measurements have been conducted to obtain the data, such as sediment discharge, bed material, and channel geometry, for model calibration and verification. The sediment discharge formulas, which have been generally used, have been assessed according to the average error, relative error, RMSE, RRMSE, discrepancy ratio and Nash-Sutcliffe efficiency coefficient for bed changes along the thalweg. From the results, Laursen formula(1958) shows the best performance to simulate the long-term bed change of Hyeongsan river.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.63-63
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• 2021

Bed shear stress is important variable in river flow analysis. The bed shear stress has an effects on bed erosion, sediment transport, and mean flow characteristics. Quadratic formula to estimate bed shear stress is widely used, 𝜏=𝜌c_fu|u| in which friction coefficient, c_f, needs to be assigned to numerical models. The aim of this study is to estimate Chezy coefficient using bathymetry data measured by ADCP. Bed form geometry variables will be estimated form bed profile, then Chezy coefficient will be determined using estimated bed form geometry variables in order to set friction coefficient to numerical model. From the probability density function obtained from the bathymetry data, Chezy coefficient will be randomly generated since Chezy coefficient is not uniform over the space and it does not depend on spatial variables such as water depth and distance from river bank. Numerical test will be performed to find to demonstrate randomly extracted Chezy coefficient is appropriate. The result of this study is valuable in that the friction coefficient is estimated in consideration of the bed profile, and as a result, uncertainty of the friction coefficient can be reduced.

• Journal of Forest and Environmental Science
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• v.15 no.1
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• pp.89-97
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• 1999

This study was carried out to obtain basic data on the kinds of aquatic insects and their living conditions in the mountain stream. The investigation was done in Bongmyung stream. Experimental Forest, Kangwon National University on aquatic insects, anions and river-bed materials. The results are as follows. 1. At every plot surveyed, diversity index, richness index and evenness index of aquatic insects appeared higher at upper stream than at lower stream in erosion control dam. 2. Anion concentrations were almost the same in plots A, B, C, D and E, but plot F at the lower stream showed 1.5 to 89 times higher concentration than the others. 3. In river-bed materials analysed, particle diameter was bigger at the upper stream than at the lower stream. At the down stream of erosion control dam showed high pebble composition ratio. 4. The number of aquatic insects showed the negative relation with the anion concentration and the positive one with the size of river-bed materials. Especially, they were affected much by the distribution chart of boulder.

• Journal of Korea Water Resources Association
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• v.48 no.1
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• pp.1-8
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• 2015

General features of sediment budget for the Nakdong River before the Four Rivers Restoration Project were analyzed using surveying, dredging, and mining data for the past 20 years, as well as sediment data measured from the tributaries, and numerical modeling, etc. As a result of the sediment budget analysis of the Nakdong River before the Four Rivers Restoration Project, sediment inflow supplied from the watershed is $2,100,000m^3/yr$ and sediment outflow including mining and dredging volumes is $10,180,000m^3/yr$. Therefore, the bed change volume estimated by the sediment budget analysis is $-8,080,000m^3/yr$ of the bed erosion volume which is similar to the analysis result ($-8,300,000m^3/yr$) of natural and artificial bed changes using the surveyed data.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.3 s.3
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• pp.93-102
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• 2001

In this study, the characteristics of river bed profile fluctuation are become possible to be used effectively in future estimation of Taehwa river general development plan through analysis and examination according to the effects of sediment protection weir located in the area of the estuary of Taehwa river's main channel using HEC-6 model. The flow conditions needed in analysis of the characteristics of river bed profile fluctuation refer the conditions of flow which secures 95 days in a year, flood flow, and design flood examined in the estimation of Taehwa river maintenance basic plan. First, in analysis result of river bed variation range, there is no significant variation in upstream section from Samho-gyo while there are the more active erosion and sedimentation as the more flow in downstream from Samho-gyo. Next, from the result of the capacity of sediment transfer, it is analyzed that sediment transfer capacity in the area of estuary of Taehwa river has no significant difference in before and after removal of the sediment protection weir when design flood flows while it is estimated that the more flow, the bigger sediment transfer capacity. Therefore, it is thought that the installation of a suitable hydraulic structure at the lowest point of Dong-chun tributary joins from the downstream of Taehwa river can be a good device to reduce the accumulation of sediments at the lowest point of Taehwa river considering the reduction plan of sediment inflow caused by removal of the sediment protection weir.

• Journal of Environmental Science International
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• v.20 no.5
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• pp.555-564
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• 2011

This study examines the potential restoration of abandoned channels of the Mangyeong River in South Korea. To analyze the morphological changes and equilibrium conditions, a flow duration analysis was performed to obtain the discharge of 255 m3/s with a recurrence interval of 1.5 year. It is a gravel-bed stream with a median bed diameter of 36 mm. The reach-averaged results using HEC-RAS showed that the top width is 244 m, the mean flow depth is 1.11 m, the width/depth ratio is very high at 277, the channel velocity is 1.18 m/s, and the Froude number is also high at 0.42. The hydraulic parameters vary in the vicinity of the three sills which control the bed elevation. The total sediment load is 6,500 tons per day and the equivalent sediment concentration is 240 mg/l. The Engelund-Hansen method was closer to the field measurements than any other method. The bed material coarser than 33 mm will not move. The methods of Julien-Wargadalam and Lacey gave an equilibrium channel width of 83 m and 77 m respectively, which demonstrates that the Mangyeong River is currently very wide and shallow. The planform geometry for the Mangyeong River is definitely straight with a sinuosity as low as 1.03. The thalweg and mean bed elevation profiles were analyzed using field measurements in 1976, 1993 and 2009. The measured profiles indicated that the channel has degraded about 2 m since 1976. The coarse gravel material and large width-depth ratio increase the stability of the bed material in this reach.