• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.472-477
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• 2006

This study aims at investigating the failure cases of the pre-cast block system in river environments which widely used nowadays and reviewing the effect and flow resistance for grass concrete structure through the physical experiments by hydraulic model test and developing application method in river slope or levee which has rigid flood resistance. Grass concrete structure has been independently tested under high velocity flow under the super critical condition, it survived the 8 m/sec maximum flow velocity. This results shows grass concrete system is also suited to use in aggressive river environments such as repairing a flood damaged embankment that had placed at risk the adjacent drainage channel with vegetation.

• Journal of the Korean Society of Industry Convergence
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• v.10 no.4
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• pp.275-283
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• 2007

This study aims at the calculation of a variation of flow characteristics of main channel for tributary inflow in river junction. So this study was analyzed the variation of flow depth and velocity in main channel for a change of inflow degree. For this purpose, FLDWAV model are carried out for variations of $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$ tributary inflow at junction. Results show that velocity ratio(V1/V3) increases and flow depth ratio(H1/H3) decreases for discharge ratio(Q1/Q3) of upstream and downstream when degree increases in junction. And FLDWAV model was applied at a real river junctions. Selected area is a junction of Gumho river and Sin stream. Results show that pattern is similar to a virtual channel.

• Journal of Korean Society on Water Environment
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• v.33 no.4
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• pp.449-459
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• 2017

In Geum River of Korea, three multi-purpose weirs were built at the downstream of Daecheong Reservoir during the Four Major River Restoration Project (FMRRP). The weirs have altered the hydraulic characteristics of the river, and consequently transformed the large areas of flowing ecosystem to deep and wide stagnant environment. In every summer, a thermal stratification occurred near the Baekje Weir having mean depth of 4.0 m, and the surface algal blooms dominated by buoyant cyanobacteria have been frequently formed after the FMRRP. The objective of this study was to investigate the relationship between flow velocity and thermal stability of the waterbody using a three-dimensional (3D) hydrodynamic model (EFDC+) after calibration against the thermistor chain data obtained in 2014. A new Sigma-Zed vertical grid system of EFDC+ that minimize the pressure gradient errors was used to better simulate the thermodynamics of the waterbody. The model reasonably simulated the vertical profiles of the observed water temperatures. The vertical mean flow velocity and the Richardson Number (Ri) that represents the stability of waterbody were estimated for various management water levels and flow rates scenarios. The results indicated that the thermal stability of the waterbody is mostly high ($Ri{\gg}0.25$) enough to establish stratification, and largely depend on the flow velocity. The critical flow velocity that can avoid a persistent thermal stratification was found to be approximately 0.1 m/s.

• Ecology and Resilient Infrastructure
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• v.5 no.3
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• pp.156-162
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• 2018

This research aimed at analyzing comparison results between in gravel and sand bed with respect to the detailed Acoustic Doppler Current Profiler (ADCP) measurement in a velocity, depth, and flow rate data based on Acoustic Doppler Velocimeter (ADV) measurement result. Conclusionally, similar results were shown for gravel and sand bed in velocity, depth and flow rate data using ADV and ADCP measurement. The results of the flow rate show a relative error mean of 3.5 - 4.8% in the gravel bed and 0.02 - 3.2% in the sand bed, which is better performance than the mean error of 5% suggested by United States Geological Survey (USGS). The results can be used as a basis data for the measurement of ADCP and potentially able to be utilized for the more detailed uncertainty analysis of ADCP flow rate measurement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.87-96
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• 2020

To use a hydraulic structure effectively, the velocity of a river should be known in detail. In reality, velocity measurements are not conducted sufficiently because of their high cost. The formulae to yield the flux and velocity of the river are commonly called the Manning and Chezy formulae, which are empirical equations applied to uniform flow. This study is based on Chiu (1987)'s paper using entropy theory to solve the limits of the existing velocity formula and distribution and suggests the velocity and distance formula derived from information entropy. The data of a channel having records of a spot's velocity was used to verify the derived formula's utility and showed R2 values of distance and velocity of 0.9993 and 0.8051~0.9483, respectively. The travel distance and velocity of a moving spot following the streamflow were calculated using some flow information, which solves the difficulty in frequent flood measurements when it is needed. This can be used to make a longitudinal section of a river composed of a horizontal distance and elevation. Moreover, GIS makes it possible to obtain accurate information, such as the characteristics of a river. The connection with flow information and GIS model can be used as alarming and expecting flood systems.

• Journal of Environmental Impact Assessment
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• v.20 no.1
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• pp.37-48
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• 2011

Recently, the social and environmental functions of nature river are important due to the increase of expectation for river restoration. So it should be considered the effect of vegetation affecting the conveyance capacity and hydraulic resistance. However, it has not yet proposed a objective standard and modeling method to estimate the effect of conveyance capacity according to vegetaion distribution in the watercourse such as water level or velocity. Therefore, this study simulates the variations of water level and velocity using 3-dimensional hydrodynamic model, EFDC, to consider a conveyance capacity in downstream of the Soyang Reservoir. The simulation results were validated using statistical index such as F-test and T-test. As results, the water level rises about 0.01 to 0.47m and velocity difference are about -0.95m/s to 0.23m/s.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.798-801
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• 2001

This research is about slurry wear of SM45C and SUS304, which using standard sand and KUM river sand. The results are as follows ; 1. Mass loss rates of both standard sand and KUM river sand were linearly increased as increasement of time and velocity. 2. The average diameter of sand from relatively, less wear rate and portion of larger particles. 3. Wear resistance was linear with time and velocity of liquid jet regardless of type of sand. Also it was able to evaluate with the formula, HV2/E calibrated with n, the velocity index. 4. The wear surface in liquid jet experiment was smooth. The maximum wear depth was observed at the location, 2~4mm apart from the center in the condition of 90$^{\circ}$of collision angle 6mm of nozzle diameter, and 20mm of collision distance. The sectional shape in radial appeared as 'W' shape.

• Journal of Korean Society on Water Environment
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• v.23 no.6
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• pp.807-813
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• 2007

Settling velocity is one of major parameters determining algal biomass in water quality modeling. In this study, the settling velocity of phytoplankton was measured in reservoir and stream sites of the Nakdong River, Korea. Settling velocities of various phytoplankton species were determined by measuring algal cell biomass settled in a sedimentation cylinder. Mean settling velocities were $0.22m\;day^{-1}$ in reservoir sites and $0.33m\;day^{-1}$ in stream sites, which were relatively higher compared with other default values suggested by water quality models (e.g. $0.1m\;day^{-1}$ in CE-QUAL-W2). The lower settling velocity in reservoirs than in stream implies the adaptation of phytoplakton to low turbulence in lentic environments. Cyanobacteria showed lower settling velocity ($0.2m\;day^{-1}$) than diatoms ($0.3m\;day^{-1}$), and this phenomenon may have resulted from buoyancy mechanisms of cyanobacteria. Cell volume did not show a significant correlation with settling velocity in this study, implying that conformation factors of colonies or other factors had large effects on settling velocity of algal cells as well as cell size. The result of this study may suggest proper coefficients of settling velocity of phytoplankton in the calibration of water quality model.

• Journal of Korea Water Resources Association
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• v.42 no.10
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• pp.867-876
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• 2009

In this study, the stage-discharge relation curve made in 2006 is selected with standard curves to seize the hydraulic and geometric characteristics for the temporal variation of the river bed. The relationships among the standard stage-discharge relation curve and the existing stage-discharge relation curves, water level, cross sectional area, and flow velocity are analyzed. Jeokpogyo and Jindong which are the key station of Nakdong river are chosen for the study, with respect to the current river bed to convert the existing stage-discharge curves. The relationships for conversion of previous data, between water level and flow velocity are got. Also the relation equation between water level and cross sectional area and water level, flow velocity are derived. These conversion relationships shows good agreement between observed values and estimated values. It will be very useful to convert past hydraulic quantitations to current one.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6558-6564
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• 2013

As the average indicator for amount of water flowing in any cross section of a river, the mean discharge has been reported to be a very important factor for examining water circle constructions in a river basin, the design and construction of a hydraulic structure, and water front area use and management. The stage-discharge curve based on discharge and stage data measured in a normal season were basically derived. Using this derivation, the necessary discharge data was obtained. The values produced in this manner corresponded to the measured data in a uniform flow state well, but showed limited accuracy in a flood season (unsteady flow). In the present paper, the mean velocity in unsteady flow conditions, which exhibited loop form properties, was estimated using the new mean velocity formula derived from Chiu's 2-D velocity. The results of RMSE and Polar graph analyses showed that the proposed equation exhibited approximately nineteen times the accuracy compared to the Manning and Chezy equations.