• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.3
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• pp.21-29
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• 1985

An effective technique of sludge separation is required for concentrated activated sludge process. The dissolved-air flotation (DAF) has been shown to be efficient process for sludge separation. The factors affecting DAF process for activated sludge separation are type and concentration of sludge, air/solid ratio, ratio of pressurized water flow, pressure, sludge detention time, temperature, sludge and hydraulic loading rate, recycle flow rate of sludge and type and quantity of chemical aid. In order to study the optimal operation condition for sludge separation, the influence factors such as type and concentration of sludge, ratio of pressurized water flow and pressure are investigated by the batch and continuous reactor experiments of DAF and sedimentation test. By the experimental investigation, the results are as follows; 1. For the bulking and concentrated sludge, DAF is more effective than sedimentation for the sludge separation. 2. In DAF, the critical ratio of pressurized water flow exist. The critical value varies with the pressure in the tank. That is, according to the pressure changes from 3 to $5kg/cm^2$, the critical value varies from 0.25 to 0.67 accordingly. 3. Pressure affects the ratio of pressurized water flow, but it does not show any influence upon the DAF efficiency directly. 4. Continuous experimental results was not better than those of batch.

• Journal of Korea Water Resources Association
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• v.51 no.9
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• pp.795-802
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• 2018

This study investigates the hydraulic characteristics and the delta development processes in the improved-pneumatic-movable weir by considering the standing angle of the weir through laboratory experiments. The delta migration speed decreases rapidly with time. As the ratio of delta height to water depth increases, the dimensionless delta migration speed decreases at the delta point. Therefore, the water depth decreases as the delta height increases. Although the delta volume is large due to the effective height of the delta, the delta migration speed and sediment deposition decreases because of the backwater effect on the delta. On the same bed slope condition, the larger the weir height, the larger the delta volume and the ratio of delta height to delta front length is close to 1.0. The delta development could be suppressed when the weir is high. Therefore, the condition that the weir is high has the suppressing effect on the delta developments.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.180-185
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• 2001

In order to regulate the physical characteristics of an ocean dumping material in the south-eastern East Sea, the diffusion characteristics with the observation, hydraulic experiment and numerical experiment data are investigated. The main results are as follows; (1) Spying CTD observation result of the area of Jung in the East Sea, the ocean dumping area had influenced the Tsushima warm current of high temperature and salinity. Horizontal turbulent diffusivity is 1.913${\times}$10$^{7}$ $\textrm{cm}^2$/sec by drogue tracking. (2) From the experiment of settling, the initial settling velocity of each material is 1.0∼2.7 cm/sec according to the specific gravity and initial concentration. In the pycnocline, particles didn't settle under the pycnocline any more and accumulated. It is signified that calculation of the sedimentation rate of the ocean dumping material including of vertical diffustion must be regard the pycnocline in the ocean area have well-developed pycnocline. (3) Vertical turbulent diffusivity were 2.219${\times}$10$^{-8}$∼8,874${\times}$10$^{-4}$ $\textrm{cm}^2$/sec from the experiment of settling. And, the pycnocline influenced the vertical turbulent diffusivity. (4) From the result of diffusion simulation in the East Sea, the co-concentration line of 0.05 ppm and 0.1 ppm are limited at dumping area after 200 days. The constant concentration line of 0.01 ppm is distributed to the vicinity of Ulleungdo and Tokdo, but isn't distributed to the coastal area of East Sea and southern area of Jung in the East Sea.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.546-556
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• 2006

The purpose of this study is to improve the polluted stream water quality by pilot-scale five different constructed wetlands (CWs). Cell 1 to 3 are newly designed 2SFCW (Surface-subsurface flow CW) with 1 to 3 flow shifters (FS) in the middle of the wetland system. Cell 4 and 5 are control CW (CCW), but Cell 5 is the same type as Cell 3. The FS, which converts the route of surface and subsurface flow between two wetlands connected in series, was able to enhance the treatability of TN via nitrification and denitrification and of SS due to filtration and sedimentation. The void fraction and dispersion number of Cell 1, 2 and 3 obtained from the RTD analysis were found to be 0.73 and 0.17, respectively. COD and TP removal efficiencies of Cell 1 to 3 were similar to that of Cell 4 and 5. SS removal efficiencies of Cell 1 to 3 and 5 with FS were 5-10% higher than that of Cell 4 without FS. TN removal efficiencies of Cell 1 to 3 were 3-14% higher than that of Cell 4 and 5. The average $R^2$ values of COD, SS, TN and TP obtained from nonlinear regression analysis were similar to the results of other researchers.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.305-313
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• 2010

River restoration or rehabilitation should be conducted in a way to maximize the channel stability with natural river configuration close to the equilibrium condition considering divers aspects of fluvial hydraulics, erosion and sedimentation, fluvial geomorphology, and ecological environment and to minimize the maintenance work. Therefore, the channel stability evaluation for present condition based on the equilibrium channel concept should be preceded for the river restoration project. Methods for equilibrium channel theory have generally been developed following either analytical regime theory or empirical regime theory. The main purpose of this paper is to evaluate the stability of present channel condition for the section of abandoned channel restoration in Cheongmi Stream using the Stable channel Analytical Model (SAM) and equilibrium hydraulic geometry equations. The results of analytical and empirical regime theories should provide fundamental and essential information to design the stable channel geometry. As a calculation result of Copeland's method for the study reach, the equilibrium channel has a narrower channel width, deeper water depth, and more gentle slope than the present channel geometry. As results of equilibrium hydraulic geometry equations, predicted equilibrium widths are less than the channel width in the field. It is represented that the current bed slope must be gentle to reach the equilibrium condition according to the results of Julien and Wargadalam method.

• Journal of The Geomorphological Association of Korea
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• v.28 no.3
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• pp.13-26
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• 2021

In mountain gully, channelized debris flow is an important phenomenon in the process of topographical change. Social infrastructure as roads may be damaged by channelized debris flows, but there has been little information about their occurrence and movement to prepare for the risk of the debris flow. Most of the channelized debris flows occur during heavy rains in mountainous valleys that are difficult to access, so there are not many field data. In this study, the topographical characteristics of the catchment, the rainfall and runoff related to the debris flow, the sedimentary pattern and the cross-sectional change of the channel bed, and the underflow velocity of the gravel bed have been investigated and analyzed in the Singi gully where the channelized debris flows occurred. In the catchment, there was almost no sediment runoff because the vegetation combine with the debris landforms and covered the surface. Therefore, the obvious cause of the channelized debris flows is the collapse of the slope and bed of the gully. Even if the gravel, cobbles, and boulders of the channel bed were lost by debris flow, the thalweg change due to debris flow may not be significant because they are supplied from the gully side slope normally. After the gabion structures were installed, the debris flow increased the thalweg change, bed erosion and side slope of the gully. Various sedimentary structures in the gully were classified according to the factors supporting the sedimentation. The hypsometric curve of the gully reflects the debris landforms and vegetation characteristics of the watershed and the sediment runoff due to debris flow, etc. The relationship between the flow velocity and the hydraulic gradient was non-linear under the condition that the porous medium with gully bed gravels is saturated with water. These results may be used as basic data for channelized debris flow research.

• Journal of Korea Water Resources Association
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• v.50 no.9
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• pp.587-595
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• 2017

Hydraulic characteristics affecting sediment transport capacity due to the weir operations were investigated and developed sediment rating curves for four gaging stations (Nakdong, Gumi, Waegwan, and Jindong) in Nakdong River. Analysis found that the sediment transportaion capability had been decreased and it could be proved from the field measurement records in 2013. Applicabilities of nine sediment transport prediction techniques, which are imbeded in GUIDE program, were examined and adopted for the four gaging stations. Analysis of sediment balance for Nakdong River, including 9 major tributaries, had been carried out with pseudo 2-D numerical model and found that: 1) sedimentation phenomena will be prevailed along the Nakdong River. 2) Engelund-Hansen technique shows the least error in estimation of sediment balance. 3) Engelund-Hansen technique most appropriately describes the sediment characteristics for four gaging stations. 4) Estimated error from the sediment balance for Nakdong River was smaller than the error caused by the estimation of sediment incomming from 9 tributries. Therefore, it is necessary to improve the accuracy of predicting the sediment incomming from the tributaties for better sediment balance analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.3
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• pp.61-71
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• 1988

The stage-discharge relation curve(rating curve) is the basic formula in hydrologic analysis. It plays an important role in converting to the discharge from available flood water level data including the daily mean stage. However, the river induces a cross section change at the gauging station because of the composed material of the river bed and three processes of the stream flow; i.e., erosion, transportation, and sedimentation. Rating curve has to be revised according to the temporal variation of the river bed due to the those factors. In this study, the basic rating curve is developed with respect to the current river bed to convert the existing rating curves and also to seize the hydraulic and geometric characteristics for the temporal variation of the river bed, relationships among the basic rating curve and the existing rating curves, water level, cross sectional area, and flow velocity are analyzed. Indogyo station, which is not only the key station of the Han river but also greatly changed the river bed after completion of the Han river development plan during the year 1983 to 1986, was chosen for the study. In this study, the river bed is assumed in a dynamic equilibrium condition. The basic rating curve is developed using hydrologic data of the physical year of 1987. For a given discharge, relationships for conversion of previous data, stage and velocity, the current one are formulated. To verify the usefulness of the relationships, stage-cross sectional area and stage velocity formula are also derived. Both hydrologic method using continuity equation and statistical method by the rating curve are compared and checked, then the validation of the both are positively shown.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1039-1049
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• 2015

The inflow estimation at large multipurpose dam reservoir is carried out by considering the water balance among the discharge, the storage change during unit time interval obtained from the observed water level near dam structure and area-volume curve. This method can be ideal for level pool reservoir but include potential errors when the inflow is influenced by the water level slope due to backwater effects from upstream flood inflows and strong wind induced by typhoon. In addition, the other uncertainties arisen from the storage reduction due to sedimentation after the dam construction and water level noise due to mechanical vibration transmitted from the electric power generator. These uncertainties impedes the accurate hydraulic inflow measurement requiring exquisite hydrometric data arrangement for reservoir waterbody. In this study, the distributed hydrologic model using UBC-3P boundary setting was applied and its feasibility was evaluated. Finally, the modeling performance has been verified since the calculated determination coefficient has been in between 0.96 to 0.99 after comparing with observed peak inflow and total inflow at Namgang dam reservoir.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.1
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• pp.58-63
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• 2009

Dissolved air flotation (DAF) process is generally considered more effective than sedimentation process in raw water containing algae, humus materials, and low density particles. This study presents the treatment efficiencies by the coagulation and flocculation conditions at a drinking water treatment plant using a laboratory tester and the full scale DAF pump system. The full scale DAF pump system (F-DAF) in this study had a capacity of 5,000 $m^3$/d and a hydraulic surface loading of 10 m/hr. F-DAF in D drinking water treatment plant was continuously operated to determine the operational performance and pretreatment (mixing and coagulation) conditions. Results in the laboratory experiment showed that the optimum coagulant (PSO-M) doses required to 2.7~4.5 mL/$m^3$/NTU with raw water turbidity from 13.8 NTU to 56.3 NTU. F-DAF in the optimum coagulant dosage could be operated in effluent turbidity of 1 NTU or below for a month.