• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.659-667
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• 2017

This study analyzes the changes in the flow characteristics due to the difference in inflow discharges from the main channel and tributary at the confluence of the Nakdong and Geumho Rivers. The analysis was done using a two-dimensional numerical method. The study site has complicated flow patterns because of the discharge variation from the main stream and tributary. The study section has a meandering main channel, and the hydraulic characteristics cannot be defined with simple conditions such as the confluence angle of the channels or the ratio of the channel widths. An actual flood event in 2012 was applied in the numerical simulation. The maximum velocity occurred in the meandering section after passing the confluence, where a rapid change was expected. A high velocity and large bed change in this section were observed in the simulation results. The variation of discharges from the main channel and tributary was a more dominant factor in the flow and bed changes for the normal flow conditions than the flood event. This indicates that countermeasures for channel stabilization should be considered in the meandering section downstream of the confluence section, and countermeasures for the study section should be investigated.

• Journal of Soil and Groundwater Environment
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• v.14 no.2
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• pp.10-16
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• 2009

Characteristics of natural radioactivity were investigated for soils collected from seven sites of different bed rocks distributed in the Keum River area of Korea by the use of a Gamma-ray spectrometry. Specific activity (SA) and SA ratio (SAR) of typical naturally occurring radioactive nuclide such as $^{226}$Ra, $^{228}$Ac and $^{40}$K were determined for the soil samples. The SA values of $^{226}$Ra, $^{228}$Ac and $^{40}$K in 41 soils of 7 sites are 26.7-485 (74.2 ${\pm}$ 72.2), 30.9-157 (90.7 ${\pm}$ 32.7) and 203-1558 (990 ${\pm}$ 203) Bq/kg, respectively. The SA of $^{226}$Ra has very different values by the soils and the sites. Especially the SA of $^{226}$Ra in a soil sample of Ogcheon site is 485 Bq/kg while most SA of 41 soil samples are < 100 Bq/kg. SA of $^{228}$Ac has a little different values with the soils and sites, however the SA of $^{40}$K has almost constant values in all soil samples. The SAR values of $^{26}$Ra/$^{228}$Ac, $^{226}$Ra/$^{40}$K and $^{228}$Ac/$^{40}$K in 41 soils of 7 sites are 0.343-6.11 (0.865 ${\pm}$ 0.883), 0.0258-0.759 (0.0814 ${\pm}$ 0.1l17) and 0.0373-0.178 (0.0945 ${\pm}$ 0.0373), respectively. The SARs of $^{226}$Ra/$^{228}$Ac and $^{226}$Ra/$^{40}$K have very different values by the soils and the sites, however the SAR of $^{228}$Ac/$^{40}$K has a little difference by the soil and sites.

• Korean Journal of Remote Sensing
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• v.36 no.2_1
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• pp.103-119
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• 2020

Recently, the rapid redeposition and erosion of rivers artificially created by climate change and the Four Rivers Restoration Project is questionable. According to the revised law in Korea, the river management agency will periodically carry out bed changes surveys. However, there are technical limitations in contrast to the trend of increasing spatial coverage, density and narrowing of intervals. National organizations are interest in developing innovative bed changessurvey techniquesfor efficiency. Core of bathymetry survey is to measure the depth of rivers under a variety of river conditions, but that is relatively more risky, time-consuming and expensive compared to conventional ground surveys. To overcome the limitations of traditional technology, echo sounder, which has been mainly used for ocean depth surveying, has been applied to rivers. However, due to various technical limitations, it is still difficult to periodically investigate a wide range of areas. Therefore, technique using the remote sensing has been spotlighted as an alternative, especially showing the possibility of depth measurement using spectral characteristics. In this study, we develop and examine a technique that can measure depth of water using reflectance from spectral characteristics. As a result of applying the technique proposed in thisstudy, it was confirmed that the measured depth and the correlation and error corresponding to 0.986 and 0.053 m were measured in the depth range within 0.95 m. In the future, this study could be applied to the measurement of spatial depth if it is applied to the hyperspectral sensor mounted on the drone.

• Ecology and Resilient Infrastructure
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• v.4 no.3
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• pp.149-155
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• 2017

Willow plants are representative biomaterials used in river restoration and main target trees in stream managements. In order to understand the changes in the growth of Salix subfragilis and S. chaenomeloides with their stand ages, we investigated the density, height and basal area of stems and biomass at their different aged stands of the riparian zone of the sand-bed stream, the Nakdong River, Korea. We also developed allometric equations for estimating the biomass of these two species by establishing the relationship between diameter at breadth height and tree height with above-ground biomass. The stem density showed a sharp decrease for 3 years after germination for S. subfragilis and 6 years for S. chaenomeloides, resulting in strong self-thinning. The stem height of the two species increased to 7.5 m in 15 years for S. subfragilis, and to 14 m in 13 years for S. chaenomeloides. Aboveground biomass also increased rapidly at the early stage of growth. The biomass increased to 17 ton DM/ha in 13 years for S. subfragilis and to 1,110 ton DM / ha in 13 years for S. chaenomeloides. It is expected that the allometric equations of two Salix species derived from this study will be applied to the objectively estimating the biomass of willow plants for the management of floodplain trees in streams.

• Explosives and Blasting
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• v.21 no.3
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• pp.23-35
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• 2003

An analytical diffusion model for flood routing with backwater effects and lateral flows is developed. The basic diffusion equation is linearized about an average depth of (H + h), and is solved using the boundary conditons which take into account the effects of backwater and lateral flows. Scouring phenomenon around pier which affects on the support function of pier and the stabilization if river bed is a complex problem depending on flow properties and river bed state as well as pier geometry. therefore, there is no uniting theory at present which would enable the designer to estimate, with confidence, the depth of scour at bridge piers. The various methods used in erosion control are collectively called upstream engineering, HEC-RAS Model, underwater blasting. They consist of reforestation, check-dam construction, planting of burned-over areas, contour plowing and regulation of crop and grazing practices. Also included are measures for proper treatment of high embankments and cuts and stabilization of streambanks by planting or by revetment construction. One phase of reforestation that may be applied near a reservoir is planting of vegetation screens. Such screens, planted on the flats adjacent to the normal stream channel at the head of a reservoir, reduce the velocity of silt-laden storm inflows that inundate these areas. This stilling action causes extensive deposition to occur before the silt reaches the main cavity of the reservoir.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.1
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• pp.13-25
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• 2007

The water treatment plants in Seoul Metropolitan Area, which are under Korea Water Resources Corporation(KOWACO)'s management, take water from Paldang Reservoir in Han River System for drinking water supply. There are taste and odor (T&O) problems in the finished water because the conventional treatment processes do not effectively remove the T&O compounds. As part of countermeasures for taste and odor control, KOWACO is planning to introduce advanced water treatment process such as ozone and GAC in near future. This study evaluated the removal characteristics of T&O and dissolved organic matter (DOM) to find design and operation parameters of advanced water treatment processes in a pilot-scale treatment plant. The GAC adsorption capacity for DOC in the two GAC system (GAC and $O_3$-GAC) at an EBCT of 14min was mostly exhausted after 9months. The differency of the removal efficiency of DOC between $O_3$-GAC and GAC increased with increasing operation time because the bioactivity in $O_3$-GAC process was enhanced by post-ozone process. Removal by conventional treatment was unable to reach the target TON(threshold odor number) of 3 but GAC systems at an EBCT(empty bed contact time) of 14 min were able to archive the target with few exception. During the high T&O episodes, PAC as a pretreatment together with GAC could be useful option for T&O control. However, substantial TON removal continued for more than two year (> 90,000 bed volumes). At the spiking of less concentration 26 to 61 ng/L in the influent of GAC systems, GAC absorber and $O_3$-GAC processes could meet the treatment target. The better spike control after 12 and 19 months of operation compared to that after 7 months of operation is a strong indication of biological control. The results presented in this study had shown that $O_3$-GAC process was found to be more effective for T&O control than GAC process. And the main removal mechanism in GAC systems were adsorption capacity and biodegradation.

• Journal of the Korean earth science society
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• v.42 no.2
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• pp.164-174
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• 2021

The study examines the shearing and crushing characteristics of land-derived subaqueous granular materials in a gravel-bed river. A series of large-sized ring shear tests were performed to examine the effect of shear time and shear velocity on the shear stress characteristics of aquarium gravels with a 6-mm mean grain size. Three different shear velocities (i.e., 0.01, 0.1, and 1 mm/sec) were applied to measure the shear stress under the drained (long-term shearing) and undrained (short-term shearing) conditions. Different initial shear velocities, i.e., 0.01→0.1→1 mm/sec and 0.1→0.01→1 mm/sec, were considered in this study. The test results show that the grain crushing effect is significant regardless of drainage conditions. The shear stress of coarse-grained materials is influenced by initial shear velocities, regardless of the drainage conditions. In particular, particle breakage increases as grain size increases. The shearing time and initial shear velocity are the primary influencing factors determining the shear stress of gravels. The granular materials may be broken easily into particles through frictional resistance, such as abrasion, interlocking and fracture due to the particle-particle interaction, resulting in the high mobility of granular materials in a subaqueous environment.

• The Journal of the Korea Contents Association
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• v.15 no.8
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• pp.544-555
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• 2015

This study aims to derivate of the relationship and rating curve for the flow discharge-total sediment using the measured field data from the main points of small-medium stream reaches in agrarian basin. The total sediment of measured data are obtained by bed load added to suspended load which analyzed using the particle size distribution curve of sieve test and the dry or the filtration method from the collected samples by samplers (DH-48, D-74 and BLH-84, BL-84) at the stream bed and the depth-averaged concentration, respectively. These field data had been collected from August 2012 to September 2014 at the seven measuring stations of the national-local channel reaches of the four study streams in the Nonsan river systems of agrarian basin. As a result, the relationships and the rating curve for the flow discharge-total sediment are derived as a function pattern of power law by analyzing on a distribution characteristic of the database set and it will be used as a useful tool to analyze erosion, deposition, and transportation in theoretical research as well as in practical application of the hydraulic sedimentation engineering.

• Journal of Korea Water Resources Association
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• v.44 no.9
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• pp.741-751
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• 2011

In this study, a methodology was devised to overcome that difficulty for thermal stratification modeling using EFDC. For the increase of reproductability for thermal stratification analysis, the effect of parameter such as distribution of solar radiation, depth of active bed temperature layer, heat transfer coefficients were analyzed. The simulation period was from June to December in 2005 and statistical index is used to analyze the model results. The results showed that distribution of solar radiation is zero and depth of active bed temperature layer is 10 m are suitable for simulation of thermal stratification in Yongdam Dam reservoir. This study results can be used for guideline to analyze the thermal stratification of large dam reservoir in Korea.

• Journal of Environmental Science International
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• v.20 no.1
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• pp.107-118
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• 2011

While the assessment of mean flow field is very important to characterize the hydrodynamic aspect of the flow regime in river, the conventional methodologies have required very time-consuming efforts and cost to obtain the mean flow field. The paper provides an efficient technique to quickly assess mean flow field by developing and applying spatial averaging method utilizing repeatedly surveyed acoustic Doppler current profiler(ADCP)'s cross-sectional measurements. ADCP has been widely used in measuring the detailed velocity and discharge in the last two decades. In order to validate the proposed spatial averaging method, the averaged velocity filed using the spatial averaging was compared with the bench-mark data computed by the time-averaging of the consistent fix-point ADCP measurement, which has been known as a valid but a bit inefficient way to obtain mean velocity field. The comparison showed a good agreement between two methods, which indicates that the spatial averaging method is able to be used as a surrogate way to assess the mean flow field. Bed shear stress distribution, which is a derived hydrodynamic quantity from the mean velocity field, was additionally computed by using both spatial and time-averaging methods, and they were compared each other so as to validate the spatial averaging method. This comparison also gave a good agreement. Therefore, such comparisons proved the validity of the spatial averaging to quickly assess mean flow field. The mean velocity field and its derived riverine quantities can be actively used for characterizing the flow dynamics as well as potentially applicable for validating numerical simulations.