• Journal of Korean Society of Environmental Engineers
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• v.37 no.10
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• pp.551-557
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• 2015

This study analyzes potentially hazardous sub-watersheds from non-point source pollution areas using an HSPF model. The watershed of the Juam dam reservoir was divided into 29 sub-watersheds, and the flow, BOD, TN and TP concentration for the Juam dam watershed were evaluated from 2009 to 2012 using a watershed model, with a warming period from 2009 to 2010. The results of the watershed model agreed well with the flow and water quality field measurements. The calculated average non-point source loadings were BOD of 8.8 and $9.1kg/day/km^2$ in 2011 and 2012, respectively; TN of 9.7 and $10.1kg/day/km^2$ in 2011 and 2012, respectively; and TP of 0.30 and $0.33kg/day/km^2$ in 2011 and 2012, respectively. The non-point source loading of the Bonghwa stream watershed was calculated, and predominantly assessed upstream of the Boseong river. Additionally, the Miryeok, Jangpyeong, Yuleo, Guam, Seokgyo, Mundeok, Incheon, and Bongnae stream watersheds, with extensive agricultural areas, were assessed to be potentially hazardous areas in terms of non-point source management. In this study, HSPF model was applied in order to aid in the selection of non-point source reduction facilities for the Juam dam watershed, where they were evaluated as to whether they would be applicable for non-point source management.

• Journal of the Korean association of regional geographers
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• v.10 no.1
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• pp.192-205
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• 2004

The purpose of this paper is to analyze the factors, which have influence upon changes of hydrological environment in time series, and evaluate water balance changes caused by urbanization. The results of the analysis and evaluation are as follow: At first, the river runoff at Gwangju River Basin keep base flow of river by storage capacity recharged in June to September and show peak in August and minimum flow in May. The groundwater recharge by urbanization accounted for 46.1% of rainfall at early-urban stage, and decreased to 36.5% and 29.9% in the 1960's and the 1990's respectively, and is likely to decrease to 27.8% in the 2010's. On the other hand, the overland flow was 9.6% of rainfall in the 1960's and 16.2% in the 1990's, and is likely to increase to 18.3% in the 2010's. When such a phenomenon is kept continuously, distorted water balance shall be worsened to create not only frequent occurrence of urban flood but also decreased base flow of Gwangju River to accelerate dry stream phenomenon. The time series study on urban redevelopment and environment maintenance describes distorted phenomenon to supply the information for nature-friendly land use, and examines relations between human activities and natural environment.

• Magazine of the Korean Society of Agricultural Engineers
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• v.24 no.2
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• pp.49-55
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• 1982

The purpose of this study is to classify the factors influenced on the damages of head works suffered from the storm flood occurred on July 22 1980 in both Musim and Bochong rivers and to find out an integral counter measures against the causes influenced on the disaster of head works in the engineering aspect of planning, design, construction and maintenance. In this survey, number of samples was taken 25 head Works, and the counter measures against the causes of their disasters summarized was as follows, 1. In the aspect of planning a. As the flood water level after the establishment of head works is more increased than the level before setting of head works owing to having more gentle slope of river bed between the head works than nature slope of river bed. Number of head works should be reduced for the appropriate annexation of them b. In the place where head works is established on the curved point of levee, the destruction of levee becomes severe by the strong deflective current. Therefore the setting of head works on the curved point should be kept off as long as possible and in case of unavoidable circumstances the construction method such as reinforced concrete wall or stone wall filed with concrete and anchored bank revetments should be considered. 2. In the aspect of design a. As scoring phenomena at up stream is serious around the weir Where the concentration of strong current is present in such a place, up stream apron having impermeability should be designed to resist and prevent scoring. b. As the length of apron and protected bed is too short to prevent scoring as down stream bed, the design length should be taken somewhat more than the calculated value, but in the case the calculated length becomes too long to be profitable, a device of water cushion should be considered. c. The structure of protected river bed should be improved to make stone mesh bags fixed to apron and to have vinyl mattress laid on river bed together with the improvement for increasing the stability of stone mesh bags and preventing the sucked sand from the river bed. d. As the shortage of cut-off length, especialy in case of the cutoffs conneting both shore sides of river makes the cause of destruction of embankment and weir body, the culculation of cut-off length should be taken enough length based on seepage length. 3. In the aspect of design and constructions a. The overturing destruction of weir by piping action was based on the jet water through cracks at the construction and expansion joints. therefore the expansion joint should be designed and constructed with the insertion of water proof plate and asphalt filling, and the construction joint, with concaved shape structure and steel reinforcement. b. As the wrong design and construction of the weep holes on apron will cause water piping and weir destruction, the design and construction of filter based on the rule of filter should be kept for weep holes. c. The wrong design and construction of bank revetment caused the severe destruction of levee and weir body resulting from scoring and impulse by strong current and formation of water route behind the revetment. Therefore bank revetment should be designod and constructed with stone wall filled with concrete and anchored, or reinforced concrete wall to prevent the formation of water flow route behind the wall and to resist against the scoring and impulse of strong stream. 4. In the aspect of maintenance When the damaged parts occurred at head works the authorities and farmers concerned should find and mend them as soon as possible with mutual cooperation, and on the other hand public citizen should be guided for good use of public property.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.269-279
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• 2015

Nowadays, the world has suffered by natural disaster of climate change due to global warming. Korea has also faced with similar situation. To prevent these natural disaster, Four Major River Management has conducted. One of conducted content in Four Major River Management is the levee maintenance which classified into fill-up the inland, levee of reinforcement and so on. These maintenances may make the characteristics of groundwater flow change and affect to the levee safety (piping phenomenon). Therefore, analysis on groundwater fluctuation according to level of riverside and inland should be required. This study focus on levee of Hoe stream, which is connected to Nakdong river, and piping safety factor in the levee analyzed by using pore water pressure. Besides, groundwater fluctuation, which is depended on level of riverside and inland, is simulated by using the SEEP/W (2D ground water model). This simulation considered steady flow and unsteady flow. As a result, piping safety factor increased due to rising the inland level. Piping safety factor of riverside was effected by only river water level. Therefore, external levee factor considering inland level raising and suitable control of river water level is need to increase piping safety factor.

• Journal of Wetlands Research
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• v.11 no.3
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• pp.21-35
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• 2009

To propose a sound direction for river rehabilitation plan, the naturalness of the river must be evaluated. In this study, the conventional methods for evaluating the naturalness of rivers proposed by Park, et al. has been improved to estimate the weights for each items subject to assessment and applied adequate Analytic Hierarchy Process (AHP). To estimate the weights, survey was conducted on a group of 83 experts in Civil and Environmental Engineering with a customized questionnaire. The results of the survey were generalized and used to estimate the weights of each items. Among the 14 evaluation items that have been generated as a result of the estimation, a total of 7 weight values such as water quality, variations in water flow, vegetation around minor bed, curve of waterway, vegetation around flood plain, variety in minor bed width, and diversity of stream bed materials appeared to be high. The improved method for evaluating the naturalness of rivers was applied to Hoe-ya River, where the method has successfully discriminated the sections having low degree of naturalness. The proposed assessment method can be employed as a criterion to determine the business zones in the river environment maintenance projects.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.397-397
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• 2011

2004년부터 4대강 물환경연구소는 수질오염총량관리제의 원활한 추진을 위해 총량관리단위유역 말단부에서 8일 간격으로 청천(晴天)시를 중심으로 유량과 수질을 동시에 측정하기 시작하였다. 그 결과 연중 하천유량과 수질의 연동 여부 및 변동 추이를 확인하는 것이 가능하게 되었다. 그러나 8일 간격으로 생산되는 유량은 지침의 정의와 맞물려 기준유량의 산정에 또 다른 어려움을 주고 있다. '한강수계 오염총량관리계획수립 지침'에 따르면 '기준유량은 과거 10년간 평균 저수량으로 한다'고 명시되어 있다. 여기서 저수량이란 유량의 크기를 누가일수로서 표시하여 1년을 통하여 275일은 이보다 더 작지 않은 유량으로 정의된다. 따라서 정확한 저수량을 산정하기 위해서는 1년 365개 매일의 유량자료가 필요하다. 하지만 8일 간격으로 유량을 측정하게 되면 1년 365개 대신 최대 45 여개의 일 유량자료만 취득 가능하므로 유황분석에 어려움이 발생할 수밖에 없다. 본 연구에서는 수질오염총량관리단위유역의 말단부에서 8일 간격으로 계측된 유량자료가 있을 때 이를 연속적인 일유량으로 확대할 수 있는 방법론 중 하나를 소개한다. 미 지질조사국(USGS)에서 주로 사용되는 이 방법은 A지점(부분계측이 이루어지는 지점)의 결측치를 동일 유역 혹은 수문학적으로 유사한 유역의 B지점(연속계측이 이루어지는 지점)의 자료를 이용하여 보완하는 방식이다. 이를 위해 먼저 부분계측이 이루어진 날과 같은 날짜의 유량자료를 연속계측자료에서 추출한 다음 두 자료(A지점에서의 모든 유량과 B지점에서의 추출된 유량)의 상관성을 비교해 본다. 두 자료간에 상관도가 높다면 이를 잘 표현하는 방정식을 통해 A지점의 결측치를 내 외삽한다. 여기서 두 자료간 상관도를 잘 묘사할 수 있는 방법으로 본 연구에서는 최소제곱법(Least Square Estimator, LSE)과 분산확장법(Maintenance of Variance Extension, MOVE)을 비교,분석해 보았다. 한강수계 수질오염총량관리단위유역 중 동일지점에 8일 간격 부분계측 유량자료와 일 연속자료가 동시에 존재하는 곳이 6지점이 있었으며 이 자료들을 바탕으로 LSE와 MOVE의 정확도를 검증해 본 결과 MOVE가 일 연속유량 확장에 더 나은 결과를 보였다.

• Journal of Wetlands Research
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• v.22 no.3
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• pp.194-199
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• 2020

Unlike in the past, the world is facing water shortages due to climate change and difficulties in simultaneously managing the risks of flooding. The Four Major Rivers project was carried out with the aim of realizing a powerful nation of water by managing water resources and fostering the water industry, and the construction period was relatively short compared to the unprecedented scale. Therefore, the prediction and analysis of how the river environment changes after the Four Major Rivers Project is insufficient. Currently, part of the construction section of the Four Major Rivers Project is caused by repeated erosion and sedimentation due to the effects of sandification caused by large dredging and flood-time reservoirs, and the head erosion of the tributaries occurs. In order to solve these problems, the riverbed maintenance work was installed, but it resulted in erosion of both sides of the river and the development of new approaches and techniques to keep the river bed stable, such as erosion and excessive sedimentation, is required. The water agent plays a role of securing a certain depth of water for the main stream by concentrating the flow so much in the center and preventing levee erosion by controlling the flow direction and flow velocity. In addition, Groyne products provide various ecological environments by forming a natural form of riverbeds by inducing local erosion and deposition in addition to the protection functions of the river bank and embankment. Therefore, after reviewing the method of determining the shape of the Groyne structure currently in use by utilizing the mobile limit flow rate and marginal reflux force, a new Critical Movement Velocity(${\bar{U}}_d$) and a new resistance coefficient formula considering the mathematical factors applicable to the actual domestic stream were developed and the measures applicable to Groyne installation were proposed.

• Korean Journal of Environment and Ecology
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• v.27 no.6
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• pp.676-689
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• 2013

This study is to understand the current situation of Wonju Stream, which flows through Wonju, Kangwon-do, and Seom River, the national river located outside of Wonju, by investigating all river areas using biotope type. Also, this research looked into the relationship between biotope and appearance of wild birds by investigating the location of their appearance. Biotope groups are 'scale', 'shape', and 'landscape'. And, biotope types are 'moisture', 'physical environment', and 'existence of vegetation'. Biotope subtypes are 'river area', 'physical environment', 'vegetation type', and 'usage of land'. Seom River is classified as 21 different sections, and Wonju Stream is classified as 19 different sections. Wild birds are investigated on breeding season, which was January and May of 2008. By marking each bird's location of appearance, it figured out properties of biotope according to the location of bird's appearance. 31 species, 795 birds in spring were founded, and 49 species, 4,348 birds are founded in winter at Seom River area. Also, 34 species, 427 birds in spring, and 33 species, 3,442 birds are founded in winter at Wonju Stream area. In winter, 26 species, 547 birds, and in spring, 12 species, 72 birds at natural river with estuaries in confluence of Seom River area are founded. Also, 34 species, 1412 birds in winter, and 24 species, 341 birds in spring are founded at natural river with estuaries and wetland plants. This means that because agricultural rivers have wide river width, slow flow speed, and many different types of biotope, these rivers can be good habitats for wild birds. The precise investigations and classifications of biotope, which especially are hard for linear rivers, were done to understand the whole and current situation of rivers. Furthermore, the data that shows the locations of wild birds can basically be used for a recovery of biological habitats, a constructing of ecological streams, a river-maintenance, and an enhancement of biodiversity of Wonju. Also, because the types of biotope are altered by rain, a continuous monitoring for maintaining ecosystem of rivers are highly needed.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.4
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• pp.763-770
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• 1997

The air abrasive technique is a non-mechanical method by which teeth are treated before restoration and stains and calculi are removed from tooth surfaces using the kinetic energy of small particles. The air abrasive technique in dentistry was first introduced in the 1950's with as instrument called 'Airdent'. But, as the main restorative materials of the period were amalgam and gold, and the instrument's inability to control the flow of particles caused the particles to be spread throughout the clinics, widespread use was not possible. In the 1990's, as these techincal problems were solved and more interest in new restorative materials rose in an effort to preserve sound tooth structure, new developements took place in instruments related to the air abrasive technique. The air abrasive technique produces less pressure, vibration and heat that might cause patient discomfort and facilitates the preservation of sound tooth structure. It also reduces the need for anesthesia and is less harmful to the pulp. Other advantages include increase in dentin bonding strength of composite resin, lower possibility of saliva contamination and maintenance of a dry field. But there is not direct contact between the nozzle and the tooth, the operator cannot use his or her tactile sense and must rely solely upon visual input. Other disadvantages are: the tooth preparation depends on the operator's ability; alpha-alumina particles, after bouncing off the tooth surface, cause damage to dental mirrors; the equipment is expensive and takes up a certain amount of space in the clinic. The author conducted case report using the air abrasive technique on patient visiting the Department of Pediatric Dentistry at Seoul National University Dental Hospital and arrived at the following conclusions. 1. The tooth preparation capability of different air abrasive devices varied widely among manufacturers. 2. It was more effective in treating early caries lesions and stains compared to lesions where caries had already progressed to produce soft dentin. 3. The cold stream and noise caused by the evacuation system was a major cause of discomfort to pediatric patients. 4. As there is no direct contact with tooth surface when using the air abrasive technique for tooth preparation, considerable experience and skill is required for proper tooth preparation.

• Journal of Korea Water Resources Association
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• v.55 no.1
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• pp.99-109
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• 2022

This study was intended to suggest the applicability of stepped boulder fishway using the concept of traditional boulder weir, focusing on the problems of existing concrete pool-and-weir fishways installed in mountain streams. To achieve this purpose, a stepped boulder fishway was designed and constructed as a pilot project in consideration of ascending capacity of the selected target fishes. Under the given discharge conditions, the hydraulic characteristics of the fishway were investigated in the field, and the characteristics and ascending capacity of the fishes were compared and analyzed. The fishway had a short length and steep slope, but the mean drops between each baffle were the range of 0.15 to 0.29 m, and this range satisfied the limit condition of about 0.40 m, which was in the limit of the drop that target fishes can ascend. The mean velocities of each baffle and pool were 0.82 to 0.87 m/sec and 0.13 to 0.24 m/sec. This result satisfied the conditions of burst speed (10 to 30 times of body length) and mean velocity of the resting pool (7 to 25% of burst speed) for target fishes. Since the bottom surface of the pool formed of boulders had a gentle reverse slope and rotational flow did not occur, the efficiency of fishway can be increased, and it will also be possible to solve the maintenance problem by flushing bed materials.