• Journal of Korea Water Resources Association
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• v.47 no.2
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• pp.145-159
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• 2014

This study is to evaluate the future climate change impact on turbidity water and eutrophication for Chungju Lake by using CE-QUAL-W2 reservoir water quality model coupled with SWAT watershed model. The SWAT was calibrated and validated using 11 years (2000~2010) daily streamflow data at three locations and monthly stream water quality data at two locations. The CE-QUAL-W2 was calibrated and validated for 2 years (2008 and 2010) water temperature, suspended solid, total nitrogen, total phosphorus, and Chl-a. For the future assessment, the SWAT results were used as boundary conditions for CE-QUAL-W2 model run. To evaluate the future water quality variation in reservoir, the climate data predicted by MM5 RCM(Regional Climate Model) of Special Report on Emissions Scenarios (SRES) A1B for three periods (2013~2040, 2041~2070 and 2071~2100) were downscaled by Artificial Neural Networks method to consider Typhoon effect. The RCM temperature and precipitation outputs and historical records were used to generate pollutants loading from the watershed. By the future temperature increase, the lake water temperature showed $0.5^{\circ}C$ increase in shallow depth while $-0.9^{\circ}C$ in deep depth. The future annual maximum sediment concentration into the lake from the watershed showed 17% increase in wet years. The future lake residence time above 10 mg/L suspended solids (SS) showed increases of 6 and 17 days in wet and dry years respectively comparing with normal year. The SS occupying rate of the lake also showed increases of 24% and 26% in both wet and dry year respectively. In summary, the future lake turbidity showed longer lasting with high concentration comparing with present behavior. Under the future lake environment by the watershed and within lake, the future maximum Chl-a concentration showed increases of 19 % in wet year and 3% in dry year respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.143-148
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• 2005

The main purpose of this study is to suggest and evaluate an operational method for assessing the potential impact of climate change on hydrologic components and water resources of regional scale river basins. The method, which uses large scale climate change information provided by a state of the art general circulation model(GCM) comprises a statistical downscaling approach and a spatially distributed hydrological model applied to a river basin located in Korea. First, we construct global climate change scenarios using the YONU GCM control run and transient experiments, then transform the YONU GCM grid-box predictions with coarse resolution of climate change into the site-specific values by statistical downscaling techniques. The values are used to modify the parameters of the stochastic weather generator model for the simulation of the site-specific daily weather time series. The weather series fed into a semi-distributed hydrological model called SLURP to simulate the streamflows associated with other water resources for the condition of $2CO_2$. This approach is applied to the Yongdam dam basin in southern part of Korea. The results show that under the condition of $2CO_2$, about $7.6\% of annual mean streamflow is reduced when it is compared with the observed one. And while Seasonal streamflows in the winter and autumn are increased, a streamflow in the summer is decreased. However, the seasonality of the simulated series is similar to the observed pattern and the analysis of the duration cure shows the mean of averaged low flow is increased while the averaged wet and normal flow are decreased for the climate change.

• Atmosphere
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• v.20 no.3
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• pp.229-238
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• 2010

The 1,000~500 hPa thickness and the $0^{\circ}C$ isotherm at 850 hPa have been used as the traditional predictors for wintertime precipitation-type forecasts. New approaches are taking on added significance as preexistence method of determination for wintertime precipitation-type exhibits more or less prevalent false alarms. Moreover thicknesses and thermodynamic profiles from ordinary upper-air observation were not adequate to monitor the atmospheric structure. In this regard, Microwave radiometric profiler microwave radiometer is useful in wintertime precipitation-type forecasts because radiometric measurements provide soundings at high temporal resolution. In this study, the determination and the predictability of wintertime precipitation-type were examined by using the calculated thicknesses, temperature of 850 hPa (T850) from a microwave radiometer, and surface observation at National Center for Intensive Observation of severe weather (NCIO) located at Haenam, Korea. The critical values for traditional predictors (thickness of 1000~500 hPa and T850) were evaluated and adjusted to Haenam region because snow rarely occurred with a 1000-500 hPa thickness > 5,300 m and T850 > $-10^{\circ}C$. Three thicknesses (e.g., 1,000~850, 1000~700, and 850~700 hPa thickness), T850, surface air temperature, and wet-bulb temperature were also evaluated as the additional predictors. A simple nomogram and a flow chart were finally designed to determine the wintertime precipitation-type using the microwave radiometer. The skill scores for the predictability of precipitation-type determination are considerably improved and the predictors showed the temporal variations in 12 hours before precipitation. We can monitor the hit and run snowfall in winter successful by realtime watch of the predictors, especially in commutes of big cities.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.856-864
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• 2006

For estimating the minimum discharge to maintain a river, low flow analysis is required and long term runoff records are needed for the analysis. However, runoff data should be estimated to run a hydrologic model for ungaged river basin. For the reason, parameter estimation is crucial to simulate rainfall-runoff events for those basins using Tank model. In this study, only runoff data recorded for dry season are used for parameter estimation, which is different to other methods based on runoff data recorded for wet and dry seasons. The Harmony Search algorithm is used to determine the optimum parameters for Tank model. The coefficient of determination ($R^2$) is served as the objective function in the Harmony Search. In cases that recorded data are insufficient, the recording interval is changed and Empirical CDF is adopted to analyze the estimated parameters. The suggested method is applied to Yongdam dam, Soyanggang dam, Chungju dam and Seomjingang dam basins. As results, the higher $R^2s$ are obtained when the shorter recording interval, the better recorded data quality, and the more rainfall events recorded along with certain rainfall amount is. Moreover, when the total rainfall is higher than the certain amount, $R^2$ is high. Considering the facts found from this study for the low flow analysis, it is possible to estimate the parameters for Tank model properly with the desired confidence level.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1268-1277
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• 2008

Recently, the high speed railway comes into the spotlight as the important and convenient traffic infrastructure. In Korea, Kyung-Bu high speed train service began in about 400km section at 2004, and the Ho-Nam high speed railway will be constructed by 2017. The high speed train will run with a design maximum speed of 300-350km/hr. Since the trains are operated at high speed, the differential settlement of subgrade under the rail is able to cause a fatal disaster. Therefore, the differential settlement of the embankment must be controlled with the greatest care. Furthermore, the characteristics and causes of settlements which occurred under construction and post-construction should be investigated. A considerable number of studies have been conducted on the settlement of the natural ground over the past several decades. But little attention has been given to the compression settlement of the embankment. The long-term settlement of compacted fills embankments is greatly influenced by the post-construction wetting. This is called 'hydro collapse' or 'wetting collapse'. This wetting collapse problem for the compressibility of compacted sands, gravels and rockfills, has been recognized by several researchers. For this wetting settlement problem, we showed the test results carried out with 4 fill materials. These tests were performed under the condition that the fill materials were inundated at the first wetting. Subsequently, in this study, we investigated the long-term settlement characteristics of the fill materials under the repeated partial wetting and rising of the ground water table happend by rainfall.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.22-31
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• 1994

Fish aggregating devices(FAD) or artificial fish reefs deployed in the ocean space have been developed in various forms. The objective of FAD is to aggregate, cultivate and proliferate aquatic resources by making changes in ocean flows around it. developing spawning grounds, improving feeding areas and protecting larvae and juveniles. Most floating fish aggregating devices(FFAD) are in the form of surface buoys or subsurface buoys with a single point mooring system(SPMS). The mooring line of SPMS for the secure positions of FFAD is expected to keep great stresses as a result of the harsh ocean environment. Laboratory static tests on synthetic fiber ropes used for the SPMS were run. The Nylon wet rope specimen tests under increasing-and-decreasing loads showed about 20% strength drop. Also the logarithmic creep-tie behavior of fiber ropes was observed in the constant load test and compared with Flessner's formula.

• Korean Journal of Agricultural Science
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• v.47 no.4
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• pp.963-978
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• 2020

Earthquakes can induce a large number of landslides and cause very serious property damage and human casualties. There are two issues in study on earthquake-induced landslides: (1) slope stability analysis under seismic loading and (2) debris flow run-out analysis. This study aims to review technical studies related to the development and application of earthquake-induced landslide models (seismic slope stability analysis). Moreover, a pilot application of a physics-based slope stability model to Mt. Umyeon, in Seoul, with several earthquake scenarios was conducted to test regional scale seismic landslide mapping. The earthquake-induced landslide simulation model can be categorized into 1) Pseudo-static model, 2) Newmark's dynamic displacement model and 3) stress-strain model. The Pseudo-static model is preferred for producing seismic landslide hazard maps because it is impossible to verify the dynamic model-based simulation results due to lack of earthquake-induced landslide inventory in Korea. Earthquake scenario-based simulation results show that given dry conditions, unstable slopes begin to occur in parts of upper areas due to the 50-year earthquake magnitude; most of the study area becomes unstable when the earthquake frequency is 200 years. On the other hand, when the soil is in a wet state due to heavy rainfall, many areas are unstable even if no earthquake occurs, and when rainfall and 50-year earthquakes occur simultaneously, most areas appear unstable, as in simulation results based on 100-year earthquakes in dry condition.

• Journal of the Korean Wood Science and Technology
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• v.46 no.1
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• pp.10-16
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• 2018

Lindera erythrocarpa is a less utilized species in Korea although that it has straight stem and it grows up to 40 cm in diameter. A proper kiln-dry schedule is required in advance to utilize an unknown species. Terazwa's quick oven-dry method was used to find it and which was confirmed by drying 25 mm thick boards in a kiln. The average green moisture content and the average green specific gravity of Lindera erythrocarpa are 72.3% and 0.53, respectively. Prospective kiln-drying conditions obtained by Terazwa's quick oven-dry method are a initial dry-bulb temperature of $50^{\circ}C$, a initial wet-bulb depression of $4^{\circ}C$ and a final dry-bulb temperature of $75^{\circ}C$, which are in a good agreement with USDA FPL kiln-dry schedule of T5-D4. 25 mm thick boards dried in a kiln with T5-D4 kiln-dry schedule did not have any severe drying defects such as honycombing and warping. A severer kiln-dry schedule of T8-C5 was developed and applied to another kiln-drying run to confirm it.

• Economic and Environmental Geology
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• v.51 no.5
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• pp.409-428
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• 2018

Yeongdong area is located on the border zone between Precambrian Yeongnam massif and central southeastern Ogcheon metamorphic belt, in which Cretaceous Yeongdong sedimentary basin exists. Main geology in this area consists of Precambrian Sobaeksan gneiss complex, Mesozoic igneous and sedimentary rocks and Quaternary alluvial deposits. Above this, age-unknown Ogcheon Supergroup, Paleozoic sedimentary rocks and Tertiary granites also occur in small scale in the northwestern part. This study focuses on the link between the various geology and Rn concentrations in groundwater. For this, twenty wells in alluvial/weathered zone and sixty bedrock aquifer wells were used. Groundwater sampling campaigns were twice run at wet season in August 2015 and dry season in March 2016. Some wells placed in alluvial/weathered part of Precambrian metamorphic rocks and Jurassic granite terrains, as well as Cretaceous porphyry, showed elevated Rn concentrations in groundwater. However, detailed geology showed the distinct feature that these high-Rn groundwaters in metamorphic and granitic terrains are definitely related to proximity of aquifer rocks to Cretaceous porphyry in the study area. The deeper wells placed in bedrock aquifer showed that almost the whole groundwaters in biotite gneiss and schist of Sobaeksan gneiss complex and in Cretaceous sedimentary rocks of Yeongdong basin have low level of Rn concentrations. On the other hand, groundwaters occurring in rock types of granitic gneiss or granite gneiss among Sobaeksan gneiss complex have relatively high Rn concentrations. And also, groundwaters occurring in the border zone between Triassic Cheongsan granites and two-mica granites, and in Jurassic granites neighboring Cretaceous porphyry have relatively high Rn concentrations. Therefore, to get probable and meaningful results for the link between Rn concentrations in groundwater and surrounding geology, quite detailed geology including small-scaled dykes or vein zones should be considered. Furthermore, it is necessary to take account of the spatial proximity of well location to igneous rocks associated with some mineralization/hydrothermal alteration zone rather than in-situ geology itself.

• Journal of The Korean Society of Grassland and Forage Science
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• v.13 no.4
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• pp.257-267
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• 1993

Optimum pasture management during the summer season is an important factor to maintain good regrowth and persistence of pasture. The field experiment was carried out to investigate the effects of cutting management on growth and reserve carbohydrates in stubble. and on dry matter yield of orchardgrass dominated pasture during the mid-summer season. Three different cutting times(July 15, 25 and August 5) as a main plot and three cutting heights(3, 6 and 10cm) as a sub plot were disigned with three replications. The experiment was done at pasture of Changsung Agricultural High School in 1988. The results obtained were summarized as follows: 1. Temperature of soil surface and underground in the cutting of July 15 and July 25 was not showed significantly different, because of low intensity of radiation with a run of wet weather, and that of August 5 cutting tends to be lowed in high cutting height during the mid-summer season. 2. Amount of soil moisture against cutting height showed that high cutting had a low content. 3. Growth rate against regrowth of plant height, lear length and leaf area showed to be fast in high cutting. 4. Rapid recovery period of carbohydrate content after cutting and large amount of carbohydrate accumulation were showed in the cutting of July 15 and 25 compared with August 5 cutting in the reserve carbohydrate content against cutting of time and height during the mid-summer season. 5. Dry matter yield of the 4th and 5th cutting showed to be remarkable in July 15 cutting compared to those of July 25 and August 5. From the above results, it is suggested that the 10cm cutting height during the mid-summer season is the most effective for good regrowth, reserve carbohydrates and dry matter yield of orchardgrass.