• Journal of the Korean earth science society
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• v.28 no.4
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• pp.478-490
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• 2007

With groundwater data of seawater intrusion monitoring network in coastal areas of Korea's main land, we analyzed types of seawater intrusion through the coastal aquifer. The data including groundwater level, temperature and electrical conductivity obtained from 45 monitoring wells at 25 watershed regions were evaluated. Based on statistical analysis, correlation analysis and variation type analysis, groundwater levels were mainly affected by rainfall and artificial pumping. About 78% of the monitoring wells showed average temperature higher than $15^{\circ}C$ and about 58% of them showed minimum variations less than $0.2^{\circ}C$. Electrical conductivities showed a large magnitude of variation and irregular characteristics compared with groundwater levels and temperatures. Average electrical conductivities lower than $2,000\;{\mu}S/cm$ were observed at 28 monitoring wells while those of higher than $10,000\;{\mu}S/cm$ were done at 9 monitoring wells. From the cross-correlation analysis, groundwater levels were mostly affected by precipitation while temperature and electrical conductivity showed very low correlation. Meanwhile tidal variations strongly affected the groundwater levels comparing to precipitation. We classified the long-term monitoring data according to variation types such as constant process, linear trend, cyclic variation, impulse, step function and ramp. Impulse type was dominant for variations of groundwater level, which was largely affected by rainfall or artificial pumping, the constant process was dominant for temperature. Compared with groundwater level and temperature, electrical conductivities showed various types like linear trend, step function and ramp. According to the discrepancy of variation characteristics for monitoring data at each well in the same region, periodical analysis of monitoring data is essentially required.

• Journal of Korea Water Resources Association
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• v.54 no.10
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• pp.795-805
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• 2021

In this study, after developing an LSTM-based deep learning model for estimating daily runoff in the Soyang River Dam basin, the accuracy of the model for various combinations of model structure and input data was investigated. A model was built based on the database consisting of average daily precipitation, average daily temperature, average daily wind speed (input up to here), and daily average flow rate (output) during the first 12 years (1997.1.1-2008.12.31). The Nash-Sutcliffe Model Efficiency Coefficient (NSE) and RMSE were examined for validation using the flow discharge data of the later 12 years (2009.1.1-2020.12.31). The combination that showed the highest accuracy was the case in which all possible input data (12 years of daily precipitation, weather temperature, wind speed) were used on the LSTM model structure with 64 hidden units. The NSE and RMSE of the verification period were 0.862 and 76.8 m³/s, respectively. When the number of hidden units of LSTM exceeds 500, the performance degradation of the model due to overfitting begins to appear, and when the number of hidden units exceeds 1000, the overfitting problem becomes prominent. A model with very high performance (NSE=0.8~0.84) could be obtained when only 12 years of daily precipitation was used for model training. A model with reasonably high performance (NSE=0.63-0.85) when only one year of input data was used for model training. In particular, an accurate model (NSE=0.85) could be obtained if the one year of training data contains a wide magnitude of flow events such as extreme flow and droughts as well as normal events. If the training data includes both the normal and extreme flow rates, input data that is longer than 5 years did not significantly improve the model performance.

• Journal of Gifted/Talented Education
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• v.22 no.4
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• pp.855-874
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• 2012

This research aimed to obtain basic data for elementary school students to form proper concepts by comparing the science gifted students and the ordinary students of elementary school with regard to the groundwater concept, formation process, existence forms, and movement. The research subjects were 65 fifth and sixth graders of the elementary school students and the spatial ability test was conducted on the subjects, and 4 science gifted students and 8 ordinary students chosen from the subjects were analyzed using half-structured interview data and ground water drawing drawn by the students. The conclusion derived in accordance with the research purpose is summarized as follows. It was found that there were no great differences in the answers to the question asking what groundwater is between the science gifted elementary school students with high spatial ability and the ordinary elementary school students with moderate spatial ability. The ordinary students with low spatial ability tended to regard groundwater as the concept of water and sewage. In the concept of the formation process of groundwater, the science gifted elementary school students with high spatial ability explained it by citing diverse surface water such as rainfall, river water, lake, and waterfall, and the ordinary elementary school students with moderate spatial ability all mentioned only rainfall and river water and could not explain diverse spatial factors. The ordinary elementary school students with low spatial ability mentioned rainfall and river water and perceived that groundwater was formed artificially. In the concept regarding the existence form of groundwater, the ordinary elementary school students with low spatial ability could not think of space perception that small pore space exists in earth or soil in the ground. The science gifted elementary school students with high spatial ability knew that groundwater exists in pore space with regarding groundwater movement, the ordinary elementary school students with low spatial ability thought that there was no groundwater movement and that it could be moved only by artificial facilities. There were differences in the perception of pore space and in the perception of existence and non-existence of groundwater movement accordingly, but for most of the elementary school students, the concept of groundwater was formed differently from the scientific concept. It is considered that most of the elementary school students formed erroneous concept about groundwater and could not connect ground water under the surface of the earth with the substances forming its surroundings with regard to the concept of groundwater.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.6
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• pp.75-83
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• 2004

Focusing on native plants that have high possibility of being introduced as rooftop material, this study was conducted to investigate extensive and easy-to-manage rooftop garden and to raise the utilization of native plants by verifying their growing response to artificial substrate soil depth and irrigation period. The study was conducted from March to September in 2002. Plants tested included Chrysanthemum zawadskii, Sedium middendorffianum, Thymus quinquecostatus, Allium senescens, and Dianthus superbus. Regarding soil depth, it was 5 cm and 10 cm. Irrigation period was non-irrigation, 1-week, 2-weeks, and 3- weeks, Its result is as follows; 1. In case of Sedum middendorffianum Maxim, mortality rate was 0% regardless of soil depth and irrigation period making it very suitable material for rooftop garden. 2. In case of Allium senescens L., mortality rate was 0% regardless of soil depth and irrigation period making it very suitable material for rooftop garden. Therefore, Provided that fertilizing is managed well, it is a plant that can be highly utilized.3. In case of Chrysanthemum zawadskii Herb. Subsp. (Nakai) Y. Lee Stat., the growth of top was lower in 10cm than in 5cm and it grew well in 10cm. When utilizing for rooftop garden, it would be desirable to keep minimum viable soil depth at over 10cm. If there is enough rainfall, soil and soil depth seem to have greater effect on growth than irrigation period does. 4. In case of Diauthus superbus L. var. longicalycinus (Maxim) Williams, rooting rate and growth were better in 10cm than in 5cm. Therefore, it is desirable to keep minimum soil depth at over 10cm. 5. In case of Thymus quinquecostatus Celak, the growth of top and flowering were better in 10cm than in 5cm. Therefore, it seems desirable to have minimum viable soil depth to be over 10cm. In conclusion, the most suitable species for rooftop garden are Sedium middendorffianum and Allium senescens in this experiment. However, Chrysanthemum zwadskii, Thymus quinquecostatus, and Dianthus chinensis also can be utilized greatly when irrigation is managed regularly in artificial mixed soil over 10cm.

• Korean Journal of Ecology and Environment
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• v.45 no.4
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• pp.378-391
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• 2012

The objective of this study was to determine temporal patterns and longitudinal gradients of water chemistry at eight artificial reservoirs and ten streams within the Han-River watershed along the main axis of the headwaters to the downstreams during 2009~2010. Also, we evaluated chemical relations and their variations among major trophic variables such as total nitrogen (TN), total phosphorus (TP), and chlorophyll-a (CHL-a) and determined intense summer monsoon and annual precipitation effects on algal growth using empirical regression model. Stream water quality of TN, TP, and other parameters degradated toward the downstreams, and especially was largely impacted by point-sources of wastewater disposal plants near Jungrang Stream. In contrast, summer river runoff and rainwater improved the stream water quality of TP, TN, and ionic contents, measured as conductivity (EC) in the downstream reach. Empirical linear regression models of log-transformed CHL-a against log-transformed TN, TP, and TN : TP mass ratios in five reservoirs indicated that the variation of TP accounted 33.8% ($R^2$=0.338, p<0.001, slope=0.710) in the variation of CHL and the variation of TN accounted only 21.4% ($R^2$=0.214, p<0.001) in the CHL-a. Overall, our study suggests that, primary productions, estimated as CHL-a, were more determined by ambient phosphorus loading rather than nitrogen in the lentic systems of artificial reservoirs, and the stream water quality as lotic ecosystems were more influenced by a point-source locations of tributary streams and intense seasonal rainfall rather than a presence of artificial dam reservoirs along the main axis of the watershed.

• Journal of Korea Water Resources Association
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• v.44 no.10
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• pp.797-807
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• 2011

Phenomenon of vegetation recruitment on the sand bar is drastically rising in the streams and rivers in Korea. In the 1960s prior to industrialization and urbanization, most of the streams were consisted of sands and gravels, what we call, 'White River'. Owing to dam construction, stream maintenance, etc. carried out since the '70s, the characteristic of flow duration and sediment transport have been disturbed resulting in the abundance of vegetation in the waterfront, that is, 'Green River' is under progress. This study purposed to identify the correlation among water level, water temperature, rainfall, soil moisture and soil texture out of the factors which give an effect on the vegetation recruitment on the sand bar of unregulated stream. To this purpose, this study selected the downstream of Naeseong Stream, one of sand rivers in Korea, as the river section for test and conducted the monitoring and analysis for 289 days. In addition, this study analyzed the aerial photos taken from 1970 to 2009 in order to identify the aged change in vegetation from the past to the present. The range of the tested river section was 361 m in transverse length and about 2 km in longitudinal length. According to the survey analysis, the tested river section in Naeseong Stream was a gaining river showing the higher underground-water level by 20~30 m compared to Stream water level. The difference in the underground water temperature was less than $5^{\circ}C$ by day and season and the Stream temperature did not fall to $10^{\circ}C$ and less from May when the vegetation germination begins in earnest. The impact factor on soil moisture was the underground water level in the lower layer and the rainfall in the upper layer and it was found that all the upper and lower layer were influenced by soil particle size. The soil from surface to 1 m-underground out of 6 soil moisture-measured points was sand with the $D_{50}$ size of 0.07~1.37 mm and it's assumed that the capillary height possible in the particle size would reach around 14~43 cm. On the other hand, according to the result of space analysis on the tested river section of unregulated stream for 40 years, it was found that the artificial disturbance and drought promoted the vegetation recruitment and the flooding resulted in the frequency extinction of vegetation communities. Even though the small and large scales of recruitment and extinction in vegetation have been repeated since 1970, the present vegetation area increased clearly compared to the past. It's found that the vegetation area is gradually increasing over time.

• Korean Journal of Ecology and Environment
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• v.47 no.2
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• pp.71-81
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• 2014

A survey was carried out to understand the influence of hydrology on the composition, abundance and adaptive strategies of phytoplankton in artificial Lake Hwaseong, an estuarine reservoir with seawater exchange through a sluice. Samples were collected seven times from May to October 2012. Hydrological events (seawater exchange, rainfall) resulted in a wide variation in salinity along with nutrients and turbidity. Shifts in the dominant phytoplankton composition occurred on every survey. Chlorophyll-a ranged from 9.7 to $104.1{\mu}g\;L^{-1}$. Multivariate analysis allowed us to identify the four phases on phytoplankton community change. Phase I (May~June) was characterized by small-sized Gymnodinium sp. and Heterosigma akashiwo dominated in warm temperature and high salinity derived from seawater exchange, and followed by Cylindrotheca closterium blooms due to rainfall and winds during phase II (July and September). During phase III (August), the dominance of Oscillatoria spp. was correlated with high temperature and low salinity. Abundant cryptomonads were associated with lower temperature during phase IV (October). Adaptive strategies were identified in the phytoplankton as morphological and physiological characteristics. These strategies identified small-sized flagellates as CR-strategists, fast-growing opportunistic species, which might favor the weak stratification of lake due to the seawater exchange during phase I and IV. Dominant species during phase II and III were characterized with R-strategists, medium-sized stress-tolerant species, which might favor turbulence by river flow. The results indicate that stronger stratification following the termination of seawater exchange for the freshening might intensify the predominance of smaller flagellates. In conclusion, this study suggests that hydrology may drive phytoplankton community change and blooms through the controls of salinity, turbulence and nutrients.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.30 no.2
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• pp.90-100
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• 2012

This study centering on 10 village - Bangjuks analyzed multifunctionality value of village Bangjuks which have been main water treatment system in Korean traditional villages. On the basis of understanding the structure and character of components such as the well, common spring, village waterway and others which making water-flow and consisting of aquatic system in Korean traditional village Bangjuk, the conclusion as the instrumental device of social and ecological role and ecological watershed management, securing the ecosystem soundness of the damaged or deteriated aquatic ecosystem due to the industrialization and urbanization is as below; 1. The traditional village Bangjuk was environmentally friendly hydraulic system which gathers waterways of village into a point including sewage water, retains and flows out to village through agricultural waterway. Through this Bangjuk, they have managed sewage and rainfall runoff flowed out village efficiently. It is not only a detention system of water but a kind of eco-friendly system that flow out water into the rivers after reusing and filtering it. 2. Around five traditional villages and five villages after modernization, this study classified the types of village Bangjuk as three types considering geographic location, size, etc; marsh type of low swamp, high water -low rice field type of natural flow stucture, low water - high rice field type requiring artificial irrigation facility. All the five traditional villages were turned out to be marsh type of low swamp. Geoji, Sanjeri, Ma-am, Yangchon of the agricultural villages were high water-low rice filed type, and Sangchoenri village was classified low water-high rice field type. 3. This study checked up the function of water purification of village Bangjuk. In Wonteo and Geji villages affected by discharge of village sewer and domestic sewage, the efficiency of ammonia nitrogen($NH_3-N$) and total phosphorus(T-P) was 56~95%, which was high. In Sangcheonri and Sanjeri villages strongly affected by stall and farmland, the efficiency of suspended solids(SS) was 70~85%, and that of total nitrogen(T-N) and total phosphorus(T-P) was 5.3~65%. 4. A water purification system can be found out in the system of village Bangjuk that filter out village sewage and rainfall runoff flowed through the settle and filter of pollution source and denitrification of plants. Through this system of village Bangjuk, it must be used as the basic facilities for the ecological watershed management. The sewage management system of village Bangjuk as a eco-filter must be used and studied as an eco-friendly facility for the ecological watershed management around the subwatershed and catchment.

• Journal of Korean Society of Forest Science
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• v.94 no.6
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• pp.496-503
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• 2005

This study was conducted to investigate the influences of sapflow flux on soil water tensions and soil moisture content at the Abies holophylla plots in Gwangneung, Gyeonggido, from September to October 2004. The Abies holophylla had been planted in 1976 and thinning and pruning were carried out in 1996 and 2004. Sapflow flux was measured by the heat pulse method, and soil water tension was measured by tensiometer at hillslope and streamside. Time domain reflectometry probes (TDR) were positioned horizontally at the depth of 10, 30 and 50 cm to measure soil moisture content. All of data were recorded every 30 minutes with the dataloggers. The sapflow flux responded sensitively to rainfall, so little sapflow was detected in rainy days. The average daily sapflow flux of sample trees was 10.16l, a maximum was 15.09l, and a minimum was 0.0l. The sapflow flux's diurnal changes showed that sapflow flux increased from 9 am and up to 0.74 l/30 min. The highest sapflow flux maintained by 3 pm and decreased almost 0.0 l/30 mm after 7 pm. The average soil water tensions were low ($-141.3cmH_2O$, $-52.9cmH_2O$ and $-134.2cmH_2O$) at hillslope and high ($-6.1cmH_2O$, $-18.0cmH_2O$ and $-3.7cmH_2O$) at streamside. When the soil moisture content decreased after rainfall, the soil water tension at hillslope responded sensitively to the sapflow flux. The soil water tension decreased as the sapflow flux increased during the day time, whereas increased during the night time when the sapflow flux was not detected. On the other hand, there was no significant relationship between soil water tension and sapflow flux at streamside. Soil moisture content at hillslope decreased continuously after rain, and showed a negative correlation to sapflow flux like a soil water tension at hillslope. As considered results above, it was confirmed that the response of soil moisture tension to sapflow flux at hillslope and streamside were different.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.606-614
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• 2020

In this paper, we analyze the influences of ship traffic and marine weather information on underwater ambient noise. Ambient noise is an important environmental factor that greatly affects the detection performance of underwater sonar systems. In order to implement an automated system such as prediction of detection performance using artificial intelligence technology, which has been recently studied, it is necessary to obtain and analyze major data related to these. The main sources of ambient noise have various causes. In the case of sonar systems operating in offshore seas, the detection performance is greatly affected by the noise caused by ship traffic and marine weather. Therefore, in this paper, the impact of each data was analyzed using the measurement results of ambient noise obtained in coastal area of the East Sea of Korea, and public data of nearby ship traffic and ocean weather information. As a result, it was observed that the underwater ambient noise was highly correlated with the change of the ship's traffic volume, and that marine environment factors such as wind speed, wave height, and rainfall had an effect on a specific frequency band.