• Journal of Korea Water Resources Association
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• v.51 no.6
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• pp.503-514
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• 2018

In recent, the hydrological regime of the Mekong river is changing drastically due to climate change and haphazard watershed development including dam construction. Information of hydrologic feature like streamflow of the Mekong river are required for water disaster prevention and sustainable water resources development in the river sharing countries. In this study, runoff simulations at the Kratie station of the lower Mekong river are performed using SWAT (Soil and Water Assessment Tool), a physics-based hydrologic model, and LSTM (Long Short-Term Memory), a data-driven deep learning algorithm. The SWAT model was set up based on globally-available database (topography: HydroSHED, landuse: GLCF-MODIS, soil: FAO-Soil map, rainfall: APHRODITE, etc) and then simulated daily discharge from 2003 to 2007. The LSTM was built using deep learning open-source library TensorFlow and the deep-layer neural networks of the LSTM were trained based merely on daily water level data of 10 upper stations of the Kratie during two periods: 2000~2002 and 2008~2014. Then, LSTM simulated daily discharge for 2003~2007 as in SWAT model. The simulation results show that Nash-Sutcliffe Efficiency (NSE) of each model were calculated at 0.9(SWAT) and 0.99(LSTM), respectively. In order to simply simulate hydrological time series of ungauged large watersheds, data-driven model like the LSTM method is more applicable than the physics-based hydrological model having complexity due to various database pressure because it is able to memorize the preceding time series sequences and reflect them to prediction.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.391-396
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• 2003

The digital map expresses natural topography and artificial things with 3D position coordinates in the computer such as the road, railway, building, river, mountain, paddy and dryland. Therefore, those should contribute to the information-oriented society by maintaining information and providing it to users quickly. However it is difficult to maintain the most recent topographic information all the time because of restricted budget and time. The purpose of this study is to investigate and analyze the updating area of the digital map using remotely sensed data, and to furnish the useful information reducing cost and time. To predict updating area of the digital map, we applied the urban changes analysis method to Landsat TM images from produced date of the digital map to up-to-date. Classification method for urban change analysis applied single band process algorithm. This study presents that updating area of the digital map is predicted by only the rate of 40% on total research area.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.203-206
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• 2007

In urban flood model, the features like roads, buildings, and river's banks have great effect on flow dynamics and flood propagation and it must be accounted for model set-up. Two-dimensional hydraulic models in high-density building areas are at the forefront of current research into flood inundation mechanisms, but they are however constrained by inadequate parameters of topography and friction due to insufficient and inaccurate data. This paper describes the development of urban flooding with the extraction of building areas and estimates the its influence on flood inundation extent, and present initial results of flood simulation varying grid size.

• Journal of Environmental Science International
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• v.22 no.3
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• pp.303-308
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• 2013

This paper proposed a new method for estimating missing values in time series rainfall data. The proposed method integrated the two most widely used estimation methods, general linear model(GLM) and ordinary kriging(OK), by taking a weighted average of covariance matrices derived from each of the two methods. The proposed method was cross-validated using daily rainfall data at thirteen rain gauges in the Hyeong-san River basin. The goodness-of-fit of the proposed method was higher than those of GLM and OK, which can be attributed to the weighting algorithm that was designed to minimize errors caused by violations of assumptions of the two existing methods. This result suggests that the proposed method is more accurate in missing values in time series rainfall data, especially in a region where the assumptions of existing methods are not met, i.e., rainfall varies by season and topography is heterogeneous.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.13 no.1
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• pp.1-5
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• 1977

A series of echo-sounding and current measurements as well as the drogue and the drift bottle experiments were carried out in Asan Bay since November 1974. Several sand bars or sand flats covered by silts were developed at ebb tide in the bay. Sand waves and sand ripples were seen on the surface of the sand bars, around which sea channels of 8~ 12 meters in depth are formed. The main stream axis of the flood current which is separated into east and west branch flows southward. A cyclonic and an anticyclonic eddy are developed at the early stage of flood tide. They are transformed into a clockwise eddy before the slack water. The maximum tidal current speed observed was 3.1 ~ 3.2 knots at the entrance of the bay, while it was 1.O ~ 2.8 knots in the bay. The location of the main stream axis of the tidal current coincides well with the sea channel. A salt wedge was observed at the estuary of the Sabgyo-cheon River.

• Journal of Environmental Impact Assessment
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• v.20 no.4
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• pp.575-583
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• 2011

In this study, the plausible grid size was estimated to increase for efficiency of reservoir management using 3 dimensional water quality model. To validate utilization of a real time water quality management tool, ELCOM-CAEDYM model was applied to Soyang reservoir in korea. 100m grid size can represent the real topography and take out exact analysis results. $400{\times}400m$ grid can be easily used to analysis because of data capacity. Consequently, the grid size of 200m or 300m was recommended to establish 3D model considering the required simulation time and the irrelevance between horizontal grid size and vertical distribution for temperature and turbidity analysis.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.179-182
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• 2008

This study simulated the flood inundations of the Nakdong River catchment running through Yangsan, a small city located in the south eastern area of Korea by using the depth averaged two-dimensional hydrodynamic numerical model. The numerical model employs the staggered grid system including moving boundary and a finite different method to solve the Saint-Venant equations. A second order upwind scheme is used to discretize the nonlinear convection terms of the momentum equations, whereas linear terms are discretized by a first order leap-frog scheme(Cho and Yoon, 1998). The numerical model was applied to a real topography to simulate the flood inundation of the Yangsan basin. The numerical results for urban district are visualized in three dimension. These results can be essentially utilized to construct the three dimensional inundation map after building the GIS-based database in local public organizations in order to protect the life and property safely.

• Journal of the Korean Society of Groundwater Environment
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• v.2 no.2
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• pp.58-63
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• 1995

Cokriging was applied for the estimation of the water levels of the basal leachate and the surrounding groundwater at the Nanjido waste landfill area. When the groundwater level is estimated at the high relief area, it makes a good result to use the data of groundwater level and elevation simultaneously because groundwater level is correlated with topography. This study determined the best semivariogram model of 87 groundwater levels and 144 elevations through cross validation test, and produced the contour maps of groundwater levels using ordinary kriging and universal kiging. Two contour maps don't make big difference at the waste site because this area has a large number of groundwater level data. However, they show big difference at the upper left part of the study area because this area has high relief and a small number of sample data. Their difference is also found at the south area near the Han river. When the topography is considered for the both areas, the contour map of cokriging is thought to be closer to the real groundwater distribution than that of kriging.

• Wind and Structures
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• v.30 no.6
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• pp.547-558
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• 2020

With the development of economy and construction technology, more and more bridges are built in complex mountainous areas. Accurate assessment of wind parameters is important in bridge construction at complex terrain. In order to investigate the wind characteristics in the high-altitude difference area, a complex mountain terrain model with the scale of 1:2000 was built. By using the method of wind tunnel tests, the study of wind characteristics including mean wind characteristics and turbulence characteristics was carried out. The results show: The wind direction is affected significant by the topography, the dominant wind direction is usually parallel to the river. Due to the sheltering effect of the mountain near the bridge, the wind speed and wind attack angle along the bridge are both uneven which is different from that at flat terrain. In addition, different from flat terrain, the wind attack angle is mostly negative. The wind profiles obey exponential law and logarithmic law. And the fitting coefficient is consistent with the code which means that it is feasible to use the method of wind tunnel test to simulate complex terrain. As for turbulence characteristics, the turbulence intensity is also related to the topography. Increases sheltering effect of mountain increases the degree of breaking up the large-scale vortices, thereby increasing the turbulence intensity. Also, the value of turbulence intensity ratio is different from the recommended values in the code. The conclusions of this study can provide basis for further wind resistance design of the bridge.

• Journal of Korea Water Resources Association
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• v.48 no.5
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• pp.357-365
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• 2015

Both exponents of distance and elevation into distance-and-elevation ratio method for estimating missing rainfall data are expressed as squares together but in this study the two exponents are differently separated and analyzed. We used 326 hourly rainfall events of precipitation data during 10 years of 2004 to 2013 observed at a base station of Pyeongchang and the five neighboring index stations-Bangrim, Suju, Cheongoksan, Jinbu, Yeongwol1-in Han River basin for a case study. As a result, exponent values of distance and elevation appropriate for a topography of the site appear as 3.7 and 0.57 respectively. The exponents of distance and elevation difference need to be applied according to topographical characteristics of site where estimating missing data or interpolation are required.