• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1737-1741
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• 2007

Using kinematic wave equation, the influence of moving rainstorms to runoff was analysised with a focus on watershed shapes and rainfall distribution types. Watershed shapes used are the oblong, square and elongated shape, and the distribution types of moving storms used are uniform, advanced and intermediate type. The runoff hydrographs according to the rainfall distribution types were simulated and the characteristics were explored for the storms moving down, up and cross the watershed with various velocity. And the hydrographs were compared in the case of varing the rainstorm intensity and varing the rainstorm length in order to make the same total runoff volume. When the rainstorm intensity was varied the shape, peak time and peak runoff of a runoff hydrograph are significantly influenced by spatial and temporal variability in rainfall and watershed shapes. The peak time of down and upstream moving strorms appeared latest in the case of the elongated shape basin, meanwhile at cross stream moving storms, the peak time of elongated shape basin is earlier than the others. For storms moving downstream peak time was more delayed than for other storm direction in the case of elongated watershed. The runoff volume and time base of the hydrograph decreased with the increasing storm speed.

• Korean Journal of Soil Science and Fertilizer
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• v.47 no.6
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• pp.425-431
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• 2014

Most fields in highland areas are covered with rye or hairy vetch for conservation during a fallow. However, using cover crops needs an effort to sow, and this makes top soil more vulnerable to loss due to surface disturbances. The aims of this study were to develop an automatic seeding-regulator device using a low-price, extensive-use GPS sensors and a DC motors and to evaluate a working efficiency of it after adaptation to partial tillage machine for reducing seeding effort. The amount of runoff water and soil loss was evaluated with partial tillage and simultaneous-seeding after harvesting soybean, in 17% slope lysimeters. In results, the seeding amount with the machine speed was stable between $0.5{\sim}0.8m\;s^{-1}$ of working sections. The automatic control device of seeding-rate could be enough to solve the slip problems of power selecting supply system or five four-wheel drive device. In partial tillage and simultaneous seeding, runoff water was 11.6% ($1.8m^3ha^{-1}$) of the scatter-seeding control ($15.5m^3ha^{-1}$) and soil loss was 13.2% ($7kg\;ha^{-1}$) of the scatter-seeding control ($53kg\;ha^{-1}$). These results suggest that partial tillage and simultaneous-seeding methods are very effective in decreasing work effort and soil loss of sloped land.

• Membrane and Water Treatment
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• v.10 no.1
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• pp.1-11
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• 2019

The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) predicted that recent extreme hydrological events would affect water quality and aggravate various forms of water pollution. To analyze changes in water quality due to future climate change, input data (precipitation, average temperature, relative humidity, average wind speed and sunlight) were established using the Representative Concentration Pathways (RCP) 8.5 climate change scenario suggested by the AR5 and calculated the future runoff for each target period (Reference:1989-2015; I: 2016-2040; II: 2041-2070; and III: 2071-2099) using the semi-distributed land use-based runoff processes (SLURP) model. Meteorological factors that affect water quality (precipitation, temperature and runoff) were inputted into the multiple linear regression analysis (MLRA) and artificial neural network (ANN) models to analyze water quality data, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), total nitrogen (T-N) and total phosphorus (T-P). Future water quality prediction of the Anseongcheon River basin shows that DO at Gongdo station in the river will drop by 35% in autumn by the end of the $21^{st}$ century and that BOD, COD and SS will increase by 36%, 20% and 42%, respectively. Analysis revealed that the oxygen demand at Dongyeongyo station will decrease by 17% in summer and BOD, COD and SS will increase by 30%, 12% and 17%, respectively. This study suggests that there is a need to continuously monitor the water quality of the Anseongcheon River basin for long-term management. A more reliable prediction of future water quality will be achieved if various social scenarios and climate data are taken into consideration.

• Journal of Environmental Science International
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• v.12 no.2
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• pp.139-144
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• 2003

The Yellow River began ceasing affected by natural factors and the unreasonable human activities. The flow broke in the Yellow River and water and sediment flowing into the sea decreased, which lowered the speed of newly formed wetland extending to the sea. The water environment deteriorated; Its composing structure tended to be unsteady; The biologic diversity decreased and wetland function reduced. To ensure that the Yellow River delta and its ecosystem develops sustainablly, it is significant to reduce times and days of the ceasing, keep certain runoff and sediments in the river to the sea and make its watercourse stable.

• Journal of Environmental Science International
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• v.20 no.9
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• pp.1165-1182
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• 2011

The evaluation of potential submarine groundwater is an important research topic for exploring an alternative water resource. Two different approaches, water budget analysis and Rn mass balance method, were employed to investigate the annual variation of submarine groundwater discharge in 2010 at a marine watershed located at the south-eastern part of Korean Peninsula. In order to obtain reliable hydrological data during study period, temporal and spatial variations of rainfall and soil moisture had been collected and hydro-meterological data such as temperature, humidity and wind speed were collected The runoff response was simulated using SCS-CN method with spatial distributions of landuse and soil texture from GIS analysis. Six different methods were used to estimate the monthly variation of evapotranspiration and field measurements of soil moisture were used to account for the infiltration. Comparisons of infiltration and surface runoff between simulation and water balance with measurements showed coincidence. The water budget analysis and Rn mass balance method provide mean daily submarine groundwater as 5.35 and 4.07 $m^3/m/day$ in 2010, respectively.

• 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 Korean Society on Water Environment
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• v.29 no.1
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• pp.88-96
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• 2013

Much attention has been needed in water resource management at the watershed due to drought and flooding issues caused by climate change in recent years. Increase in air temperature and changes in precipitation patterns due to climate change are affecting hydrologic cycles, such as evaporation and soil moisture. Thus, these phenomena result in increased runoff at the watershed. The Soil and Water Assessment Tool (SWAT) model has been used to evaluate rainfall-runoff at the watershed reflecting effects on hydrology of various weather data such as rainfall, temperature, humidity, solar radiation, wind speed. For bias-correction of RCP data, at least 30 year data are needed. However, for most gaging stations, only precipitation data have been recorded and very little stations have recorded other weather data. In addition, the RCP scenario does not provide all weather data for the SWAT model. In this study, two scenarios were made to evaluate whether it would be possible to estimate streamflow using measured precipitation and long-term average values of other weather data required for running the SWAT. With measured long-term weather data (scenario 1) and with long-term average values of weather data except precipitation (scenario 2), the estimate streamflow values were almost the same with NSE value of 0.99. Increase/decrease by ${\pm}2%$, ${\pm}4%$ in temperature and humidity data did not affect streamflow. Thus, the RCP precipitation data for Hongcheon watershed were bias-corrected with measured long-term precipitation data to evaluate effects of climate change on streamflow. The results revealed that estimated streamflow for 2055s was the greatest among data for 2025s, 2055s, and 2085s. However, estimated streamflow for 2085s decreased by 9%. In addition, streamflow for Spring would be expected to increase compared with current data and streamflow for Summer will be decreased with RCP data. The results obtained in this study indicate that the streamflow could be estimated with long-term precipitation data only and effects of climate change could be evaluated using precipitation data as shown in this study.

• Journal of Korea Water Resources Association
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• v.55 no.12
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• pp.1077-1089
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• 2022

With the construction of Seoul National University (SNU), the Mt. Gwanak watershed has undergone some urbanization. As with other campus catchments, data related to the water cycle is extremely limited. Therefore, this study began by collecting hydrological and meteorological data using Atmos-41, a complex meteorological observation instrument. The observation results of Atmos-41 were validated by analyzing the statistical characteristics and confidence intervals based on the monthly variability of data from the Korea Meteorological Administration. Results of the previous research were used to validate the simulated surface runoff and infiltration using the Storm Water Management Model (SWMM). The potential evapotranspiration (PET) simulated by the SWMM was rectified by comparing it to the Atmos-41 observation data. Multiple regression analysis was employed to adjust for the fluctuations in precipitation, relative humidity, and wind speed because the calculated SWMM PET tends to be underestimated during periods of low temperatures. R² increased from 0.54 to 0.80 when compared to the Atmos-41 PET. The rate of change in the water cycle as a consequence of the SNU's construction resulted in a 15.7% increase in surface runoff, a 14.2% decrease in infiltration rate, and a 1.6% decrease in evaporation.

• Korean Journal of Remote Sensing
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• v.27 no.3
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• pp.235-258
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• 2011

The purpose of this study is to investigate climatological variations from the temporal and spatial surface particulate organic carbon (POC) estimates based on SeaWiFS spectral radiance, and to determine the physical mechanisms that affect the distribution of pac in the Gulf of Mexico. 7-year monthly mean values of surface pac concentration (Sept. 1997 - Dec. 2004) were estimated from Maximum Normalized Difference Carbon Index (MNDCI) algorithm using SeaWiFS data. Synchronous 7-year monthly mean values of remote sensing data (sea surface temperature (SST), sea surface wind (SSW), sea surface height anomaly (SSHA), precipitation rate (PR)) and recorded river discharge data were used to determine physical forcing factors. The spatial pattern of POC was related to one or more factors such as river runoff, wind-derived current, and stratification of the water column, the energetic Loop Current/Eddies, and buoyancy forcing. The observed seasonal change in the POC plume's response to wind speed in the western delta region resulted from seasonal changes in the upper ocean stratification. During late spring and summer, the low-density river water is heated rapidly at the surface by incoming solar radiation. This lowers the density of the fresh-water plume and increases the near-surface stratification of the water column. In the absence of significant wind forcing, the plume undergoes buoyant spreading and the sediment is maintained at the surface by the shallow pycnocline. However, when the wind speed increases substantially, wind-wave action increases vertical motion, reducing stratification, and the sediment were mixed downward rather than spreading laterally. Maximum particle concentrations over the outer shelf and the upper slope during lower runoff seasons were related to the Loop Current/eddies and buoyancy forcing. Inter-annual differences of POC concentration were related to ENSO cycles. During the El Nino events (1997-1998 and 2002-2004), the higher pac concentrations existed and were related to high runoffs in the eastern Gulf of Mexico, but the opposite conditions in the western Gulf of Mexico. During La Nina conditions (1999-2001), low Poe concentration was related to normal or low river discharge, and low PM/nutrient waters in the eastern Gulf of Mexico, but the opposite conditions in the western Gulf of Mexico.

• Proceedings of the KSRS Conference
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• v.2
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• pp.973-976
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• 2006

The oscillations of the Caspian Sea level represent a result of mutually related hydrometeorological processes. The change in the tendency of the mean sea level variations that occurred in the middle 1970s, when the long-term level fall was replaced by its rapid and significant rise, represents an important indicator of the changes in the natural regime of the Caspian Sea. Therefore, sea level monitoring and long-term forecast of the sea level changes represent an extremely important task. The aim of this presentation is to show the experience of application of satellite altimetry methods to the investigation of seasonal and interannual variability of the sea level, wind speed and wave height, water dynamics, as well as of uplift of the Earth’s crust in different parts of the Caspian Sea and Kara-Bogaz-Gol Bay. Special attention is given to estimates of the Volga River runoff derived from satellite altimetry data. The work is based on the 1992-2005 TOPEX/Poseidon (T/P) and Jason-1 (J-1) data sets.