• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.690-694
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• 2003

Groundwater preferentially flows through sediment layers with high permeability such as colluvium. Its flow paths are called groundwater vein streams. An underground temperature survey is a method to locate vein streams by underground temperature anomalies associated with flowing groundwater. A groundwater flow system near an irrigation reservoir located in the upper part of a landslide block was surveyed with this method. After a geomembrane lining was installed in the reservoir, the total cross-sectional area of the vein streams in the aquifer decreased to as little as 0.35 times that before installation of the liner. A change in groundwater quality also indicated that the mixing of groundwater with leaked water from the reservoir stopped after installation of the lining.

• Current Research on Agriculture and Life Sciences
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• v.10
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• pp.35-40
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• 1992

The purpose of this study is to develop regression equations between peak flow and physical characteristic factors of watersheds. 112 irrigation reservoirs located in South Korea which are equal or larger than 200 has. in the irrigation area, are used in the analysis of this study. The results obtained from this study are as follows. 1. The results of correlation analysis of the relationships among the characteristic factors of the watersheds have been derived high significances. 2. Relationship between the peak flow and the simple correlation analysis of physical characteristic factors of the watersheds has been derived low significance. 3. The result of the multiple regression analysis between the peak flow and four physical characteristic factors of watershed such as watershed area, main stream length, average slope of main stream and elevation of reservoir are shown as the equation ; $Q_{100}=66.43A^{0.869}L^{-0.536}S^{0.456}Hs^{-0.122}$.(r=0.838)

• KCID journal
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• v.21 no.1
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• pp.118-126
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• 2014

In this study, the use of the spur of riverbank technique is being investigated. The spur of the riverbank typically reduces the velocity of flow and protects the embankments by increasing friction along the water and the banks. This also has an effect in the rise of water level upstream. It is also used for the rectification of riverside line and restoration of the waterway through sedimentation near the spur of the riverbank. In this study, physical-scaled experiments are conducted to investigate the process of creating a mild meandering channel using the spur of the riverbank with varying water flows and sedimentation functions. The hydraulics observations are taken with respect to the varying heights and length of the riverbank's spurs and the distance between each spur for the formation of the mild meandering channel. It is observed that for 1.06 times of the meander length, it requires 2 times of the interval with each spur of river width. Similarly, 1.25L times of the meander length, it requires 0.5 times of the interval with each spur of river width. The sand accumulation is induced by the spur of riverbank when the spur of riverbank's heights are more than 40% of water depth and the length of the spur of riverbank needs under than 20% of river width for avoid exaggerated sand accumulation in the center of channel.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.139-147
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• 2014

Forecasting salinity in an estuary reservoir is essential to promise irrigation water for the reclaimed land. The objective of the research was to assess salinity balance and its temporal and spatial variations in the Iwon estuary reservoir which has been issued by its high contents of salinity in spite of desalination process for four years. Seepage flows through the see dikes which could be one of possible reason of high salinity level of the reservoir was calculated based on the salinity balance in the reservoir, and used as input data for salinity modeling. A three-dimensional hydrodynamic model, Environmental Fluid Dynamics Code (EFDC), was used to simulate salinity level in the reservoir. The model was calibrated and validated based on weekly or biweekly observed salinity data from 2006 to 2010 in four different locations in the reservoir. The values of $R^2$, RMSE and RMAE between simulated and observed salinity were calculated as 0.70, 2.16 dS/m, and 1.72 dS/m for calibration period, and 0.89, 1.15 dS/m, and 0.89 dS/m for validation period, respectively, showing that simulation results was generally consistent with the observation data.

• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.2
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• pp.31-43
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• 1988

The Purpose of this study is to develop the rainfall-delayed response model (RDR Model) which influences the baseflow proportion of rivers as a result of the antecedent precipitation of the previous several months. The assesment of accurate baseflows in the rivers is one of the most important elements for the planning of seasonal water supply for agriculture, water resources development, hydrological studies for the availability of water and design criteria for various irrigation facilities. The Palukan river gauging site which is located in the Pulukan catchment on Bali Island, Indonesia was selected to develop this model. The basic data which has been used comprises the available historic flow records at 19 hydrologic gauging stations and 77 rainfall stations on Bali Island in the study. The methology adopted for the derivation of the RDR model was the water balance equation which is commonly used for any natural catcbment ie.P=R+(catchment losses) -R+(ET+DP+DSM+DGW). The catchment losses consist of evapotranspiration, deep percolation. change in soil moisture, and change in groundwater storage. The catchment areal rainfall has been generated by applying the combination method of Thiessen polygon and Isohyetal lines in the studies. The results obtained from the studies may be summarized as follows ; 1. The rainfall-runoff relationship derived from the water balance equation is as shown below, assuming a relationship of the form Y=AX+B. Finally these two equations for the annual runoff were derived ; ARO$_1$=0.855 ARF-821, ARF>=l,400mm ARO$_2$=0.290ARF- 33, ARF<1,400mm 2. It was found that the correction of observed precipitation by a combination of Thiessen polygons and Isohyetal lines gave good correlation. 3. Analysis of historic flow data and rainfall, shows that surface runoff and base flow are 52 % and 48% (equivalent to 59.4 mm) of the annual runoff, respectively. 4. Among the eight trial RDR models run, Model C provided the correlation with historic flow data. The number of months over which baseflow is distributed and the relative proportions of rainfall contributing in each month, were estimated by performing several trial runs using data for the Pulukan catchment These resulted in a value for N of 4 months with contributing proportions of 0.45, 0.50, 0.03 and 0.02. Thus the baseflow in any month is given by : P$_1$(n) =0.45 P(n) +0.50 P(n-I ) +0.03 P(n-$_2$) +0.02 P(n-$_3$) 5. The RDR model test gave estimated flows within +3.4 % and -1.0 % of the observed flows. 6. In the case of 3 consecutive no rain months, it was verified that 2.8 % of the dependable annual flow will be carried over the following year and 5.8 % of the potential annual baseflow will be transfered to the next year as a result of the rainfall-delayed response. The results of evaluating the pefformance of the RDR Model was generally satisfactory.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.95-104
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• 2022

Micro hydropower is a readily available renewable energy source that can be harvested utilizing hydrokinetic turbines from shallow water canals, irrigation and industrial channel flows, and run-off river stream flows. These sources generally have low head (<1 m) and low velocity which makes it difficult to harvest energy using conventional turbines. A horizontal-axis screw turbine was designed and numerically tested to extract power from such low-head water sources. The 3-bladed screw-type turbine is placed horizontally perpendicular to the incoming flow, partially submerged in a narrow water channel at no-head condition. The turbine hydraulic performances were studied using Computational Fluid Dynamics models. Turbine design parameters such as the shroud diameter, the hub-to-shroud ratios, and the submerged depths were obtained through a steady-state parametric study. The resulting turbine configuration was then tested by solving the unsteady multiphase free-surface equations mimicking an actual open channel flow scenario. The turbine performance in the shallow channel were studied for various Tip Speed Ratios (TSR). The highest power coefficient was obtained at a TSR of 0.3. The turbine was then scaled-up to test its performance on a real site condition at a head of 0.3 m. The highest power coefficient obtained was 0.18. Several losses were observed in the 3-bladed turbine design and to minimize losses, the number of blades were increased to five. The power coefficient improved by 236% for a 5-bladed screw turbine. The fluid losses were minimized by increasing the blade surface area submerged in water. The turbine performance was increased by 74.4% after dipping the turbine to a bottom wall clearance of 30 cm from 60 cm. The final output of the novel horizontal-axis screw turbine showed a 2.83 kW power output at a power coefficient of 0.63. The turbine is expected to produce 18,744 kWh/year of electricity. The design feasibility test of the turbine showed promising results to harvest energy from small hydropower sources.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.177-177
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• 2023

The impacts of dams on transboundary flow are complex and challenging to project and manage, given the potential moderating influence of a broad range of anthropogenic and natural factors. This study presents a global meta-analysis of 168 studies that examines the effect magnitude of dams on downstream seasonal, annual flow, and hydrological extremes risk on 39 hotspot transboundary river basins. The study also evaluates the impact of 13 factors, such as climate, basin characteristics, dams' design and types, level of transboundary cooperation, and socioeconomic indicators, on the heterogeneity of outcomes. The findings reveal that moderators significantly influence the impact of dams on downstream flow, leading to considerable heterogeneity in outcomes. Transboundary cooperation emerges as the key factor that determines the severity of dams' effect on both dry and wet season's flows at a significance level of 0.01 to 0.05, respectively. Specifically, the presence of water-supply and irrigation dams has a significant (0.01) moderating effect on dry-season flow across basins with high transboundary cooperation. In contrast, for wet-season flow, the basin's vulnerability to climate extremes is associated with a large negative effect size. The various moderators have varying degrees of influence on the heterogeneity of outcomes, with the aridity index, population density, GDP, and risk level of hydro-political tension being the most significant factors for dry-season flow, and the risk level of hydro-political tension and basin vulnerability to climate extremes being the most significant for wet-season flow. The results suggest that transboundary cooperation is crucial for managing the impacts of dams on downstream flow, and that various other factors, such as climate, basin characteristics, and socioeconomic indicators, have significant moderating effects on the outcomes. Thus, context-specific approaches are necessary when predicting and managing the impacts of dams on transboundary flow.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.149-155
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• 2013

In this study, factors that affect the air entrainment within a closed conduit by air drawn in through an air vent are investigated using a hydraulic scale model, which represents a gated circular conduit system connected to the intake tower of an irrigation reservoir. In addition, using data obtained during the hydraulic experiments, experimental equations are developed to estimate the amount of air drawn in through the air vent. In case of pressurized flow conditions downstream of hydraulic jumps, the relationships between $\frac{Q_a}{Q_w}$ and $Fr_g-1$ of the data form a experimental equation, $\frac{Q_a}{Q_w}=0.0304(Fr_g-1)^{1.0622}$; in case of free surface flow conditions, $\frac{Q_a}{Q_w}=0.0271(Fr_g-1)^{1.8205}$. Comparing two data sets observed under the two flow regimes with the results of previous researchers, patterns of the data sets are similar to the results estimated using the equations presented previously, and this indicates that the quality of the data obtained during the hydraulic experiments is ensured. In addition, it is revealed that air entrainment phenomena in the regions close to air vents are affected by the characteristics of supercritical flows downstream of gates. Finally, it is concluded that the equation developed for pressurized flow conditions can be applied to design of air vents.

• Current Research on Agriculture and Life Sciences
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• v.4
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• pp.70-76
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• 1986

The purpose of this study is to offer the basic data of the tidal river development program by grasping the diffusion between the high density-sea water and the low density-fresh water in the tidal river. The tidal range of Hyungsan river which flows at Youngil bay in Pohang was selected to analysis the phenomenon of density current. The results obtained are as follows ; The tide of Youngil bay was one time a day, 0.104m in high tide difference and 0.085m in mean tidy difference. The change of sea level by tide was negligible. The volume of reserved water by sea water was $2,700,000m^3$ and available water of irrigation was $1,200,000m^3$ that salt density is below $750{\mu}{\mho}/cm$ out of total volume. Salt intrusion phenomenon by density current was a little water level change, however, it become a salt wedge type by the much salt invasion during the spring tide and it makes a well-mixed type by the retreating salt wedge during the neap tide. As long as there were some density differences between sea water and fresh water, net upstream flow was existed along the bottom of water way from the estuary to the upstream channel.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.8-9
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• 2011

On 4 September 2010 an earthquake of magnitude 7.1 on the Richter scale occurred on the Canterbury Plains in the South Island of New Zealand. The Canterbury Plains are an area of extensive groundwater and spring fed surface water systems. Since the September earthquake there have been several thousand aftershocks (Fig. 1), the largest being a 6.3 magnitude quake which occurred close to the centre of Christchurch on 22February 2011. This second quake caused extensive damage to the city of Christchurch including the deaths of 189 people. Both of these quakes had marked hydrological impacts. Water is a vital natural resource for Canterburywith groundwater being extracted for potable supply and both ground and surface water being used extensively for agricultural and horticultural irrigation.The groundwater is of very high quality so that the city of Christchurch (population approx. 400,000) supplies untreated artesian water to the majority of households and businesses. Both earthquakes caused immediate hydrological effects, the most dramatic of which was the liquefaction of sediments and the release of shallow groundwater containing a fine grey silt-sand material. The liquefaction that occurred fitted within the empirical relationship between distance from epicentre and magnitude of quake described by Montgomery et al. (2003). . It appears that liquefaction resulted in development of discontinuities in confining layers. In some cases these appear to have been maintained by artesian pressure and continuing flow, and the springs are continuing to flow even now. In spring-fed streams there was an increase in flow that lasted for several days and in some cases flows remained high for several months afterwards although this could be linked to a very wet winter prior to the September earthquake. Analysis of the slope of baseflow recession for a spring-fed stream before and after the September earthquake shows no change, indicating no substantial change in the aquifer structure that feeds this stream.A complicating factor for consideration of river flows was that in some places the liquefaction of shallow sediments led to lateral spreading of river banks. The lateral spread lessened the channel cross section so water levels rose although the flow might not have risen accordingly. Groundwater level peaks moved both up and down, depending on the location of wells. Groundwater level changes for the two earthquakes were strongly related to the proximity to the epicentre. The February 2011 earthquake resulted in significantly larger groundwater level changes in eastern Christchurch than occurred in September 2010. In a well of similar distance from both epicentres the two events resulted in a similar sized increase in water level but the slightly slower rate of increase and the markedly slower recession recorded in the February event suggests that the well may have been partially blocked by sediment flowing into the well at depth. The effects of the February earthquake were more localised and in the area to the west of Christchurch it was the earlier earthquake that had greater impact. Many of the recorded responses have been compromised, or complicated, by damage or clogging and further inspections will need to be carried out to allow a more definitive interpretation. Nevertheless, it is reasonable to provisionally conclude that there is no clear evidence of significant change in aquifer pressures or properties. The different response of groundwater to earthquakes across the Canterbury Plains is the subject of a new research project about to start that uses the information to improve groundwater characterisation for the region. Montgomery D.R., Greenberg H.M., Smith D.T. (2003) Stream flow response to the Nisqually earthquake. Earth & Planetary Science Letters 209 19-28.