• Journal of Environmental Science International
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• v.24 no.4
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• pp.495-504
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• 2015

To estimate water balance of Pyosun watershed in Jeju Island, a three-dimensional finite difference model MODFLOW was applied. Moreover, the accuracy of groundwater flow modeling was evaluated through the comparison of the recharge rate by flow modeling and the existing one from water balance model. The modeling result under the steady-state condition indicates that groundwater flow direction was from Mt. Halla to the South Sea and groundwater gradient was gradually lowered depending on the elevation. Annual recharge rate by the groundwater flow modeling in Pyosun watershed was calculated to 236 million $m^3/year$ and it was found to be very low as compared to the recharge rate 238 million $m^3/year$ by the existing water balance model. Therefore, groundwater flow modeling turned out to be useful to estimate the recharge rate in Pyosun watershed and it would be available to make groundwater management policy for watershed in the future.

• Journal of Korea Water Resources Association
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• v.47 no.6
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• pp.547-559
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• 2014

The objective of this study is to evaluate the performance of the complementary relationship-based evapotranspiration models, namely, advection-aridity (AA) model of Brutsaert and Stricker and the CRAE model of Morton for estimating actual evapotranspiration. Both models were applied to the Bokhacheon middle-upper watershed, and their estimates were evaluated against the water balance estimate. The calculation was made on a daily basis and comparison was made on monthly and annual bases. For comparison, the water balance estimates were not obtained from the observed precipitation and streamflow data but were based on the simulated data by using integrated watershed model, SWAT-K which is the revised version of SWAT. The reason not to directly use the observed data for water balance estimate is that the credible record period is not sufficient and the streamflow has been altered due to water use and release. Overall, the results showed that both AA model and CRAE model with their original parameters overestimate annual and monthly evapotranspiration, and the large difference between the complementary relationship-based approach and the water balance approach occurs especially for the dry season from Nov. to Mar. It was found out that the parameters, particularly for the advection related parameter, must be recalibrated to accurately produce monthly and annual regional evapotranspiration for this study area.

• Ocean and Polar Research
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• v.25 no.1
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• pp.75-87
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• 2003

The water balance calculation in the IRL shows that fresh groundwater discharge is the primary factor, with surface runoff from gaged and ungaged areas as the second freshwater contributor. Precipitation and evaporation are almost in balance fer the entire IRL. Due to high freshwater discharge from ground-water, the annual net flow is outward from the IRL to the continental shelf of the Atlantic Ocean resulting in a relatively short flushing time, denoted as $T_{0.5}$ (50% flushing time) and $T_{0.99}$ (99% flushing time). $T_{0.5}$, and. $T_{0.99}$ without a tidal effect in the Northern IRL are 17 and 114 days, respectively, during the dry season. During the wet season, they are 10 and 65 days, respectively. Tidal flushing effects are considered in central IRL due to the proximity to Sebastian Inlet. In the Northern Central zone during dry season, $T_{0.5}$, and. $T_{0.99}$ are 6 and 43 days, respectively and during the wet season 5 and 33 days. In the Southern Central zone they are 2 and 16 days for the dry season,2 and 15 days for the wet season. High groundwater seepage into the IRL is considered to be a positive effect in maintaining relatively good water quality condition even with few narrow inlets.

• Journal of Soil and Groundwater Environment
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• v.11 no.1
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• pp.65-76
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• 2006

This paper outlines the methodology of grid-based water balance for estimating the spatial distribution of recharge, which is applied to Woedo catchment in the northern area of the Jeju Island. The catchment is divided into grids and a daily water balance in each grid is computed for the period of 5 years. Daily rainfall data in each grid is interpolated from the data of 10 rainfall gauging stations. The spatial distributions of parameters such as SCS curve number, soil water retention capacity and crop coefficients are derived from GIS analyses of soil and land use characteristics. The SCS curve number is obtained by calibrating simulated runoffs with respect to the observed runoffs. The results show that the average annual rainfall increases from 1,665 mm/year to 3,382 mm/year in accordance with the topographic elevation, and the average annual recharge varies from 372 mm/year to 2,576 mm/year according to the average annual rainfall increases. Spatial variability of recharge is the highest among the water balance components such as rainfall, direct runoff, evaprotranspiration and recharge because the rate of runoff and evapotranspiration in the area with relatively low rainfall is higher than the other area.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.6
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• pp.19-28
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• 2012

This study carried out farmland suitability analysis for southern-type garlic cultivation considering soil and temperature as well as water deficit conditions. The spatial extent was limited within the area derived by Kim et al. (2012) using just soil and temperature constraints. Daily soil moisture was simulated using a one-layer soil water balance model at a $100{\times}100m$ grid unit, and then annual water deficit was calculated from 2000 to 2010. The farmland suitability was classified as four steps: best suitable, suitable, possible, and low productive. As a result, total area of best suitable or suitable farmland was about 375,900 ha, and Gimje-si and Haenam-gun were appeared as the largest favorable area for southern-type garlic cultivation. The best suitable or suitable area at Haenam-gun, Goheung-gun, Shinan-gun, Namhae-gun, and Muan-gun, major production regions of southern-type garlic, were extracted as 20,187 ha, 13,018 ha, 4,715 ha, 1,319 ha, and 349 ha, respectively. On the other hand, the result showed that the adoption of sprinkler irrigation systems might be critical in cultivating the southern-type garlic at some regions having poor water balance.

• Journal of Korean Society on Water Environment
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• v.28 no.4
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• pp.582-594
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• 2012

A simple ecohydorlogic model that simulates hydrologic components and vegetation dynamics simultaneously based on equations of soil water dynamics and vegetation's growth and mortality is discussed. In order to simulate ungauged watersheds, the proposed model is calibrated with indirected estimated observation data set; 1) empirically estimated annual vaporization, 2) monthly surface runoff estimated by NRCS-CN method, and 3) vegetation fraction estimated by SPOT/VEGETATION NDVI. In order to check whether the model is performed well with indirectly estimated data or not, four upper dam watersheds (Andong, Habcheon, Namgang, Milyang) in Nakdong River watershed are selected, and the model is verified.

• Korean Journal of Agricultural Science
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• v.38 no.3
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• pp.513-524
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• 2011

To evaluate the applicability of inflow runoff model to reservoir operation in Korea, DAWAST model and TPHM model which are conceptual lumped daily runoff model and were developed in Korea, were selected and applied to simulate inflows to Daecheong multipurpose dam with watershed area of 4,134 $km^2$, and water storages in Geryong reservoir with watershed area of 15.1 $km^2$ and total water storage of 3.4 M $m^3$. Evaluating inflows on an yearly, monthly, ten-day, and daily basis, inflows by DAWAST model showed balanced scatters around equal value line. But inflow by TPHM model showed high in high flows. Annual mean water balance by DAWAST model was rainfall of 1,159.9 mm, evapotranspiration of 622.1 mm, and inflow of 644.6 mm, from which rainfall was 104.8 mm less than sum of evapotranspiration and inflow, and showed unbalanced result. Water balance by TPHM model showed satisfactory result. Reservoir water storages were shown to simulate on a considerable level from applying DAWAST and TPHM models to simulate inflows to Geryong reservoir. But it was concluded to be needed to improve DAWAST and TPHM model together from imbalance of water balance and low estimation in high flow.

• Water Engineering Research
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• v.2 no.3
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• pp.161-169
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• 2001

Present study deals with the development of a numerical model for the estimation of net annual recharge by coupling the Galerkin's finite element flow simulationl model with the Gauss-Newton-Marquardt optimization technique. The developed coupled numerical model is applied for estimating net annual recharge for Mahi Right Bank Canal (MRBC) project the norms of Groundwater Resources Estimation committee (1984, 1997) and Indian Agricultural research Institute(1983). It is observed that the estimated net recharge by inverse modeling is closer to the net recharge estimated using the water balance approach. Further it is observed that the computed head distribution from the estimated recharge agree closely with the observed head distribution. The study concludes that the developed model for inverse modeling can be successfully applied to large groundwater system involving regional aquifers where reliable recharge estimation always requires considerable time and financial resources.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.516-516
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• 2022

Agricultural reservoirs are critical water resources structures to ensure continuous water supplies for rice cultivation in Korea. Climate change has increased the risk of reservoir failure by exacerbating discrepancies in upstream runoff generation, downstream irrigation water demands, and evaporation losses. In this study, the variations in water balance components of 400 major reservoirs during 1973-2017 were examined to identify the reservoirs with reliable storage capacities and resilience. A conceptual lumped hydrological model was used to transform the incident rainfall into the inflows entering the reservoirs and the paddy water balance model was used to estimate the irrigation water demand. Historical climate data analysis showed a sharp warming gradient during the last 45 years that was particularly evident in the central and southern regions of the country, which were also the main agricultural areas with high reservoir density. We noted a country-wide progressive increase in average annual cumulative rainfall, but the forcing mechanism of the rainfall increment and its spatial-temporal trends were not fully understood. Climate warming resulted in a significant increase in irrigation water demand, while heavy rains increased runoff generation in the reservoir watersheds. Most reservoirs had reliable storage capacities to meet the demands of a 10-year return frequency drought but the resilience of reservoirs gradually declined over time. This suggests that the recovery time of reservoirs from the failure state had increased which also signifies that the duration of the dry season has been prolonged while the wet season has become shorter and/or more intense. The watershed-irrigated area ratio (W-I_ratio) was critical and the results showed that a slight disruption in reservoir water balance under the influence of future climate change would seriously compromise the performance of reservoirs with W-I_ratio< 5.

• Journal of Soil and Groundwater Environment
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• v.26 no.6
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• pp.47-64
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• 2021

In this study, the annual and monthly groundwater recharge for the Sapgyo-cheon upstream basin in Chungnam Province was evaluated by water balance analysis utilizing WetSpass-M model. The modeling input data such as topography, climate parameters, LAI (Leaf Area Index), land use, and soil characteristics were established using ArcGIS, QGIS, and Python programs. The results showed that the annual average groundwater recharge in 2001 - 2020 was 251 mm, while the monthly groundwater recharge significantly varied over time, fluctuating between 1 and 47 mm. The variation was high in summer, and relatively low in winter. Variation in groundwater recharge was the largest in July in which precipitation was heavily concentrated, and the variation was closely associated with several factors including the total amount of precipitation, the number of days of the precipitation, and the daily average precipitation. This suggests the extent of groundwater recharge is greatly influenced not only by quantity of precipitation but also the precipitation pattern. Since climate condition has a profound effect on the monthly groundwater recharge, evaluation of monthly groundwater recharge need to be carried out by considering both seasonal and regional variability for better groundwater usage and management. In addition, the mathematical tools for groundwater recharge analysis need to be improved for more accurate prediction of groundwater recharge.