• Journal of Korea Water Resources Association
• /
• v.30 no.1
• /
• pp.55-62
• /
• 1997

To quantitatively investigate the nationwide drought characteristics and to comparatively evaluate the 1994-1995 drought with several past droughts of significant magnitude regional frequency analysis is made for the meteorological stations in each of the 47 subbasins covering the whole nation. With monthly precipitation data for the period of records at the stations in each subbasin low precipitation data series of various durations are formulated with the running totals of monthly data and fitted to probability distributions. The method of L-method of L-moments is used to determine the unbiased parameters of each distribution, and using the best-fit distribution for each subbasin the low precipitations of various durations with return periods of 5, 10, 20, 30, and 50 years are estimated. The drought frequency maps are drawn with the low drought frequency analysis the drought of 1994-1995 is evaluated in its severity and areal extent in comparison with four other past drought of significance. The current practice of safety standards for the design of impounding facilities is also evaluated with reference to the recurrence interval of the severe drought, and a recommendation is made for the future design standard.

• Water for future
• /
• v.10 no.1
• /
• pp.53-70
• /
• 1977

The analysis performed here is aimed to increase the familiarity of hydrologic process especially for the small basins which are densely gaged. Kyung An and Mu Shim river basins are selected as a representative basin according to the criteria which UNESCO has established back in 1964 and being operated under the auspice of Ministry of Construction. The data exerted from these basins is utilized for the determination of characteristics of procipitation and runoff phenomena for the small basin, which is considered as a typical Korean samall watershed. The study found that the areal distribution of preciptation did not show any significant deviation from the point rainfall. Since the area studied is less than 20 km#, the pointrainfall may be safely utilized as a representative value for the area. Also the effect of elevation on the precipitation has a minor significance in the small area where the elevation difference is less than 200m. The methodology developed by Soil Conservation Service for determination of runoff value from precipitation is applied to find the suitability of the method to Korean river basin. The soil cover complex number or runoff curve number was determined by comsidering the type of soil, soil cover, land use and other factors such as antecedent moisture content. The average values of CN for Kyung An and Mushim river basins were found to be 63.9 and 63.1 respectively under AMC II, however, values obtained from soil cover complex were less than those from total precipitation and effective precipitation about 10-30%. It may be worth to note that an attention has to be paid in application of SCS method to Korean river basin by adjusting 10-30% increase to the value obtained from soil cover complex. Finally, the design flood hydrograph was consturcted by employing unit hydrograph technique to the dimensionless mass curve. Also a stepwise multiple regression was performed to find the relationship between runoff and API, evapotranspiration rate, 5 days antecedentprecipitation and daily temperature.

• Journal of Korea Water Resources Association
• /
• v.46 no.5
• /
• pp.547-558
• /
• 2013

Improved methodology of Synthetic Unit Hydrograph (SUH) utilized generally in hydrologic design work was suggested. In this study, regression analysis between peak hydrological data and geospatial data was applied to estimate specific peak flow and peak time for determining shape of SUH. Regression formulas for specific peak flow with respect to shape factors show higher coefficient of determination (0.73~0.81) than the ones with geospatial components only (0.52~0.69). The areal limitation of unit hydrograph application is regarded as 500~700 $km^2$. The validation through rainfall-runoff simulation shows encouraging results that relative error is 1.7~29.0%(Avg. 11.6%) for the case of using SUH developed in this study and 35.0~ 64.9% (Avg. 46.7%) for the SUH in the previous study except for the extraordinary cases.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2015.05a
• /
• pp.429-429
• /
• 2015

면적감소계수(ARF)는 면적강우에 대한 지점강우의 비로 정의되며, 과거 면적확률강우량 산정시 유역 내의 여러 지점강우량을 티센기법, Kriging 기법 등을 통해 공간보정을 실시하고 면적강우량을 산정하였다. 하지만 이러한 방법은 강우의 시공간분포 특성을 정확히 반영하지 못하는 단점이 있기 때문에, 최근에는 많은 연구에서 레이더 강우를 활용한 ARF를 산정한다. 기존의 연구에서 이중편파레이더를 사용하여 낙동강 유역의 호우중심형 ARF를 산정한 바 있기 때문에, 본 연구에서는 산정된 ARF 값을 적용한 설계홍수량은 분석해보고자 한다. 대상유역은 낙동강 유역내의 유역들을 대상으로 하고자 한다. 낙동강 유역에는 약 $175km^2{\sim}2000km^2$의 다양한 면적의 유역들이 존재함을 확인하였다. 따라서 면적별로 대표적인 유역을 선정하여 설계홍수량을 산정하기에 적합한 지역이라 판단된다. 설계홍수량을 산정하기 방법으로는 강우-유출 모형을 이용하고자 한다. 이용할 모형은 호주에서 개발된 IHACRES 모형으로써, 개념적인 모형으로 장기 및 단기 강우사상을 모두 모의할 수 있는 특징을 갖고 있다. 따라서 낙동강 내의 선정된 유역들을 실제 강우자료를 통해 각 유역의 매개변수를 산정하고, 확률강우량과 Huff분포를 이용한 지속시간 24시간의 설계강우량을 산정하고자 한다. 산정된 설계강우량에 앞서 소개한 이중편파레이더 ARF를 적용하여 설계홍수량을 산정하고, ARF를 적용하지 않고 산정한 설계홍수량, 두 값의 차이를 통해 ARF를 통해 감소된 설계강우량의 비와 ARF 적용 유무에 따른 설계홍수량 차이의 비를 비교하여 이중편파레이더 ARF가 면적별로 미치는 영향을 알아보고자 한다.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.17 no.3
• /
• pp.1-19
• /
• 2014

This study aims to assess the slope stability variation of Jeonbuk drainage areas by RCM model outputs based on A1B climate change scenario and infinite slope stability model based on the previous research by Choi et al.(2013). For a large-scale slope stability analysis, we developed a GIS-based database regarding topographic, geologic and forestry parameters and also calculated daily maximum rainfall for the study period(1971~2100). Then, we assess slope stability variation of the 20 sub-catchments of Jeonbuk under the climate change scenario. The results show that the areal-average value of safety factor was estimated at 1.36(moderately stable) in spite of annual rainfall increase in the future. In addition, 7 sub-catchments became worse and 5 sub-catchments became better than the present period(1971~2000) in terms of safety factor in the future.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.11 no.2
• /
• pp.72-78
• /
• 2009

The demand for rainfall data in gridded digital formats has increased in recent years due to the close linkage between hydrological models and decision support systems using the geographic information system. One of the most widely used tools for digital rainfall mapping is the PRISM (parameter-elevation regressions on independent slopes model) which uses point data (rain gauge stations), a digital elevation model (DEM), and other spatial datasets to generate repeatable estimates of monthly and annual precipitation. In the PRISM, rain gauge stations are assigned with weights that account for other climatically important factors besides elevation, and aspects and the topographic exposure are simulated by dividing the terrain into topographic facets. The size of facet or grid cell resolution is determined by the density of rain gauge stations and a $5{\times}5km$ grid cell is considered as the lowest limit under the situation in Korea. The PRISM algorithms using a 270m DEM for South Korea were implemented in a script language environment (Python) and relevant weights for each 270m grid cell were derived from the monthly data from 432 official rain gauge stations. Weighted monthly precipitation data from at least 5 nearby stations for each grid cell were regressed to the elevation and the selected linear regression equations with the 270m DEM were used to generate a digital precipitation map of South Korea at 270m resolution. Among 1.25 million grid cells, precipitation estimates at 166 cells, where the measurements were made by the Korea Water Corporation rain gauge network, were extracted and the monthly estimation errors were evaluated. An average of 10% reduction in the root mean square error (RMSE) was found for any months with more than 100mm monthly precipitation compared to the RMSE associated with the original 5km PRISM estimates. This modified PRISM may be used for rainfall mapping in rainy season (May to September) at much higher spatial resolution than the original PRISM without losing the data accuracy.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.1403-1407
• /
• 2005

In order to analyze the water storage of the Daecheong dam after constructing the Yongdam dam situated in upstream, a daily cascaded simulation model for analyzing water storages in the Yongdam-Daecheong dams was developed. Operation scenarios of the Yongdam dam were selected to 8 cases with the combinations of downstream outflows and water supplies to the Jeonju region. Daily water storages in the Daecheong dam was analyzed daily by simulating from 1983 to 2004. The results are summarized as follows. Firstly, water supplies from the Daecheong dam were analyzed to amount $1,964.2Mm^3$ on a yearly average in case without the Yongdam dam. In case with the Yongdam dam, water supplies from the Daecheong dam were analyzed to amount $1,858.7\~1,927.3Mm^3$ in case with downstream outflow of $5\;m^3$ is, and were analyzed to amount $1,994.9\~2,017.8Mm^3$ in case with downstream outflow of $10\;m^3/s $. These values are compared to $1,649Mm^3$ applied in design. Secondly, reservoir use rate which was defined rate of water supply to effective water storage reached $241.3\% in case without the Yongdam dam. In case with the Yongdam dam, reservoir use rate reached $228.3\~236.8\% In case with downstream outflow of $5\;m^3/s$, and reached $245.1\~247.9\% in case with downstream outflow of $10\;m^3/s$. Thirdly, runoff rate which is defined rate of dam inflow to areal rainfall reached $57.3\% in case without the Yongdam dam. In case with the Yongdam dam, reservoir use rate reached $62.0\~68.4\% in case with downstream outflow of $5\;m^3/s$, and reached $64.1\~68.5\% in case with downstream outflow of $10\;m^3/s$. Fourth, in case with downstream outflow of $10\;m^3/s$ is from the Yongdam dam, appropriate water supply amounts to the Jeonju region were analyzed to only $0.50Mm^3/day$ from the daily simulation of water storages in the Yongdam dam. Comprehensively, water supply capacity of the Daecheong dam was analyzed to affect in small amounts in spite of the construction of the Yonsdam dam. It is effected to achieve the effective water management of the Yongdam dam and the Daecheong dam by using the developed cascaded model.

• Journal of Korean Society for Geospatial Information Science
• /
• v.6 no.2 s.12
• /
• pp.69-79
• /
• 1998

It is one of the most crutial thing to secure efficient infrastructure of social infrastructure Including rna drinking water, sewer, gas, and electricity, etc. in modern society. Among them, the sourer system need to be properly maintained so as to sustain water quality over the large watershed thereby to provide reasonable level of living environment A few municipalities and private firms have so in been using sewer management system for assessing existing sewer network and auxiliary facilities. Such existing system can only provide functions to manage the sewer pipe itself and they can not fully estimate the amount of sewage water over the pipe through 4he network analysis due to the deficiency of the system Such a limited sewer network analysis function can only analyze the whole network under the assumption of uniformity. The results from such a process can not be fully implemented in the field. Therefore, this study emphasized the development of a sewer management system which can provide practical values from network analysts considering areal peculiarities using a zoning map utilizing a GIS. The system can support analyzing scenarios due to the changes of sewer amounts from the changes of population densities and rainfall amounts not to mention of calculating sewer amount for individual sewer pipes. furthermore, the system can support the decision making for better designing sewer facilities from the expansion of metropolitan areas and constructing satellite cities. Eventually, it will contribute to enhance the effectiveness of sewer-related works and services for residents as well as supporting a decision making for minor and major trouble-shootings.

• Journal of Korea Water Resources Association
• /
• v.31 no.6
• /
• pp.795-806
• /
• 1998

Soil moisture is affected by regional climate, soil characteristics and land surface condition, etc,. Especially, the changes in land surface condition is more than other factors, which is mainly due to rapid urbanization and industrialization. This study is to evaluate how the change of land surface condition impacts on soil moisture field evolution using a simple model of soil moisture dynamics. For the quantification of soil moisture field, the first half of the paper is spared for the statistical characterization based on the first- and second-order statistics of Washita '92 and Monsoon '90 data. The second half is for evaluating the impact of land cover changes through simulation study using a model for soil moisture dynamics. The model parameters, the loss rate and the diffusion coefficient, have been estimated using the observed data statistics, where the changes of surface conditions are considered into the model by applying various parameter sets with different second-order statistics. This study is concentrated on evaluating the impact due to the changes of land surface condition variability. It is because we could easily quantify the impact of the changes of its areal mean based on the linear reservoir concept. As a result of the study, we found; (1)as the variability of land surface condition, increases, the soil moisture field dries up more easily, (2)as the variabilit y of the soil moisture field is the highest at the beginning of rainfall and decreases as time goes on to show the variability of land surface condition, (3)the diffusion effect due to surface runoff or water flow through the top soil layer is limited to a period of surface runoff and its overall impact is small compared to that of the loss rate field.

• Journal of Korea Water Resources Association
• /
• v.57 no.5
• /
• pp.333-346
• /
• 2024

High-resolution medium-range streamflow prediction is crucial for sustainable water quality and aquatic ecosystem management. For reliable medium-range streamflow predictions, it is necessary to understand the characteristics of forcings and to effectively utilize weather forecast data with low spatio-temporal resolutions. In this study, we presented a comparative analysis of medium-range streamflow predictions using the distributed hydrological model, WRF-Hydro, and the numerical weather forecast Global Data Assimilation and Prediction System (GDAPS) in the Geumho River basin, Korea. Multiple forcings, ground observations (AWS&ASOS), numerical weather forecast (GDAPS), and Global Land Data Assimilation System (GLDAS), were ingested to investigate the performance of streamflow predictions with highresolution WRF-Hydro configuration. In terms of the mean areal accumulated rainfall, GDAPS was overestimated by 36% to 234%, and GLDAS reanalysis data were overestimated by 80% to 153% compared to AWS&ASOS. The performance of streamflow predictions using AWS&ASOS resulted in KGE and NSE values of 0.6 or higher at the Kangchang station. Meanwhile, GDAPS-based streamflow predictions showed high variability, with KGE values ranging from 0.871 to -0.131 depending on the rainfall events. Although the peak flow error of GDAPS was larger or similar to that of GLDAS, the peak flow timing error of GDAPS was smaller than that of GLDAS. The average timing errors of AWS&ASOS, GDAPS, and GLDAS were 3.7 hours, 8.4 hours, and 70.1 hours, respectively. Medium-range streamflow predictions using GDAPS and high-resolution WRF-Hydro may provide useful information for water resources management especially in terms of occurrence and timing of peak flow albeit high uncertainty in flood magnitude.