• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3D
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• pp.445-450
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• 2008

Recently, environmental and ecological approaches is in progress in urban stream, especially the guarantee of instream flow becomes very important. In this paper, it is suggested that water volume estimation method utilizing the topographical shape data obtained by field investigation and satellite image to manage the urban stream efficiently. The data obtained at Gap River is the study area are analysed and those results are as belows. First, surveying to investigate topographic shape characteristics of urban stream is carried out. In details, the gradient characteristics from water surface to bottom in case of sand area and in case of grass area are 0.013 and 0.065 respectively. In conclusion, the gradient characteristic of grass area is five times bigger than that of sand area. Besides, IKONOS image is classified by spectrum analysis and Minimum Distance Method and the sand area extraction method by the generalization method as Median filter is suggested to calculate water volume. Finally, mapping process on the sand area extracted from the topographical shape field data in river and satellite images is carried out by the GIS spatial analysis. And on the assumption that the water level was 1m at that time when satellite image was taken, the water volume was $225,258m^3$. It is clarified that the effect of water volume improvement was about 10.5% in comparison with water volume that had no consideration on the gradient characteristics of sand-bar.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.4
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• pp.517-526
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• 2018

As groundwater recharge shows the heterogeneity in space and time due to land use and soil types, estimating daily recharge by integrated hydrologic analysis is needed. In this work, the SWAT-MODFLOW model was applied to compute daily based groundwater recharge in Jangseong region. The accuracy of the model was evaluated by comparing the observed and calculated values of the unsteady groundwater flow levels after calibrating the observed and calculated flow rates of the stream for a hydrological analysis. The estimated hydrologic components showed a strong correlation with each other and significant spatial variations regarding the groundwater recharge rate in accordance with the heterogeneous watershed characteristics such as subbasin slope, land use, and soil type. Overall, it was concluded that the coupled hydrologic models were capable of simulating the spatial variation with respect to the hydrologic component process in surface water and groundwater. The average recharge rate was estimated at approximately 20.8%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1361-1375
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• 2013

The design flow considering nonstationarity is estimated to determine the design flood related to hydraulic structure quantitatively based on the design process for stream restoration in the Mokgamcheon watershed proposed by Lee et al. (2011). The purpose of this research is to suggest new ways that the design flood was calculated considering nonstationarity at the Mokgamcheon watershed. Storm-unit hydrograph method to calculate design flood and direct frequency analysis were applied and nonstationarity was considered for the frequency analysis through extRemes toolkit developed at NCAR (National Center for Atmospheric Research). Although the method of direct flood frequency analysis due to dealing with flowrates directly has a more reliable than strom-unit hydrograph method, as a result, the method of direct flood frequency analysis underestimated the design flood than strom-unit hydrograph method due to the characteristics of the flow data. Therefore, the flood of storm-unit hydrograph method (100 years frequency) was determined as the design flood in the Mokgamcheon watershed.

• Water for future
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• v.29 no.2
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• pp.209-219
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• 1996

The existing gate operation rule of Paldang hydroelectric plant has been used since the construction of the dam in 1973 except partial modification due to the construction of Chungju multipurpose dam in 1985. The water level near the downstream of Paldang dam has been lowered about 3 m because of the channel maintenance of Han River development project. Thus, the discharge estimation formula based on the submerged orifice type spillway has to be re-evaluated by considering various patterns of the gate operation rules and lowered channel bed. In this study, three types of gate openings were tested to select the proper gate operation rules through the hydraulic model test for various discharges and opening heights. Also, the numerical analysis has been performed to simulate the flow patterns of downstream. As a result, the gate operation rule, which opens 5 gates each time from the left side, was selected as the proper gate operation rule of Paldang dam.

• Journal of Korea Water Resources Association
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• v.39 no.12 s.173
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• pp.985-996
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• 2006

This study developed a model that could calculate equivalent roughness using shear stress acting on distributed grains in gravel bed stream. The estimated equivalent roughness by the model developed was used for estimation of water level and roughness coefficient in the stream without water level-discharge data. The model was applied to the Gurey-Songjeong stage station section located in the Sumjin river mid-downstream. The equivalent roughness by the model developed in this study was estimated to be 0.194m at the Gurey stage station. Calculated water level which the estimated equivalent roughness was applied to the flow model was shown ewer of within 6% in comparison with observed water level. Also, roughness coefficient was estimated using observed and calculated water level about each discharge scale by unsteady flow analysis. As a result, error of roughness coefficient estimated by observed and calculated water level was shown error of $0{\sim}0.002$ and could consider variability of roughness coefficient.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.401-401
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• 2018

최근 지구온난화에 따른 기후변화로 시공간적으로 매우 불규칙한 강우가 발생하고 있으며, 홍수피해 및 극심한 가뭄으로 수자원개발 및 관리 환경이 더욱 어려워지고 있는 실정이다. 특히 우리나라는 하천수사용허가 기준유량의 원천이 되는 강수량의 계절별 편차가 매우 크고 연 강수량의 2/3 이상이 여름철에 집중된다. 하천수사용허가 기준유량은 하천유지유량이 고시되지 않은 지점은 10년 빈도의 갈수량인 기준갈수량과 같고, 하천유지유량이 고시된 지점은 기준갈수량에서 하천유지유량을 감한 양이다. 하지만 하천 유량의 변동성이 계절에 따라 매우 큼에도 불구하고 갈수기의 한정적인 기준갈수량으로 연중 전 기간의 하천수사용허가 기준유량을 설정하면 가용한 하천수량을 과소 산정할 우려가 있다. 따라서 계절성을 고려하여 기간에 맞는 기준갈수량을 산정하는 것이 안정적인 하천수의 사용과 하천관리에 필요한 유량을 효율적으로 관리할 수 있을 것으로 판단된다.본 연구에서는 효율적인 하천수사용허가 기준유량을 검토하기 위해 지역별 계절성을 고려한 갈수량 검토를 실시하였다. 갈수량 산정을 위한 자연유량은 TANK모형을 이용하여 우리나라 112개 중권역에 대해 50년 간 일별 자연유량을 모의하였다. 모의된 자연유량을 바탕으로 112개 중권역에 대해 유황분석을 실시하여 평균갈수량과 기준갈수량을 검토하였으며, 계절별 갈수량을 검토하기 위해 기간을 여름철(5~10월)과 겨울철(11~4월) 두 개의 시기로 구분하여 여름과 겨울 갈수량을 산정하였다. 또한, 계절성 분석을 위해 세 가지 계절성 지표를 검토하였다. 첫째, 여름과 겨울 갈수량의 비율인 SR(Seasonality Ratio), 둘째, 갈수량의 평균시기를 나타내는 주기적 계절성 지수 SI(Seasonality Index), 셋째, 갈수량의 월간 분포를 나타내는 SH(Seasonality Histogram)이다. 이러한 계절성 지표를 바탕으로 공간적 패턴을 분석하고 여름과 겨울 갈수량의 기초가 되는 수문학적 근거를 판단하였다. 따라서 유역의 계절성 지표를 바탕으로 기간을 분리하고 기간별 갈수량 검토를 통해 보다 효율적인 하천수사용허가 기준유량을 검토할 수 있을 것으로 판단된다.

• Journal of Korean Society of Disaster and Security
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• v.16 no.2
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• pp.15-32
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• 2023

There are some difficulties such as safety problem and need of manpower in measuring discharge by submerging the instruments because of many floating debris and very fast flow in the river during the flood season. As an alternative, microwave water surface current meters have been increasingly used these days, which are easy to measure the discharge in the field without contacting the water surface directly. But it is also hard to apply the method in the sudden and rapidly changing field conditions. Therefore, the estimation of the discharge using the surface velocity in flood conditions requires a theoretical and economical approach. In this study, the measurements from microwave water surface current meter and rating curve were collected and then analyzed by the discharge estimation method using the surface velocity. Generally, the measured and converted discharge are analyzed to be similar in all methods at a hydraulic radius of 3 m or over or a mean velocity of 2 ㎧ or more. Besides, the study computed the discharge by the index velocity method and the velocity profile method with the maximum surface velocity in the section where the maximum velocity occurs at the high water level range of the rating curve among the target locations. As a result, the mean relative error with the converted discharge was within 10%. That is, in flood season, the discharge estimation method using one maximum surface velocity measurement, index velocity method, and velocity profile method can be applied to develop high-level extrapolation, therefore, it is judged that the reliability for the range of extrapolation estimation could be improved. Therefore, the discharge estimation method using the surface velocity is expected to become a fast and efficient discharge measurement method during the flood season.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.7
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• pp.1331-1343
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• 2000

Through the integration of USLE and GIS, the methodology to estimate the soil loss was developed, and applicated to the Sacheon river in Gangrung. Using GIS, spatial analysis such as watershed boundary determination, flow routing. slope steepness calculation was done. Spatial information from the GIS application was given for each grid. With soil and land use map, information about soil classification and land use was given for each grid too. Based upon these data, thematic maps about the factors of USLE were made. We estimated the soil loss by overlaying the thematic maps. In this manner, we can assess the degree of soil loss for each grid using GIS. Annual average soil loss of Sacheon river watershed is 1.36 ton/ha/yr. Soil loss in forest, dry field, and paddy field is 0.15 ton/ha/yr, 27.04 ton/ha/yr, 0.78 ton/ha/yr respectively. The area of dry field, which is 4% of total area, is $2.4km^2$. But total soil loss of dry field is 6561 ton/yr, and it occupies 84.9 % of total soil loss eroded in Sacheon river watershed. Comparing with the 11.2 ton/ha/yr of an average soil loss tolerance for cropland, provision for the soil loss in dry field is necessary. Run-off and water quality of Sacheon river were measured two times in flood season: from July 24, 1998 to July 28 and from September 29 to October 1. As the run-off of the river increased, SS, TN, TP concentrations and pollutant loadings increased. SS, TN, TP loads of Sacheon river discharged during the 2 heavy rains were 21%, 39%, and 19% of the total pollutant loadings generated in the Sacheon river watershed for one year. We can see that much pollutants are discharged in short period of flood season.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.6159-6166
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• 2012

A discharge measurement is difficult in flood season which is especially important in the water resources field and the continuous discharge measurement for all rivers is impossible on the present system. So, the stage-discharge curve has been used for a long time to produce discharge data of rivers. However, there has been problems from a reliability angle due to the fact that this method uses only stage-discharge relationship, although the stage-discharge curve has the convenience. Therefore, a new mean velocity equation was derived by using Chiu's 2D velocity formula of the entropy concept in this paper. The derived equation reflected hydraulic characteristics such as the depth, gravity acceleration, hydraulic radius, energy slope, kinematic coefficient of viscosity, etc. and estimated also a maximum velocity. In addition, this method verified the relationship between a mean and maximum velocity and estimates an equilibrium state ${\phi}(M)$ well presenting properties of a river cross section as the results. The mean velocity was estimated by using the equilibrium state ${\phi}(M)$, and then the discharge was estimated. To prove this equation to be accurate, the comparison between the measured and estimated discharge is conducted by using the measured laboratory data in the unsteady condition flow showing loop state and the results are consistent. If this study is constantly carried out by using various laboratory and river data, this method will be widely utilized in water resources field.

• Journal of Environmental Science International
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• v.15 no.8
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• pp.775-784
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• 2006

In this study, CN value was estimated by using detailed soil map and land cover characteristic against upper basin of Kumho watermark located on the upper basin of Kumho river and the hydrologic morphological characteristic factors were extracted from the basin by using the DEM document. Also the runoff analysis was conducted by the WMS model in order to study how the assumed CN value affects the runoff characteristic. First of all, as a result of studying the soil type in this study area, mostly D type soil was Identified by the application of the 1987 classification criteria. However, by that in 1995, B type soil and C type soil were distributed more widely in that area. When CN value was classified by the 1995 classification criteria, it was estimated lower than in 1987, as a result of comparing the estimated CNs by those standars. Also it was assumed that CN value was underestimated when the plan for Geum-ho river maintenance was drawn up. As a result of the analysis of runoff characteristic, the pattern of generation of the classification criteria of soil groups appeared to be similar, but in the case of the application of the classification criteria in 1995, the peak rate of runoff was found to be smaller on the whole than in the case of the application of the classification criteria in 1987. Also when the statistical data such as the prediction errors, the mean squared errors, the coefficient of determination and other data emerging from the analysis, was looked over in total, it seemed appropriate to apply the 1995 classification criteria when hydrological soil classification group was applied. As the result of this study, however, the difference of the result of the statistical dat was somewhat small. In future study, it is necessary to follow up evidence about soil application On many more watersheds and in heavy rain.