호우의 이동 방향을 고려한 홍수유출 해석 : 낙동왜관 유역을 중심으로 : a case study for Nakdong-waegwan basin

이명섭 고려대학교 대학원 2017 국내석사

In this study, the runoff analysis was carried out using the Clark unit hydrograph considering the storm direction. The flow direction of the rainfall event was analyzed for the parallel direction, the opposite direction and the vertical direction of the stream. For each case, a modified Clark unit hydrograph was generated and analyzed after the outflow analysis and compared with the results obtained using the general Clark unit hydrograph. First, the runoff analysis was performed on a virtual watershed. Huff's 2nd quartile was used to generate hyetograph. In order to investigate the influence of the direction of the rainfall event, we analyzed the results by changing the size of the basin, the duration, the return period, and the velocity of the rainfall event. For the runoff analysis for the target watershed, both Huff storm and real rainfall event obtained by Huff method. First, we used the virtual storm events to investigate various results that occur when the return period, the duration, and the movement speed of the rainfall event are different in the target watershed. After that, we examined the result of actual rainfall. Observed flow, results obtained using general Clark unit hydrograph, and results obtained by considering the movement of rainfall event were compared and analyzed. As a result, when the direction of the rainfall event was taken into consideration, it was confirmed that the shape of the outflow hydrograph, the peak flow rate and the peak time were significantly changed. The difference of the runoff response is affected by the change of the speed and duration of rainfall event.

독립 호우사상의 빈도해석 및 유출해석

박철순 高麗大學校 大學院 2012 국내석사

This study performed the bivariate frequency analysis and runoff analysis using the independent rainfall events, which were compared to the results by conventional method. Firstly, This study investigated the characteristics of independent rainfall events decided by applying various separation criteria to the hourly rainfall data in Seoul for the duration from 1961 to 2010. Secondly, This study investigated the method suggested to decide the annual maximum independent rainfall event and decided the annual maximum independent rainfall series through this method. Rainfall events in various durations satisfying with the specific return period were decided by bivariate frequency analysis on the annual maximum rainfall series. Lastly, flood discharges were calculated in the Jungrang-cheon, Cheonggye-cheon and Ui-cheon basins by using Clark model with the results of bivariate frequency analysis. The flood discharges were compared to the ones calculated from the conventional method. the results of this study are as follows. First, the effect of IETD and threshold was not beyond the expected level. For example, as the IETD increases, the frequencies of independent rainfall events decreased similarly in their rate for both with short and long durations. However, as the threshold increases, The frequency of those with rather long durations decreased much higher. The mean rainfall intensity of the independent rainfall events was found to remain constant regardless of their duration. This indicates that the annual maximum rainfall intensity could be found in a rainfall event with longer durations. Second, when applying the method of moments for the parameter estimation, it was found necessary to consider the correlation coefficient between the two variables as well as the mean and variance. The method of maximum likelihood was better to reproduce the mean, but the method of moments was better to reproduce the annual variation of the variance. The annual maximum rainfall events derived were very similar in both cases. The difference between the bivariate design rainfall and the univariate design rainfall was found to be different with respect to rainfall duration. The difference with rather short rainfall duration was found significantly large, which decreases with longer durations. Univariate design rainfall with short rainfall duration are larger than bivariate design rainfall. However these results were found to be reversed with increase of rainfall duration. In the case of applying Huff method, the flood discharge of Jungrang-cheon basin calculated by applying the bivariate design rainfall was found to be larger than that of applying the univariate design rainfall. On the other hand, this result was found to be reversed in the case of Cheonggye-cheon and Ui-cheon basin. However this results were found to be caused by influence of short time of concentration, storage coefficient and large CN value. In the case of applying alternative block method, the flood discharges of all watersheds calculated by applying the bivariate design rainfall was found to be larger than that of applying the univariate design rainfall. This result indicates that the flood discharge from the conventional method could be underestimated compared to the really possible flood discharge.

北極振動과 韓半島 장마前線 擧動의 相關 分析

이현 高麗大學校 大學院 2012 국내석사

In recent years, extraordinary weathers have occurred all around the world, expected that happened by climate change. The scientists try to explain those phenomena using the Arctic Oscillation. The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases. The Arctic Oscillation Index(AOI) expresses the Arctic Oscillation as index. In this paper, the correlation between the Arctic Oscillation and summer monsoon in Korea was studied focused on shift of summer monsoon. 3 factors were derived as characteristics of shift of summer monsoon. And 4 factors were derived using monthly AOI as characteristics of Arctic Oscillation. The analysis periods are total object period ('80~'10), period before '00 ('80~'99) and period after '00 ('00~'10) considering the changing trends of summer monsoon and AO. As the result, it is presumed that the AO relates the shift of summer monsoon in Korea for the total object period. But it is estimated that the correlation has changed in the period after '00 ('00~'10) because of change of AO trends.

유역 수문순환에서의 방향성 인자의 정량화 및 유역 유출응답에의 영향 평가

박창열 高麗大學校 大學院 2012 국내박사

This study quantifies the orientation or directional characteristics of major hydrological components in a basin, and models the rainfall-runoff system to see the mutual effect of the components with their directions. In this study, three topics among many problems related with ‘direction in hydrological cycle of a basin’ are discussed: (1) quantification of storm direction for a river basin, (2) quantification of directional properties of stream network and hill, and (3) evaluation of the impacts of a rainfall direction on runoff responses. The first topic in this study is to quantify the storm direction for a river basin by applying the von Mises distribution, also determined the representative storm direction. Additionally, the whole procedure was repeated for several storm types such as frontal, typhoon and convective storms for their comparison. From the results derived by analyzing a total of 101 storm events for the Naesung river basin, the von Mises distribution was found to explain the directional characteristics of storms. The representative moving directions derived for three different storm types were significantly different each other, which is coincident with the climate of Korea. The results derived in this study could be helpful to estimate more quantitatively the difference in the runoff response with respect to the moving direction of a storm. Secondly, this study quantified directional properties of channel network and hill slope for a river basin by applying the von Mises distribution, also examined the relation between them. Ultimately, it was examined that whether the directional properties of channel network and hill slope have a certain relation, which might be considered to the rainfall-runoff modeling. From the results derived by analyzing the Naesung stream basin, the von Mises distribution was found well to explain the directional characteristics of directional properties of channel network. There was a clear relation between directional properties of channel network and hill slope. The higher-order streams also showed very obvious modal characteristics. The results derived in this study could be helpful to estimate more quantitatively the difference in the runoff response with respect to the directional properties of channel network and hill slope. Finally, this study examined the difference in the runoff response depending on the rainfall orientation in a natural basin by comparing the characteristics of instantaneous unit hydrograph. The storm direction for a river basin was expressed as a vector with the direction and moving velocity of storm. In the case of channel network, the directional characteristics were acquired using the quantitative result of von Mises distribution. The instantaneous unit hydrograph was derived using the result of convolution integration of each directional distribution and this hydrograph was compared with GIUH model. As a result, if the direction of storm and channel network matches, the shape of river basin tend to elongate and if the direction of storm and channel network does not match, the shape of river basin tend to be oblong. These characteristics make the change of stream-length ratio in a river basin, it could be derived according to the match of direction of rainfall and stream network. When the direction of storm towards the downstream, the moving velocity of storm is added to the characteristics velocity of stream. So the peak discharge of river increases and the peak time appears early. In the contrast, the direction of storm towards upstream, the peak discharge of river decreases relatively and the peak time appears later. Also, the moving velocity of storm makes the influence of runoff responses in a river basin enlarged because of storm direction. It was found that when the moving velocity of storm is equal to the stream velocity, the influence of the runoff responses in a river basin because of storm direction appears the biggest. This study proposed the method to quantify the orientation or directional characteristics of major hydrological components in a basin, which could be used effectively. Expected contribution of this study can be found in many aspects. This method helps to find the representative storm direction considering the basin climatology and the geomorphological directional parameters in a river basin. Direction characteristics of extreme storm events and their occurrence probability could be found. The representative unit hydrograph ,which has a non-linearity of the rainfall-runoff processes by the storm direction, could be derived.

流域 集中時間과 貯溜常數의 理論的 特性 및 經驗式 開發

이지호 高麗大學校 大學院 2012 국내박사

This study analyzed for basin concentration time and storage coefficient through theoretical characteristic and developed empirical formulas. It evaluated how effective the use of selected rainfall events is for the decision of runoff characteristic such like concentration time and storage coefficient. The form of the empirical formula was determined based on theoretical background and was compared with the conventional empirical equations. The empirical formulas were developed for six watersheds and understood the problems of the conventional empirical equations by compared with these. The results are as follows. To select effective rainfall events, the antecedent moisture condition (AMC) was adopted as the selection criterion. That is, the storm events were divided into three groups depending on the AMC and evaluated their spatial distribution, also the runoff characteristics derived were analyzed corresponding to each AMC group, and then it was proposed what rainfall events should be used for the decision of the runoff characteristics. From analysis of spatial distribution of rainfall, the rainfall events of the AMC-III group were found to be more suitable for the decision of runoff characteristics of a basin. As a result that the empirical formula was derived theoretically by the relationship between the parameters of Clark's unit hydrograph and basin characteristic factors, it found that form of L²/S was desirable for the empirical formula of concentration time and for storage coefficient. From the empirical formulas which were derived six watersheds, it was found that the conventional empirical formulas of concentration and storage coefficient derived multiple regression analysis so called statistical method had no theoretical basis.

확률대응법을 이용한 레이더 강우 추정관계식의 매개변수 결정

노용훈 高麗大學校 大學院 2014 국내석사

Radar is widely used to observe the rain rate field and to prevent the flood damage. Since the Mt. Gwan-ak radar was introduced in 1969, the Korea Meteorological Administration has expanded its radar network covering the entire Korean peninsula. As a remote sensing tool, radar collects the reflectivity intensity from the rain drops in the air. The reflectivity data should be converted in the rain rate data to be used for various applications. The so-called Z-R relation is developed for this purpose. Parameters of the Z-R relation are generally estimated by the Least Square Method (LSM) or recently by the Probability Matching Method (PMM). This study evaluated the PMM for the parameter estimation of the Z-R relation. As a first step, the sensitivity analysis was done to decide the threshold number of data pairs and the data interval for the development of a histogram. As a result, it was found that at least 1,000 number of data pairs are required to apply the PMM for the parameter estimation. This amount of data is similar to that collected for 2 hours. Also, the data interval for the histogram was found to be at least 100(Reflectivity: 0.6 dBZ space for 0~60 dBZ, Rain rate: 0.26 dBR space for 0~25 dBR). Additionally, it was found that the matching the first moment is better than the zeroth moment, and that the data pairs comprising 30 to 100% are better for the PMM application. Finally above findings were applied to the rainfall event occurred on July 9, 2011. The radar data used were those from the Mt. Bisl radar, and the rain gauge data were the TM data within the radar umbrella. The optimal parameters were decided to be A=90, and b=1.5, which were also found to be similar to previous studies. Also, the radar rain rate derived by applying these parameters was found to be better matched to the rain gauge rain rate, than the conventional Z-R relation.

평화의댐의 다목적 활용을 고려한 홍수저류효과 평가

신현선 高麗大學校 2020 국내석사

The Peace Dam is located in near the demilitarized zone (DMZ) of the North Han River shared between South and North Korea. It was originally planned to prepare for the effects of the potential breakage of the Imnam dam in North Korea. So, it was made as a simple flood control dam that does not involve any water supply or hydropower generation. However, the recent reconciliation efforts between South and North Korea have raised the possibility for its multipurpose utilization. This Study evaluates the possible increase of the flood control ability of the Peace Dam under the condition of its multipurpose utilization, i.e., changing it from a flood control dam to a multipurpose dam. The allocation of flood control and water conservation storage for its multipurpose utilization was assumed to follow that of other similar-sized dams in Korea. The flood control ability was quantified by introducing the concept of storage coefficient based on a nonlinear reservoir model. As the results, quantified by the storage coefficient, the flood control ability of the current Peace Dam was estimated to be just 3.9 hours. However, the flood control ability after its multipurpose utilization could be significantly increased up to 22.6 hours using the reservoir operation method. Here, it was assumed that the dam was operated by the rigid ROM with a constant rate of 0.5. In addition, this result was based on the assumption that the ratio between water conservation storage and the flood control storage was three. Even though the flood control storage is set at just 25% of the total storage, the storage coefficient was increased more than five times that of the current Peace Dam.

Analysis of hydrological characteristics of volcanic sedimentary regions : focused on the Jeju island

강민석 Graduate School, Korea University 2021 국내박사

Jeju Island, a volcanic sedimentary region, has totally different hydrological characteristics from those of the inland area of mainland Korea. Basalt, a volcanic rock, shows high permeability and thus low surface runoff. This geographical characteristic affects the island’s hydrology changing most channels on Jeju Island to be dry, and runoff to occur only when the rainfall intensity is high. There are several problems in the rainfall-runoff analysis in Jeju Island. Most of the problems are related the rainfall loss by infiltration. This study proposed an appropriate SCS-CN method in Jeju Island considering these characteristics and the applicability of the proposed method was evaluated. The major results of this study can be summarized as follows. First, in this study, the SCS-CN method was re-established in consideration of the hydrological characteristics of the volcanic sedimentary region. To this end, from 2012 to 2019, major rainfall events in the Hancheon basin of Jeju were selected, and the runoff data of the 2nd Dongsan Bridge located in the downstream part of the Hancheon basin were analyzed. The initial abstraction was determined as the amount of rainfall occurred from the time when the rainfall event occurred to the time when the direct runoff occurred. Potential maximum retention and curve number (CN) were determined by applying the initial abstraction and the effective rainfall and initial abstraction of each rainfall event to the SCS-CN method. Finally, the distribution of each factor such as the potential maximum retention, initial abstract, CN, etc. was reviewed to determine the appropriate CN and initial abstraction scale of the Hancheon basin. The appropriate conditions for the antecedent moisture conditions (AMC) in the Hancheon basin were determined from the sensitivity analysis according to the AMC. Second, in this study, the re-established SCS-CN method was verified through analysis of effective rainfall. To this end, the independent rainfall event was extracted and analyzed using rainfall data from the Eongtto waterfall basin in Jeju Island from 2011 to 2019. For each independent rainfall event, the effective rainfall was estimated by applying the method proposed in Chapter 4 of this dissertation and the method of the Guideline for Design Flood Estimation. Next, the occurrence characteristics of Eongtto waterfall were analyzed by comparing the cases of Eongtto waterfalls surveyed through news, newspaper articles, and SNS with the previously estimated effective rainfall. Through sensitivity analysis on the hydrological soil group classification method, the initial abstraction ratio, and the AMC, it was confirmed that the AMC had the greatest effect in estimating the effective rainfall. Finally, in this study, the agricultural water supply in the Udo region was evaluated, using the proposed SCS-CN method. To this end, first, the topographical characteristics and the agricultural activities of Udo were investigated. Then the overall status and scale of reservoir in Udo was identified through existing literature and field survey. Next, the monthly consumptive water use for major field crop in the Udo region was estimated and compared with the monthly precipitation to estimate the agricultural water shortage. Finally, the effect of the storage of the reservoir on the field crop production in the Udo region was evaluated by comparing the irrigation intervals before and after the consideration of the reservoir.

Analytical approaches in hydrological routing for watershed subdivision issues

전창현 Graduate School, Korea University 2014 국내박사

Determination of clark unit hydrograph parameters for estimating probable maximum flood

이진욱 Greduate School, Korea University 2021 국내박사

The estimation of the exact probable maximum flood is very important for the design or evaluation of dams. The probable maximum flood was defined as the flood generated from the probable maximum precipitation. The probable maximum flood is estimated by using a unit hydrograph with the probable maximum precipitation as input. Recently, Clark unit hydrograph, which have time of concentration and storage coefficient as parameters, has been used in Korea. Until now, due to short observation period and lack of reliability verification of hydrological data, Clark unit hydrograph parameters were estimated with only a small number of storm events in a gaged basin, and no procedures have been presented for determining the parameters in an ungauged basin. In this dissertation, a method to determine unit hydrograph parameters for estimating the probable maximum flood was proposed. The summary for the total of five chapters conducted in this dissertation is as follows. First, the method for determining the time of concentration and the storage coefficient using peak velocity was examined and applicability of the method was confirmed through the observation data. Secondly, downstream variations of velocity in a storm event was theoretically derived and examined from the observation data. Third, the application method of rational formula for estimating the peak discharge for time-distributed rainfall was reviewed and examined from the observed data. Fourth, the possibility of estimating the velocity at an ungaged point in a rainfall event was inspected and the applicability of it to the downstream point was examined. Finally, a method to determine unit hydrograph parameters for estimating the probable maximum flood was proposed and evaluated. The results from the method were compared with those from the existing researches. Furthermore, consistency was examined by comparing them with the peak discharge obtained from the probability rainfall. The results from this dissertation would enable the determination of sufficiently objective unit hydrograph without subjective judgment based on the experience of each technician. Furthermore, it is expected that this method will help in the process of determining and reviewing parameters even for a gauged basin. Through this, it is expected that the methodology in this dissertation would be actively used in the new dam construction plans or safety evaluations.