• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.4
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• pp.25-32
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• 2023

KDS (Korean Design Standard) for agricultural drainage is a planning standard that helps determine the appropriate capacity and type of drainage facilities. The objective of this study was to analyze the inundation of the agricultural basin considering the current design standard and the critical rainfall duration. This study used the rainfall durations of 1-48 hour, and the time distribution method with the Chicago and the modified Huff model. For the runoff model, the NRCS (Natural Resources Conservation Service) unit hydrograph method was applied, and the inundation depth and duration were analyzed using area-elevation data. From the inundation analysis using the modified Huff method with different rainfall durations, 4 hours showed the largest peak discharge, and 11 hours showed the largest inundation depth. From the comparison analysis with the current method (Chicago method with a duration of 48 hours) and the modified Huff method applying critical rainfall duration, the current method showed less peak discharge and lower inundation depth compared to the modified Huff method. From the simulation of changing values of drainage rate, the duration of 11 hours showed larger inundation depth and duration compared to the duration of 4 hours. Accordingly, the modified Huff method with the critical rainfall duration would likely be a safer design than the current method. Also, a process of choosing a design hydrograph considering the inundation depth and duration is needed to apply the critical rainfall duration. This study is expected to be helpful for the theoretical basis of the agricultural drainage design standards.

• Journal of Korea Water Resources Association
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• v.31 no.4
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• pp.375-384
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• 1998

In determining design runoff for the design of drainage systems, the concept of critical storm duration is applied. However, rainfall distribution is usually determined without well-defined standards. In this paper, through the application of ILLUDAS model to Sanbon basin, which is a small urbanized watershed, effects of various rainfall distributing types upon the determination of critical storm duration are throughly analyzed. As a result, it is revealed that peak discharge rates as well as critical storm duration are greatly influenced by the applied of rainfall distributions such as uniform, triangular, trapezoid, huff, central type using IDF curve. Keywords : critical storm duration, rainfall distribution, urban runoff, design storm, ILLUDAS.

• Journal of Korea Water Resources Association
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• v.37 no.9
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• pp.695-706
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• 2004

This study is to propose the temporal pattern of design rainfall which causes maximum peak discharge, and to analyze the relation of catchment characteristics and critical durations for gauged midsize catchment. Hydrologic analysis has done over the 44 midsize catchments with 50-5,000$\textrm{km}^2$. The type of temporal pattern of design rainfall which causes maximum peak discharge has resulted in Huff's 4 quartile distribution method for effective rainfall(AMC III) The peak discharges of 24hr rainfall duration are similar to those of critical duration for 50-600$\textrm{km}^2$, and the peak discharges of 48hr rainfall duration are similar to those of critical duration for 600-5,000$\textrm{km}^2$. Therefore, if the proper rainfall intensity formula is selected, 24hr or 48hr rainfall duration may be regarded as the critical duration of midsize catchment. A simple regression equation is derived by using a catchment area and critical duration with high correlation for the case of effective rainfall(AMC III). Therefore, it can be used to determine the critical duration of ungauged catchment with 50-5,000$\textrm{km}^2$. Also, dimensionless regression equation is derived by using characteristic values of unit hydrograph.

• Journal of The Korean Society of Agricultural Engineers
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• v.64 no.2
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• pp.47-55
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• 2022

The objective of this study was to analyze the effect of the duration and time distribution of probability rainfall on farmland inundation for the paddy fields in the drainage improvement project site. In this study, eight drainage improvement project sites were selected for inundation modeling. Hourly rainfall data were collected, and 20- and 30-year frequency probability rainfalls were estimated for 14 different durations. Probability rainfalls were distributed using Intensity-Duration-Frequency (IDF) and Huff time distribution methods. Design floods were calculated for 48 hr and critical duration, and IDF time distribution and Huff time distribution were used for 48 hr duration and critical duration, respectively. Inundation modeling was carried out for each study district using 48 hr and critical duration rainfalls. The result showed that six of the eight districts had a larger flood discharge using the method of applying critical duration and Huff distribution. The results of inundation depth analysis showed similar trends to those of design flood calculations. However, the inundation durations showed different tendencies from the inundation depth. The IDF time distribution is a distribution in which most of the rainfall is concentrated at the beginning of rainfall, and the theoretical background is unclear. It is considered desirable to apply critical duration and Huff time distribution to agricultural production infrastructure design standards in consideration of uniformity with other design standards such as flood calculation standard guidelines.

• Water for future
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• v.26 no.2
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• pp.49-57
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• 1993

A hydrological method is performed to determine the critical duration of design rainfall for the design of storm sewer in Seoul. To seize the effect of the duration and the temporal distribution of the rainfall to the peak discharge of the storm sewer, the Huff's quartile method is used as a temporal pattern for the design rainfall of any durations (9 cases for 20-240 min.) with 10 years return period. The critical duration of design rainfall is determined as the duration which maximizes the peak discharge. This study is applied to 18 urban drainage systems in Seoul. The ILLUDAS model is applied to runoff analysis, and the result shows that the duration which maximizes peak discharge is 30, 60 minutes generally. The relation diagram between peak discharge for the critical duration and watershed area is prepared for the design of storm sewer.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.135-144
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• 2009

The objective of this study is to examine the effect of hydrological factors on critical durations, and to analyze the relationship between the watershed characteristics and the critical duration of design rainfall in the medium sized catchments. Hydrological factors are used to return period, probable intensity formula, hydrograph method, effective rainfall and temporal pattern of design rainfall. Hydrologic analysis has done over the 44 medium sized catchments with $50{\sim}5,000{\beta}{\yen}$. Watershed characteristics such as catchment area, channel length, channel slope, catchment slope, time to peak, concentration of time and curve number were used to simulate correlation analysis. All of hydrological factors except return period influence to the critical duration of design rainfall. Also, it is revealed that critical duration is influenced by the watershed characteristics such as area, channel length, channel slope and catchment slope. Multiple regression analysis using watershed characteristics is carried out for the estimation of relationship among these. And the 7 type equations are proposed by the multiple regression using watershed characteristics and critical duration of design rainfall. The determination coefficient of multiple regression equations shows $0.96{\sim}0.97$.

• Journal of Wetlands Research
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• v.6 no.3
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• pp.119-126
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• 2004

In recent, the critical rainfall duration concept is widely used but we do not have understandable criteria yet. However, the critical rainfall duration is usually calculated considering concentration time, runoff model using effective rainfall, and unit hydrograph for the estimation of design flood. This study is to derive the regression equations between the critical rainfall duration and hydrologic components such as the basin area, slope, length, CN, and so on. We use a GIS tool which is called the ArcView for the estimation of hydrologic components and the HEC-1 module which is provided in WMS model is used for the runoff computation. As the results, the basin area, basin slope, and basin length had a great influence on the estimations of peak runoff and critical rainfall duration. We also investigated the sensitivities for the peak runoff and critical duration of rainfall from the correlation analysis for the involved components in the runoff estimation.

• Korean Journal of Hydrosciences
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• v.5
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• pp.33-43
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• 1994

This study is to determine the critical duration of design rainfall and to utilize it for the design of detention pond with pump station. To examine the effect of the duration and temporal distribytion of the design rainfall, Huff's quartile method is used for the 9 cases of durations (ranges from 20 to 240 minutes) with ten years return period, and the ILLUDAS model is used for runoff analysis. The storage ratio, which is the ratio of maximum storage amounts to total runoff volume, is introduced to determine the criticalduration of design rainfall. The duration which maximizes the storage ratio is adopted as the critical duration. This study is applied to 18 urban drainage watercheds with pump station in Seoul, of which the range of watershed area is 0.24~12.70$km^2$. The result of simulation shows that the duration which maximizes storage ratio is 30 and 60 minutes on the whole. It is also shown that the storage ratios of 2nd - and 3rd-quartile pattern are larger than those of 1st- and 4th-quartile pattern of temporal distribution. A simplified empirical formula for Seoul area is suggested by the regression analysis between the maximum storage ratio and the peak ratio. This formula can be utilized for the preliminary design and planning of detention pond with pump station.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.711-714
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• 2008

The objective of this study is to analyze the relationship between the watershed characteristics and the critical duration of design rainfall. For estimation of critical duration, adjustment Huff's method and ILLUDAS urban runoff model were applied to urban 21 areas. Watershed characteristics such as area, channel length, channel slope, shape factor, and pipe density were used to simulate correlation analysis. The conclusions of this study are as follows; it is revealed that critical duration is influenced by the watershed characteristics such as pipe density, area and channel length. Also, multiple regression analysis using watershed characteristics is carried out and the determination coefficient of multiple regression equation shows 0.972.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.3 s.18
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• pp.29-39
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• 2005

The objective of this study is to analyze the relation of critical duration according to hydrologic characteristics in urban areas. RRL, ILLUDAS, SWMM, and SMADA urban runoff models were applied to the Seongnae and Banpo watershed and experiment area of the Dong-Eui University. Also, hydrologic characteristics such as temporal pattern of rainfall, rainfall intensity formula, antecedent moisture condition, return period, and urban runoff model were used to simulate the critical duration of the test areas. The results of this study are as follows; (1) The type of temporal pattern of rainfall which causes maximum peak discharge in urban area has resulted in Huff's 4th quartile distribution. (2) The critical duration in urban areas were not influenced by hydrological factors except urban runoff model. (3) Peak discharge and critical duration in urban areas were influenced by the urban runoff model, and the SWMM model using Huff's 4th quartile distribution shows maximum critical duration.