• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.493-503
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• 2014

The NRCS-CN method is generally applied for estimating effective rainfalls in practice, in which the basin-averaged CN is normally used. In order to develop a more appropriate method for estimating effective rainfalls in a basin, this study compared estimated effective rainfalls from two distinct methods with the observed direct runoff. The first method is to estimate the basin-representative effective rainfall using the basin-averaged CN (hereafter, effective rainfall I), whereas the second method to estimate the basin-averaged effective rainfall through areal-averaging sub-area effective rainfalls corresponding to the soil type and landuse type (hereafter, effective rainfall II). The overall results indicated that the effective rainfall II was higher than the effective rainfall I and closer to the observed direct runoff. The study also performed error analyses to verify that the effective rainfall II can be applied in practice in a basin as more accurate estimate of basin-representative effective rainfall.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1999.10c
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• pp.87-92
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• 1999

The evaluation of the effective rainfall is important in the desgin and operation of irrigation systems. But the difinition of the effective rainfall and the method for the estimating effective rainfall is various for each purpose . In this paper, the effective rainfall was defined as amount of rainfall which is remained in the effective soil depth that can be use to consumptive use of crop during growing season. The sol moisture was measured by Neutron prob for the effective rainfall estimation, and theexperiment was conducted for mulched and non-mulched condition of lysimeter during growing season. By the result of analysis and the former definition, the effective rainfall was estimated to be 37.2% for the mulched lysimeter and 40.7% for the non-mulched lysimeter.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.1
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• pp.29-39
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• 1993

A model for estimating daily effective rainfall of upland crops was developed. The infiltration process was described by Green-Ampt infiltration model developed by Chu(1978). The model considers delayed surface ponding and surface detention storage under a uniform soil profile. The Green-Ampt parameters, that is, average hydraulic conductivity and average capillary pressure head on a sandy loam soil were determined from field experiment using Air-entry permeameter developed by Bouwer(1966). The model was verified by comparing measured and simulated surface runoff. The ratios of effective rainfall to total rainfall for red pepper, soybean, sesame and Chinese cabbage were evaluated using Borg's root growth model( 1986) respectively. The followings are a summary of this study results; 1.In a sandy loam soil average hydraulic conductivity was 3.28cm/hr and average capillary pressure head was 3.00cm. 2.The root growth of upland crops could be expressed by Borg's root growth model successively. 3.The measured and simulated surface runoff was agreed well with each other. 4.As the rainfall amount was increased, the ratio of effective rainfall to total rainfall was decreased exponentially till a certain growing period.

• Journal of Wetlands Research
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• v.7 no.3
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• pp.41-48
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• 2005

Generally the estimation of effective rainfall is important in the rainfall-runoff analysis. So, we must pay attention to selecting more accurate effective rainfall estimation method. Although there are many effective rainfall estimation methods, the NRCS method is widely used for the estimation of effective rainfall in the ungaged basin. However, the NRCS method was developed based on the characteristics of the river basin in USA. So, it may have problems to use the NRSC method in Korea without its verification. In the NRCS method, the antecedent precipitation of 5-day is usually used for the estimation of effective rainfall. The main purpose of this study is to investigate the suitable antecedent precipitation day in Korea river basin through the case study. This study performs the rainfall-runoff simulation for the Tanbu river basin by HEC-HMS model under the condition of varying the antecedent precipitation day from 1-day to 7-day and performs goodness of fit test by Monte Carlo simulation method. The antecedent precipitation of 2-day shows the most preferable result in the analysis. This result indicates that the NRCS method should be applied with caution according to the characteristics of the river basin.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.6
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• pp.3-12
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• 2008

It is important to estimate accurate effective rainfall to analyse flood flow and long-term runoff for the rational planning, design, and management of water resource. The initial abstraction is also important to estimate effective rainfall. The Soil Conservation Service (SCS) has developed a procedure and it has been most commonly applied to estimate effective rainfall. But the SCS method still has weak points, because of unnatural assumptions such as antecedent moisture conditions and initial abstraction. The coefficient of initial abstraction(K) is depending on the soil moisture condition and antecedent rainfall. The maximum storage capacity of Umax which is calibrated by stream flow data in the proposed watershed was derived from the DAWAST(DAily WAtershed STreamflow) model. The values of K obtained from 69 storm events at the five watersheds are ranging from 0.133 to 0.365 and its mean value is 0.207. Effective rainfall could be estimated more reasonably by introducing new concept of initial abstraction. The equation of $K=0.076Sa^{0.255}$ was recommended instead of 0.2 and it could be applicable to the small-medium rural watersheds.

• Journal of Korea Water Resources Association
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• v.30 no.4
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• pp.357-366
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• 1997

This paper presents a methodology for the calculation of effective rainfall by the SCS method using 3-dimensional digital elevation map and a Triangular Irregular Network module. The effective rainfall is calculated by taking into the increases of the runoff curve number(2%, 3%) due to the 10% increases of the slope of hillside, and the result indicate that the effective rainfall varies 5.0%∼12.0% with the storm events. It is demonstrated that in case of using the SCS method for the calculation of effective rainfall in the mountainous watershed with great elevation difference, the methodology taking into the slope of hillside is more viable.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.3
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• pp.313-324
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• 2013

It is widely known that untreated Combined Sewer Overflows (CSOs) that directly discharged from receiving water have a negative impact. Recent concerns on the CSO problem have produced several large scale constructions of treatment facilities, but the facilities are normally designed under empirical design criteria. In this study, several criteria for defining CSOs (e.g. determination of effective rainfall, sampling time, minimum duration of data used for rainfall-runoff simulation and so on) were investigated. Then this study suggested a standard methodology for the CSO calculation and support formalized standard on the design criteria for CSO facilities. Criteria decided for an effective rainfall was over 0.5 mm of total rainfall depth and at least 4 hours should be exist between two different events. An Antecedent dry weather period prior to storm event to satisfy the effective rainfall criteria was over 3 days. Sampling time for the rainfall-runoff model simulation was suggested as 1 hour. A duration of long-term simulation CSO overflow and frequency calculation should be at least recent 10 year data. A Management plan for the CSOs should be established under a phase-in of the plan. That should reflect site-specific conditions of different catchments, and formalized criteria for defining CSOs should be used to examine the management plans.

• Journal of Environmental Science International
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• v.2 no.3
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• pp.193-199
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• 1993

This study has two objectives. One is developing the runoff model for Hoe-Dong Reservoir basin located at the upstream of Su-Young River in Pusan. To develop the runoff model, basic hydrological parameters - curve number to find effective rainfall, and storage coefficient, etc. - should be estimated. In this study, the effective rainfall was calculated by the SCS method, and the storage coefficient used in the Clark watershed routing was cited from the report of P.E.B. The other is the derivation of transfer function for Hoe-Dong Reservoir basin. The linear, discrete, input-output model which contained six parameters was selected, and the parameters were estimated by the least square method and the correlation function method, respectively. Throughout this study, rainfall and flood discharge data were based on the field observation in 1981.8.22 - 8.23 (typhoon Gladys). It was observed that the Clark watershed routing regenerated the flood hydrograph of typhoon Gladys very well, and this fact showed that the estimated hydrological parameters were relatively correct. Also, the calculated hydrograph by the linear, discrete, input-output model showed good agreement with the regenerated hydrograph at Hoe-Dong Dam site, so this model can be applicable to other small urban areas. Key Words : runoff, effective rainfall, SCS method, clark watershed iou상ng, hydrological parameters, parameter estimation, least square method, correlation function method, input-output model, typhoon gladys.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.5
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• pp.81-89
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• 1995

One of the most difficult problem to estimate the flood inflow is how to understand the effective rainfall. The effective rainfall is absolutely influenced by the condition of soil moisture in the watershed just before the storm event. DAWAST model developed to simulate the daily streamflow considering the meteologic and geographic characteristics in the Korean watersheds was applied to understand the soil moisture and estimate the effective rainfall rather accurately through the daily water balance in the watershed. From this soil moisture and effective rainfall, concentration time, dimensionless hydrograph, and addition of baseflow, the rainfall-runoff model for flood flow was developed by converting the concept of long-term runoff into short-term runoff. And, real-time flood forecasting model was also developed to forecast the flood-inflow hydrograph to the river and reservoir, and called RETFLO model. According to the model verification, RETFLO model can be practically applied to the medium and small river and reservoir to forecast the flood hydrograph with peak discharge, peak time, and volume. Consequently, flood forecasting and warning system in the river and the reservoir can be greatly improved by using personal computer.

• Journal of Korea Water Resources Association
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• v.43 no.6
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• pp.533-541
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• 2010

It is basic for a flood prediction to calculate direct runoff from rainfall in a basin by the rainfall-runoff model. The direct runoff is calculated from rainfall excess or effective rainfall based on a rainfall-runoff model. The total rainfall minus rainfall loss equals rainfall excess with time. This loss can be treated equal to an infiltration loss under the assumption that the infiltration is a major one among the losses in the rainfall-runoff model. Practically obtaining the infiltration loss $\Phi$ index method, W index method or modified ones of these have been used. In this study it is assumed the loss of rainfall in a basin be a well-known Horton infiltration mechanism. And in case that the parameter set is given in the Horton infiltration model a procedure and assumption for calculating hourly infiltration loss and rainfall excess are offered and the results of its application are compared with those of $\Phi$ index method. By this study it is well shown the value of Horton infiltration function is exponentially decay with time as the Horton infiltration mechanism.