• Title/Summary/Keyword: SCS-CN method

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A Study for the Efficiency to Extract Hydrologic-Topographical Parameters Using GIS (GIS를 이용한 수문지형인자 추출에 관한 효용성 연구)

  • Choi, Hyun;Ahn, Chang-Whan;Lee, Je-Yun;Han, Ho-Wook
    • Proceedings of the Korea Contents Association Conference
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    • 2007.11a
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    • pp.937-941
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    • 2007
  • For Hydrologic analysis of the river, the exact Dividing Watershed and Hydrologic-Topographical Parameters affect enormously Hydrologic analysis of the river basin. Therefore the extraction of Hydrologic-Topographical Parameters as well as Dividing Watershed are stiuied by several ways. However the definite standard of all those means are not settled. Recently GIS is applied to the field of water resources so that we can divide Watershed and calculate Hydrologic-Topographical Parameters of the targeted area easily and objective way for using DEM. Thanks to DEM, we don't have to spend much time as we did before. However other problems are generated such as the parameter value is changed by the precision of established NGIS(National Geographic Information System), etc. In this study, using GIS which is popular recently, we suggested efficient extract method of Hydrologic-Topographical Parameters SCS(Soil Conservation Service) CN(Curve Number) in watershed.

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Land Cover Classification and Effective Rainfall Mapping using Landsat TM Data (Landsat TM 자료를 이용한 토지피복분류와 유효우량도의 작성)

  • Shin, Sha-Chul;Kwon, Gi-Ryang;Kim, Seong-Joon
    • Journal of Korea Water Resources Association
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    • v.35 no.4 s.129
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    • pp.411-423
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    • 2002
  • Accurate and real time forecasting of runoff has a high priority in the drainage basins prone to short, high intensity rainfall events causing flash floods. To take into account the resolution of hydrological variables within a drainage basin, use of distributed system models is preferred. The Landsat Thematic Mapper(TM) observations enable detailed information on distribution of land cover and other related factors within a drainage basin and permit the use of distributed system models. This paper describes monitoring technique of rainfall excess by SCS curve number method. The time series maps of rainfall excess were generated for all the storm events to show the spatiotemporal distribution of rainfall excess within study basin. A combination of the time series maps of rainfall excess with a flow routing technique would simulate the flow hydrograph at the drainage basin outlet.

A Study of Soil Moisture Retention Relation using Weather Radar Image Data

  • Choi, Jeongho;Han, Myoungsun;Lim, Sanghun;Kim, Donggu;Jang, Bong-joo
    • Journal of Multimedia Information System
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    • v.5 no.4
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    • pp.235-244
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    • 2018
  • Potential maximum soil moisture retention (S) is a dominant parameter in the Soil Conservation Service (SCS; now called the USDA Natural Resources Conservation Service (NRCS)) runoff Curve Number (CN) method commonly used in hydrologic modeling for event-based flood forecasting (SCS, 1985). Physically, S represents the depth [L] soil could store water through infiltration. The depth of soil moisture retention will vary depending on infiltration from previous rainfall events; an adjustment is usually made using a factor for Antecedent Moisture Conditions (AMCs). Application of the method for continuous simulation of multiple storms has typically involved updating the AMC and S. However, these studies have focused on a time step where S is allowed to vary at daily or longer time scales. While useful for hydrologic events that span multiple days, this temporal resolution is too coarse for short-term applications such as flash flood events. In this study, an approach for deriving a time-variable potential maximum soil moisture retention curve (S-curve) at hourly time-scales is presented. The methodology is applied to the Napa River basin, California. Rainfall events from 2011 to 2012 are used for estimating the event-based S. As a result, we derive an S-curve which is classified into three sections depending on the recovery rate of S for soil moisture conditions ranging from 1) dry, 2) transitional from dry to wet, and 3) wet. The first section is described as gradually increasing recovering S (0.97 mm/hr or 23.28 mm/day), the second section is described as steeply recovering S (2.11 mm/hr or 50.64 mm/day) and the third section is described as gradually decreasing recovery (0.34 mm/hr or 8.16 mm/day). Using the S-curve, we can estimate the hourly change of soil moisture content according to the time duration after rainfall cessation, which is then used to estimate direct runoff for a continuous simulation for flood forecasting.

Assessment of Hydrological Impact by Long-Term Land Cover Change using WMS HEC-1 Model in Gyeongan-cheon Watershed (WMS HEC-1 모형을 이용한 경안천 유역의 경년 수문변화 분석)

  • Lee, Jun-Woo;Kwon, Hyung-Joong;Shin, Sha-Chul;Kim, Seong-Joon
    • Journal of the Korean Association of Geographic Information Studies
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    • v.6 no.1
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    • pp.107-118
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    • 2003
  • The purpose of this study is to assess the hydrological impact on a watershed from long-term land cover changes. Gyeongan-cheon watershed($558.2km^2$) was selected and WMS(watershed modeling system) HEC-1 model was adopted as an evaluation tool. To identify land cover changes, five Landsat images(1980/2/15, 1986/4/15, 1990/4/26, 1996/4/26, 2000/5/17) were selected and analyzed using maximum likelihood method. As a result, urban areas have increased by 5.6% and forest areas have decreased by 6.1% between 1980 and 2000. SCS curve number increased by 9.8. To determine model parameters and evaluate HEC-1 model, five storm events(1998/5/2, 1998/8/23, 1998/9/30, 1999/5/3, 2000/7/29) were used. The simulated stream flow agreed well with the observed one with relative errors ranging from 9% to 36%. For 254 mm daily rainfall of 30 years frequency, due to the increase of urban areas peak flow increased by $455m^3/sec$ and the time of peak flow reduced about four hours for 20 years land cover changes.

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A Sensitivity Analysis of Model Parameters involved in Clark Method on the Magnitude of Design Flood for urban Watersheds (CLARK 유역추적법에 의한 계획홍수량 산정에 미치는 매개변수의 민감도 분석)

  • Yoon, Kwang-Wonn;Wone, Seog-Yeon;Yoon, Yong-Nam
    • Water for future
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    • v.27 no.4
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    • pp.85-94
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    • 1994
  • A Sensitivity analysis on the model parameters involved in the Clark watershed routing method is made to demonstrate the effect of each parameter on the magnitude of 50-year design flood for small urban streams. As for the rainfall parameter the time distribution pattern of design storm was selected. For short duration storms Huff, Yen & Chow and Japanese Central type distributions were selected and the Mononobe distribution of 24-hour design storm was also selected and tested for Clark method application. The effect of SCS runoff curve number for effective rainfall and the methods of subbasin division for time-area curve were also tested. The routing parameter, i.e. the storage constant(K), was found to be the dominating parameter once design storm is selected. A multiple regression formula for K correlated with the drainage area and main channel slope of the basin is proposed for the use in urban stream practice for the determination of design flood by Clark method.

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LIDMOD2 Development for Evaluation of LID/BMPs (LID/BMPs 효과분석을 위한 LIDMOD2 개발)

  • Jeon, Ji-Hong;Choi, Donghyuk;Na, Eun Hye;Park, Chan-Gi;Kim, Tae-Dong
    • Journal of Korean Society on Water Environment
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    • v.26 no.3
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    • pp.432-438
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    • 2010
  • LIDMOD2 was developed for evaluation of low impact development (LID) and best management practice (BMP) by modification of Site Evaluation Tool (SET). The modification includes employment of SCS-CN method for annual runoff simulation, unit load method for annual pollutant loads simulation, and the method proposed by Korean TMDL for calculating pollutant reduction by BMPs. The CN values were updated with regionalized parameters within Nack-Dong River basin because these are important parameters for simulating hydrology. LIDMOD2 was tested by applying to Andong Bus terminal. As a simulation results, pollutant loads and surface runoff will be significantly increased by post-development without LID compared with those from pre-development. LID technique was simulated to efficiently reduce surface runoff and pollutant load and increase infiltration. LIDMOD2 is screening level tool and easy to use because LIDMOD2 is based on spread sheet and most of parameters are regionalized. LIDMOD2 was illustrate that it could evaluate LID well by summarizing and graphing annual hydrology, annual pollutant loading, and hydrograph for event storm. The calculation methods related with pollutant loads are employed from the guideline of Korean TMDL and it can be useful tool for Korean TMDL to evaluate the effect of LID/BMP on developing area.

Estimation of Groundwater Storage Change and Its Relationship with Geology in Eonyang Area, Ulsan Megacity (울산광역시 언양지역의 지하수 저류 변화량 산정 및 지질과의 관련성)

  • Kim, Nam-Hoon;Hamm, Se-Yeong;Kim, Tae-Yong;Cheong, Jae-Yeol;An, Jeong-Hoon;Jeon, Hang-Tak;Kim, Hyoung-Soo
    • The Journal of Engineering Geology
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    • v.18 no.3
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    • pp.263-276
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    • 2008
  • In diverse hydrogeologic fields, estimation of groundwater storage change is one of the most critical issues. Accurate estimation methods for determining groundwater storage change are required more and more. For Yeonyang area of Ulsan Megacity, groundwater storage change was estimated by using water balance method and hydrogeological analyses. The estimates of groundwater storage change was 240 mm corresponding to 18.7% of mean annual precipitation. Direct runoff was calculated as 137 mm (10.6% of mean annual precipitation) by using SCS-CN method. Evapotranspiration based on the Thornthwaite method was calculated as 776 mm (60.5% of mean annual precipitation). Hydraulic properties of the soil types do not show any distinct relation with hydraulic conductivity of the rocks. This fact suggests that hydraulic property on the surface is different from that of subsurface geology. According to multi-linear regression analysis between groundwater storage change and hydraulic parameters, a regression equation of groundwater storage change, which was explained by precipitation and evapotranspiration, was established.

Estimation of Flows and Pollutant Loads from GIS Analysis using Cell-based Geospatial and Georgraphic Information Data (격자기반의 지형 및 지리정보자료와 GIS분석기법을 이용한 유역의 유출량 및 오염부하량 추정)

  • Cho, Jae-Myoung;Lee, Mi-Ran;Yun, Hong-Sik
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.29 no.4
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    • pp.381-392
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    • 2011
  • Pollutant loads calculated with unit factor method can not identity seasonal variations of pollutant inputs. Estimation of pollutant loads considering rainfall runoff can overcome these limits. SCS curve number method was applied to estimate runoff of each event of Koeup watershed of Koheung estuary lake. SCS curve numbers were calculated based upon land use, soil types of the catchment using GIS. Point and nonpoint source pollutant loads were summed up for total loads estimation. Those from nonpoint source were estimated by multiplying the calculated runoff and expected mean concentrations (EMC) presented by the Minister of Environment of Korea. DEM can present three dimensional views of a terrain, identity stream networks and flow accumulation. Furthermore, it can examine accumulated pollutant loads of specific point of a catchment. Therefore, cell based pollutant load estimation was attempted using DEM. ArcView was utilized to collect, store and manipulate spatial and attribute data of pollutant sources and features of the catchment. Cell-based DEM which was established by the GRID module of ARC/INFO was employed to estimate flows and pollutant loads.

Evaluation of Percolation Rate of Bedrock Aquifer in Coastal Area (해안지역 암반대수층의 침누수량 평가)

  • Lee, Jeong-Hwan;Jung, Haeryong;Park, Joo-Wan;Yoon, Jeong Hyoun;Cheong, Jae-Yeol;Park, Sun Ju;Jun, Seong-Chun
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.14 no.1
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    • pp.21-33
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    • 2016
  • Estimation of groundwater hydrologic cycle pattern is one of the most critical issues in sustainable management of groundwater resources in coastal area. This study estimated groundwater percolation by using the water balance methodology and hydrogeological characteristics of land use and soil. Evapotranspiration was computed by using the Thornthwaite method, and surface runoff was determined by using the SCS-CN technique. Groundwater storage change was obtained as 229 mm/a (17.8% of the average annual rainfall, 1286 mm/a), with 693 mm/a (60.1%) of evapotranspiration and 124 mm/a (9.6%) of surface runoff. Rainfall and groundwater storage change was highly correlated, comparing with the relationships between rainfall and evapotranspiration, and between rainfall and surface runoff. This result indicates that groundwater storage change responds more sensitively to precipitation than evapotranspiration and surface runoff.

Fundamental Theory of flow of water in bends of open channel (하천의 만곡류에 관한 이론적 고찰)

  • 선우중호;윤영남
    • Water for future
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    • v.10 no.1
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    • pp.53-70
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    • 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.

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