Stepwise modeling and the importance of internal fluxes validation to improve hydrological model realism: three case studies in cold regions of China
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<p>Model realism testing is of vital importance in science of hydrology, in terms of realistic representation of hydrological processes and reliability of future prediction. We conducted three modeling case studies in cold regions of China, i.e. the upper Heihe River basin, the Urumqi Glacier No.1 basin, and the Yigong Zangbu River basin, to test the importance of stepwise modeling and internal fluxes validation to improve model realism.</p><p>In the upper Heihe River basin, we used four progressively more complex hydrological models (FLEXL, FLEXD, FLEXT0 and FLEXT), to stepwisely account for distributed forcing inputs, tailor-made model structure for different landscapes, and the realism constraints of parameters and fluxes. We found that the stepwise modeling framework helped hydrological processes understanding, and the tailor-made model structure and realism constraints improved model transferability to two nested basins.</p><p>In the Urumqi Glacier No. 1 basin, with 52% of the area covered by glaciers, we developed a conceptual glacier-hydrological model (FLEXG) and tested its performance to reproduce the hydrograph, and separate the discharge into contributions from glacier and nonglacier areas, and establish estimates of the annual glacier mass balance (GMB), the annual equilibrium line altitude (ELA), and the daily snow water equivalent (SWE). We found that the FLEXG model, involving effects of topography aspect, was successfully transferred and upscaled to a larger catchment without recalibration.</p><p>In the Yigong Zangbu River basin, with 41.4% glacier area, we designed three models (FLEXD, FLEX-S, FLEX-SG) to stepwisely understand the impact of snow, glacier to reproduce historic streamflow. We found that by involving snow and glacier modules, the model performance was dramatically improved. Although the daily streamflow of FLEX-SG reached up to 0.93 Kling-Gupta Efficiency (KGE) in calibration, it significantly overestimated snow cover area (SCA) and glacier mass balance (GMB). With satellite measured precipitation lapse rate, we improved FLEX-SG model realism not only to reproduce hydrography but also SCA and GMB.</p>This study investigates the shape characteristics of hydrograph components of the Wu-Tu watershed in Taiwan based on observations of rainfall and streamflow. Component hydrographs were modeled using a model of three serial tanks with one parallel tank. The block kriging method was used to calculate the hourly mean rainfall of events, and eight model parameters of 34 cases were derived from the shuffled complex evolution optimal algorithm. The remaining 18 events were used to verify the applicability of the calibrated parameters. Results show that (1) times to peak of hydrograph components are positively nonlinearly correlated to peak time of rainfall; (2) peak discharges of hydrograph components are linearly proportional to those of streamflow hydrograph; and (3) relationships of total discharges also have direct ratios between hydrograph components and observed streamflow. Using the procedures proposed in this study, three evaluated shape characteristics of component hydrographs can be easily used to rapidly determine shapes of simple hydrographs.
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The present research entitled Study of Synthetic Unit Hydrograph Model of Bayur River Basin at Samarinda, East Kalimantan was aimed to analyze and identify the best-suited synthetic unit hydrograph to apply in Bayur river basin. The research was carried out by developing models, and then those models were compared to main unit hydrograph based on 2004 field measurement. Comparative analysis was performed on two stages. The first was to calculate and compare three-unit hydrograph parameters (Tp, Qp and Tb) of two synthetic unit hydrograph to main unit hydrograph. Second stage was to develop direct runoff hydrograph of two synthetic unit hydrograph models and of the main unit hydrograph using rainfall data of April 9, 2004. Then, deviation percentage averages of the two synthetic direct runoff hydrograph were calculated. Through the two analysis stages, the best-suited synthetic unit hydrograph model to apply in Bayur river basin presumably was obtained by identifying smallest deviation percentage average on main unit hydrograph. By calculating deviation averages of direct runoff hydrograph in the two models of synthetic unit hydrograph, it was found that GAMA I model provided smallest deviation average compared Snyder model. Based on the two analysis, it was showed that GAMA I was the closest model to main unit hydrograph compared to Snyder model. Key word: synthetic unit hydrograph, river basin, direct runoff, Snyder model, GAMA I model.
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The Way Besai River is located in Sumber Jaya District, West Lampung Regency. River discharge is an indicator of watershed function in transforming rain into stream flow. River discharge is generally presented by hydrograph. There are two methods to derive unit hydrograph, i. e. Measured Unit Hydrograph method (HST) and Synthetic Unit Hydrograph method (HSS). Synthetic Unit Hydrograph is used if the watershed does not have sufficient hydrometry data for calculating flood discharge. The purpose of this study is to analyze Synthetic Unit Hydrograph Gama I, Synthetic Unit Hydrograph SCS (HEC-HMS), and measured unit hydrograph for Way Besai River. The method used in this study includes Synthetic Unit Hydrograph Gama I, Synthetic Unit Hydrograph SCS (HEC-HMS), and Measured Unit Hydrograph. The results of this study show that Unit Hydrograph derive d from Synthetic Unit Hydrograph SCS (HEC-HMS) is better than the result derive d from Synthetic Unit Hydrograph Gama I based on peak discharge, peak time, base time and base flow values. Keywords: Watershed, Discharge, Synthetic Unit Hydrograph, Measured Hydrograph Unit, SCS (HEC-HMS), Gama I.
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Geomorphology-based instantaneous unit hydrographs have been proposed by several engineers as a tool to produce runoff hydrographs from rainfall for ungauged watersheds. A difficulty in applying the geomorphology-based unit hydrographs is the determination of travel time that is actually a hydraulic problem. In this paper, kinematic-wave theory is used to analytically determine the travel times for overland and channel flows in a stream-ordering subbasin system. The resultant instantaneous unit hydrograph is a function of the time rate of water input (intensity of rainfall excess in application); hence the linearity restriction of the unit hydrograph theory is relaxed. In applying the instantaneous unit hydrographs for hydrograph simulation, the model deals with temporally nonuniform rainfall through convolution integration of the instantaneous unit hydrographs applied to the rainfall excess of varying intensities with time. The proposed model is tested by comparing the simulated and observed hydrographs of an example watershed for several rainstorms with good results. Sensitivity of surface runoff unit hydrographs to the model parameters is also investigated.
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The results of a hydrograph study for small watersheds in Indiana are presented. The main purpose is to determine the shape of the hydrograph and the peak discharge for those areas where no stream gaging station is available. A mathematical expression of the hydrograph containing certain parameters that can be correlated with identifiable and readily obtainable watershed characteristics provides the theoretical basis for establishing the synthetic hydrograph. Seventeen small watersheds in Indiana were analyzed to determine the relationship between two hydrograph parameters (time to peak and storage coefficient) and three watershed characteristics (drainage area, length of main stream, and mean slope of main stream). A complete procedure for the design of the storm hydrograph for small, ungaged, watersheds is presented. The basic mathematical expression for the hydrograph is considered appropriate for general application.
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The purpose of the graduation thesis is to present the theoretical basics of runoff hydrograph, timing
parametres and their estimations and also the affecting watershed characteristics. The practical part is
composed of defining timing parametres from gauged hydrographs of selected basins and comparing
to the results of empirical equations.
In the first part the graduation thesis presents the runoff basics, as part of the hydrologic circle, are
presented. There is also the description of the hydrograph, its components and characteristics. The use
and characteristics of the unit hydrograph are given. Furthermore, there is a chapter about the
geographical and meteorological characterisctics of the watershed and their affect on the shape,
duration and maximum runoff volume of the hydrograph. Timing parametres and their definictions are
described. In case of parametres with multiple definictions, all of them are descibed and their
differences are submited. The following part contains the methods and equations for calculating the
values of these parametres. The methods are divided into three approaches: the analysis of gauged
hydrographs, the velocity method and the empirical equations. Numerous equations are listed with
details. The process of defining timing parametres from gauged hydrographs and rainfall is presented.
For the selected basins multiple hydrographs were defined from measured data. Timing parametres
were then gathered from the hydrographs. The watershed characteristics for empirical equation
calculation were obtained by geographic information systems. The results were examined and
compared.
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유역 추적에 자주 쓰이는 합성 단위 유량도 방법의 일종인 Snyder 방법에 있어서의 계수를 남한강 수계에서 재조정하는 과정을 제시하였다. 그 과정은, 과거의 조사에서 구한 남한강 수계의 Snyder 공식에서 초기값을 구한 다음, 이 값을 HEC-1 모델에 적용시켜 계수를 재조정한 후에 그 계수로부터 Snyder의 개선공식을 구하게 된다. 이와 같은 과정으로 구한 개선 공식은 기존 공식에 비해 계산 수문 곡선의 첨두 유량의 크기가 커지게 되며, 첨두 유량에 도달하는 기울기도 기존 공식보다 급격하게 되는 특성을 가지게 된다. 또한 첨두 유량이 발생하는 시간을 결정하여 주는 지체 시간이 기존 공식에 비해 개선 공식에서 작게 되기 때문에 첨두 유량이 발생되는 시간도 개선 공식을 사용하게 되면 기존 공식을 사용한 경우보다 더 빨라지게 된다. 【The synthetic unit hydrograph is commonly used for the derivation of a design hydregraph. The existing Snyder's equation for the syntheses of unit hydrograph was found to give relatively a flat hydrograph in comparison with observed hydrograph and a revision is required. HEC-1 model is used to simulated observed hydrograhp in the South Han River basin and results are used as an input for the regression. The basin is subdivided into small drainage areas and the synthesized hydrograph is routed through channels. After the calculated hydrographs are compared with observed one, the synthesized hydrograph of each subbasisn is revised and the new snyder's equation is derived . The revised equation gives rapid increase of discharge in rising limb and larger peak.】
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A method to convert a known unit hydrograph to unit hydrographs of different durations, as an alternative to the S-Hydrograph method, is introduced. The method—called the Complementary Hydrograph method—involves a process of decomposing a known unit hydrograph of duration to into a pair of “complementary” hydrographs associated with two sequential rainfalls with the sum of their durations equal to to. In converting the to-hour unit hydrograph into a ta-hour unit hydrograph, the method produces a unit hydrograph of duration tb=(to-ta) concurrently. In hydrograph conversion, the Complementary Hydrograph method produces an identical result to the well-established S-Hydrograph method and involves a comparable number of computational steps. In certain special cases, such as converting a unit hydrograph into one with half its duration, the new method requires fewer computational steps. While the two methods employ different approaches in their solutions of hydrograph conversion problems, the agreement in their results stems from the fact that both methods are founded on the same principles of superposition and linearity of the unit hydrograph method. The S-Hydrograph method can also be viewed as a special case of the Complementary Hydrograph method in which the known hydrograph is associated with a storm of infinite duration and uniform intensity. The Complementary Hydrograph method offers a more unified and versatile approach in dealing with various types of unit-hydrograph conversion problems. For example, the method can be extended to derive unit hydrographs from a hydrograph associated with a multiperiod, varied intensity rainfall. The use of S-Hydrograph method for hydrograph derivation can only be applied to hydrographs resulting from a single-period rainfall of uniform intensity.
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Dimensionless quantity
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