Sensitivity Analysis of the GIUH based Clark Model for a Catchment

For estimation of runoff response of an ungauged catchment resulting from a rainfall event, geomorphologicalinstantaneous unit hydrograph (GIUH) approach is getting popularbecause of its direct application to an ungauged catchment. Itavoids adoption of tedious methods of regionalization of unithydrograph; wherein, the historical rainfall-runoff data of anumber of gauged catchments are required to be analyzed. In thisstudy, the GIUH derived from geomorphological characteristics ofa catchment has been related to the parameters of Clark IUH modelfor deriving its complete shape. The DSRO hydrographs estimatedby the GIUH based Clark model have been compared with the DSROhydrographs computed by the Clark IUH model option of the HEC-1package and the Nash IUH model by employing some of the commonlyused error functions. Sensitivity analysis of the GIUH basedClark model has been conducted with the objective to identify thegeomorphological and other model parameters which are moresensitive in estimation of peak of unit hydrographs computed bythe GIUH based Clark model. So that these parameters may beevaluated with more precision for accurate estimation of floodhydrographs for the ungauged catchments.     

Overland Flow on a Pervious Surface

ABSTRACT

This article presents the analytical solutions for overland runoff hydrographs produced by a uniform rainfall with decay soil infiltration rates. It was found that the kinematic wave travel time through a catchment under such a nonuniform rainfall excess is not a constant, but varies between the time of concentration and the time of equilibrium according to the soil moisture condition. The analytical solutions reveal that kinematic wave travel times are part of the hydrograph convolution process and can hardly be measured from observed hydrographs. The findings of this article suggest that the time of concentration of a small catchment shall be estimated by velocity-based methods rather than those empirical formulas developed for and calibrated by the time difference between the center of mass of the rainfall excess and the inflection point on recession of the observed runoff hydrograph.     

Karst Spring Discharges Analysis in Relation to Drought Periods,Using the SPI

Based on the long hydrological time series, the correlation between karst spring discharge series and rainfall has been analysed, using the Standard Precipitation Index (SPI). Analysis has been focused on the drought periods. Data come from a large karst system (Campania, Southern Italy), in an area characterised by a distribution of the precipitation prevalently during autumn-winter period. Insufficient recharge due to poor rainfall results in flat spring hydrographs (with no peak during spring season) that indicate a continuously decreasing discharge. Specifically, it has been found that 12 months cumulative rainfall, expressed by SPI₁₂, and spring discharge have similar trend. When SPI₁₂ will be equal or less that − 1, springs reduce the discharge, and a flat spring hydrograph will be produced when SPI reaches value less than − 1.5. In these cases, the prolonged shortage of accumulated rainfall causes a reduction in spring discharge also during the following year as well, pointing out a memory effect of the karst aquifer, and more complex rainfall–discharge relationship is observed.     

A physically based stochastic-deterministic procedure for the estimation of flood frequency

A procedure based on the method of derived distributions is proposed for the estimation of flood frequency from ungauged watersheds. The results of previous research on rainfall characteristics and watershed response are incorporated into the proposed procedure. These rainfall characteristics are storm depth, storm duration, space and time distribution. A simplified watershed model is used which has previously given good simulation of the watershed response. Some of the rainfall and watershed model parameters are stochastic in nature and are assumed to follow various probability distributions. Monte Carlo simulation is used for the generation of the various parameter values and simulation of the peak flow hydrographs. After 5000 realizations, the frequency of the hourly and daily peak flow and the flood volume is estimated. The proposed procedure is applied to eight coastal British Columbia watersheds and the results compare well with the observed data and with fitted probability distributions. The method is easy to apply, requires limited data and is shown to be reliable. Sensitivity analysis shows that the procedure is not very sensitive to uncertainty of the parameter values and is not dependent on the parameter probability distributions used.     

一种新的辨识流域单位线的专家系统及其应用

为克服在使用单位线法中过于简化的问题，根据流域降雨特征的时空变化，本文提出了一种用专家系统逐时段辨识单位线的新方法。研究了流域降雨特征与单位线的关系；研究了专家系统的知识表示形式、知识库的结构和专家系统的推理机；基于最新开发软件系统PB5.0，将该方法应用在柘溪防洪决策支持系统(简称FcDSS)中。结果表明，预报精度有较大的提高。     

Runoff characteristics and application of HEC-HMS for modelling stormflow hydrograph in an oil palm catchment.

Rainfall-runoff processes in a small oil palm catchment (8.2 ha) in Johor, Malaysia were examined. Storm hydrographs show rapid responses to rainfall with a short time to peak. The estimated initial hydrologic loss for the oil palm catchment is 5 mm. Despite the low initial loss, the catchment exhibits a high proportion of baseflow, approximately 54% of the total runoff. On an event basis, the stormflow response factor and runoff coefficient ranges from 0.003 to 0.21, and 0.02 to 0.44, respectively. Peakflow and stormflow volume were moderately correlated with rainfall. The hydrographs were satisfactorily modelled using the Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS). The efficiency indexes of the calibration and validation exercises are 0.81 and 0.82, respectively. Based on these preliminary findings, it could be suggested that an oil palm plantation would be able to serve reasonably well in regulating basic hydrological functions.     

Design Flood Estimation Using GIS Supported GIUHApproach

Quantitative understanding and prediction of theprocesses of runoff generation and its transmission to theoutlet represent one of the most basic and challenging areasof hydrology. Traditional techniques for design floodestimation use historical rainfall-runoff data for unithydrograph derivation. Such techniques have been widelyapplied for the estimation of design flood hydrograph at thesites of gauged catchment. For ungauged catchments, unithydrograph may be derived using either regional unithydrograph approach or alternatively GeomorhologicalInstantaneous Unit Hydrograph (GIUH) approach. The unithydrograph thus derived may be used for the simulation offlood events for the ungauged catchments. In this study Gambhiri dam catchment located inRajasthan, India is selected for applying this approach. Gambhiri river is a small tributary of the Berach/Banasriver of the Chambal basin in Rajasthan, India. Theobjective of the present study is to apply GeographicalInformation System (GIS) supported GIUH approach for theestimation of design flood. A mathematical model has beendeveloped at the National Institute of Hydrology, whichenables the evaluation of the Clark Model parameters usinggeomorphological characteristics of the basin. This modelhas been applied for the present study.From this study it is observed that the peakcharacteristics of the design flood are more sensitive tothe various storm pattern as well as method of criticalsequencing followed for the computation of design stormpatterns. Earlier estimates for the peak and time to peakhydrograph was 9143.74 cumec and 18 hrs. respectively.However, the estimates for the peak characteristics ofdesign flood hydrograph obtained from the GIUH basedapproach are 11870.6 cumec and 19 hrs. respectivelyconsidering the same design storm pattern.     

Case study evaluation of the geomorphologic instantaneous unit hydrograph

Several issues related to the probabilistic and hydraulic structure of the geomorphologic instantaneous unit hydrograph (GIUH) are addressed. These issues are: (1) accuracy of the geomorphologic expressions of the probabilities of surface runoff movement in a watershed, (2) identifying, for a given storm, a representative time-average velocity for surface runoff, (3) estimation of this velocity for the ungauged watersheds and effect of velocity estimation errors on the GIUH predictability, and (4) suitability of incorporating a linear expression for infiltration in the GIUH as well as the estimation problem of the infiltration coefficient and its effect on the reliability of predicted hydrographs. These issues are analyzed through application of the GIUH for two gauged watersheds in the southwestern region of Saudi Arabia. Twelve storm events are used in the analysis and the results are presented.Irrigation and Hydraulics Department, Faculty of Engineering, Cairo University, Giza Egypt.     

Parameters Optimization using Fuzzy Rule Based Multi-Objective Genetic Algorithm for an Event Based Rainfall-Runoff Model

The calibration of an event based rainfall-runoff model for steam flow forecasting is challenging because, it is difficult to measure the parameters physically on the field for each rainfall event. In the present study, Fuzzy rule based Multi-objective Genetic Algorithm (MGA) is developed to optimize the infiltration and roughness parameters of an event based rainfall-runoff model. Nash Sutcliffe Efficiency (NSE), Coefficient of Determination (R²) and transformed volume difference (f(V)) are used as the objective functions of the MGA and all Pareto optimal solutions are identified using Nondominated Sorting method. As three objective functions are included in the calibration, the number of Pareto optimal solutions are also increases and hence, the optimization problem now becomes a decision making problem. Therefore, to select the best solution from all Pareto optimal solutions, a Fuzzy Rule-Based Model (FRBM) is developed to get alternative values of each Pareto optimal solution. First, the Fuzzy rule based MGA is developed by integrating the FRBM with the MGA. Then the Fuzzy rule based MGA is integrated with an event based runoff model. The developed Fuzzy-MGA based runoff model is tested on three different watersheds and the simulation results of Fuzzy-MGA based runoff model are compared with observed data and previous study results. From the simulated events of three watersheds using Fuzzy-MGA based runoff model, it is observed that the mean percentage error in any criteria (i.e. volume of runoff, peak runoff, and time to peak) of the developed model for a watershed is less than 16.33%. It is also noted that the developed Fuzzy-MGA based runoff model is able to produce hydrographs that are much closer to the measured hydrographs.     

Influence of Rainfall,Model Parameters and Routing Methods on Stormwater Modelling

Quantification of the uncertainty associated with stormwater models should be analyzed before using modelling results to make decisions on urban stormwater control and management programs. In this study, the InfoWorks Integrated Catchment Modelling (ICM) rainfall-runoff model was used to simulate hydrographs at the outfall of a catchment (drainage area 8.3 ha, with 95% pervious areas) in Shenzhen, China. The model was calibrated and validated for two rainfall events with Nash-Sutcliffe efficiency >0.81. The influence of rainfall, model parameters and routing methods on outflow hydrograph of the catchment was systematically studied. The influence of rainfall was analyzed using generated rainfall distributions with random errors and systematic errors (± 30% offsets). Random errors had less influence than systematic errors on peak flow and runoff volume, especially for two rainfall events with larger depths and longer durations. The Monte Carlo simulations using 500 parameter sets were used to verify the equifinality of the nine model parameters and determine the prediction uncertainty. Most of the monitored flows were within the uncertainty range. The influence of two routing methods from rainfall excess to hydrograph was studied. The InfoWorks ICM model incorporating double quasilinear reservoir routing was found to have a larger effect on the simulated hydrographs for rainfall events having larger depths and longer durations than using the U.S. EPA’s Storm Water Management Model nonlinear reservoir routing method did.

     

WetSpa Model Application for Assessing Reforestation Impacts on Floods in Margecany–Hornad Watershed,Slovakia

The spatially distributed hydrologic model WetSpa working on a daily or hourly time scale combines elevation, soil and landuse data within GIS, to predict flood hydrographs and spatial distribution of hydrologic characteristics in a watershed. The model is applied to the Margecany–Hornad river basin (1,131 km²) located in Slovakia. Daily hydrometeorological data from 1991 to 2000, including precipitation data from nine stations, temperature data from four stations and evaporation data measured at one station are used as input to the model. Three base maps, i.e., DEM, landuse and soil types are prepared in GIS form, using 100×100 m cell size. Results of the simulations show good agreement between calculated and measured hydrographs at the outlet of the basin. The model predicts the daily/hourly hydrographs with good accuracy, between 75–80% according to the Nash–Sutcliff criteria. For assessing the impact of forests on floods, the calibrated model is applied for a reforestation scenario using the hourly data of the summer of 2001. The scenario considers a 50% increase of forest areas. The model results show that the reforestation scenario decreases the peak discharge by 12%. Investigation of peak discharges from the whole simulation period, shows that the scenario results are reduced by 18% on average. Also, the time to peak of the simulated hydrograph of the reforestation scenario is 14 h longer than for the present landuse. The results show that the effect of land cover on flood is strongly related to storm characteristics and antecedent soil moisture.     

Analysis of Rainfall Severity and Duration in Victoria,Australia using Non-parametric Copulas and Marginal Distributions

The analysis of joint probability distributions of rainfall characteristics such as severity and duration is important in water resources management. Deriving their distributions using standard statistical techniques are often problematical due to its complexity. Standard methods usually assume that the rainfall characteristics are independent or that their marginal distributions belong to the same family of distributions. The use of copulas based methodologies can circumvent these restrictions and are therefore increasingly popular. However, the copulas and marginal distributions that are commonly used belong to specific parametric families and their adoption could lead to spurious inferences if the underlying assumptions are violated. For this reason, we recommend a nonparametric or semiparametric approach to estimate the joint distribution of rainfall characteristics. In this paper, we introduce and compare several copula–based approaches, each involving a combination of parametric or nonparametric marginal distributions conjoined by a parametric or nonparametric copula. An empirical illustration of the different approaches using rainfall data collected from six stations in the state of Victoria, Australia, demonstrated that a nonparametric approach can often give better results than a purely parametric approach.     

基于预报调度规则的云峰水库特大洪水调度研究

针对当前极端天气频发的形势,对极端暴雨洪水进行准确预报、合理调度是水库调度管理不可回避的问题。以应对云峰水库流域特大暴雨洪水、提前建立预报及调度预案为目标,基于现有的预报方案及精度,将云峰水库防洪调度规则中引入累积净雨量判别指标,提前预报入库洪水,采取预泄手段提前腾空库容,消纳入库洪水,使整个泄洪的流量过程比较平缓,并对典型年及各频率设计洪水过程线的洪峰值与对应的累积净雨量进行了相关分析。研究表明:洪峰滞后于净雨量峰值约18 h,同时累积净雨量与洪峰流量呈较好的线性相关性;采用累积净雨量作为防洪调度的判别指标可以延长调度的预见期,并提高防洪与兴利互相结合的程度。研究成果为优化云峰水库特大洪水调度方案创造条件。     

Derivation of Unit Hydrograph from GIUH Analysis for a Himalayan River

Unit Hydrograph (UH) is the most popular and widely used method for predicting flood hydrograph resulting from a known storm in a basin area. However, the non-availability of UH due to poor network of raingauge stations in flood prone Indian river basins is a major concern. The computation of Horton's ratios and their application in generating the Geomorphological Instantaneous Unit Hydrograph (GIUH) can provide a solution for ungauged rivers. A detailed drainage network analysis was carried out for a 5th order flood- prone Himalayan river system in order to highlight its significance in flood management program. The equations for GIUH of 5th order stream were derived through Markov Chain analysis. The GIUH model for the 5th order stream was used to derive the first ever analytical UH of the river. Further, it was applied to determine the 50-yr return period flood. The 50-yr return period flood matches with the result of flood frequency analysis based on observed peak discharge data. This drainage network analysis and application of GIUH can provide a significant contribution towards flood management program.     

Forecasting of Hydrographs to Simulate Long Term Recharge From Rivers in Numerical Models of Mining Reservoirs; Application to A Coal Mine in NW Spain

Although the natural permeability of rocks in the Asturian Central Coal Basin (NW Spain) is generally low, intensive mining activities over many decades has given rise to fracture flow paths that are far more permeable than those associated with the natural lithology. Abandoned and flooded mining works set up artificial ‘pseudo‐karst’ aquifers, which can act as underground reservoirs, with many potential applications. In particular, a mining reservoir shaped by two connected mining shafts within the River Turón basin has been studied. A runoff model was used to produce accurate simulations of streamflow in three different gauging stations during a monitored period of 2 years. The purpose was to use this model in the forecast situation, in order to predict long‐term situations in a hydrogeological FEFLOW model. It was necessary to develop depletion curves for each gauging station based on the available daily effective rainfall and measured flow data, as well as the knowledge of the basin characteristics. The resulting simulated hydrographs were very similar to the measured hydrographs during the monitored period, so the adequate adjusting allows input of the flow for forecast purposes. The model produced forecast hydrographs that had a r = 0.8 and difference in annual volume ranging from 1.6% to 5%. The defined model was applied to a rainfall data set of 30 years, and the average recharge from the river to the mining reservoir could be adequately estimated. The method developed needs to be refined and tested on additional years, but the approach appears to be applicable to operational runoff forecasting for numerical models input data. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluation of three unit hydrograph models to predict the surface runoff from a Canadian watershed

The predictability of unit hydrograph (UH) models that are based on the concepts of land morphology and isochrones to generate direct runoff hydrograph (DRH) were evaluated in this paper. The intention of this study was to evaluate the models for accurate runoff prediction from ungauged watershed using the ArcGIS^® tool. Three models such as exponential distributed geomorphologic instantaneous unit hydrograph (ED-GIUH) model, GIUH based Clark model, and spatially distributed unit hydrograph (SDUH) model, were used to generate the DRHs for the St. Esprit watershed, Quebec, Canada. Predictability of these models was evaluated by comparing the generated DRHs versus the observed DRH at the watershed outlet. The model input data, including natural drainage network and Horton's morphological parameters (e.g. isochrone and instantaneous unit hydrograph), were prepared using a watershed morphological estimation tool (WMET) on ArcGIS^® platform. The isochrone feature class was generated in ArcGIS^® using the time of concentration concepts for overland and channel flow and the instantaneous unit hydrograph was generated using the Clark's reservoir routing and S-hydrograph methods. An accounting procedure was used to estimate UH and DRHs from rainfall events of the watershed. The variable slope method and phi-index method were used for base flow separation and rainfall excess estimation, respectively. It was revealed that the ED-GIUH models performed better for prediction of DRHs for short duration (≤6 h) storm events more accurately (prediction error as low as 4.6–22.8%) for the study watershed, than the GIUH and SDUH models. Thus, facilitated by using ArcGIS^®, the ED-GIUH model could be used as a potential tool to predict DRHs for ungauged watersheds that have similar geomorphology as that of the St. Esprit watershed.     

Bivariate Flood Frequency Analysis of Upper Godavari River Flows Using Archimedean Copulas

In this paper, a copula based methodology is presented for flood frequency analysis of Upper Godavari River flows in India. By using the specific advantages of copula method in modeling the joint dependence structure of uncertain variables, this study applies Archimedean copulas for frequency analysis of flood characteristics annual peak flow, flood volume and flood duration. To determine the best fit marginal distributions for flood variables, few parametric and nonparametric probability distributions are examined and the best fit model is adopted for copula modeling. Four Archimedean family of copulas, namely Ali-Mikhail-Haq, Clayton, Gumbel-Hougaard and Frank copulas are evaluated for modeling the joint dependence of annual peak flow-volume, and flood volume-duration pairs. The performance of two parameter estimation methods, namely method-of-moments-like estimator based on inversion of Kendall??s tau and maximum pseudo-likelihood estimator for copulas are investigated. On performing Monte Carlo simulation to assess the performance of copula distributions in modeling the joint dependence structure of flood variables, it is found that the developed copula models are well representing the observed flood characteristics. From standard statistical tests, Frank copula has been identified as the best fitted copula for both bivariate models. The Frank copula function is used for obtaining joint and conditional return periods of flood characteristics, which can be useful for risk based design of water resources projects.     

城市流域径流峰值对降雨时空异质性的响应

基于高时空分辨率的降雨产品,采用RainyDay暴雨生成器生成具有不同时空分布情景和降雨历时的设计降雨,通过分布式水文模型GSSHA模拟分析径流峰值对降雨时空异质性的响应规律,结合协方差分析方法和所构建的降雨时空异质性指标体系,定量研究不同降雨时空异质性指标对径流峰值的影响。结果表明:耦合短时序(2008—2016年)栅格降雨数据和RainyDay暴雨发生器,可以生成与实际降雨时空分布相似的流域设计降雨;降雨时空异质性对径流峰值具有显著的影响,其影响比降雨历时和降水量对径流峰值的影响大;雨峰系数、降雨集中度、1 h最大降水量对径流峰值的影响较大,其中雨峰系数的影响随着降雨历时或降雨重现期增大而减小,而降雨集中度则相反。     

Impacts of Snowmelt on Peak Flows in a Forest Watershed

Using data of long-term observations at three gauging stations and one climatic station in a forest region in southeast Germany, the impacts of snowmelt on peak flow have been investigated in this paper. Results show that the major climatic feature was found to be a precipitation maximum during the hydrological summer, and the major hydrological feature was a discharge maximum during the hydrological winter. Empirical equations describing snow depth and snow water equivalent for the studied climatic station have been developed for both snow accumulation period and ablation period. Through introducing snowmelt-rainfall depth as a new variable, the present work investigates the simultaneous occurrence of snowmelt and rainfall on snow cover, assesses the characteristics of runoff including peak flows, calculates the runoff from the snowmelt and rainfall. A hydrological model has been applied to generate hydrographs resulted from snowmelt and rainfall-on-snow.     

Goodness-of-fit tests for multi-dimensional copulas:Expanding application to historical drought data

The question of how to choose a copula model that best fits a given dataset is a predominant limitation of the copula approach, and the present study aims to investigate the techniques of goodness-of-fit tests for multi-dimensional copulas. A goodness-of-fit test based on Rosenblatt’s transformation was mathematically expanded from two dimensions to three dimensions and procedures of a bootstrap version of the test were provided. Through stochastic copula simulation, an empirical application of historical drought data at the Lintong Gauge Station shows that the goodness-of-fit tests perform well, revealing that both trivariate Gaussian and Student t copulas are acceptable for modeling the dependence structures of the observed drought duration, severity, and peak. The goodness-of-fit tests for multi-dimensional copulas can provide further support and help a lot in the potential applications of a wider range of copulas to describe the associations of correlated hydrological variables. However, for the application of copulas with the number of dimensions larger than three, more complicated computational efforts as well as exploration and parameterization of corresponding copulas are required.