Instantaneous Unit Hydrograph Research Articles

The Compare Derived Flood from Laplace Transform and H2U-Nash Instantaneous Unit hydrograph Models (Case Study: Jooneghan Catchment)

Achievement to sustainable development is dependent upon integrated watershed management. In other hand without detailed analysis of the rainfall runoff observations, high risk of flood predictions will be translated into flood-induced capital losses. Considering the fact that not always hydrometric data are available, using synthetic unit hydrograph is one of the most popular methods of flood simulations for ungauged watersheds. This method has operational limitation for duration of runoff but in Instantaneous Unit Hydrograph (IUH) assumed to all take place at a discrete point in time therefore can be converted into and desired durations.According to literature few studies have been focused on Laplace transforms, H2U-Nash Unit Hydrograph in Iran, this work is an attempt to investigate model performance in Jooneghan catchment, located in northern part of Karoon great basin.Laplace synthetic hydrograph was derived base on effective rainfall while H2U-Nash model was simulated using moments technique and lag time.The mean absolute relative error of Laplace transforms, H2U-Nash was 0.42 and 0.25 respectively. Visual interpretation and statistical comparison of Nash-Sutcliffe efficiency coefficient of the models confirms that H2U-Nash model performs better than Laplace transforms model.

Effects of Spatial-Temporal Imperviousness on Hydrological Responses of Various Areas in an Urbanized Watershed

This study examined changes in the division responses caused by imperviousness changes in time. Each response is represented by an instantaneous unit hydrograph with storage parameters. The critical work in this study was to ensure that the calibrated storage coefficients reasonably respond to their corresponding imperviousness. Estimating the spatially different mean rainfall of each division by adopting traditional methods (e.g., the Thiessen polygon method) may be difficult because of the lack of raingauge data in a division. The storages cannot be measured directly and were generally calibrated using an optimization method with parameter bounds. The upper bounds, which imply an ultimate of each corresponding physical property, are particularly difficult to determine directly. This study applied block Kriging and nonlinear programming to estimate spatiotemporal effective rainfall. An approach was proposed to determine suitable upper bounds for each storage parameter in a calibration. An examination of the calibrated storages at three stages revealed that the values resulting from a calibration with suitable bounds are more reliable compared with those based on a calibration without bound limitation. Finally, we concluded that (1) suitable bounds are essential for ensuring that significant calibrated storages can be applied to achieve a favorable regression result; (2) the analytic results indicate that large changes in imperviousness in downstream areas reduced the time to peak by at least 15 %, increasing the peak discharge by nearly 40 %; and (3) hydrograph characteristics of the watershed outlet reduced the time to peak by approximately 10 %, increasing the peak discharge by nearly 15 %.

Changeability of simulated hydrograph from a steep watershed resulted from applying Clark’s IUH and different time–area histograms

Reflecting the shape and drainage characteristics of the watershed, time–area histogram (TAH) seems to be the most important parameter for derivation of the transformation hydrograph. In this study, a semi-distributed instantaneous unit hydrograph was established and applied to the steep 103 km2-Galazchai watershed in Iran to improve the results of the rainfall–runoff modelling. Towards this attempt, twenty-three runoff producing events with wide different characteristics were used for the analysis. The direct surface runoff hydrographs (DSRHs) were obtained and consequently compared for the study area using Clark’s instantaneous unit hydrograph (IUH) and through applying different TAHs calculated based on channel profile, dimensionless TAH, average velocity and spatially distributed travel time methods. A weight grid developed from kinematic wave travel time equation for overland flow was prepared and used as input to derive the spatial TAH of the watershed. The results indicated that the different TAHs had noticeable impacts on the estimated hydrographs. The results also proved that the spatial TAH method performed well with efficiency criteria of 0.75 and 0.69 in calibration and validation steps. The implemented method also offered the advantages of flexibility, efficiency and physically powerful links to the spatial data set and GIS software.

Ratio of basin lag times for runoff and sediment yield processes recorded in various environments

Abstract. River basin lag time (LAG), defined as the elapsed time between the occurrence of the centroids of the effective rainfall intensity hyetograph and the storm runoff hydrograph, is an important factor in determining the time to peak and the peak value of the instantaneous unit hydrograph (IUH). In the procedure of predicting a sedimentgraph (suspended sediment load as a function of time), the equivalent parameter is the lag time for the sediment yield (LAGs), which is defined as the elapsed time between the occurrence of the centroids of sediment production during a storm event and the observed sedimentgraph at the gauging station. Data of over 150 events recorded in 11 small river catchments (located in Poland, Germany, UK and USA) with a drainage area of 0.02 km2 to 82 km2 have been analysed to estimate the ratio of LAGs/LAG. The ratio, in majority of cases was smaller than 1, and decreased with increase of river basin slope. Special attention is given to the data collected in a small agricultural catchment and also during snowmelt periods, which is located in central Poland.

Coupling the Xinanjiang model with geomorphologic instantaneous unit hydrograph for flood forecasting in northeast China

The Xinanjiang (XAJ) model has been successfully applied in humid and semi-humid regions. Considering the geomorphologic factors to accurately estimate floods, this study adopted the geomorphologic instantaneous unit hydrograph (GIUH) method to calculate the surface runoff instead of the experience unit hydrograph (EUH) in the original model. The geomorphologic factors of the case study basin were obtained by using a digital elevation model (DEM) and the Terrain analysis using Digital Elevation Models (TauDEM). Furthermore, the dynamic Muskingum model was used for the channel flood routing. This study focused on the simulation of heavy precipitation and floods over the Chong River, which is a tributary river to the Songhua River on the right bank in northeast China. The detailed steps of the method were shown, up to the estimated value of flood runoff discharges and flood peaks and their comparison with observed values. The average deterministic coefficients (DCs) of model calibration and validation were 0.89 and 0.83, respectively. The results show that the model precision is high and the model is feasible for flood forecasting. Lastly, some methodological perspectives to enhance the method are presented.

순간단위도의 왜곡된 형상에 대한 지형학적 접근

This paper presents the systematic approach to positively skewed shape of instantaneous unit hydrograph (IUH), that is one of the universal features of hydrologic response function. To this end an analytical expression of statistical moments for IUH is derived within the framework of geomorphologic instantaneous unit hydrograph (GIUH) theory and quantified according to the concept of hydrodynamic, geomorphologic and kinematic heterogeneity. There is a big scale difference between hillslope and channel flow path system. Although the former has the much smaller level of scale its variation coefficient tends to be higher and coefficient of skewness has the different trend than the latter. The shape of IUH is likely to be much more affected by kinematic heterogeneity rather than hydrodynamic heterogeneity and its combined effect with geomorphologic heterogeneity is the major cause of skewing hydrologic response function. Statistical features of hillslope and channel flow path can be transferred into hydrologic response function in the form of dimensionless statistics and their relative importance forms the general shape of hydrologic response function.

Erratum for “Optimal Instantaneous Unit Hydrograph from Multistorm Data” by Sushil K. Singh

Erratum for “Optimal Instantaneous Unit Hydrograph from Multistorm Data” by Sushil K. Singh

The importance of the objective functions and flexibility on calibration of parameters of clark instantaneous unit hydrograph

The paper compares the results of automatic calibration of Clark’s synthetic unit hydrographs. Optimal values of model parameters were determined by the objective functions: percentage error in peak flow (PEPF), percentage error in volume (PEV), peak-weighted root mean square error (PWRMSE), sum of absolute residuals (SAR) and sum of squared residuals (SSR). The last part of the analysis assesses the flexibility of studied model. The research was performed in the upland watershed of Grabinka – left tributary of the Wisloka river located in Southern Poland. The analysis reveals that the smallest differences between the maximum flow in the observed and calculated flood culmination were obtained when applying PWRMSE function. This paper also indicates, that Clark’s model was efficient for describing the analyzed floods.

Derivation and Analysis of Dimensionless Hydrograph and S Curve for Cumulative Watershed Area

Unit Hydrograph (UH) is the most popular and widely used method for analyzing and deriving flood hydrograph resulting from a known storm in a basin area. However, the non-availability of flood runoff details due to poor network of stream gauges in flood prone Indian river basins is a major concern. Traditional techniques for design flood estimation use historical rainfall-runoff data for unit hydrograph derivation. For ungauged catchments, unit hydrograph are derived either by regional unit hydrograph approach or alternatively Geomorphological Instantaneous Unit Hydrograph approach. Central Water Commission (CWC) derived the regional unit hydrograph relationships for different sub-zones of India relating to the various unit hydrograph parameters with some prominent physiographic characteristics. The study area is located between 12°30′ N and 13°05′ N Latitude and 77°15′ E and 77°40′ E Longitude which is derived from Carto DEM 30 m resolution. The study area covers an area of 349.06 km2, having maximum length of 21.36km and the study area elevation varies from 700 m to 900 m. The study area is extracted using methodology Fill sinks, Flow direction, Flow accumulation, Watershed pourpoints, Snap pourpoints and Delineate watershed. Watersheds are also delineated from SOI toposheet 57H/5, 57H/9, 57G/12 using Arc GIS software. The extracted study area from Carto DEM 30 m is used for extraction of hourly runoff by pixel method for cumulative watershed area, time area diagram is prepared and derivation of unit hydrograph is carried out using CWC method for both toposheet and DEM data set. Unit hydrograph is derived using the regional relationships as proposed by Central Water Commission (CWC), for Kaveri basin subzone-3(i). This information is useful to derive flood hydrograph along any reach of stream. It helps in getting more appropriate values of flood discharge and time to peak with minimum calculation by interpolation techniques.Unit hydrographs and S curve of watersheds are tried to analyze with the help of dimensionless Unit Hydrograph and dimensionless S curve to understand the parameters of unit hydrograph for cumulative watershed areas.

Geomorphology Based Semi-distributed Approach for Modeling Rainfall-runoff Modeling Using GIS

Simulation of rainfall-runoff process for ungauged catchments is one of the most important areas of research in surface water hydrology. The Unit Hydrograph (UH) technique is widely used for runoff estimation, especially for design flood estimation. Geomorphology of a catchment has a strong relationship with the transformation process of rainfall in to runoff. For ungauged catchments, unit hydrograph may be derived using either regional unit hydrograph approach or alternatively Geomorphological Instantaneous Unit Hydrograph (GIUH) approach. The concept of the GIUH is a catchment transfer function in relating the shape, stream network topology and channel characteristics.In this study, Katteri watershed located in Tamilnadu, India is selected for applying the GIUH approach. Two different approaches are studied (1) Conventional Nash Unit hydrograph model, (2) Geomorphological based linear cascade model (GLCM). The geomorphological information of each sub-watershed i.e. cell to cell flow path, stream network are extracted from the ASTER Digital Elevation Model (DEM) of 30 m resolution. In the IUH based on geomorphologic association of linear reservoirs, it is assumed that the water courses are classified from the outlet to upstream. Effective rainfall is determined using the Soil Conservation Service Curve Number (SCS-CN) method. The developed model was applied to five storm events and the results are compared with observed hydrographs. According to these results, the derived flood hydrograph by using GLCM and Nash's IUH model were closely matching with the flow records of the watershed. This indicates the suitability of present modeling approach for predicting the flood hydrograph for an ungauged watershed.

Stream Flow Prediction in a Typical Ungauged Catchment Using GIUH Approach

Stream flow measurement in Rivers have significant effect on various applications in the field of water resources. Yet, in many parts of the world, Rivers are either poorly gauged or completely ungauged and in some cases the existing system is continuously declining. Stream flow prediction at such “ungauged” drainage basins require information transfer from donor catchments (gauged) to receiver catchments (ungauged) that are apparent to be hydrologically homogeneous to them. Geomorphologic instantaneous unit hydrograph (GIUH) approach can be used as a transfer function for modelling the rainfall – runoff process. The present study provides an effective approach which deals with the geomorphologic features of the ungauged drainage basin and derives the GIUH based transfer function and consequently geomorphologic unit hydrograph (GUH) for the study area. Koel River basin of India has been chosen as the study area. Before applying the approach on the Koel River basin it is applied on another basin where unit hydrograph data was available. To validate the derived GUH of the Koel River basin, a comparison was executed with the synthetic unit hydrograph (SUH) attained using the Central Water Commission (CWC) procedure. The closest GUH to the SUH was determined based on the comparison.

Impacts of urban development on runoff event characteristics and unit hydrographs across warm and cold seasons in high latitudes

Summary The impacts of urbanization on catchment hydrology are widely studied by comparing how different urban catchments respond to storm events, but rarely by realizing long-term observations of hydrological changes during the construction process at urbanizing small catchments. In this study, the changes occurring in runoff generation were monitored in a developing catchment under construction and in two urban control catchments. As the imperviousness of the developing catchment increased from 1.5% to 37%, significant increases were observed in event runoff depths and peak flows during rainfall–runoff events. At the same time, the only statistically significant changes that were observed for the cold period runoff events were the shorter duration and smaller runoff depths. The effect of urbanization on event runoff dynamics was studied in terms of changes in the instantaneous unit hydrographs (IUH). Negative trends were detected in the gamma parameters of IUHs, which became more consistent across events and produced a sharper shape of the hydrograph as the construction works progressed. Because urban development caused the greatest relative changes in runoff during frequently occurring minor rainfall events, the study results underlined the importance of small storms in urban runoff management for maintaining the predevelopment water balance. During infrequent major rainfall events and the cold period snowmelt events the impacts of urbanization were less pronounced. The impact of urbanization on runoff was best detected based on peak flow rates, volumetric runoff coefficients, or mean runoff intensities. Control catchments were essential to distinguish the hydrological impact caused by catchment characteristics from those caused by changes in the meteorological conditions or season.

Geomorphologic Instantaneous Unit Hydrograph Based Hydrologic Response Models for Ungauged Hilly Watersheds in India

Hydrologic response of two fourth-order hilly watersheds of the Ramganga river basin in the central Himalayan region of India has been predicted in this study. Geomorphologic Instantaneous Unit Hydrograph (GIUH) was derived using two models: (i) Horton’s stream-order ratios based model (GIUH-I); and (ii) Nash’s two-parameter gamma distribution based conceptual model (GIUH-II). The travel times for the overland-flow and the stream-flow in Horton-Strahler stream ordering system of the watersheds were determined analytically and probabilistically for GIUH-I model; while a dynamic component (mean velocity of flow) was estimated for the GIUH-II model using two approaches: (a) as a function of effective rainfall intensity (GIUH-IIa); and (b) on the basis of time of concentration concept (GIUH-IIb). Based on eight single-peaked isolated storm events for each watershed, the statistical analysis and coefficient of efficiency showed better overall correlation between predicted and observed direct runoff hydrographs, particularly in terms of the magnitude and time of occurrence of peak runoff rate, by GIUH-IIb as compared to GIUH-I and -IIa models. Moreover, the GIUH-IIb has additional advantage (compared to GIUH-IIa) for being independent of the measured velocity of flow corresponding to the peak flow rate at the watershed outlet. Since, these models require no historical data of rainfall and runoff, they can be effectively used to predict direct runoff from ungauged hilly watersheds for water resources planning and management in the region.

Simple Parametric Instantaneous Unit Hydrograph

A new, simple, parametric instantaneous unit hydrograph (IUH) with conceptual and physical justification is proposed. The new IUH has only two parameters, one of which is the time base of the unit hydrograph, an obvious physically conceivable parameter. The new mathematical form of the IUH has the properties of a statistical frequency distribution, which qualifies it for a new statistical distribution, although this distribution is not addressed in statistical books. The use of the new IUH simplifies the computations involved in obtaining the runoff from a complex rainfall event, and the calculations can even be performed on a handheld calculator or an Excel worksheet. The applicability of the proposed IUH is illustrated by using several sets of published multistorm data, wherein an optimization method is used for estimating the representative parameters of the new IUH from a single representative rainfall-runoff event obtained by processing all multistorm events. The performance criteria used in this paper give equal weight to small and large peak storm events. The new IUH with the proposed method performs better than the more computationally complex IUHs or UHs. It outperforms the least squares and linear programming approaches by prior investigators for identifying the UH based on the normalized standard error of estimate. The new IUH and proposed method are useful to field engineers and practitioners with enhanced practical utility. The new bounded statistical distribution, developed as a by-product, may find applications in other branches of applied science, economics, and engineering.

Spatial characterization of catchment dispersion mechanisms in an urban context

Previous studies have examined in-depth the dispersion mechanisms in natural catchments. In contrast, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. This has the ability to modify the variance of the catchment’s travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. The U-McIUH computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment in France as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2–3km2, after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion in the catchment, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further study with other catchments is needed to asses if the latter is a general feature of urban drainage networks.

Sediment Graphs Based on Entropy Theory

AbstractUsing the entropy theory, this paper derives an instantaneous unit sediment graph (IUSG or USG) to determine sediment discharge and the relation between sediment yield and runoff volume. The derivation of IUSG requires an expression of the effective sediment erosion intensity whose relation with rainfall is revisited. The entropy theory provides an efficient way to estimate the parameters involved in the derivations. Sediment discharge is also computed using the instantaneous unit hydrograph (IUH), which can also be derived using the entropy theory. This method works as well as the IUSG method, especially when the peak sediment discharge and peak runoff occur at the same time. The entropy theory yields the probability distribution of sediment yield and of sediment discharge, which can then be used to estimate uncertainty in sediment yield prediction.

Effects of hillslope geometry on surface and subsurface flows

Dividing a catchment to subcatchment or hillslope scales allows for better scrutiny of the changes in spatial distribution of rainfall, soil attributes and plant cover across the catchment. An instantaneous unit hydrograph model is suggested for simulating runoff hydrographs for complex hillslopes. This model is able to estimate surface and subsurface flows of the catchment based on the Dunne-Black mechanism. For this purpose, a saturation model is used to separate the saturated and unsaturated zones in complex hillslopes. The profile curvatures (concave, straight and convex) and plan shapes (convergent, parallel and divergent) of complex hillslopes are considered, in order to compute the travel time of surface and subsurface flows. The model was used for prediction of the direct runoff hydrograph and subsurface flow hydrograph of Walnut Gulch No. 125 catchment in Arizona (USA). Based on results, the geometry of hillslopes can change the peak of the direct runoff hydrograph up to two-fold, either higher or lower. The divergent hillslopes show higher peaks in comparison with the parallel and convergent hillslopes. The highest and lowest peak flows correspond to divergent-concave and convergent-straight hillslopes, respectively.

Comparison of Clark, Nash Geographical Instantaneous Unit Hydrograph models for semi arid regions

This paper compares the results obtained from three hydrologic techniques namely Clark, Nash and Geographical Instantaneous Unit Hydrograph. Underpinning of these models and calibration of parameters for these models was a demanding assignment which was performed by downhill simplex optimization method. A semi-arid region of Pakistan was selected for testing the models. Computer coding was prepared for all the models. SPOT maps of the study area were collected from NESPAK (National Engineering Services of Pakistan). The rainfall runoff data was taken from Punjab Irrigation and Power Department. The maps were digitized using ERDAS and Arc GIS to determine the geographic parameters of the watershed. Field surveys and measurements were used to estimate the discharge data. The shape of direct runoff hydrograph, peak flows and time to peak flow obtained from the three models were compared. The model efficiency was determined by a statistical parameter coefficient of determination. It was found that the Clark model simulated superior results in comparison with Nash and Geographical Instantaneous Unit Hydrograph models.

Improving the flood prediction capability of the Xinanjiang model in ungauged nested catchments by coupling it with the geomorphologic instantaneous unit hydrograph

Summary Improving the predictive capabilities of rainfall-runoff models in ungauged catchments is a challenging task but has important theoretical and practical significance. In this study, we investigated the predictive capabilities of the conceptual Xinanjiang model (XAJ), which is widely used for flood forecasting and simulation in China, in ungauged catchments. We further produced a hybrid rainfall-runoff model (named XAJ-GIUH) by coupling the XAJ model with the geomorphologic instantaneous unit hydrograph (GIUH) to achieve improved flood predictions in ungauged catchments. The flood prediction capabilities of the original XAJ model and the XAJ-GIUH model were investigated and compared at an hourly time scale in a mountainous catchment with six nested catchments located in the south of Anhui province, China. The two models were first calibrated for each individual catchment by comparing with the observed streamflows. Then, the nested catchments were treated as ungauged and modeled using the parameter values regionalized by transposition from the downstream catchments. The results show that the performance of both models is comparable and satisfactory on different catchment scales in the case that model parameters are calibrated in each catchment. However, the models perform differently in the case that model parameters are transposed from the downstream catchments. The XAJ-GIUH model produced markedly improved estimates of peak discharge and peak time as compared to the original XAJ model in the latter case, indicating that the runoff routing is a major uncertainty source for the application of the XAJ model in this case. Coupling XAJ with topography-based GIUH has the potential to substantially improve the flood prediction capability of the XAJ model in ungauged catchments. Our analysis further reveals that the models do not necessarily perform better when the parameter values are transposed from closer donor catchment. Instead, adopting the parameter values from the catchment with more similar topographic characteristics is more likely to produce better model performance. This study implicates the necessity of including remotely sensed geomorphologic characteristics of ungauged catchments to improve flood predictions in these regions.

Modeling and forecasting river flows by means of filtered Poisson processes

To model and forecast daily river flows, filtered Poisson processes with a response function that generalizes the one commonly used in hydrology are considered. The form of the response function is based on the concept of the instantaneous unit hydrograph and improves the quality of the classical model. A statistical procedure based on the theoretical autocorrelation coefficients is used to estimate the model parameters. Then, the quality of the model is assessed by comparing the theoretical autocorrelation coefficients obtained with both the generalized and the classical models to the corresponding empirical coefficients. Furthermore, an estimator of the flow at time t+1, given the flows at time t-1 and t, is developed in a particular case and the forecasting power of the model is checked, using some indicators of difference, compared to the classical model and to an autoregressive model. An application to the Delaware and the Hudson Rivers, located in the United States, is presented.