Hydrograph Volume Research Articles

The role of flood hydrograph in the remobilization of large wood in a wide mountain river

Floods can mobilize large amounts of unconsolidated material, which also includes large wood in forested river basins. Yet, the influence of the shape and volume of flood hydrographs on wood dynamics in rivers remains poorly understood. Quantitative data on this relation are, however, critically needed to properly address management strategies and to improve the relevant understanding of wood dynamics in rivers. In this work we used a deterministic model, run in a multi-scenario mode, to simulate the transport of wood pieces fully coupled to hydrodynamics. The goal was to analyze how the transport of large wood occurs under different unsteady flood scenarios. We applied the model to two contrasting geomorphic configurations (channelized, single-thread and multi-thread reaches) in the Czarny Dunajec River in Poland, where extensive field observations of wood transport and deposition after floods of different magnitude were available to validate, interpret, and discuss model results. We show that the peak of wood transport is generally reached before the flood peak, and that the wood remobilization ratio is not always positively correlated to peak discharge. We found a positive correlation between the number of mobilized wood pieces and the duration of the rising limb. In addition, hysteresis was observed in the relationship between wood remobilization and discharge. We conclude that numerical modelling allows analysis of wood dynamics in a detail which cannot typically be achieved in field observations. Therefore, modelling improves our understanding of the process and helps disentangling the complex linkages between flood hydrographs and large wood transport dynamics in rivers.

A complete procedure for multivariate index-flood model application

Multivariate frequency analyses are needed to study floods due to dependence existing among representative variables of the flood hydrograph. Particularly, multivariate analyses are essential when flood-routing processes significantly attenuate flood peaks, such as in dams and flood management in flood-prone areas. Besides, regional analyses improve at-site quantile estimates obtained at gauged sites, especially when short flow series exist, and provide estimates at ungauged sites where flow records are unavailable. However, very few studies deal simultaneously with both multivariate and regional aspects. This study seeks to introduce a complete procedure to conduct a multivariate regional hydrological frequency analysis (HFA), providing guidelines. The methodology joins recent developments achieved in multivariate and regional HFA, such as copulas, multivariate quantiles and the multivariate index-flood model. The proposed multivariate methodology, focused on the bivariate case, is applied to a case study located in Spain by using hydrograph volume and flood peak observed series. As a result, a set of volume-peak events under a bivariate quantile curve can be obtained for a given return period at a target site, providing flexibility to practitioners to check and decide what the design event for a given purpose should be. In addition, the multivariate regional approach can also be used for obtaining the multivariate distribution of the hydrological variables when the aim is to assess the structure failure for a given return period.

Incorporating seepage losses into a 1D unsteady model of floods in an ephemeral stream

Zangemar River is an ephemeral river located in the northwestern part of Iran. Maku and Poldasht are hydrometric stations located upstream and downstream of Zangemar River, respectively. The measured flood hydrograph indicates that the output hydrograph volume from Poldasht station is significantly less than the input hydrograph for Maku station, though there are no lateral outflow branches and the amount of evaporation and direct removal from the river reach during flood events is negligible. These transmission losses can be caused by infiltration into the streambed and floodplain. Due to transmission losses and lack of initial flow, flood routing in these rivers is impossible to achieve through conventional methods and it is essential to develop new flood routing methods. Therefore, in this study a computer model for natural river cross-sections has been developed in which partial differential equations of non-uniform unsteady flow (Saint-Venant equations) are solved by finite difference methods. These equations have been developed by adding Muskat’s equation in such a way that seepage losses can be calculated simultaneously. The results showed that with consideration of seepage losses the developed model can predict the output hydrograph with good accuracy, compared to the field data. The results of flood routing for 13 input hydrographs showed that the seepage loss volume in the river reach is about 74% of the input hydrograph volume, on average. The model predicts seepage losses with a mean error of about 9.93% and the maximum error is less than 20%.Keywords: flood routing, seepage losses, unsteady flow, Zangemar River

Hydrologic Modeling of Flow through Sinkholes Located in Streambeds of Cane Run Stream, Kentucky

AbstractHydrologic modeling of karst watersheds requires detailed information on geologic settings and hydrologic properties for efficient simulation of spring and streamflow hydrographs. In this paper, sinkholes located in the streambed of a karst watershed in Kentucky were conceptualized as orifices, and flow through these orifices was modeled as a function of sinkhole diameter. The karst flow components were incorporated in a soil and water assessment tool (SWAT), called KarstSWAT in this study. The KarstSWAT was able to reproduce the observed hydrographs better than the SWAT model in terms of both peak flow and hydrograph volume. Flow through a groundwater basin that is partly fed by the sinkholes and is discharged from a spring was estimated using a method called the successive summation routing algorithm (SSRA) in this study. The time series analysis of simulated spring flows showed that the quantity of water recharging the sinkholes was sufficient to reproduce the observed spring hydrographs. The p...

Trivariate Frequency Analyses of Peak Discharge, Hydrograph Volume and Suspended Sediment Concentration Data Using Copulas

Copula functions are often used for multivariate frequency analyses, but discharge and suspended sediment concentrations have not yet been modelled together with the use of 3-dimensional copula functions. One hydrological station from Slovenia and five stations from USA with watershed areas from 920 km2 to 24,996 km2 were used for trivariate frequency analyses of peak discharges, hydrograph volumes and suspended sediment concentrations. Different parametric marginal distributions were applied and parameters were estimated with the method of L-moments. Maximum pseudo-likelihood method was used for copula parameters estimation. With the use of statistical and graphical tests we selected the most appropriate copula model. Symmetric and asymmetric versions of Archimedean copulas were applied according to the dependence characteristics of the individual stations. We selected Gumbel-Hougaard copula as the most appropriate model for all discussed stations. Primary joint return periods OR and secondary Kendall’s return periods were calculated and comparison between selected copula functions was made. We can conclude that copula functions are useful mathematical tool, which can also be used for modelling variables that are presented in this paper.

Bivariate flood frequency analysis using the copula function: a case study of the Litija station on the Sava River

As an alternative to the commonly used univariate flood frequency analysis, copula frequency analysis can be used. In this study, 58 flood events at the Litija gauging station on the Sava River in Slovenia were analysed, selected based on annual maximum discharge values. Corresponding hydrograph volumes and durations were considered. Different bivariate copulas from three families were applied and compared using different statistical, graphical and upper tail dependence tests. The parameters of the copulas were estimated using the method of moments with the inversion of Kendall's tau. The Gumbel–Hougaard copula was selected as the most appropriate for the pair of peak discharge and hydrograph volume (Q-V). The same copula was also selected for the pair hydrograph volume and duration (V-D), and the Student-t copula was selected for the pair of peak discharge and hydrograph duration (Q-D). The differences among most of the applied copulas were not significant. Different primary, secondary and conditional return periods were calculated and compared, and some relationships among them were obtained. Copyright © 2014 John Wiley & Sons, Ltd.

The intrinsic dependence structure of peak, volume, duration, and average intensity of hyetographs and hydrographs.

[1] The information contained in hyetographs and hydrographs is often synthesized by using key properties such as the peak or maximum value Xp, volume V, duration D, and average intensity I. These variables play a fundamental role in hydrologic engineering as they are used, for instance, to define design hyetographs and hydrographs as well as to model and simulate the rainfall and streamflow processes. Given their inherent variability and the empirical evidence of the presence of a significant degree of association, such quantities have been studied as correlated random variables suitable to be modeled by multivariate joint distribution functions. The advent of copulas in geosciences simplified the inference procedures allowing for splitting the analysis of the marginal distributions and the study of the so-called dependence structure or copula. However, the attention paid to the modeling task has overlooked a more thorough study of the true nature and origin of the relationships that link , and I. In this study, we apply a set of ad hoc bootstrap algorithms to investigate these aspects by analyzing the hyetographs and hydrographs extracted from 282 daily rainfall series from central eastern Europe, three 5 min rainfall series from central Italy, 80 daily streamflow series from the continental United States, and two sets of 200 simulated universal multifractal time series. Our results show that all the pairwise dependence structures between , and I exhibit some key properties that can be reproduced by simple bootstrap algorithms that rely on a standard univariate resampling without resort to multivariate techniques. Therefore, the strong similarities between the observed dependence structures and the agreement between the observed and bootstrap samples suggest the existence of a numerical generating mechanism based on the superposition of the effects of sampling data at finite time steps and the process of summing realizations of independent random variables over random durations. We also show that the pairwise dependence structures are weakly dependent on the internal patterns of the hyetographs and hydrographs, meaning that the temporal evolution of the rainfall and runoff events marginally influences the mutual relationships of , and I. Finally, our findings point out that subtle and often overlooked deterministic relationships between the properties of the event hyetographs and hydrographs exist. Confusing these relationships with genuine stochastic relationships can lead to an incorrect application of multivariate distributions and copulas and to misleading results.

Design hydrograph estimation in small and ungauged watersheds: continuous simulation method versus event‐based approach

AbstractThe proper assessment of design hydrographs and their main properties (peak, volume and duration) in small and ungauged basins is a key point of many hydrological applications. In general, two types of methods can be used to evaluate the design hydrograph: one approach is based on the statistics of storm events, while the other relies on continuously simulating rainfall‐runoff time series. In the first class of methods, the design hydrograph is obtained by applying a rainfall‐runoff model to a design hyetograph that synthesises the storm event. In the second approach, the design hydrograph is quantified by analysing long synthetic runoff time series that are obtained by transforming synthetic rainfall sequences through a rainfall‐runoff model. These simulation‐based procedures overcome some of the unrealistic hypotheses which characterize the event‐based approaches. In this paper, a simulation experiment is carried out to examine the differences between the two types of methods in terms of the design hydrograph's peak, volume and duration. The results conclude that the continuous simulation methods are preferable because the event‐based approaches tend to underestimate the hydrograph's volume and duration. Copyright © 2011 John Wiley & Sons, Ltd.

Rainfall-runoff modelling and palaeoflood hydrology applied to reconstruct centennial scale records of flooding and aquifer recharge in ungauged ephemeral rivers

Abstract. In this study we propose a multi-source data approach for quantifying long-term flooding and aquifer recharge in ungauged ephemeral rivers. The methodology is applied to the Buffels River, at 9000 km2 the largest ephemeral river in Namaqualand (NW South Africa), a region with scarce stream flow records limiting research investigating hydrological response to global change. Daily discharge and annual flood series (1965–2006) were estimated from a distributed rainfall-runoff hydrological model (TETIS) using rainfall gauge records located within the catchment. The model was calibrated and validated with data collected during a two year monitoring programme (2005–2006) at two stream flow stations, one each in the upper and lower reaches of the catchment. In addition to the modelled flow records, non-systematic flood data were reconstructed using both sedimentary and documentary evidence. The palaeoflood record identified at least 25 large floods during the last 700 yr; with the largest floods reaching a minimum discharge of 255 m3 s−1 (450 yr return period) in the upper basin, and 510 m3 s−1 (100 yr return period) in the lower catchment. Since AD 1925, the flood hydrology of the Buffels River has been characterised by a decrease in the magnitude and frequency of extreme floods, with palaeoflood discharges (period 1500–1921) five times greater than the largest modelled floods during the period 1965–2006. Large floods generated the highest hydrograph volumes, however their contribution to aquifer recharge is limited as this depends on other factors such as flood duration and storage capacity of the unsaturated zone prior to the flood. Floods having average return intervals of 5–10 yr (120–140 m3 s−1) and flowing for 12 days are able to fully saturate the Spektakel aquifer in the lower Buffels River basin. Alluvial aquifer storage capacity limiting potential recharge by the largest floods is a common problem in arid environments, with the largest infiltration volumes favoured by increasing depth to groundwater levels.

Design flood hydrographs from the relationship between flood peak and volume

Abstract. Hydrological frequency analyses are usually focused on flood peaks. Flood volumes and durations have not been studied as extensively, although there are many practical situations, such as when designing a dam, in which the full hydrograph is of interest. A flood hydrograph may be described by a multivariate function of the peak, volume and duration. Most standard bivariate and trivariate functions do not produce univariate three-parameter functions as marginal distributions, however, three-parameter functions are required to fit highly skewed data, such as flood peak and flood volume series. In this paper, the relationship between flood peak and hydrograph volume is analysed to overcome this problem. A Monte Carlo experiment was conducted to generate an ensemble of hydrographs that maintain the statistical properties of marginal distributions of the peaks, volumes and durations. This ensemble can be applied to determine the Design Flood Hydrograph (DFH) for a reservoir, which is not a unique hydrograph, but rather a curve in the peak-volume space. All hydrographs on that curve have the same return period, which can be understood as the inverse of the probability to exceed a certain water level in the reservoir in any given year. The procedure can also be applied to design the length of the spillway crest in terms of the risk of exceeding a given water level in the reservoir.

Characteristics of the extreme rainfall event and consequent flash floods in W Slovenia in September 2007

Abstract. During a weather front that passed over large parts of Slovenia on 18.9.2007, extreme rainfall events were triggered causing several severe flash floods with six casualties. Out of 210 municipalities in Slovenia, 60 were reporting flood damages, and the total economic flood damage was later estimated at close to 200 million Euro; highest damage was claimed by Železniki municipality in NW Slovenia. The main purpose of the study presented in this paper was to put together available meteorological and hydrological data in order to get better insight into temporal and spatial dynamics and variability of the flash flood event along the Selška Sora River flowing through the town of Železniki. The weather forecast by the Environmental Agency of the Republic of Slovenia (ARSO) lead to early warning of floodings but has underestimated rainfall amounts by a factor of 2. Also meteorological radar underestimated ground rainfall as much as by 50%. During that day, in many rainfall gauging stations operated by ARSO in the area under investigation, extreme rainfall amounts were measured, e.g. 303 mm in 24 h or 157 mm in 2 h. Some of the measured rainfall amounts were the highest registered amounts in Slovenia so far. Statistical analysis using Gumble distribution was performed and rainfall return periods were estimated. When assessing rainfall return periods, a question of the sampling error as a consequence of short rainfall records used was raised. Furthermore, measured rainfall data were used to reconstruct hydrographs on selected water stations along the Selška Sora River. The cumulative areal precipitation for the Selška Sora River catchment upstream of Železniki amounted to 219 mm, while the modeled effective precipitation used to simulate the hydrograph peak was only 57 mm. The modeled direct runoff coefficient therefore amounts to 0.26. Surprisingly low value is mainly caused by the applied unit hydrograph method that seeks to meet the peak discharge rather than hydrograph volume. However, the spatial distribution of the rainfall in the area was highly variable and present spatial positioning of rain gauges is obviously inadequate for proper representation of the actual spatial amount of rainfall. The study confirmed that post-flood investigation should focus on discharges and hydrological response of the catchment rather than simply analyzing statistical characteristics of rainfall.

Importance of Tail Dependence in Bivariate Frequency Analysis

This paper highlights the importance of taking into account the tail dependence in the context of bivariate frequency analysis based on copulas. Three nonparametric estimators of the tail-dependence coefficient are compared by simulations with seven families of copulas. We choose the two estimators most adapted to a bivariate frequency analysis of the annual maximum flows and the corresponding flow hydrograph volumes of the Loire River France. In this example, the bivariate return period and the conditional density of the volume given that the flow exceeds a given threshold are computed. The results show, as can be expected, that out of the seven copula families tested, five overestimate the return periods of correlated extreme events. These results bring to the forefront the importance of taking into account the tail dependence in order to estimate the risk adequately.

Use of a geomorphological transfer function to model design floods in small hillside catchments in semiarid Tunisia

In the beginning of the 1990s, the Tunisian Ministry of Agriculture launched an ambitious program for constructing small hillside reservoirs in the northern and central region of the country. At present, more than 720 reservoirs have been created. They consist of small compacted earth dams supplied with a horizontal overflow weir. Due to lack of hydrological data and the area's extreme floods, however, it is very difficult to design the overflow weirs. Also, catchments are very sensitive to erosion and the reservoirs are rapidly silted up. Consequently, prediction of flood volumes for important rainfall events becomes crucial. Few hydrological observations, however, exist for the catchment areas. For this purpose a geomorphological model methodology is presented to predict shape and volume of hydrographs for important floods. This model is built around a production function that defines the net storm rainfall (portion of rainfall during a storm which reaches a stream channel as direct runoff) from the total rainfall (observed rainfall in the catchment) and a transfer function based on the most complete possible definition of the surface drainage system. Observed rainfall during 5-min time steps was used in the model. The model runoff generation is based on surface drainage characteristics which can be easily extracted from maps. The model was applied to two representative experimental catchments in central Tunisia. The conceptual rainfall-runoff model based on surface topography and drainage network was seen to reproduce observed runoff satisfactory. The calibrated model was used to estimate runoff from 5, 10, 20, and 50 year rainfall return periods regarding runoff volume, maximum runoff, as well as the general shape of the runoff hydrograph. Practical conclusions to design hill reservoirs and to extrapolate results using this model methodology for ungauged small catchments in semiarid Tunisia are made.

Dam-Breach Flood Wave Propagation Using Dimensionless Parameters

An analytical model of flood wave propagation is used to study the sensitivity of dam-breach flood waves to breach-outflow hydrograph volume, peak discharge, and downstream-channel bed slope. Dimensionless parameters are identified for discharge and distance along the channel. A dam-breach Froude number is defined to enable analysis through a wide range of site and flow conditions. It is found that, at a certain distance downstream, the attenuated peak discharge is independent of the magnitude of the discharge at the breach site. This attenuated peak discharge is termed the “ultimate discharge,” and the distance associated with it, the “ultimate distance.” These ultimate values are a function, primarily of the downstream-channel bed slope and, secondarily, of the breach-outflow hydrograph volume.

Consistency of patterns in concentration‐discharge plots

Concentration‐discharge (c‐Q) plots have been used to infer how flow components such as event water, soil water, and groundwater mix to produce the observed episodic hydrochemical response of small catchments. Because c‐Q plots are based only on observed streamflow and solute concentration, their interpretation requires assumptions about the relative volume, hydrograph timing, and solute concentration of the streamflow end‐members. Evans and Davies [1998] present a taxonomy of c‐Q loops resulting from three‐component conservative mixing. Their analysis, based on a fixed template of end‐member hydrograph volume, timing, and concentration, suggests a unique relationship between c‐Q loop form and the rank order of end‐member concentrations. Many catchments exhibit variability in component contributions to storm flow in response to antecedent conditions or rainfall characteristics, but the effects of such variation on c‐Q relationships have not been studied systematically. Starting with a “baseline” condition similar to that assumed by Evans and Davies [1998], we use a simple computer model to characterize the variability in c‐Q plot patterns resulting from variation in end‐member volume, timing, and solute concentration. Variability in these three factors can result in more than one c‐Q loop shape for a given rank order of end‐member solute concentrations. The number of resulting hysteresis patterns and their relative frequency depends on the rank order of solute concentrations and on their separation in absolute value. In ambiguous cases the c‐Q loop shape is determined by the relative “prominence” of the event water versus soil water components. This “prominence” is broadly defined as a capacity to influence the total streamflow concentration and may result from a combination of end‐member volume, timing, or concentration. The modeling results indicate that plausible hydrological variability in field situations can confound the interpretation of c‐Q plots, even when fundamental end‐member mixing assumptions are satisfied.

Peak Flow and Volume Predictions Using Frequency-Equivalent Hydrographs

A new method for calculation of frequency-equivalent storms and hydrographs is presented. This procedure is an extension of the frequency-equivalent nonlinear hydrograph (FENLH) methodology. Streamflow data records for a total of 129 basins in the state of Kansas have been used. A new storm criterion for generating frequency-equivalent storms was selected. Peak flow rates, hydrograph volumes, and peak reduction factors, produced by the storm criterion, were related to the basin physiographic and climatic data. The combination of index flood and multiple regression techniques were used to obtain predictive equations for peak flow rates and hydrograph volumes for six different return intervals. The use of the FENLH model as a prototype and the selection of the criterion utilized in this study to determine frequency-equivalent conditions, provided storm dimensions that appeared realistic. The accuracy of the results obtained indicated that the methodology presented in this study can be applied to other areas.

Analysis of storm run‐off sources using oxygen‐18 in a headwater swamp

AbstractA combination of hydrometric data and observations of natural isotope (oxygen‐18) variations in saturation overland flow and stream discharge were used to investigate the sources of storm run‐off in a headwater swamp located in a permanent groundwater discharge zone near Toronto, Canada. The results of a two‐component hydrograph separation indicated that pre‐event water formed 80–90% of the stream hydrograph volume for six of the seven storms analyzed in June–November 1990. However, the instantaneous event water contribution showed considerable variability, ranging from maximum values of 20–25% for four moderate intensity storms to 63% for a high intensity thunderstorm with a return period of two years. The relative contribution of event and pre‐event water to storm run‐off from saturated areas and small streamlets within the swamp was similar to the main outlet stream. The dominance of pre‐event water during storms could be accounted for by the mixing of a small volume of event water with a large pool of pre‐event water on the surface of permanently saturated areas within the swamp. Occasional storms of high intensity or long duration produced a greater shift towards an event water signature in the saturated areas and a larger event water contribution to the outlet stream hydrograph.

Selection of Stormwater Model Parameters

Stormwatrer models, which are used extensively for stormwater drainage design and management, require calibration. The parameters usually estimated by calibration include infiltration and roughness. Parameters that can be determined by measurement include catchment area, slope, and length of flow path. The dependency of parameter values on the level of model discretization was investigated. Experiments were performed on a small urban catchment, and results of different levels of discretization were compared to observed hydrograph volume and peak runoff. The only factor found to require adjustment based on the level of discretization and the size of subcatchment was the overland flow time. Small-scale discretization required a longer flow path or a higher Manning roughness coefficient than coarse discretization to predict lag times correctly.

USE OF TOPOLOGICAL INFORMATION IN HYDROGRAPH ESTIMATION1

ABSTRACT: Discharge hydrographs computed from the theory of linear flow through topologically random channel networks are compared to actual discharge hydrographs for basins in semiarid regions of central Wyoming. The basins drained by the channel networks range in size from 0.69 to 10.8 square miles. Topological information consisting of stream‐network magnitude and link ‐length distribution parameters are used in calibrating celerity values that ensure that the peak discharge and excess rainfall volume of the resulting computed hydrographs match the peak discharge and excess‐rainfall volume of the actual hydrographs. Results indicate that, for a given peak discharge and excess‐rainfall volume in a basin, the sensitivity of the calibrated celerity values to excess‐rainfall duration is small if the ratio of excess‐rainfall volume to peak discharge is at least 1.75 times the excess‐rainfall duration.

Storm Runoff Generation in Humid Headwater Catchments: 2. A Case Study of Hillslope and Low‐Order Stream Response

Previous hydrometric and dye tracer studies in Maimai 8, a highly responsive catchment in the Tawhai State Forest, Westland, New Zealand, suggest that storm runoff generation is by rapid transmission of “new” (current storm rain) water to the stream via macropores. We used hydrometric and natural tracer (oxygen 18, deuterium, electrical conductivity, chloride) observations in two first‐ and one second‐order stream and in six throughflow pits, to evaluate the roles of “old” (stored) and new water during three storm events (return periods from 4 weeks to 3 months) in September 1983. New water contributions were small (<25% of the hydrograph volume) and could be accounted for by saturation overland flow. Hillslope response varied areally but all sites issued old water‐dominated throughflow. Ridge top sites had larger new water contributions (∼ 30–40%) than valley sites (< 10%). Macropore flow of new water therefore cannot explain streamflow or throughflow response in the Maimai catchments.