Annual Maximum Peak Discharge Research Articles

POST‐DAMMING FLOW REGIME DEVELOPMENT IN A LARGE LOWLAND RIVER (VOLGA, RUSSIAN FEDERATION): IMPLICATIONS FOR FLOODPLAIN INUNDATION AND FISHERIES

ABSTRACTPeriodic flooding plays a key role in the ecology of floodplain rivers. Damming of such rivers can disturb flooding patterns and have a negative impact on commercial fish yield. The Volga River, the largest river in Europe, has a regulated flow regime after completion of a cascade of dams. Here, we study effects of damming on long‐term discharge variability and flood pulse characteristics. In addition, we evaluate the effects of the altered flood pulse on floodplain ecosystem functioning and commercial fish yields. Our results indicate that both flood pulse and fish populations of the Volga–Akhtuba floodplain have varied considerably over the past decades. After damming, annual maximum peak discharges have decreased, minimum discharges increased, but average discharges remained similar to pre‐damming conditions. Moreover, because of bed level incision of over 1.5 m, a higher discharge is needed to reach bankfull level and inundate the floodplains. Despite this significantly altered hydrological regime and subsequent morphological changes, current discharge management still provides significant spring flooding. However, commercial fish catches did decrease after damming, both in the main channel and in the floodplain lakes. All catches were dominated by species with a eurytopic flow preference, although catches from the main channel contained more rheophilic species, and floodplain catches contained more limnophilic and phytophilic species. The strong increase of opportunistic gibel carp (Carassius gibelio) around 1985 was apparent in the main channel and the floodplain lakes. Despite the hydrological changes, the decrease in overall catches, and the upsurge of gibel, we found a strong positive effect of flood magnitude in the previous year on commercial fish yield in the floodplain lakes. This suggests that under the current discharge management there still is an increased fish growth and/or survival during high floods and that functioning of the floodplain is at least partly intact. Copyright © 2011 John Wiley & Sons, Ltd.

Flood peak distributions for the eastern United States

Annual maximum peak discharge time series from 572 stations with a record of at least 75 years in the eastern United States are used to examine flood peak distributions from a regional perspective. The central issues of this study are (1) “mixtures” of flood peak distributions, (2) upper tail properties of flood peaks, (3) scaling properties of flood peaks, (4) spatial heterogeneities of flood peak distributions, and (5) temporal nonstationarities of annual flood peaks. Landfalling tropical cyclones are an important element of flood peak distributions throughout the eastern United States, but their relative importance in the “mixture” of annual flood peaks varies widely, and abruptly, in space over the region. Winter‐spring extratropical systems and warm season thunderstorm systems also introduce distinct flood peak populations, with spatially varying control of flood frequency distributions over the eastern United States. We examine abrupt changes in the mean and variance of flood peak distributions through change point analyses and temporal trends in the flood peak records through nonparametric tests. Abrupt changes, rather than slowly varying trends, are typically responsible for nonstationarities in annual flood peak records in the eastern United States, and detected change points are often linked to regulation of river basins. Trend analyses for the 572 eastern United States gaging stations provide little evidence at this point (2009) for increasing flood peak distributions associated with human‐induced climate change. Estimates of the location, scale, and shape parameters of the generalized extreme value (GEV) distribution provide a framework for examining scaling properties of flood peaks and upper tail properties of flood distributions. It is shown that anomalously large values of the GEV shape parameter estimates are linked to the role of tropical cyclones in controlling the upper tail of flood distributions. Scaling analyses of flood peaks highlight the heterogeneities in flood magnitudes over the region with maxima in scaled flood magnitudes in the high‐elevation Appalachian Mountains and minima in the low‐gradient Coastal Plain.

Flood frequency analysis for nonstationary annual peak records in an urban drainage basin

Flood frequency analysis in urban watersheds is complicated by nonstationarities of annual peak records associated with land use change and evolving urban stormwater infrastructure. In this study, a framework for flood frequency analysis is developed based on the Generalized Additive Models for Location, Scale and Shape parameters (GAMLSS), a tool for modeling time series under nonstationary conditions. GAMLSS is applied to annual maximum peak discharge records for Little Sugar Creek, a highly urbanized watershed which drains the urban core of Charlotte, North Carolina. It is shown that GAMLSS is able to describe the variability in the mean and variance of the annual maximum peak discharge by modeling the parameters of the selected parametric distribution as a smooth function of time via cubic splines. Flood frequency analyses for Little Sugar Creek (at a drainage area of 110 km 2 ) show that the maximum flow with a 0.01-annual probability (corresponding to 100-year flood peak under stationary conditions) over the 83-year record has ranged from a minimum unit discharge of 2.1 m 3 s - 1 km - 2 to a maximum of 5.1 m 3 s - 1 km - 2 . An alternative characterization can be made by examining the estimated return interval of the peak discharge that would have an annual exceedance probability of 0.01 under the assumption of stationarity ( 3.2 m 3 s - 1 km - 2 ) . Under nonstationary conditions, alternative definitions of return period should be adapted. Under the GAMLSS model, the return interval of an annual peak discharge of 3.2 m 3 s - 1 km - 2 ranges from a maximum value of more than 5000 years in 1957 to a minimum value of almost 8 years for the present time (2007). The GAMLSS framework is also used to examine the links between population trends and flood frequency, as well as trends in annual maximum rainfall. These analyses are used to examine evolving flood frequency over future decades.

Analytical derivation of the flood frequency curve through partial duration series analysis and a probabilistic representation of the runoff coefficient

The authors propose a procedure for estimating the discharge with an assigned return period based on a probabilistic formulation of the rational formula referred to a generic flood event. In this manner it is possible to represent the natural variability in the runoff coefficient and at the same time to relate rainfall depths to the corresponding flood events. The link between the probability distributions of the annual maximum rainfalls and floods and the frequency of the corresponding events in partial duration series is established through relations deriving from the assumption of Poissonian occurrences of the relative events over the year. The proposed procedure makes it possible to display the effect of the first and second moments of the random variable ‘runoff coefficient’ on the shape of the flood frequency curve. In particular, it may be shown analytically that the second moment of the probability distribution of the runoff coefficient controls the third moment of the distribution of annual maximum peak discharges and hence its curvature. The procedure is applied to several basins of the Romagna–Marche region (Italy), for which the results of a regional analysis conducted using the index method were already available, both in relation to annual maximum rainfall depths and peak discharges. A comparison of the results obtained by the two different procedures provides a basis for advancing some considerations regarding the potential of the proposed procedure and highlights aspects, which warrant further investigation.

Impulse response of the kinematic diffusion model as a probability distribution of hydrologic samples with zero values

It is hypothesized that the unit impulse response of a linearized kinematic diffusion (KD) model is a probability distribution suitable for frequency analysis of hydrologic samples with zero values. Such samples may include data on monthly precipitation in dry seasons, annual low flow, and annual maximum peak discharge observed in arid and semiarid regions. The hypothesized probability distribution has two parameters, which are estimated using the methods of moments (MOM) and maximum likelihood (MLM). Also estimated are errors in quantiles for MOM and MLM. The distribution shows an equivalency of MOM and MLM with respect to the mean value—an important property for ML-estimation in the case of the unknown true distribution function. The hypothesized KD distribution is tested on 44 discharge data series and compared with the Muskingum-like (M-like) probability distribution function. A comparison of empirical distribution with KD and M-like distributions shows that MOM better reproduces the upper tail of the distribution, while MLM is more robust for higher sample values and more conditioned on the value of the probability of the zero value event. The KD-model is suitable for frequency analysis of short samples with zero values and it is more universal than the M-like model as its modal value cannot be only equaled to zero value but also to any positive value.

Frequency Estimation for Hydrological Samples with Zero Values

This paper develops an estimation method for discontinuous distributions used for fitting hydrologic series with several zero events. Such series are observed in arid and semiarid regions, and may include monthly precipitation in dry seasons, annual low flow, etc. The study consists of a derivation of the basic equation of the frequency distribution, derivation of distribution moments and parameters, plotting positions for positive values that form a part of the series instead of the full sample as conditional distribution, and transformation of the conditional distribution parameters into those of the marginal distribution. Using monthly precipitation and annual low-flow data from China, and annual maximum peak discharge data from the United States, the suitability of the distribution and the estimation method is assessed.

A regional frequency study of extremal rainfall and runoff processes

The annual maximum daily rainfall and annual maximum flood discharges in Lesotho were subjected to regional analysis. The mean of both time series was found to be a satisfactory parameter for regional study. The nondimensional series generated by using the mean as the divisor rendered the sequences homogeneous in the statistical sense throughout the whole country. The processes in question obey a lognormal probability law and are random in their sequential evolution. The annual maximum daily rainfall does not produce the annual maximum peak discharge in the rivers of Lesotho.

NONPARAMETRIC STATISTICAL ANALYSIS OF ANNUAL PEAK FLOW DATA FROM A RECENTLY URBANIZED WATERSHED1

ABSTRACT. In order to demonstrate the feasibility of a nonparametric statistical application in investigating the hydrologic impact of the rapid land use change accompanying intense urbanization, annual maximum peak flow data from an actual example (the Northeast Branch Basin, a recently urbanized Washington, D.C., suburban watershed) were analyzed. Annual peak flow data from the Patuxent Basin above Unity, Maryland, a rural watershed in close proximity to the study area, were compared to data from the Northeast Branch for the Same period utilizing the Wilcoxon matched‐pairs signed‐ranks test. A change in central tendency of each series was noted at the 0.01 significance level; however, the change was negative in the rural basin and positive in the urbanized Northeast Branch Basin. This central tendency change was considered indicative of an average decrease in the size of rainstorms producing annual maximum peak discharges. Rainstorm data from the Northeast Branch Basin were divided into two equal periods (before urbanization and after) and the Wilcoxon test was applied. It was found that rainstorms producing maximum annual peak discharges in the urbanized period were indeed smaller than those in the prior period (0.01 level of significance); however, larger annual peaks were produced. It was concluded that nonparametric statistical methods can be used readily with conventional methods to isolate and clearly analyze the various problems in an actual urban hydrologic study.