Failures of small dams can pose a serious threat to people and property even if the size of the schemes is relatively low. In many cases, small dams are situated in a cascade along streams, meaning that the failure of the uppermost dam may cause the dams downstream to fail. In this paper, a cascade of three small reservoirs, Lichnov II (14.6 m high), Lichnov III (10 m high), and Pocheň (8.5 m high), is the subject of the dam break analyses carried out via various methods such as empirical formulae, analogy, and hydraulic modeling. The dam-break flood routing was simulated using a shallow water flow hydraulic model. The simulations confirm that the attenuation effect of the peak discharge is governed by the flood volume, slope, and morphology of the floodplain and increases with the distance from the breached dam following an approximately exponential trend. When estimating peak discharge, empirical formulae derived for a single dam break should be applied carefully as they may underestimate the peak outflow by up to 10% in the case of a dam cascade. The attenuation volume of small reservoirs is small when compared to the flood volume, meaning that the attenuation of the peak discharge usually varies between 5–10%.

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Jednou z častých příčin poruchy vodního díla je vnitřní eroze v tělese hráze. Pro simulaci těchto jevů je k dispozici řada softwarů umožňující výpočet porušení sypaných hrází v důsledku vnitřní eroze zemin. V rámci příspěvku byl zvolen software (SW) A Rapid Embankment Breach Analysis (AREBA), pro který byla provedena jednocestná citlivostní analýza. Příspěvek má za cíl pochopení klíčových geotechnických parametrů vstupujících do SW AREBA a jejich vliv na hydrogram odtoku, velikost průlomového otvoru a také na časové charakteristiky poruchy. Nejvíce citlivými parametry ovlivňující výstupy jsou drsnostní součinitel dle Manninga a koeficient erodibility. Tyto dva parametry by měli být variovány metodou Monte-Carlo v SW AREBA.

The modelling of solid transport in open channels requires good knowledge about parameters related to basic processes such as hydrodynamic dispersion, advection and decay rates. Such parameters are usually determined by dye tests. Numerous tracer studies have been performed on laboratory flumes and natural rivers. However, on-site sampling is often difficult, expensive and needs special apparatus. The main aim of the study was to justify simplified method based on the monitoring of the dye cloud shape in order to determine both longitudinal and transversal dispersion coefficients. In this study, four dye tests were carried out on a small local stream (the Lipkovsky) using Rhodamine WT fluorescein dye as a tracer. The tests were carried out in such a manner that both longitudinal and horizontal transversal dispersion data were obtained. For this purpose, the visually determined extent of the dye cloud was interpreted via the analytical solution of the advection-dispersion equation. The results obtained by this simplified approach indicated that the longitudinal dispersion coefficient Dx = 0.051–0.057 m2/s and the coefficient of horizontal transversal dispersion Dy = 0.00024–0.00027 m2/s. The method was justified by corresponding root mean square error (RMSE) counting RMSE = 0.65–1.02 m for the dye cloud centre, RMSE = 1.87–2.46 m for the head and tail of the cloud and RMSE = 0.025–0.11 m for the cloud width, the Nash-Sutcliffe efficiency coefficients ranged from 0.9 to 0.998. The comparison of these values with empirical formulae and other tracer studies indicated significant overestimation of the mentioned values of Dx , which can be attributed to the uniform velocity distribution along the width of Lipkovsky Stream. Much better agreement was achieved for Dy .

Dam incidents and failures mainly occur during extreme floods. In the Czech Republic (CR), large-scale regional floods were recorded in different regions in 1985, 1987, 1997, 2002, 2006, 2010, and 2013, while local floods especially occurred in 1991, 1996, 1997, 1998, 2002, 2004, 2005, 2009, and 2010. During these events, numerous incidents and total breaches of small dams were recorded, and a few large dams were also critically endangered, although they were not completely breached. This paper presents a comprehensive summary of incidents and failures affecting small dams in the CR since 1985. The most significant incidents concerning large dams are listed as well. The statistics show that 62 small dams were completely breached and that 350 were seriously damaged over 35 years in the period 1985–2020. The annual frequency amounts to 1.85 collapsed and 10 small damaged dams per year. The most common causes of the complete breaching of dams were overtopping (85 %) and internal erosion (15 %).