Estimation of peak discharges of historical floods

Abstract

Abstract. There is no doubt that the hazard assessment of future floods, especially under consideration of recent environmental change, can be significantly improved by the consideration of historic flood events. While flood frequency inventories on local, regional and even European scale have already been developed and published, the estimation of their magnitudes indicated by discharges is still challenging. Such data are required due to significant human impacts on river channels and floodplains, though historic flood levels cannot be related to recent ones or recent discharges. Based on experiences from single local key studies, we present the general outline of an approach to estimate the discharge of the previous flood based on handed-down flood level and topographic data. The model for one-dimensional steady flow is based on the empirical Manning equation for the mean flow velocity. Background and potential sources of information, acceptable simplifications and data transformation for each element of the model equation are explained and discussed. Preliminary experiences regarding the accuracy of ±10 % are documented, and potential approaches for the validation of individual estimations are given. A brief discussion of benefits and limitations, including a generalized statement on alternative approaches, concludes the review of the approach.

Evolving flood patterns in a Mediterranean region (1301–2012) and climatic factors – the case of Catalonia

“…The major documentary historical sources containing climatic information and details of its effects are local and state government records, religious collections, private collections, notaries' archives and taxation records Brázdil et al, 2014). Whenever possible, the historical flood classification should be based on discharge estimates, with a sensitivity analysis to assess the specific errors of the hydraulic model for the conversion of historical flood levels into discharge (Brázdil et al, 2006;Herget et al, 2014). On the contrary, in order to have the longest possible flood series, a scale of event magnitude can be proposed using the effects of the floods on the river channel system and surrounding areas.…”

Quantitative historical hydrology in Europe

“…This quantification may be numerical (peak flow) or categorical (damage classification). Regarding numerical data, the observed flood water levels associated with a given historical flood can be transformed by hydraulic calculations into velocities and discharges in a procedure analogous to the depth-discharge relationships used to determine the flow rate in gauge stations (Cook, 1987;Herget et al, 2014). Flood magnitudes can also be classified in terms of resulting damages or social impacts (e.g.…”

“…The typical method for estimating Manning's n is obtained from reference tables, from examination of photographs of typical channels whose roughness coefficients are known, or based on the experience of the researcher in similar river settings. Herget et al (2014) proposed a method based on the Manning equation in which discharge is calculated separately for individual homogeneous units of the inundated cross-section area. At each sub-section, the intervenient parameters of the Manning equation (R, S, n) are assessed at the time of the historical flooding based on old maps and written descriptions.…”

Historical changes in frequency of extreme floods in Prague

“…The peak discharges from 1825 to 1880 were assessed earlier, with an assumption of the 1880-1890 rating curve validity (Richter, 1893). Water levels and peak discharges for Prague after 1954 are in the Czech Hydrometeorological Institute database, concurrently in simulation without the influence of the Vltava River dams (Hladný et al, 2004). The 2012 flood, with peak discharge of 5160 m 3 s −1 , is the most important case over the instrumental period (Hladný et al, 2004).…”

“…Two of these were classified as 500-year or even 1000-year events (Blöschl et al, 2013;Hladný et al, 2004); two out of the four stroke the Vltava River catchment. Taking into account the entire region of central Europe, further extreme summer floods can be added: in the Alps in 2005, and in Slovakia and Poland in 2010.…”