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.

The paper aims to reconstruct peak discharges ot historic tloods in an urbanized area ot the historic city ot Prague based on documentary sources trom pre-instrumental and the early instrumental period . Approximately 20-30 maximum water levels are denoted by tlood-marks, accounts describing or related at unchanged sites, or by early instrumental measurements. The challenge in this reconstruction is the identitication and consideration ot man-made tloodplain moditications intluencing the cross-section area and the hydraulic roughness. In order to overcome this problem, a simple approach to estimate peak discharges ot historic tloods has been developed and applied to the River Vltava. This approach includes a procedure tor reconstructing the hydraulic parameters ot the river channel and inundated floodplain, coupled with an approach tor the veritication ot estimated peak discharge reliability. As a result ot the different hydraulic characteristics associated with ice jam tloods all winter-tlood events are excluded to avoid their potential inclusion. We present 18 reconstructed discharge maxima. The validation ot the technique by comparison with the recent gauged tlood ot 2002 reveals results ot adequate accuracy. The comparison also shows that the tlood event ot 2002 was conspicuously greater than all calculated summer tloods in 1481-1825.

In the presented paper, peak discharges of historic floods in urbanized areas of different cities on the River Ahr in western Germany are reconstructed based on documentary sources from pre instrumental and the early instrumental period (1804-1937). Maximum water levels of five floods are denoted by flood-marks, with one of these events additionally documented by old photographs. The main challenge is the reconstruction of historic floodplain conditions and modifications influencing the cross-section area and the hydraulic roughness. In order to overcome this problem, a simple approach to estimate peak discharges of historic floods has been applied to the River Ahr. This approach includes a procedure for reconstructing the hydraulic parameters of the river channel and overflooded areas, coupled with an approach for the verification of estimated peak discharge reliability. Five reconstructed discharge maxima are presented. One of these events is well documented by numerous photographs, taken at different times of day, which allow the reconstruction of a hydrograph peak. The validation of the technique by comparison with recent gauged floods reveals results of adequate accuracy. The results show that reconstructed historic floods were partially larger than any gauged flood of the River Ahr. Zusammenfassung: Der Artikel behandelt die Rekonstruktion von Scheitelabflüssen historischer Hochwasser in besiedelten Gebieten verschiedener Städte an der Ahr, basierend auf anthropogen erstellten Quellen aus der Zeit vor hydrologischen Messungen bis zur Zeit früher Messungen (1804-1937). Für fünf Hochwasserereignisse sind Höchstwasserstände in Form von Hochwassermarken überliefert. Eins dieser Hochwasser ist zusätzlich durch alte Fotoaufnahmen dokumentiert. Als hauptsächliche Herausforderung gilt die Rekonstruktion der Beschaffenheit sowie der Umwandlung der historischen Aue, welche sich auf das Querprofil und die hydraulische Rauigkeit auswirken. Um dieses Problem zu bewältigen, wurde ein simpler Ansatz zur Berechnung von Scheitelabflüssen historischer Hochwasser für die Ahr angewandt. Der Ansatz umfasst ein Verfahren zur Rekonstruktion hydraulischer Parameter im Flussbett sowie weiterer überspülter Bereiche und ist mit einem Plausibilitätstest der berechneten Scheitelabflüsse gekoppelt. Insgesamt werden fünf rekonstruierte Scheitelabflüsse präsentiert, wobei eines der rekonstruierten Hochwasser so umfangreich durch Fotomaterial, welches zu verschiedenen Zeiten im Verlauf des Ereignisses entstand, dokumentiert ist, dass die Rekonstruktion eines Teils der Hochwasserganglinie möglich ist. Die Plausibilitätsprüfung des Rekonstruktionsverfahrens durch Vergleiche zu rezent gemessenen Hochwassern zeigt, dass die Ergebnisse von hinreichender Genauigkeit sind. An den Ergebnissen ist abzulesen, dass die historischen Hochwasser von deutlich größerem Ausmaß waren, als sämtliche rezent gemessenen Hochwasser der Ahr.

Abstract. There is no doubt, that the hazard assessment of future floods especially under consideration of the 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 are already developed and published, the estimation of their magnitudes indicated by discharges is still challenging. Such data are required due to significant human impact on river channels and floodplains though historic flood levels cannot be related to recent ones or recent discharges. Based on own experiences from single local key studies the general outline of an approach to estimate the discharge of the previous flood based on handed down flood level and topographic data is presented. 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 on the accuracy of ±10% are documented and potential approaches for the validation of individual estimations given. A brief discussion on benefits and limitations including a generalized statement on alternative approaches closes the review presentation of the approach.

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Pleistocene megafioods generated several large-scale obstacle marks that could not be interpreted hydraulically with the present knowledge of submerged obstacles. Thus, flume and field data of classical obstacle marks, characterised by a frontal scour hole and an adjacent depositional ridge, are analysed to estimate flow velocities from obstacle mark geometry, especially scour depths, length, width and ridge width. These data reveal a consistency of correlations between obstacle mark morphometries across a wide spatial scale. Two existing analytical models, basically integrating obstacle size, flow velocity as well as sediment size and grading, are transformed so that the magnitude of individual geometric parameters can be used as variables for the estimation of mean and tip flow velocities. These reconstructed velocities have to be regarded as minimum velocities during the rising limb of the hydrograph, as peak discharge might not last long enough to significantly influence the obstacle mark dimensions. A universally applicable practical outline is developed for palaeohydraulic reconstruction. This framework is applied on three examples of obstacle marks generated by Pleistocene megafioods. The reliability and scale-invariance of these reconstructions is confirmed by similar results of velocity estimations by other independent approaches at the same locations.

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