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In the Siberian Altai Mountains, where the sources of the River Ob are located, ice-dammed lake outburst fl oods, so-called jökulhlaups, occurred in Pleistocene times. Valley glaciers extended within the upper Chuja River catchment and dammed the river upstream of the village of Aktash, which generated ice-dammed lakes in the intramountainous Kuray and Chuja Basins. Indicated by shorelines and ice-rafted boulder deposits, the maximum lake level reached an altitude of 2100 m above sea level, which reveals a maximum lake volume of 607 km 3 . The failure of the ice dam caused outburst fl oods, which left traces by giant bars, fl uvial gravel dunes, and boulder deposits. Run-up sediments deposited in front of local obstructions along the valley slopes indicate a maximum depth of fl ow of 400 m above the valley bottom. Like the giant bars, they consist of characteristic relatively fi ne suspension gravels. Occasionally, secondary lakes are formed in tributary valleys that were blocked by giant bar deposits. The alternation of lacustrine deposits and suspension gravels in the tributary Injushka valley near Inja village give evidence for at least three large outburst fl oods. Age estimations by a variety of dating methods, such as luminescence methods, exposure dating, and accelerator mass spectrometry radiocarbon applied on different fl ood features and lake sediments, indicate that the outburst fl oods occurred between 40 ka and 13 ka. This estimation should be taken as preliminary, as problems occurred with the different dating techniques, resulting in partly contradictory results. This study focuses on the paleohydraulic reconstruction of the fl ood rather than describing fl ood-related features in detail. Seven different approaches are applied to estimate the discharge of the fl oods. Several new methods are developed within the study, partly based on previous approaches carefully considering the hydraulic background. Data for paleohydraulic estimations are obtained during repeated fi eld trips by observations, surveys, and sedimentological investigations in Chuja and Katun valleys. Peak discharge is estimated by the elevation of the surfaces of the giant bars indicating the depth of fl ow and additionally by the run-up sediments, which reveal information about the velocity head of the fl ood fl ow along the valleys. A value of 10 × 10 6 m 3 /s is estimated for peak discharge, which is considerably less than previous estimations derived. Dimensions of gravel dunes and obstacle marks obtain information of fl ow conditions during the decreasing fl ood. The application of regression formulae between drained lake volume and peak discharge, an established method to estimate discharges of jökulhlaups, and estimation of fl ow velocity considering fl ow *herget @giub.uni-bonn.de on May 27, 2015 specialpapers.gsapubs.org Downloaded from 2 J. Herget competence indicated by transported boulders yield problems as the magnitude of the outburst fl oods and the size of the boulders are beyond the level of experience.Based on the...

The heat waves of 2003 in Western Europe and 2010 in Russia, commonly labelled as rare climatic anomalies outside of previous experience, are often taken as harbingers of more frequent extremes in the global warming-influenced future. However, a recent

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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.

Büntgen et al. (2015; hereinafter B15) present the result of new research which question the results of Wetter et al. 2014, ( hereinafter W14) and Wetter et al. (2013, hereinafter W13) regarding European climate in 1540. B15 conclude from tree-ring evidence that the results based on documentary data of W14 Bprobably overstated the intensity and duration of the 1540

Numerical simulations of the catastrophic draining of Pleistocene glacial-lake Kuray-Chuja quantify the discharge history of the draining event in detail. The plan-view basin flows are modelled as water emptied due to the instantaneous failure of the impounding ice-dam when the lake was at maximum capacity. The Chuja Basin water exited as a jet-flow into the Kuray Basin via a narrow conjoining valley. The peak discharge from the Chuja Basin is determined to be 1.20 × 10 7 m 3 s −1 , and the peak discharge (3.19 × 10 7 m 3 s −1 > Q ≤ 2.0 × 10 7 m 3 s −1 ) that flowed from the Kuray Basin at the failed impoundment is also calculated for two limiting conditions. The variations in lake volume and depth indicate complete drainage within 50 h. In both basins, fields of relict gravel bedforms reflect sediment transport due to entrained lake-bed sediments. Thus, in addition to the general overview of drainage, the detailed temporal and spatial evolutions of drainage parameters are reported, including for the locations of the bedform fields. Local flow above the bedforms is considered in relation to thresholds for sediment motion, bedform development, and orientations. Within the simple bathymetry of the Chuja Basin, the flow field was fairly uniform with flow conducive to bedform evolution only occurring close to the exit from the basin, which accords with field evidence. In contrast, within the Kuray Basin, the flow responded sensitively to the complex bathymetry, which included rapid changes in flow direction due to interaction of the Kuray water with the jet-flow from Chuja, and as submerged ridges shoaled. Thus the Kuray flow field was complex but with time-dependent flow conditions in accordance with bedform development. It is concluded that the location of the bedforms can be explained in terms of the flow modelling and suggestions are made as to how future drainage models might be improved. ARTICLE HISTORY

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.