ABSTRACTS 'Extreme Discharges' - CHR-KHR

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Table 1: Modelled changes in water level [cm] at five main gauging stations of the Rhine, due to scenarios of land-use change and river training (river retention) measures, for three different meteorological scenarios. Explanations for land-use and climate scenarios are given in the text Rhine gauging station (km down Lake Constance) Worms (km 444) Meteorological Scenario M95 M95+ M95++ D1 0 (0/0) 10 (0/10) 16 (0/16) D2 0 (1/0) 9 (0/10) 16 (-1/17) D3 0 (-1/1) -10 (-1/-9) 15 (-1/16) Kaub (km 546) D1 1 (-1/2) 8 (-1/9) 9 (-2/11) D2 1 /-1/2) 8 (-1/9) 9 (-1/11) D3 -5 (-7/3) 3 (-6/8) 3 (-9/11) Andernach (km 614) D1 0 (-1/1) 5 (-1/6) 6 (-1/8) D2 1 (0/1) 6 (-1/6) 7 (-1/8) D3 -5 (-7/2) 1 (-5/6) 2 (-6/8) Köln (km 688) D1 0 (-2/1) 5 (-1/6) 4 (-2/6) D2 1 (0/1) 5 (-1/6) 5 (-1/6) D3 -8 (-9/2) -1 (-7/6) -3 (-9/7) Lobith (km 857) D1 2 (-1/3) 2 (-1/3) 2 (-1/3) D2 2 (-1/3) 3 (-1/3) 2 (-1/3) D3 -1 (-5/3) -2 (-6/3) -5 (-8/3) In Tab 1 a summary of the model results is presented by listing the combined effects of land-use and meteorological scenarios. The modelled differences in water levels (in cm) at five main gauging stations of the Rhine are given. The non-parenthetic values are due to the combined effects of land-use change (increase of urban areas) and river training (increase of flood-discharge retention in river polders). The values in parenthesis are due to land use change only (1 st value) and due to river training only (2 nd value). Positive numbers imply a decrease in water level, negative ones imply an increase. From the differences in water levels listed in Table 1 one can draw several conclusions: - The increase of flood peak level due to a further moderate (realistic) increase of urbanised areas (D1) is very small (water level increase 2cm of less) and therefore almost negligible. - The influence of the proposed management of urban storm water results in a very limited mitigation of flood peaks (water level decrease 2cm or less) and therefore is almost negligible, too. - The effects of water retention in flood polders (between Maxau and Lobith) have a stronger but still small effect (water level decrease of 3cm of less for the M95 scenario, up to 10cm for the M95+, and up to 17 67
cm for M95++). It is important to understand that consideration of the possible retention polders upstream of Maxau would yield an additional reduction in the range of 10 cm, in particular for the Upper Rhine area. - The unrealistic, extreme land-use scenario (50% increase of urban areas) would result in a water level increase not much more than 10cm. - The M95+ and even more the M95++ scenario results in higher reduction of flood levels in the case where the flood polders are active. This is due to the fact that according to the operation rules, the flood polders are to be filled only if flood discharge exceeds the 200-year value. In January/February 1995 (M95) the flood discharge along most stretches of the Rhine was above the 100-year value, but below 200 years. That is why the polders were used only at a few stretches resulting in small water level reduction only. Some more general results from the whole study are summarised in the following: (1) At the lower meso-scale level the influence of land-use on storm-runoff generation is stronger for convective storm events with high precipitation intensities than for long advective storm events with low precipitation intensities, because only storm events associated with high rainfall intensities are at least partially controlled by the conditions of the land-cover and/or the soil-surface. Convective storm events, however, are of minor relevance for the formation of floods in the large river basins of Central Europe because the extent of convective storms is usually local. (2) An estimated, rather dramatic, further increase of urban areas of about 50% may result in an increase of medium-size flood peak discharge (e.g. return intervals between 2 and 8 years) in catchments of the lower meso-scale (up to ca. 1000 km²): ⎯ Between 0% and 4% for advective rainfall events, and ⎯ up to 30% for convective rain storms. (3) The flood impacts due to a more realistic representation of urbanisation increase are in the order of 1 to 5 cm in the main channel, while the effects are even less for extreme rainfall amounts. (4) The decentralised storage, detention, and infiltration of urban storm water yields reduction of flood peaks in catchments of the lower meso-scale which are about the same size as the increase due to urbanisation. (5) The superposition of flood waves originating in different sub-basins shows that the maximum effect of water retention in the landscape generally occurs in the rising limb of the flood wave in the main channel. The flood mitigation effect at the peak is considerably smaller. (6) Water retention measures in polders along the Upper and Lower Rhine, under the given boundary conditions, yield flood peak attenuation along the Rhine all the way down to Lobith of between 1 cm and 15cm. The optimised and co-ordinated control of the polders can result in a considerable stronger decrease of the peaks. Final report: Bronstert, A., Bárdossy, A:, Bismuth, C., Buiteveld, H., Busch, N., Disse, M., Engel, H., Fritsch, U., Hundecha, Y., Lammersen, R., Niehoff, D., Ritter, N., (2003): Quantifizierung des Einflusses der Landoberfläche und der Ausbaumaßnahmen am Gewässer auf die Hochwasserbedingungen im Rheingebiet. Reports of the <strong>CHR</strong>, Series II, No. 18, 78pp. 68
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ABSTRACTS OF ORAL AND POSTER CONTRI
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lungen, jahreszeitliche Verteilung
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Extreme discharges in the Meuse bas
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esults obtained with this new metho
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Does the perception of extremity ch
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Discussion and conclusion According
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Extreme Niederschläge in Deutschla
Page 21 and 22: lich, die selteneren Sommerereignis
Page 23 and 24: Tab. 12b Relation zwischen den HQ(T
Page 26 and 27: Climate Change and Hydrological Ext
Page 28 and 29: Regional Flood Process Types Ralf M
Page 30: Based on these indicators and diagn
Page 34 and 35: Estimating design river discharges
Page 36: The flood routing in the Rhine from
Page 40 and 41: Modeling series of extreme flood ev
Page 42 and 43: Uncertainty in flood quantiles from
Page 44: the tributaries of the Rhine exceed
Page 47 and 48: One advantage of this approach is t
Page 50: Extremwertstatistik für instation
Page 53 and 54: • ausschließlich anthropogen unb
Page 56: Impact assessment of flood mitigati
Page 60 and 61: Increasing flood losses indicate in
Page 62: evising land use regulations, adopt
Page 65 and 66: Using the SOBEK-model the effect of
Page 67 and 68: 5. References Buishand, T.A. and Br
Page 69: The following paragraph presents th
Page 73 and 74: Meuse. The areas where these calcul
Page 76: Die mögliche Verschärfung des Hoc
Page 80 and 81: Floods in Europe - Loss experience
Page 82: Figure 2: Proportions of numbers an
Page 86 and 87: Peter Schmoker Berner Fachhochschul
Page 88 and 89: Some comments on the estimation of
Page 90: Discharge [m³/s] 4000 6000 8000 10
Page 94: Risk management of extreme flood ev
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ABSTRACTS 'Extreme Discharges' - CHR-KHR

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