Extreme event (T> 100 a) for plant safety and flood protection
Description
The extreme values of precipitation with a return time T greater than 100 years for the design of water management systems for flood protection represent an extrapolation of the data of the “coordinated heavy precipitation regionalisation and evaluation” published on 1.1.2023 by the German Weather Service (KOSTRA-DWD 2020).
KOSTRA-DWD 2020 provides precipitation heights depending on a precipitation duration D = 5 minutes to D = 7 days and a return time (annual) T = 1 year to T = 100 years as grid in a resolution of 5x5 km for all Germany. However, the water management design practice in the field of flood protection on surface waters also requires recurrence times of precipitation of more than 100 years. Especially for the consideration of flood assessment cases BHQ1 and BHQ2 for dams according to DIN19700, these precipitation annuals are required.
Due to the so-called heavy tail behavior of the selected 3-parametre Generalised Extreme Value Distribution (GEV) for KOSTRA-DWD 2020, direct extrapolation of the GEV to estimate precipitation levels for recurrence periods exceeding 100 years is not recommended. Interim, until the “practice-relevant extreme values of precipitation” (PEN) of the Federal Government/Länder-Arbeitsgemeinschaft Wasser (LAWA) have been adapted and published to the new basis KOSTRA-DWD 2020, special extrapolated extreme values of precipitation are made available for Baden-Württemberg. The use is recommended according to the work aid for DIN 19700 for flood retention basins in Baden-Württemberg (https://pd.lubw.de/93810). Extrapolation includes the provision of recurrence times T = 200, 500, 1,000, 2,000, 5,000 and 10,000 years over the duration levels according to KOSTRA-DWD 2020.
The estimation of precipitation heights with a return time greater than 100 years is based on an adjustment of the parameters u(D) and w(D) of the KOSTRA-DWD-2010 base equation hN(D,T) = u(D) + w(D)· ln(T), which has been used for previous extrapolation of precipitation for annualities exceeding 100 years in Baden-Württemberg. The two parameters are adjusted to the KOSTRA-DWD 2020 precipitation levels of the recurrence times T=1 year and T=100 years per continuous stage. The calculations of a return time greater than 100 years, estimated according to this methodology, shall be checked for plausibility as well as the flow lines modeled therefrom.
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