Study — Global hydrological study of the Moselle Basin

The watershed of the French Moselle is managed by multiple partners. The Grand Est Region having taken the competence “facilitation and consultation in the field of water” since June 2018, this is what led the regional community to carry out this study, in partnership with the Syndicat Mixed Moselle downstream. This study is funded by the State under the Fund for the Protection of Major Natural Hazards (FPRNM), the Rhine Meuse Water Agency and the Greater East Region. The purpose of the study: Synthesise existing hydrological data during flood and low-water periods on the watershed; \- Update and/or determine the characteristic flow rates for floods and lows. A common methodology allows the modelling of flood flows (for 38 stations) and low (for 19 stations), and to return the data to the territory. For flood flows: Estimate of flow rates Q2 (raw having a chance of occurring annually), Q5, Q10 and Q30 based on observations and statistical laws; Use of hydrometeorological methods for flow rates Q50, Q100 and Q1000; \- Characterisation for each station of flood hydrograms. Deviations in flood estimates from previous studies: \- For tributaries of the upstream Moselle: estimates of centennial flow above previous studies by 15 to 26 %. For many related to the methodology used: GradeX instead of Gumbel’s law; \- For the upstream Moselle: estimate close to bibliographic values (maximum deviation of 8 %); \- For the Murthe and its tributaries: consistent results; \- For the downstream Moselle: estimate close to the AZI study, except the Custines station where the estimate is approximately 10 % higher for the longer periods. The lowlands, an issue for the territory: \- Calculation of QMNA monthly flow rates for return periods of 5 years, 10 years and 20 years; \- Calculation of the minimum flow rates over 10 consecutive days (VCN10) and 3 days (VCN3). Impacts of climate change on flow rates: Taking into account climatic projections (4.5 IPSL and 8.5 CNRM) for precipitation and temperatures; Application of the methods used with these chronicles and estimation of flows in 2030 and 2050; \- Upward trend of average flow rates; \- Downward trend of QMNA5 on the upstream Meurthe, upward trend on the rest; \- Results to be compared with the MOSHAR21 study and the regional quantitative study that provided a different vision; \- Strong uncertainties related to climate projections related to rain.