Deriving a practical analytical-probabilistic method to size flood routing reservoirs

• An analytical-probabilistic method to sizing routing reservoirs is developed.
• Improvements in the routing hydraulics are implemented.
• Assessments from alternative approaches are compared with reference to a test case.
• The proposed method reliability is supported by continuous simulations.
• Traditional design storm approach validity is discussed.

In the engineering practice routing reservoir sizing is commonly performed by using the design storm method, although its effectiveness has been debated for a long time. Conversely, continuous simulations and direct statistical analyses of recorded hydrographs are considered more reliable and comprehensive, but are indeed complex or seldom practicable. In this paper a handier tool is provided by the analytical-probabilistic approach to construct probability functions of peak discharges issuing from natural watersheds or routed through on-line and off-line reservoirs. A simplified routing scheme and a rainfall-runoff model based on a few essential hydrological parameters were implemented. To validate the proposed design methodology, on-line and off-line routing reservoirs were firstly sized by means of a conventional design storm method for a test watershed located in northern Italy. Their routing efficiencies were then estimated by both analytical-probabilistic models and benchmarking continuous simulations. Bearing in mind practical design purposes, adopted models evidenced a satisfactory consistency.

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