Estimation of synthetic flood design hydrographs using a distributedrainfall–runoff model coupled with a copula-based single stormrainfall generator

In this paper a procedure to derive synthetic flooddesign hydrographs (SFDH) using a bivariate representationof rainfall forcing (rainfall duration and intensity) via copulas,which describes and models the correlation between twovariables independently of the marginal laws involved, coupledwith a distributed rainfall–runoff model, is presented.Rainfall–runoff modelling (R–R modelling) for estimatingthe hydrological response at the outlet of a catchment wasperformed by using a conceptual fully distributed procedurebased on the Soil Conservation Service – Curve Numbermethod as an excess rainfall model and on a distributed unithydrograph with climatic dependencies for the flow routing.Travel time computation, based on the distributed unit hydrographdefinition, was performed by implementing a procedurebased on flow paths, determined from a digital elevationmodel (DEM) and roughness parameters obtained fromdistributed geographical information. In order to estimate theprimary return period of the SFDH, which provides the probabilityof occurrence of a hydrograph flood, peaks and flowvolumes obtained through R–R modelling were treated statisticallyusing copulas. Finally, the shapes of hydrographshave been generated on the basis of historically significantflood events, via cluster analysis.An application of the procedure described above has beencarried out and results presented for the case study of theImera catchment in Sicily, Italy.