Investigating the spatial variability of hillslope flow velocities in the Width-Function

The width function (WF), measuring the number of channel links or the portion of contributing area at the same hydrologic distance (i.e. the distance measured along the downhill flow path) to the outlet, is an important river basin and stream network parameter for hydrogeomorphic applications. The rescaled WF, obtained weighting the hydrologic travel distances with the corresponding surface flow velocity, is commonly used in the so-called WF-based Instantaneous Unit Hydrograph or simply WFIUH. The basic assumption of assigning two different constant flow velocities respectively to the hillslope and to channel network has already proven to improve the ability of the WFIUH in characterizing the runoff timing formation and the behaviour of the river basin hydrologic response. Nevertheless, a complete spatially variability of hydraulic conditions at the river basin scale has never been broadly investigated. Aim of this work is to investigate the impact of WF rescaled using a fully spatially distributed field of flow velocities as related to the different terrain morphologic (slope) and land cover properties(vegetation, soil type)