The morphological river evolution at long-time (centuries and even millennia) and large spatial scale (watersheds of several square kilometres) can be described by means of simplified 1D models, able to simulate the variation of bed elevation and grain size composition at non-detailed scales, involving a reduced computational effort. The erosion and deposition phenomena acting along rivers can be modeled by a simplified approach based on the Local Uniform Flow hypothesis and on the instantaneous propagation of the water flow. Such an approach computes the sediment yield of large watersheds at long-time scale relatively quickly, taking into account the non-sorted granulometry of river systems. In the paper, a 1D simplified model is described and applied to the Adige River (Italy), in order to study the morphological evolution of the watercourse after a redesign of some cross sections in its lowland part. Local variations of river altimetry propagate downstream and upstream, in relation to the Froude number and to the changes magnitude. The results highlight the reliability of the code to simulate the long-term effects of human works in rivers at non-detailed scale. In addition, the outcomes of 1D simulation can be used as input data for detailed models (2D or 3D) to study local changes at shorter time scale.