Thanos Papanicolaou
IIHR - Hydroscience & Engineering, The University of Iowa

Modeling mountain streams:  Modeling of sediment transport in mountain streams remains a challenge due to the lack of understanding of the interrelationship between sediment and flowing water.  At present there is no general theory on the subject.  Mountain streams have steep slopes greater than 0.1 percent beds comprised of sand through boulder sized particles, low relative submergence, and large seasonal flow variability.  The proposed model, Steep Stream Sediment Transport (3ST1D) is a 1-D model that consists of a hydrodynamic component and a sediment transport component.  The hydrodynamic portion calculates depth and average velocity in subcritical, critical, and supercritical flows.  The sediment transport section deals with the flow-bed interaction including the non-uniform nature of bed materials, the high flow resistance, turbulent structures, and the role of bursting events.  The code can update the bed characteristics including the surface material composition and elevation.  The proposed model predicts sediment entrainment for slopes up to 10 %.  3ST1D is a 3-layer model: the top layer refers to the flow region where sediment is moved downstream, the intermediate one is an active layer where sediment is exchanged between the bed and the flow, and the bottom one is a parent layer that supplies sediment to the active layer.  Data collected from steep flume experiments has been employed to validate the performance of the model.  The model predicts transport rates within 40 % of the actual value.  The bed surface evolution follows the same trend as the experimental data.