Boundaries, Junctions and Hydraulic Structures

Boundaries

At upstream boundaries the user must specify the sediment inflow as rate against time, concentration against time or concentration against flow rate. The bed elevation is free to move at both the upstream and downstream boundaries (this includes the nodes immediately upstream and downstream of junctions and structures such as cross regulators). This requires a special implementation of equation (2)) at the upstream boundary nodes and at the nodes immediately downstream of structures and junctions. At these locations, position index k-1 does not exist, so the change in cross section area is set equal to the change at location k+1. The change in cross section does not directly relate to any change in Gand there is no length of river upstream to convert the change in area to a change in volume. Therefore, these section changes at upstream boundaries are not recorded as a deposition/erosion volume in the output.

Junctions

At junctions the sediment outflow is equal to the sum of the sediment inflows (mass is conserved). All inflow node sediment transport rates are determined before the outflow nodes are calculated. If there is more than one outflow node then the concentrations at all outflows are assumed equal.

Hydraulic Structures

All hydraulic structures are considered simply as two-noded junctions and thus the outflow sediment transport rate equals the inflow sediment transport rate.