Warning: Use Equilibrium Load with Caution
Like the Normal Depth downstream flow condition, the equilibrium load sediment boundary condition is popular because it is easy. It avoids difficult and data intensive preprocessing involved in developing a sediment rating curve or a sediment time series. However, the equilibrium load sediment boundary is often insufficient. Most sediment models are commissioned because the modeled reach is either depositing or eroding, departing from equilibrium by definition. Additionally, the equilibrium boundary condition is extremely sensitive to the bed gradation at the upstream cross section and the selected transport function, which can easily distort it by orders of magnitude. Even without data, users are often better off specifying a speculative rating curve and then calibrating it to observed bed change. When the equilibrium load boundary condition is used, assign it to a cross section well upstream of the area of interest, in a reach know to be in dynamic equilibrium.
