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A special version of the SRH-1D model was created to simulate the establishment and growth or mortality of riparian vegetation in addition to the simulation of river hydraulics, sediment transport, and erosion or deposition (Murphy et al., 2001). The vegetation components of this model are described in this section of the report. This model is primarily based on a one-dimensional representation of river hydraulics and sediment transport and uses a series of cross sections to define the morphology of the river channel. The flow and sediment transport are distributed laterally across each section based on the local conveyance properties.

The model simulates the processes of seedling growth and mortality as a function of species type, changing river stage and groundwater level, the rate of root growth, and the potential for scour velocity.

The model assumes that the river has an abundant seed source. During the seed dispersal and germination season, the model assumes that seeds will germinate and begin to grow at all points above the wetted channel that are free of existing vegetation. The model then applies a species dependent growth rate to the plant roots and stem and tracks the root depth in relation to the groundwater level. If root growth can keep pace with a falling capillary fringe due to groundwater lowering, then the model assumes the plant can continue to grow. Otherwise, the model assumes the plant will die from desiccation.

The model also tracks the potential for plant mortality due to drowning, velocity scour, and burial. In the model, a seedling is initially very vulnerable to mortality, but as it continues to grow, the plant becomes more resistant to the plant stresses induced by desiccation, drowning or burial and it increases the local hydraulic roughness of the channel. If a cottonwood seedling survives to an age of three years, the cottonwood tree then becomes very resistant to removal by scouring erosion.

Presently, the model does not consider the effects of species competition. The model assumes that seedling vegetation begins to establish above the water level and on ground free of existing vegetation.

The model does not consider the aging process of vegetation and that cottonwood trees or willows will, in the future become less resistant to destruction by river erosion or wind damage, and will eventually succumb to age or disease.

The primary use of the model output is to evaluate the effects of alternate management scenarios that result in different hydrology or land management practices.

SRH-1DV is currently a research model and unavailable for general release. Contact Tim Randle for availability and more information.