Platte River Resource Linkages Sediment-Vegetation Model

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Vegetation growth rates are determined by specie;s, season, and age. • Cottonwoods and Willows can germinate during June and July. • Prairie Cordgrass and spike rush can gernunate during the peaiod Mazch through October. Depending on species, vegetation root growth can be limited by the water table elevation. Vegetation scour is deternvned by•the sediment transport rate. • The potential for vegetation scour increases with the sediment transport rate. • Vegetation scour will not be possible unless it occurs when the plants aze young. Vegetaxion drowning is determined by the species and duration of inundation. • Depending on species, death by drowning may take two to tvvelve months. • Spike rush cannot be killed by drowning. Vegetation desiccation (death by drought) is deternuned by the species and duration of drought. • Depending on species, desiccation may take one to two years. • Prairie cordgrass and willows cannot be killed by drought. MODEL ASSUMP'rIONS The river hydraulics (width, depth, and velocity) at a given cross section are independent of the hydraulics at the next downstream or upstream cross section (normal depth equation). The chosen sediment transport equation is accurate. The indicator species for vegetation are representative of the Platte River community. Vegeration growth rates are accurate. Vegetation removal (scour, drowning, or drought) criteria are accurately defined. Habitat characteristic criteria aze accurate. MODEL VERIFICATION Replication of three historic periods • Pre-development period (before 1930) • Transition period (1930-1970) • Current conditions (1970-1990) 4