Calibrating a Riparian Vegetation Model for Sacramento River Studies

Abstract

A one-dimensional flow and sediment transport model (Sedimentation and River Hydraulics- one dimensional, SRH-1D), was expanded to incorporate and assess riparian vegetation in the flood plain. The combined flow, sediment transport, and vegetation model SRH-1DV includes a ground water and vegetation module linking ground water fluctuations (in response to river flow) and the growth and removal of vegetation to geomorphic processes of river hydraulics and sediment transport. The various components of SRH-1DV were calibrated to measured data on the Sacramento River. Modeled flow was calibrated to the water surface elevation between gaging stations, and ground water was calibrated to well data. Sediment transport was calibrated to gravel bedload measurements at the Hamilton Bridge gaging station on the Sacramento River, but ultimately sediment transport computations were not used in the simulations. Cottonwood germination, growth, and removal were simulated for the Sacramento River from RM 300 to RM 150, including Red Bluff to Colusa. Data from two field studies (2005 and 2006) of cottonwood growth on sand bars at three sites were used to calibrate the cottonwood model and improve cottonwood desiccation methods. In a second round of simulations, the Sacramento SRH-1DV model was expanded to multiple vegetation types. Cottonwood vegetation was validated using repeat vegetation mapping from 1999 and 2007, and four additional vegetation types: mixed forest, Gooding’s black willow, narrow leaf willow, and the invasive plant, arundo, were calibrated with the 1999 and 2007 vegetation mapping of the Red Bluff to Colusa Reach (RM 250 to RM 143). Based on results, the arundo vegetation type was eliminated. Narrow leaf willow and Gooding’s black willow proved to be successful indicators of riparian lands in model simulations. Model simulations of cottonwood forest and mixed forests also compared well with mapped results when combined.