Author(s): Gregory Egger; Rohan Benjankar; Linda Davis; Klaus Jorde
Keywords: Lucky Peak Dam; Boise River; Populus trichocarpa; Dynamic floodplain vegetation modelling; Succession; Recycling
Abstract: In this study we present the preliminary results of a dynamic floodplain vegetation model which was developed for a short reach of the Boise River in Idaho, USA. The river reach is heavily impacted by upstream reservoir operation, which changes the hydrological regime, and water diversions which reduce flows. The model is based on a combination of results from hydrodynamic modelling combined with a digital elevation model of the floodplain. After an initial vegetation pattern is established based on elevation above mean water level, the rule based dynamic vegetation model simulates in yearly time steps succession if no disturbance occurs or retrogression if disturbance occurs through excessive shear stress. The model is calibrated based on comparison with existing floodplain vegetation. The model was then used to simulate a long time period from 1855 to 2005 starting with natural hydrologic conditions followed by a period with water diversions and reservoir operation. For a comparison, the model is also run without the influence of the diversions and reservoirs to see what types of floodplain vegetation were to be expected today if those impacts did not exist. The results show quantitatively, how early vegetation stages, such as bare gravel bars and pioneer vegetation, is lost to large extents, as well as young transition stages, whereas more mature stages gain larger areas.