RIVERINE LARGE WOOD DISTRIBUTION IN RELATION TO FLOW REGIME IN THE WESTERN US

The cumulative volume and spatial distribution of large wood (LW) along channels and floodplains reflect interactions between rates and volumes of LW recruitment and channel transport capacity through time. We hypothesize that, in the interior western US, dryland rivers with predominantly rainfall-generated streamflow have episodic floods and debris flows that move LW onto floodplains and create longitudinally non-uniform LW distributions. The non-uniformity of LW distribution also reflects time since the last substantial flood/debris flow, because continual treefall tends to create more uniform distribution with time. In contrast, rivers dominated by snowmelt have more instream LW, with the longitudinal distribution of LW strongly influenced by channel size and transport capacity, such that transport-limited channels have more uniform LW distribution than channels in which transport can create logjams. We make specific predictions about relative volumes and spatial distribution of LW in channels and floodplains and test these predictions using three characteristics of LW data from channels in New Mexico and Colorado: the total volume of LW in the river corridor; the relative proportions of LW in the channel and floodplain; and the longitudinal distribution of LW in channel and floodplain. These data are used to develop a conceptual model of LW load through time in relation to flow regime, disturbance history, channel size, and riparian forest characteristics.