LONGITUDINAL VARIABILITY OF CHANNEL RESPONSE TO FLOODS

Channel morphodynamic response to a flood occurs within the context the relative magnitude of erosive and resisting forces along with sediment transport capacity and supply, all of which manifest at multiple scales. Relating channel response to floods with reach-scale metrics such as flood stream power and channel confinement can be confounded if, for example, upstream conditions influence downstream response. We relate longitudinal variations of channel widening and reach-scale sediment balance to longitudinal variations of stream power and channel confinement for selected rivers impacted by the 2013 Colorado Front Range floods. These rivers transition from steep and relatively confined in the canyons of the foothills to less steep and unconfined on the high plains. Though the unconfined reaches tend to have lower values of stream power relative to confined reaches, they tend to exhibit great geomorphic responses due to a reduction in stream power from upstream. A concomitant aggradational response (channel braiding and avulsion) with loss of sediment transport capacity is observed. Lags between upstream stream power and downstream channel response are observed, the length of which vary by river. These findings indicate that longitudinal decreases in stream power played an important role in channel response to the 2013 Front Range Floods and highlight areas of high geomorphic flood hazard within these transitions.