The influence of river sensitivity and sediment connectivity on geomorphic response and effectiveness in the Lockyer Valley, SEQ

The sensitivity of river channels to geomorphic adjustment and the dynamics of sediment connectivity along channel networks are key controls on the ability of a geomorphic system to respond to flood events. In turn, the cumulative impact of geomorphic responses to successive floods determines the geomorphic effectiveness of any flood event. River sensitivity and sediment connectivity can change significantly over space and time. Corre spondingly, the ability of a geomorphic system to respond is also variable so that geomorphic effectiveness is not definitively characterized by a static relationship between event magnitude and geomorphic response, but rather is a dynamic comparison betwe en geomorphic response and an actively changing capacity for geomorphic adjustment. Herein, this thesis presents a characterization of river sensitivity and sediment connectivity for the Lockyer Valley, Queensland, Australia. Sensitivity and connectivity d atasets are used to establish expectation s of geomorphic channel behavio r and are linked to concomitant geomorphic factors (i.e. geomorphic thresholds, self - organization, geomorphic recovery, and geomorphic effectiveness). The data chapters in this thesis detail a history of geomorphic channel adjustment along Lockyer Creek and its tributaries and provides a method for analysing the nature of coarse sediment (dis)connectivity within the catchment. This research shows that the sensitivity to, and capacity fo r, geomorphic adjustment varies significantly with channel morphology and valley position. Additionally, the nature of bedload sediment connectivity changes with the distribution of geomorphic landforms and channel barriers that can impede sediment transfe rence through the system. In the Lockyer Valley, this variability in river sensitivity and sediment connectivity influences the severity, distribution, and form of geomorphic adjustments that occur in response to sporadic, and sometimes catastrophic, flood events. Therefore, river management philosophies that incorporate concepts of river sensitivity and sediment connectivity are better suited to predict and i nterpret future channel behavio r. Ultimately, the geomorphic effectiveness of flood events in the L ockyer Valley can only be determined by comparing geomorphic responses with the ability of this geomorphic system to respond.