Restoring Longitudinal Connectivity of an Anthropogenically Fragmented Stream Network: The Hunter River Catchment

Abstract

Connectivity is a fundamental attribute of riverine landscapes, critical to the functioning of freshwater ecosystems. Riverine landscapes are longitudinally connected and at the drainage basin scale the network of streams provide pathways for the downstream dispersal of water, sediments, organisms and nutrients, while also connecting freshwater habitats. A multitude of anthropogenic barriers, including dams, weirs, floodgates and road crossings have disrupted connections and natural processes within stream networks. Fragmentation has compromised the integrity of, and connections within, freshwater ecosystems worldwide. Improving longitudinal connectivity through activities such as barrier removal has become a common objective of river ecosystem restoration. However, river restoration projects are commonly implemented over relatively small scales. The need for restorations to be carried out within a catchment context is increasing in prominence but the knowledge and approaches to restoring connectivity of entire stream networks remains limited. This thesis contributes to our understanding of restoring riverine connectivity within the context of drainage basins. It presents an optimisation-based approach to stream network connectivity restoration that is robust and applicable to rivers and ecosystems worldwide. This is in contrast to the majority of current approaches that are focused at-a-site and on northern hemisphere fish species. The findings of this thesis have significance to river science and management, by identifying the important regions for restoring connectivity in the Hunter River catchment. In addition, it elucidates the influence of riverine landscape character on optimally restoring stream network connectivity.