POTENTIAL FOR VEGETATION-BASED RIVER MANAGEMENT IN DRYLAND, SALINE CATCHMENTS

摘要

The approaches used to manage rivers have been developed and adapted to many different problems and settings. Because of their relatively low cost, vegetation-based approaches implemented at the reach, landholder and catchment scales have become the foundation for river management in most landscapes. In many dryland agricultural catchments, secondary (anthropogenic) salinity caused by clearing native vegetation has resulted in rising saline groundwater, streamflow salinity values that exceed seawater and severe the degradation of riparian vegetation communities. The potential effectiveness of vegetation-based strategies in these landscapes remains largely unknown, yet these strategies are still widely pursued. This study initially investigated the patterns of vegetation recovery and recolonization following a large flood in a saline river that disturbed the system. A conceptual model was developed to describe spatial patterns of where different vegetation types had regrown and recovered in relation to controls exerted by streamflow salinity, surface texture characteristics, topography and reach morphology. Using this model, vegetation-based river management options for different reaches were developed, and their potential effectiveness in stabilizing reaches was investigated using a 1-D hydraulic modelling approach. This study finds that in a dryland catchment with high stream salinity (20000-93000mgL~(-1)), there is still a strong potential for successful vegetation-based management, but only in selected reaches. Results showed that changes in stream power and channel velocity were not associated with the areas of most severe vegetation degradation. Rather, there is a complex interplay between channel morphology, channel slope and places of potential vegetation growth within a reach. This paper outlines an approach to evaluate the potential success of vegetation-based river management in saline landscapes. It identifies the need to prioritize investment based on the following: an understanding of factors controlling revegetation potential, the likely impact of revegetation in mitigating adverse channel changes and the proximity of reaches to high-value infrastructure and biodiversity assets.