The cost-benefit of working with recovery in river management

<p dir="ltr">With the impact and cost of continued river degradation and extreme rainfall and floods associated with climate change, there is growing urgency to achieve and maintain good river health to meet global sustainable development goals. Limited resources and competing interests mean it is critical that river managers make cost-effective and environmentally sustainable conservation and rehabilitation decisions. This thesis investigates the identification, prioritisation, and valuation of sections of river for rehabilitation using a working with recovery approach. The thesis begins by systematically analysing where corridors of river recovery could be created via conservation or rehabilitation, in areas where fragmentation has occurred, for NSW coastal catchments, using the NSW River Styles database. Reach connections, defined as upstream-to-downstream sections of river connected end-to-end, and loci connections, defined as more isolated sections of river from which recovery can be seeded and extended into adjacent reaches, are identified for rehabilitation prioritisation. Combined with local on-ground knowledge, this provides practitioners with a user-friendly distillation of where to focus river conservation and rehabilitation activities, forming an important input to evidence-based prioritisation and decision-making. From this analysis a simplified GIS workflow was created, providing non-technical GIS users in river management with the ability to obtain information quickly and efficiently from the database to assist in catchment-scale rehabilitation prioritisation. The thesis then explores the critical need to up-scale and work with nature-based solutions at regional, catchment and riparian corridor scales. The thesis estimates geomorphologically informed rehabilitation costs for all NSW coastal catchments. Marxan, an extensively used conservation planning tool, is then applied in a novel manner to undertake the first cost-benefit analysis for geomorphologically informed rehabilitation of river systems, using selected NSW coastal catchments and subcatchments as a case study. Scenarios are based on three broad approaches to river management: <i>ad hoc</i> and <i>reactive</i>, <i>working with recovery</i> and <i>corridors</i>, across both current and future time periods. This analysis reveals considerable current and flow-on future financial and non-financial benefits, and lower initial total and per-hectare rehabilitation costs, by fully adopting <i>working with recovery</i> or <i>corridors </i>approaches and transitioning from <i>ad hoc</i> and <i>reactive </i>approaches that dominate current practice. Implementing targeted rehabilitation based on a rolling sequence of corridors scenarios over time provides optimal holistic solutions to enhance geomorphic condition and recovery potential at landscape-scale. The analysis demonstrates Marxan’s suitability as an accessible tool to address prioritisation complexity, run and cost landscape-scale rehabilitation scenarios over time, and reveal the positive offsite feedbacks that occur through multiplier effects, as recovery occurs, and corridors are built. Accordingly, geomorphologically informed decision-making becomes more robust, transparent, cost-effective, consistent across catchments, and adaptive to local situations and evolving river management priorities. This thesis concludes with a discussion of riparian corridor valuation as year-on-year measurable assets included in natural capital accounting. It investigates apparent gaps in current ecosystems classifications that prevent river managers and interested stakeholders from monitoring rehabilitation progress, and quantifying riparian corridor valuation, over time. This thesis serves the development of river management practice in identification, prioritisation, and valuation of rehabilitation strategies to achieve more sustainable environmental outcomes.</p>