During the reporting period, the project successfully executed its core technical programme, delivering major empirical datasets, analytical advances, and modelling frameworks underpinning Objectives O1–O3. Extensive field campaigns in Australia and Tanzania established high‑resolution hydrological and sediment monitoring networks, providing the empirical foundation for sediment‐budget development, tracer analysis, and model construction.
Objective O1 – Quantifying temporal dynamics of fine sediment and phosphorus transport is largely achieved. More than two years of near‑continuous measurements of discharge, suspended sediment concentration, particle size, and phosphorus dynamics were collected across gully, riverine, and catchment outlets. These high‑frequency datasets enabled reconstruction of storm‑event sediment behaviour, hysteresis patterns, seasonal dynamics, and long‑term sediment fluxes. Integration into catchment‑scale sediment budgets (Bonnie Doon and Albert River) revealed pronounced nonlinear sediment responses during extreme events, early evidence of geomorphic regime shifts, and strong linkages between hydrology, sediment connectivity, and catchment condition. Remaining work focuses on final budget synthesis and publication.
Objective O2 – Determining dominant sediment sources and erosion processes is also largely achieved. Extensive laboratory analyses, including sequential extractions, ICP‑MS, CSSIA, and synchrotron spectroscopy (MEXAS), produced a novel tracer suite capable of discriminating between surface soils, subsurface sources, alluvial banks, gullies, and distal hillslopes in deeply weathered tropical soils. These tracers were validated using artificial mixtures and applied to both integrated sediment budgets and event‑scale samples. Results demonstrate shifting sediment sources and strong source hysteresis during extreme floods, with alluvial and gully erosion dominating sediment supply in tropical savannah catchments. Tracer datasets are now fully integrated with sediment budgets, with multiple manuscripts in advanced preparation.
Objective O3 – Modelling remediation efficacy under future climatic conditions has been successfully initiated. A novel SWAT+Gully modelling architecture, adapted from the OPTAIN workflow, was designed to explicitly represent gullies as functional hydrological response units with dynamic sediment routing and connectivity. Historic and contemporary gully datasets, geospatial inputs, hydrological time series, and tracer‑derived source data have been compiled and prepared for calibration and scenario analysis. While process implementation and calibration are scheduled for the next phase, the modelling framework and data foundations are firmly established.
Across work packages, the project delivered: (i) fully operational monitoring networks in Australia and Tanzania; (ii) high‑quality, high‑frequency sediment and hydrological datasets; (iii) validated novel sediment tracers; (iv) near‑complete sediment budgets; and (v) a new, connectivity‑explicit modelling framework. Collectively, these outputs represent substantial technical progress toward all scientific objectives and provide a robust platform for final synthesis, modelling, and publication in the concluding project phase.
