Fine sediment production during urban development: the damage is done early!

Sediment production is often intensified in peri-urban areas, due to the transition from predominantly rural to urbanized landscapes. Although sediment dynamics in urbanizing areas remain complex and poorly understood, urban development can generate significant fine sediment, emphasizing the importance of monitoring the impacts of each stage of urban development. We monitored suspended solids concentration and loads in six stormwater drainage systems with small, street-scale catchments for 6 months using low-cost automatic monitoring stations in southeast Australia. The study was conducted in a peri-urban area undergoing urbanization, where different stages of urban development were observed, ranging from bulk earthworks and road construction to fully urbanized sites. The results showed that during urbanization, event mean suspended solids concentrations commonly exceed 5 g/L (~100× more than fully urbanized sites). Suspended solids yields (SSY) in early-stage urbanization areas can be up to 30 times higher than in fully developed areas. The median particle size of sediments in early development stages was up to six times finer than those in the later development stages. The results highlight that early urbanization stages contribute significantly to fine sediment production, presenting a high risk to sensitive water bodies. The findings highlight the value of combining innovative IoT (Internet of Things) monitoring technologies, with geospatial and time series analysis to better understand sediment dynamics in a complex and rapidly urbanizing landscape. Additionally, the findings underscore that erosion and sediment control measures are vital, particularly during the early stages of urbanization, requiring proactive management throughout this process to mitigate fine sediment impacts and protect downstream waterbodies.