Assessing the Long-Term Production of Suspended Sediment and the Climate Changes Impact on Its Deposition in Artificial Lakes—A Case Study of Lake Trakošćan, Croatia

A prevalent engineering task in practice is calculating the annual balance of sediments on some watercourses. This is particularly challenging when assessing the backfilling of river reservoirs that have a multifunctional purpose. Trakošćan Lake was built in the period from 1850 to 1862 as a pond and landscape addition to the park and Trakošćan castle. After 60 years, the lake was drained in 2022, and the work began on sediment excavation to improve the lake’s ecological condition due to about 200,000 cubic meters of deposited silt in the lake. In this research, the annual sediment production is calculated for the long-term period 1961–2020, based on empirical parametric methods (Fleming, Brunne). The results are compared with results from previous projects and recent sediment deposit investigations. Since there are no changes in LC/LU on this natural catchment, the decreasing trends in long-term sediment transport were compared with meteorological values, daily rainfall, and snow days. It is concluded that the intensity characteristics of the rainfall should be investigated more in detail and could provide much more tangible information regarding climate change impacts. Some targets for future monitoring design and research techniques are set.