Using In Situ Monitoring to Assess How Flood Intensity Can Be Inferred From Lake Sedimentary Archives (Kamech, Tunisia)
Abstract
Understanding the frequency and magnitude of extreme hydrological events is crucial for assessing flood risk. However, long‐term monitoring data are lacking to better capture flood variability with past and present climate changes; thus, sedimentary archives are needed to extend such data back in time. In this study, we use lacustrine sediment archives from the Kamech reservoir (Cap Bon, Tunisia), located at the outlet of a semiarid rural catchment characterised by intermittent streamflow and severe erosion. The catchment has been instrumentally monitored since the dam reservoir was built in 1994 at its outlet. Monitoring includes high‐resolution measurements of rainfall and stream flow since 1994, and of sediment flux since 2006. Here, the main objective is to compare sedimentary records with in situ hydro‐erosive measurements to assess how well sedimentary deposits can be used to estimate the streamflow and erosive intensity of past floods. In 2022, sediment cores up to 3 m deep were collected from the reservoir, capturing the full post‐construction infill history since 1994. The sediment sequence is varved allowing for annual to sub‐annual resolution. Using a combination of sedimentological (grain size, hyperspectral imaging) and geochemical (XRF core scanning) analyses, along with short‐lived radionuclide dating, we identified 35 distinct flood layers corresponding to major events over the past 24 years. We demonstrate that the thickness of flood layers is closely correlated with the sediment flux measured in the catchment. Furthermore, we show that the maximum grain size ( D 90 ) in flood layers is strongly correlated with the maximum 30 min flood discharge ( Q 30max ) and daily precipitation amounts. Our results highlight the potential of lake sediments to quantitatively reconstruct flood intensity chronicles, complementing modern monitoring in the critical zone and helping to assess the long‐term impact of climate variability on flood and erosion regimes.