We report a new methodology to estimate the impact of extreme events on sediment transport in rivers. Our approach relies on two complementary instruments developed and tested during a 1.5 years field survey performed from june 2007 to january 2009 on the Capesterre river located on Basse-Terre island (Guadeloupe archipelago, Lesser Antilles Arc). The first one, CAPMES, performs real-time in-situ measurements of the water stage together with the concentration and the average grain size of suspended silts and sand particles. The second one, DRELIO, acquires high resolution stereophotogrammetric images of river beds used to compute DEMs and to estimage how flash floods impact the granulometry and the morphology of the river. The combined use of these two instruments provides a platform of investigation of the erosive impact of extreme events in rivers exposed to the risk of flash floods. This platform can be used for either field campaigns of limited duration or long-term surveys of riverine sediment transport.