Abstract

The Claps Lake near Luc-en-Diois is a naturally dammed palaeo-lake fed by the Drôme River sediment load during the Little Ice Age (LIA). The present assessment is based on a valley reconstruction using a geomorphic model. It illustrates the potentiality and limits of the geomorphic analysis to accurately predict the buried topography. This method indeed may help to reduce the prospecting work required in classical evaluations of fill volumes of such natural dams.

The lake was rapidly filled with sediments, indicating enhanced erosion of the watershed during the LIA. Several studies have attempted to quantify the volume of the lake fill and use it to assess erosion rates during the LIA. Very little is known, however, about the geometry of the buried valley. Estimated lake volumes and erosion rates vary depending on how the buried valley is reconstructed and what correcting factors are used for calculating erosion rates.

The present assessment is based on a valley reconstruction using a geomorphic model calibrated by the surrounding drainage network, as well as the introduction of correcting factors that improve the corrections applied in the previous works.

The resulting lake volume is 71–81.106 m3, and the mean erosion rate at 0.7-1.2 mm.yr-1, a high value compared to previous estimates. This rate is compared to the results obtained by various methods and over different timescales in the surrounding region.

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