Can tree tilting be used for paleoflood discharge estimations?

• We hypothesis tilted by floods trees provide information about flood magnitude.
• A root-plate rotational stiffness model is proposed and applied in three gauge rivers.
• The model evidence a correlation between the inclination of trees and flood magnitude.
• Source of uncertainties are defined and quantified.
• Results can be used as censored-data in paleodischarge estimation.

SummaryPaleoflood hydrology typically deals with the reconstruction of floods in ungauged and poorly gauged basins by combining different sources of indirect evidence. Botanical indicators have been used repeatedly in the past, mostly through the study of scars in trees or germination dates of plants on newly created surfaces. In this paper we test the hypothesis that the inclination of trees – as induced by floods – can provide information on flood magnitude, and that this source of information can therefore be used for flood reconstructions. We used a mechanical root-plate rotational stiffness model in three gauged river reaches in Central Spain to test our hypothesis and combine approaches typically applied in dendrogeomorphic, dendrometric, mechanical structure, and hydraulic research. Results show a correlation between modeled and observed deformation at the stem base of trees induced by floods (coefficient of correlation 0.58 for all observations). However they also point to a clear underestimation of peak discharge reconstructions. We used different efficiency criteria to test the reliability of results and differences between river reaches. In addition, we carried out a sensitivity analysis and discussed sources of uncertainties which may reach up to 112%, mainly due to difficulties to determine the rotational stiffness of the root plate system a posteriori. The approach presented here is promising, but more research is clearly required to improve the quality of peak discharge estimations based on stem tilting.