Résumé
Karst areas are ubiquitous worldwide and cover 20 % of Europe land surface. Physico-chemical properties of karst rocks promote surface water / groundwater interactions and thus favor specific flood processes at the catchment scale: fast infiltration, groundwater flooding, and interbasin groundwater flows (IGF). For those reasons, karst catchments show complex hydrological responses, challenging to quantify and predict. The aim of this thesis is to define and analyze hydrological signatures of karst catchments, in order to draw a typology of their flood processes and to propose ways to improve their modeling. Hydrological signatures are indicators that allow quantifying several aspects of catchments streamflow response. This thesis includes four main chapters, written as scientific papers (two are published, one is under review, and one in preparation), and which analyze several aspects of catchments hydrological response, in order to define their hydrological signatures. The study area (total area of 25 000 km²) covers three karst regions of contrasted hydrometeorological settings in France: the Cévennes Mountains, the Jura Mountains, and Normandy. 120 gauging stations are available, providing streamflow time series of 10 years mean duration, analyzed together with rainfall data. Chapter 1 gives an overview of the state of the art of hydrological approaches used in this thesis. Chapter 2 provides information on the studied sites and data sets. Chapter 3 investigates karst influence on catchment hydrology by analyzing annual water budget (adaptation of Budyko and L’Vovich theories) performed at the river stream scale. Water budgets include IGF and highlight losing and gaining subcatchments. Chapter 4 quantifies karst influence at the storm-event timescale using several descriptors derived from hydrographs (water budget indices, characteristic times, diffusive wave inverse modeling simulations). Despite a great variability of karst influences, some specificities are highlighted, such as important IGFs and peakflow attenuation. Chapter 5, based on streamflow simulation using two rainfall-runoff lumped models (Gardénia and GR5H), investigates (i) the ability of conceptual models to help understanding catchments hydrological functioning and (ii) the benefits of karst-specific hydrological processes knowledge to improve rainfall-runoff simulation on such catchments. Chapter 6 presents a first typology of flood processes in two contrasted karst catchments, according to seasons and karst type (unary, binary). It is based on the development of a new method for analyzing concentration-discharge relationships, applied to electrical conductivity data. In chapter 7, the synthesis of these studies, performed at different space scales (year, storm-event) and time scales (catchment, river reach), allows drawing – by using hydrological signatures – regional patterns of karst hydrological processes, and discussing how models consider them. Recommendations are also made to extend the use of hydrological signatures as a tool for identifying karst-specific hydrological processes, and to better take them into account in flood modeling.