Distributed water level sensors for hydrological network monitoring
Suivi des réseaux hydrographiques à l'aide d'un réseau de capteurs de niveau d'eau
Résumé
In this study we considered that hydrological network is a central feature of the catchment. We assumed that hydrological regime depends on the activation and expansion of the drainage network witch controls flow lengths. The degree of drainage network expansion is not uniform in volume and timing. This spatial knowledge is essential to understand catchments behaviours conditioned at fine scale level by the connectivity between hillslope and channels. To efficiently achieve this monitoring, numerous, low cost and easy adaptable sensors have to be promoted with a specific sampling strategy. An experimental distributed water level sensor network was carried out in the temporary hydrological network of the Mercier catchment (7 km²) located near Lyon (France). This study site is one of the headwater research catchments of the Yzeron watershed (142 km²). Land use is principally composed of pasture, crops and some urbanized areas in the downstream part with a couple of road side ditches connected to the streams. Forest is concentrated on steepest hillslopes in the upper part. The catchment is located in small metamorphic mountains where infiltration and subsurface flow predominate during most rainfall events. Saturation excess runoff is the major process contributing to channel network. The device consisted of 18 sensors set up since 2008 in nested locations from high order streams to the outlet. The data logger recorded water levels directly by measurements of an electric capacity. By means of 4 rain gauges located in the catchment, rainfall events were selected with a reasonable spatial heterogeneity in volume, intensity and duration. Resultant pattern highlighted over all the attenuated response of the upstream channels to some filling degree of local storages and capacities. Differences were pointed out between upstream sub-catchments responses and breaks in propagation and discharges toward downstream channels were precisely located. For most of rainfall events the downstream part of the channel network controlled most of the quick flow response recorded at the outlet. Channel network expansion to upstream locations depended on rainfall threshold and antecedent condition expressed by the base flow. Upstream contribution became significant during only some consequent rainfall events, around 5 to 10 by year. Data recorded provided spatial representation of flow initiation and propagation improving the understanding of the Mercier catchment in the purpose of distributed hydrological modelling.