Groundwater–Surface Water Interaction: Process Understanding, Conceptualization and Modelling (Proceedings of Symposium HS1002 at IUGG2007, Perugia, July 2007). IAHS Publ. 321, 2008, 124-133.

Effect of a nonlinear runoff response on flood statistical properties: the case of a tile-drained watershed

B. Augeard, Y. Nédélec, F. Birgand, C. Chaumont, P. Ansart & C. Kao

UR Cemagref “Hydrosystèmes et Bioprocédés”, BP 44, 92163 Antony cedex, France

benedicte.augeard@cemagref.fr

Abstract The present work aims at better understanding the effect of hydraulic processes on flood generation in artificially drained areas by considering the threshold behaviour of this particular pipe flow response. The study treats three extreme hydrological processes occurring during peak flows in a subsurface drained watershed: (i) the occurrence of surface runoff; (ii) the occurrence of full section discharge; and (iii) the submersion of the collector outlet. Plot-scale experiment and modelling of drainage discharge measurements at the outlets of three drainage networks provide information to identify flow rate thresholds corresponding to peak flow processes. These thresholds were also observed at the watershed scale in the peak flow distribution curve. For a return time from 1.5 to 20 years, the water retentions due to surface runoff accumulation at the soil surface and limitation in the pipe flows lead to a decrease in the slope of the distribution. However, for highest discharge, the strong increase in the slope of the statistical curve might be related to the connection of surface runoff accumulations to the main ditch, allowing a direct contribution to the peak flow.

Key words subsurface drainage; peak flow; flood distribution; nonlinear response