Articles | Volume 373
12 May 2016
 | 12 May 2016

Spatially-smooth regionalization of flow duration curves in non-pristine basins

Daniele Ganora, Francesco Laio, Alessandro Masoero, and Pierluigi Claps

Abstract. The flow duration curve (FDC) is a fundamental signature of the hydrological cycle to support water management strategies. Despite many studies on this topic, its estimation in ungauged basins is still a relevant issue as the FDC is controlled by different types of processes at different time-space scales, thus resulting quite sensitive to the specific case study.

In this work, a regional spatially-smooth procedure to evaluate the annual FDC in ungauged basins is proposed, based on the estimation of the L-moments (mean, L-CV and L-skewness) through regression models valid for the whole case study area. In this approach, homogeneous regions are no longer required and the L-moments are allowed to continuously vary along the river network, thus providing a final FDC smoothly evolving for different locations on the river. Regressions are based on a set of topographic, climatic, land use and vegetation descriptors at the basin scale. Moreover, the model ensures that the mean annual runoff is preserved at the river confluences, i.e. the sum of annual flows of the upstream reaches is equal to the predicted annual downstream flow.

The proposed model is adapted to incorporate different "sub-models" to account for local information within the regional framework, where man-induced alterations are known, as common in non-pristine catchments. In particular, we propose a module to consider the impact of existing/designed water withdrawals on the L-moments of the FDC.

The procedure has been applied to a dataset of daily observation of about 120 gauged basins on the upper Po river basin in North-Western Italy.

Short summary
The flow duration curve is a widely used tool to support water resources management, planning of hydropower plants and many other problems in hydrological engineering. This paper describe a procedure to estimate the flow duration curve in river sections where no data are available by exploiting observations from other gauged river basins. The procedure also allows one to include information about existing water intakes that alter the natural flow in the river.