Flow and flow routing in upland channel networks / L'écoulement et le calcul du cheminement de l'écoulement dans les réseaux des canaux montagneux

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Abstract
This paper is based on the premise that the distribution of discharge source areas in relation to the channel network may have a significant effect on the form of the basin hydrograph, and that, in consequence, it is of value to investigate routing models for application to the channel networks of upland catchments. The channels of such networks are generally small, steep and rough with complex flow through a sequence of pools and riffles or rapids. The gulp dilution gauging method provides a useful technique for investigating the bulk properties of flow over complete channel reaches. At least for low to medium flows it is shown that average flow velocities increase nonlinearly both downstream and with increasing discharge, in a manner that is not compatible with traditional analysis in terms of uniform flow equations. The dilution gauging measurements may be used to provide parameters for a nonlinear kinematic routing model. The model is applied to channel networks of two small British basins (≃8 km2) and the response to different hydrograph magnitudes is explored. The model provides a suitable compromise between the requirements of simplicity and the inclusion of the nonlinearity in channel response, but, at the scale of application, the model parameter values derived from the field measurements may overestimate velocities at high discharges.