Bedload transport in the instrumented catchment of the Rio Cordon, Part II: Analysis of bedload rate.

Sediment transport is monitored by a specially designed instrumentation installed on a steep mountain streams (the Rio Cordon). The variability of bedload rate and yield reflects the variability in flow discharge. Bedload and flow data for ‘ordinary’ (low peak flow floods) and ‘exceptional’ sediment transport events are used to test the range of application of the bedload equations proposed for high gradient streams. Such equations overestimate bedload rate for ordinary events while their reliability increases when used to predict high bedload transport rates like those recorded during the exceptional flood that affected Rio Cordon on September 14, 1994. The best agreement between computed and measured values of cumulated bedload volumes is found by using the Bagnold [Bagnold, R.A., 1956. The flow of cohesionless grains in fluids. Philos. Trans. R. Soc. London 249A, 235–297.], Smart and Jaeggi [Smart, J.M., Jaeggi, M.N.R., 1983. Sediment transport on steep slopes. Mitteil. 64, Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie, ETH-Zürich, Switzerland, 191 pp.] and Rickenmann [Rickenmann, D., 1991. Hyperconcentrated flow and sediment transport at steep slopes. J. Hydraul. Eng., Zurig 117 (11) 1419–1439] formulas. The Schoklitsch equation [Schoklitsch, A., 1962. Handbuch des Wasserbaues, 3rd edn. Springer, Wien.] also provides good estimations for instantaneous bedload rates at high-sediment transport intensity and unlimited sediment supply conditions. The formal type of the last equation is still valid and can be calibrated for low intensity bedload rates.