geomorphology; hydraulics; steep stream; fluvial system;

Geomorphological processes, bed morphology, and hydraulics of steep mountain channels significantly differ from typical gravel bed or meandering rivers. This chapter describes morphological, hydraulic and sediment transport aspects of first- and second-order channels with bed gradients greater than 3 % and drainage areas smaller than 10 km2. Downstream variability in channel-reach morphologies is described on the example of Montgomery-Buffington (1997) process-based classification. Several examples of flow velocity, flow resistance and bedload transport equations used for calculations in steep streams are provided and explained in detail. Uncertainties in bedload transport modelling in these streams are discussed, when local sediment transport during flood events is rather dependent on direct sediment delivery from adjacent hillslopes and individual sediment inputs (e.g., bank failures, gullies) than absolute value of flow discharge. Also note that bed material of steep streams contains high variety of particle sizes from sand to large boulder fractions. The brief summary of human interactions with mountain channels (construction of check-dams, restoration techniques) closes this chapter.