New approach for the estimation of extreme roughness in torrents by hydraulic and photogrammetry

In this paper we present an approach to estimate extreme roughness in torrents based on the transformation of an irregular bed geometry of a torrent reach into a geometrically well determined `idealized' channel. One basic parameter is the surface of the water, which was determined by a photogrammetric method using stereo photos on the Analytical Plotter WILD AC1. Two torrent segments were photographed with two synchronized Rollei 6006 metric cameras, which were installed above the torrent while the mean velocity was simultaneously measured by the salt-dilution method. The Strickler coefficients derived from our studies at two torrent reaches in the Swiss Alps are also given in this paper.