Roughness coefficients of watercourses revetted with half-circular concrete pipes. Results of field measurements in watercourse S 333 at Maarkedal

Abstract

Watercourse S 333 at Maarkedal drains a hilly area. Half-circular concrete pipes were used to protect the bottom against erosion. The part of the watercourse chosen for the roughness measurements was over its entire length revetted with half-circular concrete pipes of 1 m diameter. Above it, a natural vegetation has developed on one side; the other bank, adjacent to a pasture, had a short grass cover. All water depths were obtained from water level recorders and a measuring weir allowed discharge determinations. Only peak values were considered to determine the roughness coefficients. Water level calculations were used without considering additional energy loss coefficients, so that all the channel irregularities are included in the roughness coefficients. Over nearly the whole range of flows, the K M-value decreased with increasing water depths. A value of 43 m 1 3 s −1 is calculated at a depth of half the diameter of the pipe. This type of revetment proved to be an excellent protection against erosion, even in reaches with steep slopes, where supercritical flow conditions occur.