Physical Experiments To Determine The Stability Of Step-Pool Systems In Mountain Torrents

Volker Weitbrecht, Benjamin Hohermuth, Lukas Hunzinger

Wednesday 1 july 2015

8:45 - 9:00h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics

Parallel session: 8B. Sediment - River

Laboratory experiments have been conducted to test the stability of self-formed step-pool systems if the initial condition is natural bed material fully-mixed with much larger blocks. Four different measurement series were tested, with various block sizes, block fractions within the bed material and bed slopes. Each series consisted of six different runs starting with constant discharges representing smaller flood events, followed by extreme floods involving particular flow and sediment hydrographs. The resulting longitudinal bed profiles indicate that an optimal block diameter can lead to a stable bed for slopes up to 0.08. For extreme flood events (HQ300) the bed degrades gradually. With slopes up to 0.15 the channel bed degrades beyond acceptable conditions already during HQ100. A comparison with existing approaches to determine the bed stability reveals that the formulas do not lead to satisfactory results for small channel width-to-block diameter ratios.