Modeling bed level changes and sediment sorting processes for pool-riffle sequences in gravel bed rivers

Mina Tabesh, Mohammad Reza Majdzadeh Tabatabai, Amir Reza Zarrati

Tuesday 30 june 2015

17:39 - 17:42h at Oceania (level 0)

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

Parallel session: Poster pitches: 7B. Sediment - River

One of the main features of gravel-bed rivers is the pool-riffle sequence. Investigation on morphological changes in pool-riffle topography plays a key role in environmental engineering and river training practices. In the present work, the morphological response of a river to sediment input in a bed with pool-riffle sequence is studied. Gstars4.0 which is a computer code for simulation of sediment transport, scour and deposition processes in alluvial rivers was employed. Experimental data measured by Hassan et al. (2006) was first used to find the model capability in predicting sediment transport rate and bed composition changes in an alluvial bed. The model was then employed to simulate the experimental study of morphological changes conducted by Harrison (2007). The experiments were carried out over a pool-riffle topography in a flume with non-uniform gravel bed at low, moderate and high flow discharges. Sediment input, in form of a 0.5 cubic meter sediment pulse, composed of mixed sand was introduced at the upstream section of the flume. The experiments were conducted with various discharges and transport of the input sediment pulse over the pool-riffle topography was studied. Comparison of the observed and computed results demonstrated that the model was capable of predicting bed changes and grain sorting processes in the pool-riffle sequence of non-uniform sediments with satisfying trend. Results from this study showed that at low flow discharge, sediment was deposited in the pool, meanwhile, a thin deposit was observed in riffle region. In higher flow discharge, sediment input was initially deposited in pool and then transported gradually through the pool and the adjacent riffle. As flow discharge increased, the pool riffle topography approached its initial elevation. The results also showed a gradual coarsening of bed sediment in the pool as well as the riffle region in higher discharges.