Streamwise turbulence modulation in non-uniform open-channel clay suspension flows

Cohesive sediment particles are ubiquitous in environmental flows. The cohesive properties of clay promote the formation of clay flocs and gels and relatively small suspended clay concentrations can enhance or suppress turbulence in a flow. Furthermore, flows are naturally non-uniform, varying in space and time, yet the dynamics of non-uniform open-channel clay suspension flows is poorly understood. For the first time, the adaptation time and length scales of non-uniform clay suspension flows were quantified using novel experiments with spatially varying but temporally uniform flow. Different levels of turbulence enhancement and attenuation were identified as the flow decelerates or accelerates. Results highlight that decelerating clay suspension flows crucially have a longer adaptation time than accelerating clay suspension flows. This is explained by the longer timescale required for the formation of bonds between cohesive particles in turbulence attenuated flows after deceleration than the rapid breakdown of bonds in turbulent flows after acceleration of clay suspension flows. This hysteresis is more pronounced for higher concentration decelerating flows that pass through a larger variety of clay flow types of turbulence enhancement and attenuation. These different adaptation time scales and associated clay flow type transitions are likely to affect clay flow dynamics in a variety of fluvial and submarine settings

Sedimentation Hazar Port

Hazar Port is located in Turkmenistan on Cheleken Peninsula, which is situated on the eastern coast of the Caspian Sea. Dragon Oil, an international oil and gas exploration company, is engaged in exploration and exploitation of oil and gas in the Caspian Sea. Dragon Oil would like to use the harbour of Hazar as supply base for the expanding of their fields. Therefore, the entrance channel to the harbour basin of Hazar Port needs to maintain a certain depth. Currently there is a significantly amount of sediment settling in the harbour, which result in high dredging costs. Dragon Oil would like to redesign the harbour or have a dredging plan, to reduce the costs. This research focusses on the processes that influence the sedimentation. With a numerical study insight in the sedimentation rate is obtained. Wind is one of the most important aspects for the circulation in the Caspian Sea. The salinity changes near the harbour are relatively small and therefore not taken into account. Near the harbour the current is always directed along the coastline, either to the north with an eastern wind or to the south with a northern wind. Northern and eastern winds are dominant in the wind data and these two representative directions are used to get insight into the sedimentation. For these two wind directions each 3 stationary situations with daily conditions and 3 situations with storm conditions are compared with each other. A northern wind result in sediment transport to the south and inflow into the harbour through the harbour entrance. Near Hazar Port both non-cohesive and cohesive sediment is found and implemented in the Delft3D model. Non-cohesive sediment almost directly settles in the entrance channel near the harbour entrance despite of the wind speed. Cohesive sediment is spread over the harbour. With higher wind speeds, cohesive sediment is deposited further into the harbour. An eastern wind result in sediment transport to the north and inflow into the harbour through the opening at the south. Non-cohesive sediment only settles near the coastline. Cohesive sediment spreads out over the harbour, however the highest sedimentation rate is in the south of the harbour. Therefore, the influence of the sedimentation of this situation is limited, since the sedimentation in the entrance channel with this wind direction is limited. Both daily and storm conditions are taken into account. Storm conditions result in more sedimentation, but are less frequently occurring. If the results are combined with the occurrence of the wind speed and the direction, the 5% exceedance wind speed is dominant for the sedimentation. The sedimentation rate over the year is dominated by cohesive sediment. During the summer period, the highest sedimentation rate is expected. The Caspian Sea has shown large variations in the water level. Variations are possible due to long term changes, seasonal influences, wind forces and the tide. Tidal variations are limited and not taken into account. The other water level variations can result in overflow over the northern breakwater of the harbour. This results in an increase in the rate of sedimentation.Hydraulic EngineeringCivil Engineering and Geoscience