intro story Lake

Lake

Lakes and reservoirs are important resources for communities around the globe. They provide food, drinking and irrigation water and can also offer spots for recreation. Under certain conditions lakes can also represent a threat for local communities, such as flooding or limnic eruptions. The ecological state of shallow lakes may be hampered by suspended sediments due to wind driven currents and waves. In deep lakes, stratification can cause undesirable anoxic conditions in the deeper areas. Understanding these systems is crucial to enable a sound management of these water bodies.

 
Delft3D is the state-of-the-art modelling framework for hydrodynamics, water quality, ecology, waves and morphology.
 
Here, in this space, we share knowledge & experiences, and discuss issues related to modelling of lakes.

 

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D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems


 

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Fluid mud simulation in a lake

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Eliisa Lotsari, modified 7 Years ago.

Fluid mud simulation in a lake

Youngling Posts: 1 Join Date: 3/24/14 Recent Posts
Hi,

I found from Delft3D-FLOW's user manual, that there is a possibility to simulate fluid mud (underwater debris flow) with the 2-layer fluid mud model. However, I have not found many references related to model (only for example Merkelbach and Winterwerp, 2007) and detailed information from the user's manual, how to perform the simulations in practice. There is a case from lake Geneva, where a c. 40 m thick fluid mud flow has happened (it had c. 100-200 m water above the fluid mud layer). There would be the following parameters available, i.e. the fluid mud flow height, distance of the fluid mud flow, mud density, grain sizes, water density, approximate velocity, slope of the river bed and fluid mud flow, and the river bed geometry (approximately a 2x2 m grid). Since this is a lake, tide or salinity do not influence on the fluid mud flow. Based on your expertise, would a Delft 2-layer fluid mud model be possible to run with these parameters, or would something else be needed?

I have earlier performed simulations in river environment, but never in lake and debris flow environment. Are the initial conditions, e.g. geometry, created for fluid mud simulations similarly as for hydro-/morphodynamic simulations of rivers? According to user's manual, the fluid mud simulations are performed with Delft-FLOW, but I was not able to find any fluid mud options from the Delft-model interface. It is said that the MDF files are need to be created, one for the suspension layer and one for the fluid mud layer: would you have some tips for the creation of these files for the fluid mud simulation purposes? I would be happy to hear any tips related to the fluid mud simulations and how to get started with that.

-Eliisa-
U
Bas van Maren, modified 7 Years ago.

RE: Fluid mud simulation in a lake

Hi Eliisa,

The best description of the 2-layer fluid mud model is

J. C.Winterwerp, Z. B.Wang, J. A. Th. M. van Kester and J. F.Verweij (2002), Far-field impact of water injection dredging in the Crouch
River: Water & Maritime Engineering 154, Issue 4.

The 2-layer fluid mud model is not easy to use. You create 2 mdf files, where one mdf represents the fluid mud layer, and 1 represents the water layer, which you run simultaneously. The way to do this is described in the flow manual.

It is not used very frequently, partly explaining why you will not find many references. An alternative would be to simulate it in standard Delft3D. If you prescribe a high suspended sediment concentration near the bed (eg 200 g/l), with a low settling velocity (eg setting Cref to 300 g/l), and turn off sedimentation, you will also create a sediment-induced density flow. This may overestimate the flow velocity of the layer, since there is no yield stress / increased viscosity to slow down the turbidity current.

The best way to model such a turbidity current is using our 3D mud model, which has flocculation, consolidation, and rheology implemented in 3D. This is, however, a research version which also is not easily used. It requires some basic knowledge of soil mechanics (consolidation / rheology) as well. If you are planning to spend longer time on this topic, and have data to calibrate, we may find ways to let you use the model.

regards,
bas