# 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.

## Message Boards

### problem with temperature modeling in a reservoir

JO

#### problem with temperature modeling in a reservoir

Youngling Posts: 4 Join Date: 12/19/17
Hello everybody,

I set up a very simple model of a reservoir. I am modeling a stationary scenario using two boundary conditions which are based on measurements:
-upstream: discharge (inflow)
- downstream: (outflow) the corresponding water level (see Fig. 1 for the location of the open boundaries and the flow direction).
When I run Delft3d-Flow for this simple case, the results are just as expected (regarding water level in the model area and flow direction).
The problem appears, when I include temperature in the model. In the GUI, I have to introduce the temperature at the two open boundaries. I understand that I need the temperature for the upstream open boundary, since this is the temperature of the incoming water. I thought that for the outflow, I could put any value for the temperature and the model would calculate the correct one (normally we do not have the temperature at the outflow). But this temperature reversed back on the model area. I tried this for different temperatures at the outflow, for all the temperature reversed back!.
For an inflow temperature of 15°C, initial temperature of the water of 20°C and air temperature of 18°C, I obtained the results shown in the Fig 2. (longitudinal profile of the reservoir, when using a temperature of 0°C a the downstream boundary), Fig 3 (velocity vectors for the longitudinal profil) and Fig 4 (velocity vectors for the water surface) . More Info: I am using the heat flux model 1.
Do you have any idea of what I am doing wrong? Do I have to know the temperature at the outflow in order to model the temperature in the reservoir?

Regards,
Johana

### Attachments:

DK

#### RE: problem with temperature modeling in a reservoir

Jedi Knight Posts: 108 Join Date: 11/9/12
Hi Johana,

You can try to specify negative values for the time lag for temperature at the outflow boundary. Thus, the influence of this temperature on the inner solution will be excluded. See section 9.4.2.2 of FLOW User Manual and this thread.

Kind regards,

Dmitry.
JO

#### RE: problem with temperature modeling in a reservoir

Youngling Posts: 4 Join Date: 12/19/17
Hi Dmitry,

Thanks for your answer. I already tried using a negative time lag for the downstream boundary condition. Although the temperature range is realistic (between 15 and 19 °C- see Fig6), the velocity vectors show odd patterns (see Fig7 and 8).

Best regards,
Johana

### Attachments:

VL

#### RE: problem with temperature modeling in a reservoir

Youngling Posts: 1 Join Date: 4/21/20
Dmitry Kushnir:

Hi Johana,

You can try to specify negative values for the time lag for temperature at the outflow boundary. Thus, the influence of this temperature on the inner solution will be excluded. See section 9.4.2.2 of FLOW User Manual and PrepaidCardStatus

Kind regards,

Dmitry.
Thank you for the information and advice!