tkershaw

Thanks for the reply Giovanni. The images shown in the original post are with a 10X vertical exaggeration. The vertical scale is 316m and the horizontal scale 12000m X 300m. I would agree that more layers would create more resolution and possibly clean up the concentrations, but i first wanted to get a simplified model to exhibit predictable behavior and it is already quite computationally intensive with only 4 layers. Attached is a 1X vertical exaggeration for comparison.

Hello,
To follow up on a previous post regarding a vertical model vs. horizontal model for modeling seawater intrusion (thank you Pete and Peter for your input): I am pursuing a simplified horizontal model but having trouble making it behave predictably. I have a simple 4 layer model with a sloped seawater boundary represented by the top first slice and with the slices below following the upper sea-slope with a minimum distance below in order to abide by the FEFLOW rule of having each layer extend through the entire model boundary. My problem is that even when I leave [i]all layers with default material property parameters[/i], their landward saltwater migration seems to be quite segmented for each layer as shown in the image attached. Also there is not much of a seawater intrusion toe with more migration on the lower elevations. The run seems to take quite a long time (12hrs for a 6.5 day run) so maybe this migration stepping (and toe behavior) will even out after a longer runtime but I am suspicious.

My questions are as follows:

1. Are there certain material properties that need to be set for these very thin stacked layer sections that would promote a more uniform mass migration? I will eventually want migration stepping behavior when I add aquitards but is is not intuitive when the layers have the same material properties.
2. Should I only put seawater boundary conditions (saltwater head: 0m, mass concentration: 35000mg/L, min mass flow constraint: 0g/d) on the first slice's nodes or on the slices below where the thin layer sections are very close to offshore?
3. My model is very simple structurally yet seems to have a very long runtime. Is this most likely from the thinly layered sections?

In case there is anyone interested in helping I have attached the model file and would love if anyone had the time to look at it to see if there are any egregious oversights.

Thank you very much!

Hello all,
Please bear with me as I know this is a long post but I am in desperate need of some advice.

I am in the process of trying to model a seawater intrusion scenario with FEFLOW v6.0 which involves a very irregular coastal interface and I am struggling with the most appropriate method to approach it. I am really hoping that some of you FEFLOW experts have some recommendations.

The model involves a complexly layered aquifer system with an upper shallow, unconfined aquifer layer and several confined aquifer layers below it that extend seaward significantly far from the coast. There is also a submarine canyon running through the middle of the coastal basin.

I am trying to decide if it is best to try a model using the horizontal method or the vertical cross-section method (with gravity in the -y direction). The vertical method is described in a tutorial with a highly simplified shape representing an aquifer, so it seems promising for a simple 2D model, but seems to get a little tricky for 3D models with irregular boundaries.

[u]Horizonatal Model:[/u]
I have some geologic data for a potential horizontal model but because of the limitations of FEFLOW (no layer intersection or breaks between layers), the slanted land-sea interface of the confined aquifer layers below can only be modeled with a steep vertical face. This would either mean that I would have to:
[list type=decimal]
[li]Have a sheer boundary at the shoreline and miss the seaward seawater/freshwater interface interaction for the confined offshore aquifer layers below which is not acceptible in my mind.
[/li][li]Try to synthetically extend the upper layers to meet the appropriate offshore extent of the lowest, most-offshore aquifer and assign the above offshore boundary conditions such that they just represent seawater.[/li]
[/list]
I am concerned that this second option might have trouble with a convergent solution because it would require a very large amount of boundary conditions.

[u]Vertical Model:[/u]
Because the vertical model has the ability to represent cross sectional slopes as essentially a polygon, there is a better chance that the land/sea interface and offshore aquifers will be more appropriately represented. However, there will obviously be some difficulty trying to represent the physically horizontal geologic aquifer layering by connecting adjacent vertical layers among the slices. Also, from the simplified vertical model I did build, I am not quite sure it is faithfully representing the physical scenario that I am interested in because saline migration seemed to be insensitive to changes in saltwater head boundary conditions at the land sea interface.

Attached is a plan view with the basin boundaries in green and offshore portion in blue-green and also a transect showing the offshore boundaries.

I would love to hear if there is anyone that has had experience successfully building a seawater intrusion model that can capture the offshore behavior of multilayered confined aquifers or if there are any other resources that might be helpful.

Cheers

-Tim

Hello all,
I am currently trying to model seawater intrusion in a coastal aquifer using FEFLOW v6.01 and, as a starting point, I am trying to build a simplified 2D cross sectional model. I have the following boundary conditions:
[list]
[li]Along the ground surface (top of the model domain) I have a Fluid Flux BC with a 0mg/L Mass Concentration BC[/li]
[li]Along the inland boundary (left of model domain) I have a Fluid Flux BC and a 0 mg/L Mass Concentration BC[/li]
[li]Along the slanted seaward boundary (right of model domain) I have a 0m Saltwater Head (SWH) BC and a 35000 mg/L Mass Concentration BC with a Minimum Mass Flow Constraint of 0 g/d[/li]
[/list]
The density ratio is constant throughout the domain at 0.0245
My run of 1000days shows a saltwater wedge encroaching landward as predicted.

My problem is that when I change the SWH BC to a higher value (simulating sea level rise), the mass contours are the same for 1m, 10m, even 100m of SWH after 1000 days.
Shouldnt the contour lines look significantly different (more inland) with increasing SWH?
Is there something that I am missing?

Thanks so much for the help!