seep/w parameters

I’m always looking for this piece of paper, so I posted it here for easy access.

seep/w is a groundwater flow model – its 2D (although can be axisymmetric and there is a 3D version these days) but its very quick to solve and reliable, and a useful tool.  Unlike many other groundwater models, it seems to work better when it is solved in transient state, and using saturated / unsaturated model of hydraulic conductivity (ie hydraulic conductivity changes as a function of saturation).  If you leave it as a saturated model, it assumes the world is saturated at the start of the simulation, doesn’t converge so well, and can end up with strange results.  I prefer setting up my own starting conditions and then running the model as a transient simulation for a long period until it stabilises.  I don’t mind these characteristics of seep/w as, in reality, the world is transient and hydraulic conductivity does change as a function of saturation.  The problem is that you need lots of parameters (some for ‘storage’ – because its transient, and others for the saturation function – because its a saturated / unsaturated  model) and you also need the model to converge well.

That is where this sheet comes in – its a screen grab showing parameters in seep/w I have found to help the model converge well.

It also contains various scrawls and equations by a colleague (hello Allison 🙂 ) regarding storage and unsaturated hydraulic conductivity.

Note that seep/w uses a parameter ‘mv’ for compressibility – this is a function of the Young’s modulus and Poisson’s ratio.  For the hydrogeologists, this is seep/w’s way of expressing specific storage – the equations on the sheet show this.   seep/w doesn’t ask for the user to input specific yield (ie drainable porosity), but rather the saturated and residual porosities (the difference between these two is approx. equal to specific yield).

A bit of further background is in the other piece of scape paper, which I found yesterday:

Anyway, may these parameters help you to converge :). Power up.

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