<p>What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics? I want also to understand the difference between the different storage coefficients (Ss, S,..).</p>

<p>Both are differential equations:</p>

<p><strong>Diffusivity equation</strong>: $$\ Ss. ∂h/ ∂t = −∇ ·(− K \nabla h) − G$$.(for Incompressible liquid)(the flux (q), source terms (G), the specific storage (Ss), hydraulic head (h)) (<a href="http://en.wikipedia.org/wiki/Groundwater_flow_equation" rel="noreferrer">source</a>)</p>

<p><strong>Richards equation</strong> (headed based form (there two other forms of this equation)): $$C(h) . ∂h/∂t = ∇ · K(h)∇H$$ (specific moisture capacity C(h), (H) total hydraulic head, h is the matric head) (<a href="http://en.wikipedia.org/wiki/Richards_equation" rel="noreferrer">source</a>) </p>

<p>Aren't they supposed to describe unsaturated flow ???  </p>

CC BY-SA 3.0
2017-05-16T11:16:24.113Z
Both are differential equations:

Diffusivity equation: Ss. ∂h/ ∂t = −∇ · (−K∇h) − G.(for Incompressible liquid)(the flux (q), source terms (G), the specific storage (Ss), hydraulic head (h)) (source:https://en.wikipedia.org/wiki/Groundwater_flow_equation)

Richards equation (headed based form (there two other forms of this equation)): C(h) . ∂h/∂t = ∇ · K(h)∇H (specific moisture capacity C(h), (H) total hydraulic head, h is the matric head) (source: https://en.wikipedia.org/wiki/Richards_equation)

Aren't they supposed to describe unsaturated flow ???
Rabah Akrour
CC BY-SA 3.0
2017-05-16T12:19:42.120Z
Voila, easy to use !
Rabah Akrour
<models><soil><groundwater><fluid-dynamics><unsaturated-zone>
What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics?
Rabah Akrour
# What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics?

(Asked by: username_0 on 2017-05-16)

What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics? I want also to understand the difference between the different storage coefficients (Ss, S,..).

Both are differential equations:

**Diffusivity equation**: $$\ Ss. ∂h/ ∂t = −∇ ·(− K \nabla h) − G$$.(for Incompressible liquid)(the flux (q), source terms (G), the specific storage (Ss), hydraulic head (h)) ([source](http://en.wikipedia.org/wiki/Groundwater_flow_equation))

**Richards equation** (headed based form (there two other forms of this equation)): $$C(h) . ∂h/∂t = ∇ · K(h)∇H$$ (specific moisture capacity C(h), (H) total hydraulic head, h is the matric head) ([source](http://en.wikipedia.org/wiki/Richards_equation))

Aren't they supposed to describe unsaturated flow ???

**Tags:** models, soil, groundwater, fluid-dynamics, unsaturated-zone

> **Comments:**
> **username_0**: Both are differential equations:  Diffusivity equation: Ss. ∂h/ ∂t = −∇ · (−K∇h) − G.(for Incompressible liquid)(the flux (q), source terms (G), the specific storage (Ss), hydraulic head (h)) (source:https://en.wikipedia.org/wiki/Groundwater_flow_equation)  Richards equation (headed based form (there two other forms of this equation)): C(h) . ∂h/∂t = ∇ · K(h)∇H (specific moisture capacity C(h), (H) total hydraulic head, h is the matric head) (source: https://en.wikipedia.org/wiki/Richards_equation)  Aren't they supposed to describe unsaturated flow ???  
> **username_0**: Voila, easy to use !  

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