#420 added class 'soil drainage'

[KrishnaTO]

closes #420

[marieALaporte]

Thanks @cmungall. We moved 'soil drainage' under 'hydrological process', and defined it as 'A hydrological process during which water moves across, through, and out of the soil as a result of the force of gravity.' We added a subClassOf axiom 'occurs in some soil' We need this term for the EiA initiative, where people record the soil drainage rate. We will create a PR for the rate term once this PR is accepted

[pbuttigieg]

I still see this under "flux" rather than process.

[marieALaporte]

@pbuttigieg soil drainage is under 'flux'

[marieALaporte]

I misunderstood your comment. Will make the change

[smrgeoinfo]

soil drainage process: a process by which water (or other liquid) is transported through a soil body. NOTE: typically gravity driven, and requires pressure gradients through connected soil porosity (e.g. permeability) soil drainage flux: the volume of fluid transported through a soil volume per unit of time.