HydrogeoUnit

[mbeaufils]

Source definition : OGC GroundWaterML2, also candidate for IFC

These are distinct volumes of earth material that serve as containers for subsurface fluids. The boundaries of a unit are typically discriminated from those of another unit using properties related to the potential or actual ability to contain or move water. The properties can be geological or hydraulic, and typically include influences from the surrounding hydrological environment. More specifically, the conceptual model delineates two types of hydrogeological units, with slightly different orientations: aquifer-related units have boundaries delimited by the hydrogeological properties of the rock body, while groundwater basins have boundaries delimited by distinct flow regimes. Aquifer-related units are subdivided into aquifer systems, which are collections of aquifers, confining beds, and other aquifer systems. Confining beds are units that impede water flow to surrounding units, and supersede notions such as aquitards, aquicludes, and aquifuges, which are not included herein, as it is difficult to differentiate these in practice.

[IHalfon]

I don't see the use in geotechnics ? example ?

[jjkaelin]

HydrogeoUnit: the use of Aquifer and GroundwaterBasin should be considered, being more understandable.

Other attributes, as mentioned above by mbeaufils, can be added as semantic expressions.

[dponti]

Yes it does seem that hydrogeounit may not be necessary when we have two common terms to define the types of hydrogeological units included in the definition (aquifer and groundwater basin). Perhaps we should instead consider if there's value in defining a "hydrogeologic system" rather than a unit, that incorporates both the groundwater basin and the aquifer systems it contains. Boundaries of a groundwater basin can be modified by pumping, whereas the hydrologic properties of aquifers are generally static (unless altered by overpumping induced compaction) so consideration of the system might be warranted.

[neilchadwick-dg]

I'm not an expert in hydrogeology, but I've worked with hydrogeologists so have some experience. Based on this and a little bit of research here are my thoughts...

I quite like this definition - perhaps oversimplified but easy to understand...

A hydrogeological unit is defined as any soil or rock unit or zone that by virtue of its hydraulic properties has a distinct influence on the storage or movement of groundwater. (source)

Geological units normally form the basis of hydrogeological units, but like geotechnical units the mapping is not always 1:1. A hydrogeological unit may combine geological units, or a geological unit (e.g. with different lithologies) may be split into different hydrogeological units.

Hydrogeological units are a critical part of the hydrogeological model.

Hydrogeological units are NOT bodies of water or groundwater, as such. These exist separately, albeit influenced by the hydrogeological units of course. I'll comment on those under the relevant headings.

The only thing that bothers me is that at the moment we are not differentiating between hydrogeological units in an observational model and hydrogeological units in an analytical (design - synthesis) model, whereas we have distinct geological (observational model) and geotechnical units (design model). Slightly inconsistent. Not sure what the answer is, or whether it matters.