Talk:Groundwater

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[edit] Restored discussion

Is the ground water flow parallel to water table? why?

in an unconfined aquifer (an aquifer with a water table), if there is no recharge from above, the water table is a no-flow boundary or streamline. This means that flow would move parallel to the water table.

If there is significant recharge or flow down through the vadose zone, there would be a component of flow normal to the water table, and flow would therefore not be parallel to it (but unless the recharge is large, flow will *nearly* be parallel to the water table). --kris 23:52, 5 December 2005 (UTC)

[as an aside, I don't think this talk page is probably the best place to learn about groundwater.]

Just a note, when I checked the Environment Canada Website and the Coastal Ocean Institute Website, I got the impression that the vast majority of usable freshwater is groundwater (Coastal Ocean Institute Website says 97%). I don't doubt the statistic that 20% of the world's total freshwater is groundwater, but the statistic can be a bit misleading to someone who doesn't know the other 80% of this freshwater is in the icecaps and inaccessable to nearly everyone. —The preceding unsigned comment was added by 129.21.112.186 (talk • contribs).

[edit] Later discussion

'Groundwater' is the correct spelling in Australia in any case

Are you sure? Many engineers in US use the single term out of poor education in english. It's easier for them to remember. But it is still incorrect. —The preceding unsigned comment was added by Dbt23 (talk • contribs) 14:25, 7 September 2006 (UTC)

[edit] Subsidence and aquifer capacity

The section on subsidence seems entirely wrong to me - I was under the impression that subsidence occurs where the aquifer is of compressible soil, and that only some part of the subsidence is recoverable, and with it, the capacity. Can someone provide a reference for the theory expounded in the subsidence subsection? Argyriou (talk) 02:03, 21 November 2006 (UTC)

A small fraction of the subsidence is elastic, and therefore recoverable. The vast majority of the land subsidence in most cases is non-elastic, since the clays and silts in aquitards have re-arranged and cannot simply re-inflate back to their pre-development state. If you Google for "USGS subsidence California", you will find lots of USGS report and papers which state the theory and show consolidation data to back it up (I can remember seeing some figures which show there were feet of subsidence and a few inches of rebound in San Jose). There was subsidence in the central valley and San Jose area which the USGS did a bunch of reports on over the years. --kris 18:42, 21 November 2006 (UTC)

I understand consolidation and rebound (I'm a geotechnical engineer). However, it's the contention that subsidence comes from consolidation of the aquitard that I question. There are plenty of soil deposits in which water flows moderately well horizontally, but poorly vertically, including those in the Bay margins and the Central Valley. Those layers are subject to consolidation, and thus would lose capacity as aquifers as they settled. The article as written appears to believe that all aquifers are essentially granular soils or rock formations, and that subsidence is related to water draining out of the aquitards, not the aquifers. Argyriou (talk) 19:06, 21 November 2006 (UTC)