Talk:Water table

Old talk

The definition of water table given here is, unfortunately, plain wrong. The water table is a pressure surface, where water below the ground surface is at atmospheric pressure. There is now abundant evidence that many soils are unsaturated below the water table (as given by the free-water surface in wells). For example, in peat soils, biogenic gas bubbles form below the water table due to anaerobic decay. Andy Baird, Professor of Physical Geography, Queen Mary, University of London (4th November 2005).

This point seems to be an exception, and this article is to explain the standard concept of what a water table is under standard conditions (alluvial aquifer and vadose zone), not recent research on what it may be in peat aquifers, which are atypical. The water table is customarily taken to be the zero-pressure isobar (taking p_atm = 0), which for most purposes is the level to which water rises in a shallow open borehole. --kris 19:36, 4 November 2005 (UTC)

The definition of "water table" here is extremely similar to the definition of "aquifer" at aquifer. Could anyone clarify the situation?

Apparently, much of the information in this article belongs in groundwater and aquifer, so I'm going to move it there. -Smack 20:44 7 Jul 2003 (UTC)

True that you don't need an aquifer to have a water table, but I was just trying to put the links which were in context at the beginning of the article.

Shouldn't this entry have the definition of a water table (the surface where the water is at atmostpheric pressure)? :Those other things (air+water vs water) are consequence or come from the definition. Some of this might be repeated from Aquifer#Saturated_vs._Unsaturated, so maybe it should just link to there? or move it over here? - kris 16:42, 11 Feb 2005 (UTC)

I have a graduate school education, and I cannot make heads or tails of this definition. --Flange the Flee (talk) 23:03, 1 May 2014 (UTC)

Australia

I added in a subject about the rising salt water tables in Australia. it would really help if someone expanded it since it is a good subject for this page but I know just some infromation about it. 66.229.47.105 04:24, 15 January 2006 (UTC)userBrenda

"In Australia, because of farming, salt water tables have risen nearer to the surface, endangering plant life and farm economy as the soil grows more salty. These salt water tables were formed millions of years ago when parts of Australia were covered by ocean. As the continent dried, the water became trapped underground." - Do you have sources for this, because it doesn't make sense as written (at least to me). Usually when the water table rises due to farming practices, this is because they are using saline water to irrigate which requires a certain amount of leaching. This water must be drained away or it will get too close to the soil surface resulting in salt problems. The salt is likely coming from the irrigation water, not fossil groundwater. Maybe it's different in this case, but I'd like to see some verification. H2O 21:22, 29 January 2006 (UTC)

What's said above is generally a bit of a misconception

Usually (in the Australian rising watertable problem), groundwater becomes saturated with minerals as it moves through the soil profile. Minerals enter the system in the Recharge Zone, move through the subsurface aquifer, and are discharged downstream.

Generally the situation with rising dryland water tables in Australia is, due to deforestation there is now an increased level of water entering the groundwater system in the recharge zone. this moves throught the aquifer and is leading to a rise in the water table downstream within the groundwater system. It generally is leached minerals from within the system which are leading to dryland salinity within much of Australia.

Related is the problem with rising water tables due to typically flood irrigation throughout previously arid/dryland areas of Australia such as the Murray and Murrumbidgee Irrigation Areas of New South Wales, whereby locally water is applied to leaking irrigated fields of eg rice which are flood irrigated - as there is excessive leaking of the field, the irrigation water percolates through the soil profile. it becomes saturated with minerals throughout this process. At the point at which the irrigation is occurring the "water table" is above "ground level", and the water "syphons" to a point outside the flood dykes (countour banks) around the field to a point where wetland salinity becomes a problem.

There is a similar problem with urban salinity throughout the region - see [1]

I hope that is a reasoned discussion of the problem throughout (at the least) Western New South Wales.

Another more general reference (The National Dryland Salinity Program (NDSP) ) states:

Dryland salinity occurs when salt stored deep underground is brought to the surface by rising underground water. This is the result of land clearing for agricultural or urban development when too much water enters ground water, causing it and the salts to rise to the surface.

(This is a copyvio!) Source: [2]

I'm not a scientist but in the early 90's was a technician working to monitor rising watertables in Western NSW

Garrie 04:42, 28 March 2006 (UTC)

need help

im doing work on the water table for science i need to know "why we need to draw water several feet below the water table and not above it or on it." but i cant find the answer ive been searching for a few days can someone tel me that b-4 tomorrow PLZ I NEED THIS THIS THANGS DO TOMORROW —The preceding unsigned comment was added by 68.154.242.62 (talk) 23:13, 8 March 2007 (UTC).

need help

I cannot see where long-term fluctuation of water tables is addressed at all under that heading in the article. How the long-term fluctuations affect surface streamflow is what I'd really like to hear something about. Is channelized streamflow greater or lesser in a region as water tables rise in the geological long haul? Would a constantly flowing stream be changed to intermittent with rising water tables, or with falling water tables. — Preceding unsigned comment added by 69.246.166.209 (talk) 02:30, 3 February 2015 (UTC)

Definition question

I temporarily removed the following confusing statement from the intro paragraph:

The water table is also often erroneously defined as the surface that separates the phreatic from the vadose zone, below which all rocks are saturated with water.

Image:Vadose zone.gif from the USGS depicts these as the same thing. Can anyone explain a circumstance in which the phreatic-vadose boundary would be different from the water table? The articles linked to by the above sentence and the other text in the intro seem to treat them as if they were the same thing. -- Beland 18:59, 25 March 2007 (UTC)

As an an unsaturated soil engineer I take the Phreatic Surface to be the level at which the ground water is at atmospheric pressure (i.e. no more positive hydrostatic pressure) and the Water Table to be the interface between fully-saturated ground and partially saturated ground. In gravel layers this means they are the same thing, but in clays with large suctions they can be metres apart. I'll try and find an internet page to back this up, instead of the books I have. If no-one has any objections I will then change the page. Philip Wallbridge 14:41, 1 November 2007 (UTC)

Diagram question

Why does the water table vary in height in the diagram? Is it because the river is draining water at a high rate, but it flows slowly through the soil? The article seems to imply it is due to variations in the gravitational field of the planet due to topography, which, if the image is taken to be at scale, is incorrect. -- Beland 19:02, 25 March 2007 (UTC)

I have never seen a river surface that was curved like the one in the diagram. Bjartmarr (talk) 18:41, 12 May 2008 (UTC)

The drawing tool used probably made a continuous smooth curve. Either that or it is a Meniscus. Ferritecore (talk) 14:46, 27 July 2008 (UTC)

In Archetecture

"Water table" has a completly different meaning in architcture, see: water table (architecture) Ferritecore (talk) 14:46, 27 July 2008 (UTC)

Rivers vs Water Table

I think the relationship between the water table and rivers can be clarified. The article and illustrations currently give the impression that the water of a river is (all, mostly) originating from the water of the phreatic zone along its course. Large rivers it seems get most of their water from tributaries, and those tributaries may start as runoff, not ground water.

So what proportion of a typical river's water is being added from the phreatic zone along its course? Must a river surface always be not higher than the water table -- or can water from elsewhere flow through a channel that is entirely above the water table (depending on flow volume and geology)? Are there situations where the river channel is well above the water table, and leeching water downwards into it?

I would expect a river to usually be close to equlibrium with the water table. Net water table<->river flow could be either way, depending on circumstance, but usually small compared to the ammount of flow in the river. A river flowing out of of a swamp may be draining its water table. A river flowing through a desert (Colorado?, Nile?) may be feeding the local water table. Ferritecore (talk) 02:13, 1 October 2008 (UTC)

capillary effect

The text under Surface Topography refers to capillary effects, which seem off-base to me. Hydraulic gradient is not affected by capillary rise, because it is based on phreatic (atmospheric pressure). The relationship between surface topography and subsurface hydraulic gradient is something I'm trying to study in more detail, by comparing gradients in calibrated groundwater models to the observed surface topography gradient. Fundamentally, the discharge elevation (eg, river water level) is the driver behind gradient direction, and recharge in conjunction with aquifer transmissivity drives gradient magnitude. Dave.Tamblyn (talk) 22:38, 27 November 2024 (UTC)