Talk:Water content

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Water Content Calculation

I doubt that the calculation for the gravimetric water content is correct in this article: "$u={\frac {m_{w}}{m_{b}}}$". It should be $u={\frac {m_{w}}{m_{T}}}$, with $m_{T}=m_{w}+m_{s}$, leading to no higher percentages than 100%. Otherwise you couldn't even use the density to convert u in $\theta$.

Water Content Definition

I notice that the variable used to indicate gravimetric water content is "u". I am curious to know in what field this is the case. In geotechnical engineering, the common practice in the English speaking world is to use "w". I do not want to make an unwarranted edit, but at least it should be added to clarify the point (in geotechnical practice, "u" normally denotes the pore water pressure).

It might also be useful to point out, that in the field of geotechnical engineering, when the term water content is used without the terms "gravimetric" or "volumetric" it is invariably assumed to be the gravimetric water content. This may not be the case in other fields and as such the distinction should be made clear.

Juaninse (talk) 20:04, 10 September 2008 (UTC)

Double take

I didn't fully absorb this statement: "classical view that saturation is effectively zero above the water table". I've never encountered this view. Whose is it? Daniel Collins 18:20, 10 May 2005 (UTC)

Well, in civil engineering the use of flownets to calculate the "free surface" flow under a dam is one example. Flownets solve the laplace equation and even if they do account for recharge through the vadose zone, they simply apply a vertical recharge term at the water table.

Another example would be unconfined pumping test analysis, where it is assumed that when the water table is drawn down it releases water from storage, ignoring the complicating unsaturated flow above the water table (which in most cases really is minor).

I guess it wasn't clear "classical to who" in that. --kris 22:14, 10 May 2005 (UTC)

I didn't think about those assumptions. So, I think it would clearer to say that certain g/w analyses do not explicitly account for vadose zone dynamics, or assume them to be negligable for the quantities and rates concerned. How accurate would it be to bin these analyses as common approaches in "industry" or water resource planning? It would not be classical in surface hydro to consider the vadose zone as completely unsaturated, and nor in other considerations of hydrogeo. Daniel Collins 00:10, 11 May 2005 (UTC)

I think it is just that they ignore it; to them it is either saturated (aquifer) or unsaturated (not aquifer) and they don't worry about the fact that it is probably more accurate to say it is all variably saturated, since that is a much harder, nonlinear equation to solve.

I guess in the things I pointed out, any contribution which is left out by treating the aquifer as "on or off" is quite minor, and they are adequate "engineering approximations". Not conceptually or physically correct, but they work. --kris 14:37, 11 May 2005 (UTC)

We're on the same page. Now let's clarify and justify the assumption. Daniel Collins 16:14, 11 May 2005 (UTC)

Saturation

I have corrected the following statement:

The water table (or more precisely the top of the capillary fringe above the water table) is the dividing line between saturated and unsaturated conditions.

Saturation requires 100% of the pore space to be filled. Due to the variaton in pore sizes typically available in a soil or aquifer medium, a water content of "1" is not typically achieved throughout the observed capillary fringe. When one observes the fringe moistened by capillary action above the level of free water, one is not observing saturated conditions throughout the material. Saturation is only occuring in the smallest pores within the moistened fringe. Significant air content is present and increases with distance above the free water depth. Reading the information at [http://en.wikipedia.org/wiki/Aquifer#Saturated_vs._unsaturated] I see I can look forward to some discussion on this. I have posted my sources at [http://en.wikipedia.org/wiki/Talk:Aquifer]

Paleorthid 04:28, 12 September 2005 (UTC)

Merge Soil moisture and Water content

These articles are very similar, and would make a bit more sense to have in a single article. Probably the most confusing question is which article name should be kept. +mwtoews 04:48, 10 March 2007 (UTC)

• On this soil moisture talk, I can't agree with the "merge" idea. Naturally if a term is really "rare" then it would be better to merge it with another rare term. Is "soil moisture" a rare term? May be, may be not, depending on if your work touches on it. In my work, "water content" can cover a great deal, while "soil moisture" covers not that much but still a lot. Therefore, even if I consider merging I wouldn't merge these two terms.—Preceding unsigned comment added by Kuenluenmt (talk • contribs) 14:06, March 13, 2007

• There are some similar things, however water content isnt only soil moisture, it can be other things.—Preceding unsigned comment added by 138.130.182.60 (talk • contribs) 05:51, May 15, 2007

• Water content is usually only used in the context of soil moisture. For other uses, there is moisture content. This merge proposal if for the context of the soil science definition. +mwtoews 23:29, 15 May 2007 (UTC)

• Well, I have added moisture content to the proposed merger. Even if these words have different connotations and definitions in different fields, it still may be positive for the encyclopedia to have them in one article in order to maximize the concentration of content and user focus and eliminate redundancy since I believe they are at least inter-related words. Basar 00:53, 3 July 2007 (UTC)

Alright. After many months with the merge tags up on these pages, I think it is time to do something about it (and thanks for the input). Here is what I think I'll do:

• Keep the water content article to describe the physical definition (i.e., the ratio), which can pertain to soil, and other materials (ceramics, wood, etc.). Merge moisture content into this article.
• Keep the soil moisture article to describe how the water content influences characteristics of the vadose zone, such as soil water movement (i.e., unsaturated flow). Also, this article can discuss measurement methods that relate strictly to soil, such as using geophysics and tensiometers. There is a great deal of literature that deal with soil moisture, and I think it would be a mess to include this into a water content article, which describe a property.

Does this seem alright? Really, there is only one merge here, and re-organization of content, and that's about it. I'll probably do this in a few days if I don't see anything. +mt 20:26, 21 July 2007 (UTC)

That seems reasonable to me. Good work. -- Basar (talk · contribs) 01:36, 24 July 2007 (UTC)

Merge complete. In the end, it turned out that I merged it all together—I hope this isn't too much of a mess! My last minute change to merge "Soil moisture" to "Water content" is that it is the same material property, and text describing unsaturated water flow (i.e., soil water movement) would be better described in a new article (of which there is no Wiki-content at the moment), rather than calling it "soil moisture". This article still needs some good references, and further reworking to make it up to snuff (note that "soil moisture"-> now this article was tagged by someone to be included on the "2007 Wikipedia for Schools"). +mt 20:55, 24 July 2007 (UTC)

I only briefly looked over it, but I think it looks good :) -- Basar (talk · contribs) 02:17, 25 July 2007 (UTC)

Methods Corrections

I propose a change to the geophysical methods section of the site. As far as I know, generally capacitance and FDR sensors are the same thing. TDR and FDR sensors are two types of dielectric sensors, which measure dielectric permittivity to obtain volumetric water content. I don't know if this is very clear and I would like to expand upon this. Also, tensiometers are used to measure water potential rather than water content so I propose that we either have two sections (water potential and water content) or remove tensiometer from the methods section. —Preceding unsigned comment added by Laurenleighb (talk • contribs) 17:13, 6 September 2007 (UTC)

Please, dig in and edit and rearrange! I'm not completely familiar with TDR and FDR technologies, but if you can add any primary or secondary (e.g., Handbook of Hydrology) sources to support the paragraphs, please add them (I can help wikify and format these if needed). Also, I agree that tensiometers don't measure water content; however, anything that is completely saturated has a soil suction of zero (I'm not sure if this is worth mentioning or not). +mt 18:49, 6 September 2007 (UTC)

The unit for gravimetric and volumetric water content is %. Does anyone know how to convert % into mm? —Preceding unsigned comment added by Orthoklas (talk • contribs) 08:08, 12 July 2010 (UTC)

unit convertion

The unit for gravimetric and volumetric water content is %. Does anyone know how to convert % into mm? —Preceding unsigned comment added by Orthoklas (talk • contribs) 08:13, 12 July 2010 (UTC)

This article is about a ratio. You are probably looking for something similar, but certainly different. +mt 03:01, 16 July 2010 (UTC)

Defining terms

Hi all. When defining residual water content, I see that h is not defined: "\theta_r is the residual water content, defined as the water content for which the gradient d\theta/dh becomes zero." It would be nice to denifine the term for someone with no background knowledge. Maybe something like this: "\theta_r is the residual water content, defined as the water content for which the gradient d\theta/dh becomes zero (where h = pressure head)." Also maybe link to the pressure head article? Unfortunately I do not have enough of a background to distiguish hydraulic head vs pressure head wiki articles. — Preceding unsigned comment added by Ssdesv (talk • contribs) 15:44, 10 October 2013 (UTC)

Lead paragraph wording

The average reader will be flummoxed by the wording of the article's first paragraph. Water content is not an esoteric subject; therefore, this phrase ought to be reworded so as not to repel readers:

"...is expressed as a ratio, which can range from 0 (completely dry) to the value of the material's porosity at saturation."

If water content is a ratio, then it requires two different numbers in order to be calculated. "the value of the material's porosity at saturation" may be a ratio, but, by calling something a ratio, the two entities being compared by the ratio ought to be mentioned. Can anyone fix this? I am not qualified to do it.--Quisqualis (talk) 00:02, 21 January 2017 (UTC)

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unitless quantity

Dimensionless_quantity reads: Moisture content may be defined as a ratio of volumes (volumetric moisture, m3⋅m−3, dimension L3⋅L−3) or as a ratio of masses (gravimetric moisture, units kg⋅kg−1, dimension M⋅M−1); both would be unitless quantities, but of different dimension. --Backinstadiums (talk) 17:18, 14 April 2021 (UTC)