Water table depth 1

[Nole954]

What is the best way to find average water table depths of a site without a geotech report. USDA soils survey is what I used, but just wanted to know if there was a better source out there

 

[beej67]

Soil survey is a very bad source of water table depth unless you're talking about a very large, very flat property, and you're looking for generic averages.

If a full blown geotechnical study isn't an option, send someone out with a hoe to dig some test pits. If water table is an issue for your design, then it's imperative you find out what that is first.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[gbam]

It depends on the extent of area you are investigating. One way to get information is to contact your department of water resources and get the registered well information for the area to get the static elevation. You can use this information to create and groundwater contour map so you can interpolate or extrapolate an elevation.

 

[GeoPaveTraffic]

The only way to get acurate water depths is to have monitoring wells or preferably piezometers on your site. The use of wells from "the general area" will not be acruate for most sites.

As for using USDA soil maps, you might as well just guess.

Mike Lambert

 

[beej67]

If this is for a civil design in Florida, and you're using the testing to set your control elevation of a surface pond, then your geotechnical engineer will need to tell you not only the current water table, but the "Wet Season Water Table," or "Seasonal High Water Table," which are both terms for the same thing that show up in different places in the literature. Your geotech will set this elevation by looking for a band of discoloration in the core samples he takes, that comes from organics floating to the top of the water table as it fluctuates, and getting deposited at the upper bound of where the WT fluctuates. You can also sometimes get your environmental sub to establish wetland elevations based on environmental markers in surface wetlands, and go off of those.

It's important to get this right in Florida so you don't accidentally draw down a neighbor's water feature by setting your control elevation lower than the permanent pool on his property. Doing so could damage the value of his property and you'd be liable.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[FundyBayEngr]

Testpits are the economical approach to determining local conditions at your site. Boreholes with piezometers are the better approach. The BHs will also allow you to collect discrete soil samples, SPTs or CPTs, N values, etc., and reduce uncertainties.