Fwd: difference between “Initial depth of water in the shallow/deep aquifer” and “Initial groundwater height”

[Azizallah Izady]

Dear SWAT users,
What is a difference between “Initial depth of water in the
shallow/deep aquifer” and “Initial groundwater height” in the
(000010001.gw) files?
I have simulated groundwater flow using MODFLOW. I want to use
groundwater level obtained from MODFLOW in the SWAT as initial
groundwater level. Now, I have no idea about which option (initial
depth of water in the shallow/deep aquifer” or “Initial groundwater
height”) can be used to replace MODFLOW groundwater level in the SWAT.

Any helps/insights would be appreciated.




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Best,

------------------------------------

Azizallah Izady
Dept. of Water Engineering
Ferdowsi University of Mashhad
Mashhad, Iran.
Cell Phone: +98-915-187-1219
E-mail: az.i...@gmail.com

[Jim Almendinger]

I believe "depth of water" is a measure of volume in the aquifer(s), not a measure of head.  

I'm not sure of "initial height" in the .gw files.  SWAT doesn't deal with groundwater flow as a function of head gradient and permeability -- it is pretty much all based on volume of water percolating past the bottom soil layer.  This volume (measured as a depth of water over the area of each HRU) is released to baseflow according to the alpha-baseflow parameter (subject to other complications such as gw-delay, revap, and capture by ponds and wetlands).  

There may be ways of backing out an estimated groundwater potential (water-table) surface, and perhaps SWAT has some of these auxiliary calculations imbedded -- I'm not sure.  But the estimates must be very approximate and based on a very simple (rectangular?) geometry for each HRU.  

Hopefully others know more and can correct my guesses. 

-- Jim

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Dr. James E. Almendinger, Senior Scientist
St. Croix Watershed Research Station
Science Museum of Minnesota
16910  152nd St. N
Marine on St. Croix, MN  55047
tel: 651-433-5953 X 19
fax: 651-433-5924
email: din...@smm.org
web: www.smm.org/SCWRS/

[lei qiao]

    Jim is right for the "depth of water " definition. And I think the "initial height" is just "depth of water" divided by the specific yield of aquifers. The specific yield could be varied for different aquifers, but I think SWAT default parameter is a fixed one. I have a paper just published in the JAWRA, which has some discussion how to find the specific yield for the Lower Missouri River Basin in US. Jim was acknowledged due to his help and answer to my question here.  The paper link is no MODFLOW involved, but has application about surface and groundwater integrated for SWAT. You can check if you are interested. It is titled Parameter Uncertainty Reduction for SWAT Using Grace, Streamflow, and Groundwater Table Data for Lower Missouri River Basin (http://onlinelibrary.wiley.com/doi/10.1111/jawr.12021/abstract)

Lei Qiao, Ph.D. 

Postdoctoral Research Fellow

 

Advanced Radar Research Center, and

School of Civil Engineering & Environmental Sciences

University of Oklahoma, Norman, OK 73019, USA

http://hydro.ou.edu/

 

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