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Last modified
1/26/2010 2:22:40 PM
Creation date
10/12/2006 1:36:51 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8027
Description
Section D General Correspondence - Federal Agencies - USDA - Agricultural Research-Service
State
CO
Basin
Statewide
Date
8/1/1975
Author
USDA
Title
Field Observations of Transient Ground Water Mounds Produced by Artificial Recharge into an Unconfined Aquifer
Water Supply Pro - Doc Type
Report/Study
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<br />o l) 0 7'1 ~~i <br /> <br />~~~ <br /> <br />~~~t~ <br /> <br />neath this pond and the possible restrictions on its rate of release thJ:ough <br />the perching layer theJ:e. Taking the difference between vr' and Vf' in table 2, <br />we see that for pond No.1 only 2.74 acre-feet of the 27.04 acre-feet was de- <br />livered to the mound after the fall began; however, 3.00 acre-feet out of the <br />total 8.40 was delivered at pond No.2. Note that for pond No.2 the deviation <br />disappears as time advances and vadose drainage decreases. Thus, if the mound <br />is small, vadose drainage can greatly influence the falling hydrogJ:aph. <br /> <br />DISCUSSION <br /> <br />The major assumptions regarding ground wateJ: flow are listed in table 3 <br />with comment as to what extent they may have influenced the comparison of theory <br />to observation in our two field trials. <br />The Dupuit-Forschheimer (D-F) (7,9) assumptions as applied by Glover (10)9 <br />seemed to be quite acceptable. This may be due in part to our use of the well <br />test method for determining K and V, as the Theis nonequi1ibrium method is also <br />based on the D-F assumptions, this could bias K and V towaJ:d horizontal flow. <br />Rigorously, the Theis method does not apply to the water table case here; ho~ <br />ever, it is the one most commonly used and can provide acceptable values when <br />applied with the reservations stated by FeJ:ris (8). <br /> <br />Table 3.--Inf1uence rating of assumptions apparent from field trials <br /> <br />Assumption <br /> <br />Acceptable <br /> <br />Questionable <br /> <br />Unacceptable <br /> <br />Rising mound: <br />D-F flow theoJ:Y <br />Well test for K and V <br />Square area transformed to circle <br />Stratigraphic definition of D <br />D constant with time <br />Uniform i <br />to from wet front <br />Horizontally uniform V <br /> <br />x <br />X <br />X <br /> <br />X <br /> <br />X <br />X <br /> <br />X <br /> <br />X <br /> <br />Falling mound: <br />No vadose drainage <br />Disk-shaped mound height (H) <br />from center of pond; volume <br />corJ:ected for vadose storage <br /> <br />X <br /> <br />X <br /> <br />In the static water table, the stratigraphic analysis and piezometric head <br />loss used to define possible perching above the water table and the wetted depth <br />(D) proved in error. The hydraulic response of individual layers in the profile <br />cannot be evaluated unless monitored under flow conditions closely approaching <br />those associated with recharge. Also, exclusion of the mound height from the <br />evaluation of D had a recognizable influence on the comparison in the pond where <br />D was small. <br />The time dependency of the initial i after to determined from the wet front <br />position led to some deviation between theory and observation during the initial <br /> <br />9Also see footnote 2. <br /> <br />14 <br /> <br />.:~ytv~~;~..~;-;t~s: <br />~~~~;g'~:i <br /> <br />i;.,.~.~~- ;'; <br /> <br /> <br />Ii~ <br /> <br /> <br />:-...:-:...;>: <br /> <br />)?-~;~->:-:~ :~:.<;~;; <br /> <br />~.: ....... .~-: <br />, ........, <br />l~~;.~;;:~:~~;:~:-;:.:~ -. <br />:.:. -"~- '". <br /> <br />,-". ... <br />.' ".'c_". <br /> <br />
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