Graphs based on
relation (ratio or difference) of drawdowns in two wells provide
some support methods for aquifer parameters estimation. To some
extent these methods are similar to point methods widely applied
before. The difference is that in method considered the parameters
are averaged by the entire time interval while in point methods –by
one or two observation points only. To apply the method user must
choose two observation wells (menu "Choose
> Well") and
corresponding plot (menu "Choose
> Plot").
For twowell
graphs inversion of drawdown values is available as well as
ordinate axis change (for example
s1
/
s2
can
be replaced by
s2
/
s1).
For inversion use menu "Tools
> Inversion") or function
keys Shift+F5
Graph of
drawdown difference vs lg(t):
(s1

s2)

lg(t)
for
most conceptual schemes at steadystate represents a horizontal
segment to which straightline method can be applied to estimate
transmissivity value (menu "Analysis
> Graphical method").
Plot of drawdown difference in two wells: transmissivity estimation
by horizontal line.
Plot of drawdown
ratio vs lg(t): (s1
/
s2)

lg(t).
For several conceptual schemes calculated drawdown graph plotted in
such coordinates is not dependent of transmissivity within the
entire time range, thus allowing parameters matching by hydraulic diffusivity
value alone (menu "Analysis
> Direct solution").
Plot of drawdown ratio in two wells.
The graph based
on observation data in two wells is also used for parameter
estimation by method of bisecting line.
