Geology Reference
In-Depth Information
of more powerful computers, computation with large number of grids/mesh
is not a difficulty but the data preparation that is to assign the aquifer
parameters to each grid/mesh becomes cumbersome. Thus an appropriate
estimation procedure is required to provide an unbiased, minimum variance
and with unique value over the entire area of the mesh.
Rouhani (1985) used composite programming with a combination of
Geostatistics and multicriterion decision-making in optimizing network of
measuring thickness and porosity of a two-layer aquifer system. Aspie and
Barnes (1990) suggested the criterion by minimizing the expected cost of
classification errors. Das (1995) developed an analytical method integrating
the practical implementing aspects and applied to a multilayered groundwater
flow system for contaminant detection. Agnihotri and Ahmed (1997) analyzed
a number of ambiguities arising in the existing methods of data collection
network design using a few worked examples. Hughes and Lettenmaier
(1981) have suggested an algorithm to optimize the location of data collection
points by minimizing the variance of the error in estimating the parameter
over the entire area of the aquifer. Sophocleous et al. (1982) have applied
the technique of Universal Kriging in analyzing the network of wells for
water level measurement in Kansas, USA with respect to cost of the network
and the accuracy obtained. However, it has been limited to the data regularly
spaced along a square grid. Virdee and Kottegoda (1984) have proposed a
map of kriging estimation error (
k
) and located new measurement points at
places where a high value of
k
was calculated. They have applied this
method to a network of transmissivity and water level measurements. This
procedure has two drawbacks: (1) it is difficult to decide a limit to compare
the
k
values to, and (2) an additional point improves the estimation variance
not only at that point but also at the neighbouring points forcing the procedure
to work in an iterative way only. Carrera et al. (1984) proposed an iterative
procedure based on non-linear programming to select the optimal location of
measurement points and applied it to optimize monitoring fluoride
concentration in the San Pedro River basin, Arizona. Bogardi et al.(1985)
proposed a methodology combining two concepts: Geostatistics and
Multicriterion decision making (MCDM) to design a regular observation
network for spatially correlated and anisotropic parameter in a multiplayer
aquifer system, where the composite solutions is quite robust with respect to
variogram parameters and changes in the weight set assigned to the parameter.
Dillon (1988), Rouhani (1985) and Rouhani and Hall (1988) have used the
method of estimation variance reduction calculated at the centre of a set of
discretized blocks in the area. Hudak and Loaiciga (1993) developed an
analytical method integrating practical implementation aspects applied to a
multilayered groundwater flow system for contaminant detection. Gao et al.
(1996) presented a simple algorithm to rapidly compute the revised kriging
estimation variance when new sample locations are added. Moreover, we
believe that this algorithm is useful only if a network has to be improved
