Geography Reference
In-Depth Information
GIS provides excellent and powerful functions to capture and collate the
water quality data. It is also seen that water quality studies involving
repetitive, archival and historic use of the data requires the data be stored in a
formal database that can be used for exploratory purposes. Water quality
database to be utilized for GIS applications requires spatial coordinates, i.e.
latitude and longitude (or x- and y- coordinates) to be attached with the data.
The water quality data is further characterized by the depth at which the
sample is taken (vertical z-coordinate).
Monitored data must also be characterized with regard to time t at which
sample is taken. Thus, concentration (c) of any physical, chemical and
biological parameter can be defined by the following function:
c
f
(
x
,
y
z
t
)
(1)
In surface waterbodies such as rivers where discharge (Q) is a significant
quantity, the flux determination and data interpretation also require knowledge
of water discharge, and thus the concentration should also be a function of Q
as shown below.
c
f
(
x
,
y
z
t
,
Q
(2)
Firstly, the sampling locations based on their spatial coordinates are
located within GIS environment. Then, spatial locations of the sampling points
are attached with related attribute tables where different attributes of all
individual sites/points are stored such as concentration of all major ions,
calcium, magnesium, chloride, carbonate, etc. for one spatial point is stored.
Finally, the concentrations of a water quality parameter can be displayed
over the entire space through spatial interpolation. There has been evolved a
lot of spatial interpolation techniques over the time. An overview of the spatial
interpolation techniques is provided in subsequent section.
5.2. Overview of Spatial Interpolation Techniques
In numerical analysis, spatial interpolation or multivariate interpolation is
interpolation on multivariable functions. The spatial interpolation consists of
interpolating the multivariable function, known at given points, to yield values
at arbitrary points.
