boat necessitated collection of 19 water samples along the laXe
shore on 9th April 1981, the boat was available on 21st April ena-
bling 18 samples to be collected well in the interior of the lake
avoiding bottom reflectance effects. The samples were analysed
for, in addition to the various parameters listed in regard to the
Godavari survey, chlorophyll. since monitoring lake eutrophication
status was one of the major objectives.
3.3 Water quality mapping
As multivariate categorisation algorithms proved inadequate in
the case of water quality mapping, a different approach was attem-
pted. The sampling sites vere identified and targeted in the Mul-
tispectral Data Analysis system (MDAS) at NHSA Headquarters in Hy-
derabad. Sufficient pixels around the sample point were included
within the cursor to compensate for spectral and spatial uncertan-
ties. 4 statistical analysis yielded the mean and standard devia-
tion of pixel values contained in each training set. The mean re-
flectance values in all the 11 wave bands of the scanner were ob-
tained and all the possible band ratios computed. A stepwise re-
gression programme correlated each individual water quality para-
meter such as turbidity or chloride with the spectral varicbles of
bands and band ratio values. The resulting multiple regression
equations (Fig.5) were used as input to the next phase of analysis
In this second phase, a mapping programme was developed for produ-
cing colour coded.water quality maps. In the first. step of the
programme water pixels were edited from non-water pixels and the
water pixels digital values were input into the appropriate re-
gression equation and the water quality parameter estimated, and
assigned group numbers based on specified group number - range of
water quality parameter relstionships. Then dummy training sets
and groups were entered into MDAS along with desired colours. The
categorised water quality information was then filmed, using the
dummy group number-colour data, on the optronics recorder. The
three black-and-white colour separates were then composed in the
photo laboratory to yield categorised colour composite transparen-
cies and prints.
Colour coded maps showing surface distribution of turbidity,
total suspended and dissolved solids, chlorides, chlorophyll etc.
were obtained for Godavari and Husainsagar areas.
3.4 Discussion of results
After an evaluation, chloride level was chosen as the indica-
tor for tracing pollution dispersion in the Godavari river area
upstream of Rajahmundry town. The dilution of the paper mill ef-
fluent by river waters was graphically illustrated by the gradual
decrease in chloride level, from high at pollution influx point to
fresh water levels within about 4 km downstream of the influxe
point. Thus the downstream uses of river water for paper mill in-
take, municipal water intake, human use for bathing and washing
clothes etc. are not affected by the papermill effluent. Since
this is the case with minimum river flow conditions, at any other
time the dilution will be higher and consequently the impact of
pollution on downstream use can be safely ignored.
Husainsagar lake in Hyderabad is affected by significant
614
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