14
SUPPLEMENT TO THE ANNUAL REPORT OF THE
The other rivers with more flowing water in them such as the Vuppuvagu,
the Pillaperu and the second part of the Maneru after it receives the Pillaperu,
also have breeding places along the banks in isolated pools or pools behind rocks
but to nothing like the extent of the first portion of the Maneru. The Vuppu
- v a g u i s m u c h f u r t h e r f r o m t h e v i l l a g e s o f t h e M o p a d i r r i g a t e d a r e a t h a n i s t h e
Maneru and so probably plays little or no part in producing malaria in that
tract, but it is probably partly responsible for malaria in Dukkanur which is on
its bank. The other breeding places here are several pools in apparently natural
streams. Irrigation of a few fields of this village has been. begun but at present
seems to be to so small an extent as to be of no importance in producing breeding
places, hence the grouping of this village along with those of the Maneru River
group but possibly the presence of the canal on the higher land to the north is
responsible for some of the water in the streams east of Dukkanur.
River breeding places are partly responsible for anophelines in . the Mopad
extension area—villages of group D, but in addition there are the ordinary type
of breeding places found in irrigated areas.
The last breeding place worth mentioning is the Mopad Reservoir itself on its
south western side towards Inimerla, where the shore is the country that was
inundated without being excavated so that along the edges of the reservoir, there.
are small old tanks, wells and other shallow depressions containing water which
breed anophelines. These breeding places are probably mainly responsible for
the small amount of malaria in the “ control” dry crop villages west of Mopad
—so these are not altogether removed from the influence of the reservoir in
producing malaria.
6. Discussion— Examining Tables II and X (of the first report), and con
- t r a s t i n g t h e v i l l a g e s o f g r o u p s C a n d D w i t h t h e v i l l a g e s o f t h e M o p a d i r r i g a t e d
area group A, and the neighbouring villages along the Maneru of group D, it is
evident that malaria prevails more severely in the last two groups. From the
description of breeding places and the density of anopheline populations it is also
evident that the reason for this is to be found in the great abundance of anopheline
breeding places in areas A and B.
Now it is difficult to say at this time what the conditions were before the
reservoir was built and before the land was irrigated. It may have been bad in
places where many facilities for breeding existed as now exists at Dukkanur—-
p o o l s a l o n g a r i v e r a n d p o o l s i n n a t u r a l s t r e a m s ( a s a l r e a d y e x p l a i n e d t h i s m a y b e
partly due to the canal). But, on the whole judging from the evidence given in
the first report, we imagine that most probably malaria was much less severe than
at present, being about the extent now prevalent in groups C and D.
Irrigation seems to have affected the area in three ways :
—
(a) By raising the sub-soil water level making it far easier for all depre
s - s i o n s t o h o l d w a t e r a n d b r e e d a n o p h e l i n e s . T h e r a i s i n g o f t h e s u b - s o i l w a t e r
level appears to be a fact according to the evidence presented in the first report,
but we should like to hear if any definite measurements have been made by
engineers.
(b) By forming many breeding places in water collections made by seepage
or drainage. Water is brought to a place in a regular way but apparently is
allowed to get off it in every possible irregular way. This appears to be the
rule in irrigation in India, but it is time that a change was made in works initiated
by Government.
(c) By blocking the Maneru with a dam to make the reservoir, the next
few miles of its course has been converted as described into a long chain of exten-
sive breeding places.
In considering these points it is clear that if wet crop irrigation is to co
n - t i n u e , t h e w h o l e o f t h e M o p a d t r a c t w i l l h a v e t o b e c a r e f u l l y d r a i n e d s o a s t o
abolish the breeding places formed under cause (b) mentioned above and to some
extent reduce them under cause (a ), secondly a certain amount of filling in of
such minor areas and pits as cannot be drained. will be necessary.
The alternative is to diminish the amount of water spread on the land by
irrigating only dry crops. The water needed is so much less, that probably the