MANAGEMENT OP WATER FOR MALARIA CONTROL 
329 
or may become endemic, it is desirable that 
a surcharge be provided so that drift and 
flotage may be stranded at the initiation of 
anopheline breeding. In addition to this, 
it is important that a seasonal recession be 
followed, combined with whatever weekly 
(cyclical) fluctuation is permissible in the 
operation of the project. The alternatives 
of either a wide seasonal recession or weekly 
fluctuation may be used if of sufficient 
scope. 
Shoreline Maintenance 
Although it appears to be established that 
water level fluctuation is an absolutely 
essential factor in the prevention of anoph¬ 
eline breeding in reservoirs, it must be re¬ 
peated that the efficiency of this measure is 
dependent first on adequate reservoir prep¬ 
aration and, second, that it might be supple¬ 
mented by shoreline maintenance. It is 
unfortunate that the latter is a continuing 
operation which may become expensive 
under certain conditions. The cost may be 
justified directly on the basis of anticipated 
savings from larvicidal operations. There 
are three types of shoreline improvement: 
(1) drainage maintenance; (2) drift re¬ 
moval; and (3) vegetation control. 
As pointed out above, it is important that 
where depressions exist in the fluctuation 
zone, adequate drainage should be provided, 
otherwise standing pools would be left at 
the time of the drawdown. Obviously these 
ditches, whether constructed by dragline or 
by hand, must be maintained in a service¬ 
able condition. The experience to date in 
the Tennessee Valley Authority has been 
that the cost of such maintenance is very 
low. Naturally this will vary with the type 
of soil encountered, the grade and section 
of the ditch, amount of silt being carried, 
etc. However, these factors can be taken 
into consideration in designing the ditches. 
Attention is called to the fact that this type 
of drainage differs from the usual surface 
drains in that it is subjected to extended 
periods of flooding. 
Despite the greatest care in reservoir 
preparation, a considerable quantity of 
drift and flotage (smaller debris) will be 
found on any large reservoir following im- 
poundage. Furthermore, lesser amounts 
will continue to find entrance into the im- 
poundage throughout the life of the project. 
Tributary streams are responsible for the 
entrance of a large amount of this ma¬ 
terial, especially during flood periods. The 
death and decay of marginal timber is the 
origin of much of it. In reservoirs in which 
a flood surcharge is not possible the removal 
of a certain amount of the larger drift will 
have to be considered. The operation 
should be undertaken at the time of mini¬ 
mum lake elevation. The drift may be 
handled either by hand or by mechanical 
equipment, mounted on a barge or oper¬ 
ating from land. Any of these procedures 
are costly since the material usually must 
be piled, dried and burned. The latter 
operations may be facilitated by certain 
preimpoundage clearing at the heads of 
hollows and bays where drift may be 
expected to accumulate. 
The problem of control of vegetation is 
of paramount importance and is not con¬ 
fined to malaria control on impounded 
waters. A. quadrimaculatus breeds 
amongst vegetation, in flotage or in a com¬ 
bination of the two. Since flotage is largely 
of vegetable origin, the control of anophe¬ 
line larvae is intimately associated with 
control of vegetation. 
The stumps of water-tolerant trees may 
survive extended periods of inundation and 
retain ability to send out young shoots fol¬ 
lowing a drawdown. The control of such 
second growth is difficult and usually will 
necessitate hand removal at a season when 
the lake is at minimum elevation. The most 
effective method of control is through limi¬ 
tation of the rate of recession of water level 
during the first season of impoundage and 
the low cutting of stumps during reservoir 
preparation. 
The problem of survival of woody species 
may be reduced to a minimum by proper 
planning. Unfortunately, such is not the 
case for herbaceous species. From a ma¬ 
laria control point of view, the herbs may 
be grouped into three classes: (1) terres¬ 
trial species, (2) wetland species and (3) 
aquatic species. In the present discussion 
