DRAINAGE AND FILLING IN MALARIA CONTROL 
323 
In order to obtain an accurate finished 
grade, batten boards are set across the ditch 
at intervals not to exceed 50 feet. Small 
blue top stakes are set on the center line 
of the ditch at six-foot intervals. The tops 
of these stakes are set on finished grade. 
It is relatively easy to obtain a true flow 
line by checking the flow line of the invert 
with a straight edge resting on the blue top 
stakes just before the concrete takes its 
initial set. 
Benefits. The principal benefits result¬ 
ing from inverts are: first, the elimination 
of mosquito-breeding areas with the corre¬ 
sponding reduction in the cost of mosquito 
control by oiling; second, the reduction in 
ditch maintenance costs; third, the protec¬ 
tion of culvert and bridge structures; 
fourth, the reduction in the amount of 
household insecticides used; and fifth, the 
conservation and beautification of both 
public and private property. 
Underground Drains 
Underground drains were used by 
Gorgas and LePrince in Panama with 
much success. They are constructed of 
small tile set in broken rock, brickbats, or 
gravel and covered with at least 6 inches 
of straw, leaves, pine straw, or any other 
material which will act as a filter and pre¬ 
vent the dirt from filtering into the drain 
and filling the joints. In sandy soil it will 
be necessary to cover not only the top, but 
also the sides of the porous material to 
prevent sand from entering the drain 
(Diagram No. 7). 
DIAGRAM NO-7 
UKOtRGROUND DRAIN USING TILE: 
Fill 
»(Uove« or pioo Stroup 
Pilfer 
Satisfactory drains may be constructed 
of poles set in broken rock, brickbats, or 
similar material (Diagram No. 8). It is 
necessary to use more straw and filter 
material on pole drains in order to pre¬ 
vent filling of the voids by sand. In heavy 
zu/j/fTTr* 
ftoefc 
F i l+« 
Reck 
Tile 
• DIAGRAM N 0-3 
UNOERGROUND POLE DRAIN 
soils the pole drains may be covered with 
strips of sod cut the exact width of the 
drain and placed upside down to act as a 
filter. 
These underground drains are frequently 
utilized in deep contour ditches to inter¬ 
cept the seepage flow, to carry the overflow 
from artesian wells, and as outlets for 
drinking fountains. Wherever possible 
this type of drainage should be used, as it 
eliminates mosquito breeding completely, 
reduces maintenance costs to a minimum, 
will be effective for a long period of time 
if properly executed, and constitutes an 
improvement to the property. Farmers 
favor this type of drainage as they can 
plow over the ditch, and city officials like 
it because the maintenance is very small. 
Filling 
Filling can be used in almost any town 
or city, without the expense of skilled 
supervision. Under certain conditions it is 
an ideal malarial control method, as mos¬ 
quito-breeding areas are eliminated com¬ 
pletely and permanently. In many towns 
and cities unsightly areas which formerly 
bred mosquitoes and were very difficult or 
impossible to drain have been transformed 
into parks by filling them with garbage, 
trash, or other debris. During fly-breeding 
season, dependable labor must be kept on 
the dump to sort the material, working the 
putrescible portion to the bottom. The fill 
is then topped with not less than six inches 
of dirt. 
The popularity of this type of work has 
been due largely to the fact that local offi¬ 
cials have reduced their hauling costs, have 
eliminated the need for oiling, and have 
created valuable building lots and beauti¬ 
fied the city. 
