DRAINAGE AND PILLING IN MALARIA CONTROL 
321 
TABLE I 
Mississippi State Board op Health 
Invert Data 
Concrete mix 1:3:5 For all slopes Mortar 1: 3 
100' 
section con. bottom 
o 
o 
section brick bottom 
Chord 
length 
Radius 
feet 
Depth 
inches 
Cu. yds. 
per 100' 
Cement 
sacks 
Sand 
cu. yds. 
Gravel 
cu. yds. 
Cement 
sacks 
Sand 
cu. yds. 
No. of 
bricks 
V 
0.63 
3 
1.3 
5.6 
0.6 
1.1 
4.8 
0.5 
545 
2' 
1.25 
6 
2.4 
10.5 
1.2 
2.0 
9.1 
1.0 
1026 
3' 
1.87 
9 
3.4 
15.3 
1.8 
2.9 
13.1 
1.4 
1490 
4' 
2.50 
12 
4.5 
19.9 
2.3 
3.8 
17.1 
1.9 
1940 
5' 
3.12 
15 
5.6 
24.8 
2.9 
4.8 
21.3 
2.4 
2420 
6' 
3.75 
18 
6.6 
29.4 
3.4 
5.6 
25.3 
2.8 
2870 
Riprap or masonry construction requires approximately 25 sacks of cement and 3 cu. yds. of sand 
per 100 sq. yds. of invert. This table is for inverts whose thickness is three inches. Ten per cent should 
be added to the amounts for aprons, spillways, curtain walls, etc. 
be more than 2 feet per second. In sections 
where it is absolutely impossible to secure 
velocities above 2 feet per second, small 
inverts should be used with shoulders on 
each side to take care of the storm water 
flow. If the velocity is found to be more 
than 4 feet per second, it will be necessary 
to construct spillways to drop sharply from 
one elevation to another. Increasing the 
grade of the invert on curves tends to pre¬ 
vent the deposition of silt. 
Subgrade. On many projects it has been 
necessary to remove the muck, sometimes 
to a depth of 3 feet, and to replace this 
unsatisfactory material with clay, brick¬ 
bats, broken stone, oyster shells, sand and 
gravel, or any other material that can be 
satisfactorily compacted to form a solid 
subgrade. If the invert traverses a seepage 
area or one fed by springs, open jointed 
tile set in broken rock, brickbats, or gravel, 
is laid under, or to one side of, the invert 
to collect the underground water and 
stabilize the foundation. Hasell and 
Weathersbee have laid a relatively large 
amount of small bore butt joint tile for 
dewatering drainage ditches. They state 
(1938) that if an ample amount of porous 
material is placed around the tile to pre¬ 
vent the entrance of solid matter, these tile 
will function satisfactorily on a grade as 
flat as 0.1 per cent. 
Protection of banks. Thick Bermuda or 
carpet grass sod has been found to be the 
best available material for the protection of 
ditch banks. Blanket sodding is much more 
satisfactory than strip or checkerboard. 
The blocks of sod should be cut approxi¬ 
mately 2 to 3 inches thick and about the 
same average shape. In laying the squares 
on the ditch bank, care should be taken to 
lay them in the same manner as brick are 
laid, so as to eliminate erosion between the 
rows of sod and to conserve the water in it 
and rain water to promote its growth. 
In urban areas, it is not always possible 
to secure the necessary width for the con¬ 
struction of inverts with sodded banks. 
Under these conditions, retaining walls con¬ 
structed of rock, brick, or concrete offer the 
best solution. If a solid masonry or con¬ 
crete wall is used, the bottom width should 
be approximately 0.4 of the height, the 
height being the total distance from the 
bottom of the footing to the top of the wall. 
Riprap made of broken concrete, native 
stone, brick set in mortar or precast con¬ 
crete slabs are necessary to stop erosion on 
ditch banks on the outside of curves, under 
bridges, at junctions of ditches above and 
below spillways, and in unstable soils. If 
the system is properly designed, it will not 
be necessary to use a large amount of rip¬ 
rap. 
Low areas on each side of the invert sys¬ 
tem are drained into the paved ditches by 
