2 BULLETIN 1098, U. S. DEPARTMENT OF AGRICULTURE. 
in time and in reduced efficiency of the plantation hands during the 
season of the year when the crops are most in need of attention. 
The bayous or streams of the region are an important source of 
the Anopheles mosquitoes which convey malaria, and since the higher 
ridges offered by the bayou banks are the logical locations for the 
plantation roadways, the homes of the tenants are located along these 
banks. While control of the breeding of Anopheles in a bayou is but 
one factor in the ultimate control of the malaria mosquitoes in the 
Delta, it is an important factor, for these bayous offer a near-by 
source of Anopheles in locations on the plantations which are other- 
wise favorable in respect to distance from breeding areas of these 
mosquitoes. 
Since the general topography of the Delta and the slight fall in 
the bed of the bayous do not. permit drainage, the common practice 
in disposal of surplus surface water, it became necessary to devise 
some method of control, practical from the standpoint of plantation 
management, to prevent breeding of Anopheles in bayous. The 
Bureau of Entomology has demonstrated that the breeding of Ano- 
pheles mosquitoes can be controlled in a bayou by clearing the vege- 
tation and impounding the water. The work was located on Hecla 
plantation at Mound, Madison Parish, northeastern Louisiana. This 
bulletin deals with the natural conditions of the bayou before the 
work was done and with the changed conditions brought about by 
the work, especially with reference to the breeding of mosquitoes. 
It also discusses the impounding of water in a bayou from the stand- 
point of plantation economy. 
TOPOGRAPHY AND FORMATION OF THE REGION. 
To gain an idea of the relation of the streams of this region to 
the surrounding topography, it is necessary to discuss in a very gen- 
eral manner the formation of the region. The soil is an alluvial 
deposit of considerable depth and the formation is characteristic of 
delta accumulations. There is a slight fall in the general direction 
of the main stream, the Mississippi River. This river in times past 
has followed an irregular, winding course through the Delta of its 
lower valley, often forming new channels. The old channels are 
marked by the ridges which are peculiar to the region. The bayous, 
or streams, of the region are in reality old spillways of the river 
when at flood, formed before the days of the protective levee system by 
the tendency of the river at stages of high water to break through its 
built-up banks and form new channels for the surplus water. Before 
the levees were built, the river and these bayous overflowed their 
banks at regular seasonal intervals. The heavier particles carried 
by the water in suspension were deposited first and in larger quan- 
tity. The finer particles were deposited in smaller amounts as one 
