2 BUIXETIN 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 Eiver. 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 baj^ous, 

 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 



