WET LANDS OF SOUTHERN LOUISIANA. 17 



tically impossible to measure; the run-off from these drainage areas. It is 

 probable that the natural run-off is very low, .owing to small slopes and the 

 rank vegetation on all the land, only about 10 per cent along the bayous being 

 under cultivation. The bayous of sedimentation are quite free from growth 

 of vegetation, many having a considerable boat traffic, which lends to keep 

 them cleared out and in good condition as drainage channels. Those of tidal 

 erosion are apt to be overgrown with water hyacinths, but owing to their 

 greater depth these are also quite efficient channels. 



As shown in figure 1, many parts of this section discharge their drainage 

 water almost directly into the Gulf or into large interior lakes that undergo 

 very little fluctuation in water surface. Thus these areas are relieved of all 

 drainage water due to direct precipitation without great rise of water in the 

 carrying channels. In the interior portions, such as that contiguous to the upper 

 part of Bayou Lafourche, there often are rises of water level of several feet in 

 the main drainage channels. In this flat country a rise or 3 to 4 feet in the 

 main drainage outlet is a very serious matter and one that demands attention. 



In reclaiming land in this section the usual practice is to inclose the district 

 with levees to keep out the surrounding water ; the drainage water of the land 

 so inclosed is then pumped over the levee into some natural bayou that leads 

 to the Gulf. If the fluctuation in water level in this outlet bayou is great, not 

 only is a more expensive pumping plant equipment necessary, but the cost of 

 the levees is very greatly increased. As the usual height of the levees is but 

 from 3 to 5 feet above the ground level of the marsh, a rise of 3 to 4 feet in 

 the outlet bayou will often endanger the levees, or at least cause a considerable 

 seepage through them. The danger from seepage is especially great, because 

 the fluctuation of the water level takes place very slowly. Several times in the 

 past seven years the water has stood 1.5 feet above mean tide level for more 

 than a month, and at one time it stood for more than a month 2 feet above mean 

 tide. As a result, levees that were satisfactory in ordinary times allowed much 

 seepage to enter the district they protected, and heavy and continued pumping 

 was necessary. 



Up to the present time little attention has been given to the problem of the 

 disposal of the drainage water after it is pumped over the levees. Some 

 sections never will be compelled to give this matter consideration, owing to 

 their favorable locations on or near the Gulf or some other large body of water. 

 On the other hand, there are sections of wet prairie that are isolated from any 

 large bodies of water by distances of from 20 to 75 miles along the shortest 

 natural outlet channel. In the first years of reclamation no difficulty was 

 experienced in getting outlets, for the surrounding limitless prairie was so little 

 above sea level that the drainage water spread out immediately, causing no 

 trouble ; but in some localities so much land now has been reclaimed that the 

 effect on the carrying capacity of the natural watercourses is becoming notice- 

 able. As the work of reclamation goes forward and district after district is 

 reclaimed until a considerable portion of the whole area is appropriated, the 

 drainage water, when pumped over the levees, can not spread over the sur- 

 rounding prairie, for the latter will be inclosed by the levees of adjoining dis- 

 tricts. The water then will be forced to flow through long winding channels 

 to the Gulf, the distance often being as great as 75 miles. This will mean 

 that the water level on the outside of these interior districts must rise until 

 sufficient head is created to cause a movement of the water to the Gulf, thus 

 greatly increasing the cost of reclamation and rendering unsatisfactory much 

 of the work that is now apparently finished. 

 30444°— Bull. 652—18 3 



