DRAINAGE OF WET LANDS OF SOUTHERN LOUISIANA. 25 



and side slopes of 1£ to 1. The unusual height is accounted for by the fact that 

 at the time of construction danger from high water, due to breaks in the Mis- 

 sissippi levees, was still great. 



Reservoir Canals. 



As indicated in the description of the levees, the reservoir canals on this 

 district were cut with a dipper dredge. By using the canal so excavated as a 

 reservoir, it was necessary to construct only a comparatively short canal into 

 the interior of the district in order to give outlet to the collecting ditches. 

 These ditches are mostly about 5 feet deep, with 10-foot top widths and 3-foot 

 bottoms, and serve as outlets to the small lateral ditches. 



Owing to an extensive silting up of the reservoir canals, their capacity is 

 very much less than it originally was. During the whole time since their con- 

 struction no attempt has been made to remove this deposit of silt. As a result 

 the canals are not deep enough to afford outlet facilities to the ditches in the 

 back lands. The pumping operations are also interfered with, in that the water 

 is not brought to the pump rapidly enough to insure continuous operation at 

 full capacity of plant during the removal of the run-off of a rain. This lack 

 of reservoir capacity also makes the operation of the plant very unsatisfactory, 

 as the water level must be kept nearly at the bottom of the canals to afford 

 sufficient depth of drainage to the land. During the coming year it may be that 

 the reservoirs will be cleared of silt with a dredge. This will allow opportunity 

 to see what effect increased reservoir capacity will have on the pumping opera- 

 tions. Doubtless the greatest effect will be to decrease the number of days on 

 which it will be necessary to operate the plant, although it is not likely that the 

 total hours of operation or the amount pumped will be greatly affected. 



Ditches. 



The ditches on this plantation are of about the usual cross section, having 

 depths of 3 feet, top widths of 3 feet, and bottom widths of 1J feet. The aver- 

 age spacing varies with the character of the land. Thus, on the front lands 

 which are rather impervious the spacing is about 100 feet, while on the back por- 

 tion the ditches are from 300 to 500 feet apart. On the front lands the lengths 

 of the laterals, between collecting ditches, are quite small considering the large 

 slope of the surface of the land. Conditions on similar plantations where the 

 ditches are twice as long indicate that the laterals of this district could safely 

 have been made nearly twice as long as they are. 



On the back lands, however, the ditches are already about as long as it would 

 be advisable to have them, since the land is almost level and the reservoir canal 

 quite shallow. At present these ditches are too shallow to give adequate drainage. 

 Some measurements of the depth of water table were made during the early part 

 of the summer of 1910. The results of these measurements are shown graph- 

 ically in figure 5. It is apparent that as yet this soil is not very impervious, 

 when compared to the lands of the vicinity of Bayou La Fourche and as 

 shown by other similar measurements on area No. 2. (Figs. 8 and 8a, pp. 31 

 and 32.) Even after heavy rains the profile of ground water is not excessively 

 steep. The ditches are spaced too far apart for the best results, although if 

 they were of full depth they would very nearly drain the ground. It is the 

 intention of the owners of this tract to deepen the present ditches to the usual 

 depth of 3 feet and to construct new ditches midway between the present ones. 

 The situation appears to be favorable to the placing of lines of tile instead of 

 the new set of ditches. As the surface water is already handled by the present 

 25102°— Bull. 71—14 4 



