RECLAMATION OF LOUISIANA WET PRAIRIE LANDS. 



427 



a certain stage of water to insure the successful operation of an 

 hydraulic dredge which was engaged in clearing and deepening the 

 reservoir canal. 



The data which have been collected would indicate that a much s^reater run-off 

 may be expected from the better ditched and fully cultivated lands than from those 

 that are more nearly in a natural state. While this may be true, it is probable that a 

 long series of uninterrupted records will show a less striking variation. It will be 

 noted that the records on the New Orleans Land Company tract did not begin until 

 the effects of the 5-inch rainfall of the first part of June had passed and that they 

 were suspended during and after the severe storm of September 20, thus not in':'lud- 

 ing the heaviest storms of the season, with the exception of that of December, when 

 the rainfall was heavy and mostly fell in a few hours' time, thus giving the largest 

 percentage of run-off of any recorded. The decreased evaporation of December no 

 doubt also increased the run-off. 



Owing to the fact that at times of extreme high water a few acres 

 are drained by gravity on the Willswood plantation, it is probable 

 that the run-off records for that tract show a slightly less quantity 

 than they should. 



The fact is well known that very heavy storms cause a larger per- 

 centage of run-off than smaller ones, but for storms of all magnitudes 

 there is a variation in the ratio of run-oif to rainfall, due to the 

 varying conditions of the soil and to its character and state of mois- 

 ture, the duration of the storm, amount of evaporation and seepage, 

 slope of ditches and fields, and arrangement and capacity of reser- 

 voirs, manner of pumping, and probably to other causes not yet 

 determined. In the table below, the records of a few typical heavy 

 storms are presented for the Smithport and Willswood plantations, 

 as they more nearly represent normal agricultural conchtions than 

 the two other experimental tracts and they also were under the 

 closest observation. On account of the effects of preceding and 

 succeeding storms it is didicult always to determine the effect of a 

 single storm, •onsequentiy errors are liable to arise. It will be seen 

 that the percentages for the two tracts are very nearly equal and that 

 the combined percentage of 50.8 for the three storms recorded 

 is much higher than the combined percentage of 35 for the four 

 tracts for the six-months period shown in the table on page 426. 



Precipitation and run-off from heavy storms, Smithport and Willswood plantations. 



Total for both stations: Precipitation, 24.21; run-off, 12.29. Ratio of run-off to precipitation, SO.S per 

 sent. 



