ALLUVIAL BASIN OF THE MISSISSIPPI 253 



of the flood plain, a levee less high might suffice as well as one built on 

 the back-slope. Where the original four-foot levee stood in Louisiana 

 is a levee about 16 feet high. The top is not much higher than the top 

 of the original levee, but, being situated at some distance from the 

 banks, its base is 10 feet lower. The immediate banks of the river are 

 so subject to caving that they do not make, in all cases, a safe founda- 

 tion for a levee. It has been considered safer and wiser in many in- 

 stances to build a more stable foundation. Furthermore, if the levees 

 are built upon the higher and immediate parts of the flood plain, the 

 levees would be nearer each other. The nearer they approach one 

 another, the higher they must be. Any detraction from the horizontal 

 expansion of the waters must be evidenced in a vertical expansion. 

 With the levees placed further apart, a less height is possible. The 

 thing that determines the height to which they shall be built is the flood. 

 There is an endeavor to place the grade of the levees at from 2 to 4 

 feet above the gauge measurements of the highest floods. Thus for a 

 while the provisional grade was 2 to 3 feet above the 1897 flood. 

 Later the 1903 flood set a new mark and a grade 2 to 2.5 feet above the 

 1903 high-water line is suggested. At Lake Providence, the 1903 

 water mark was 2 feet above the 1897; at Greenville, it was 2.4 feet 

 above. Accordingly, the high water of 1903 reached approximately 

 to the tops of the levees suggested after the 1897 flood, and a new 

 height, 2 to 3 feet above the former, is now demanded. This latter 

 height is about 5 feet above the provisional grade of five years ago. 

 As the levees approach completion, higher and higher grades must 

 inevitably result. As long as there is relief of the waters by incom- 

 pleted levees and crevasses, the necessary height can not be determined. 

 When the remaining 29 per cent, of levee is constructed and the system 

 withstands one of the greater floods without a crevasse, the excessive 

 flood will determine the height of the levees. Even then certain fac- 

 tors of flood conditions may so unite as to cause a flood which will 

 overtop the system. The statement of the character and condition 

 of the system under the strain of the 1903 flood indicates that there 

 is much left to be done. In the upper part of the basin, the levees were 

 reported too low and of insufficient dimensions. The high water 

 reached to the top for one half of the entire length of the lower St. 

 Francis district and for many miles was above the tops, being restrained 

 from spreading over the basin by capping the levees with planks, dirt 

 and sand-bags. In the district below, it is reported that because of the 

 settlement of the embankment and because about 20 miles of the line 

 in the lower end of the district had not been raised to the provisional 

 grade, considerable work was required to prevent the water from over- 

 flowing the levees. Again in Louisiana, the topping of the levees by 

 planks and sand-filled bags was necessary over a distance of 71 miles 

 of the line in order to prevent a wash-over. An engineer reports that 



