328 KANSAS CITY REVIEW OF SCIENCE. 



ENGINEERING. 



THE IMPROVEMENT OF THE MISSISSIPPI RIVER. — BOTH SIDES 



OF THE QUESTION. 



I. The Levee System. — At a late meeting of the St. Louis Civil Engi- 

 neers' Club a paper upon " Protection of the Lower Mississippi Valley from Over- 

 flow," was read by Mr. J. B. Johnson, of which the following is an abstract : 



The extent of the overflowed region is 20,000 square miles. The great 

 floods always come out of the Ohio in the early spring, and are likely to increase in 

 size and frequency as the country becomes more generally cleared and drained. 

 There were five parties in the field for the River Commission taking daily ob- 

 servations for discharge for the whole of the year 1882, four of which were below 

 Cairo. The results of these observations are now published, together with ob- 

 served discharges over the banks and through the swamps for the flood of that 

 year. If all the overflow water had been confined to the channel, the channel 

 discharge would have been increased on the upper portions of the St. Francis 

 front by 12 per cent, along the central portions by 50 per cent, along the lower 

 portions and upper part of the Yazoo front by 25 per cent, along the central por- 

 tions of the Yazoo front by 90 per cent, in the vicinity of Vicksburg by 25 per 

 cent, at Red River by 20 per cent, and at New Orleans by 100 per cent of the 

 amounts that actually did pass in the channel at these points. 



Four methods of treatment were presented : 



I. To have no levees whatever and let the water find such natural outlets 

 into the swamps and finally into the Gulf as nature had provided. This method 

 of treatment would result in the abandonment of this region by the better classes, 

 since agriculture could not be made profitable. It was thought, however, that 

 with the present excessive variations in the width of the channel this method of 

 dispersion was really in the interest of low-water navigation. The gist of the 

 argument on this question seemed to be that since the bars are all formed at high 

 stages, and the higher the stage the higher the bars are built, so, any addition 

 to the high stages by means of levees increases this bar-building influence. In 

 high stages the river always scours in the deep places and fills on the shoals, 

 which is exactly the reverse of what is desired. 



It was shown that the bars were caused by the inordinate variations in the 

 velocity of the water at successive sections, owing to the great changes in width. 

 Bars are wholly formed by the deposit of sand which had been in temporary sus- 

 pension for a few miles, coming from the first deep pool above. The variations 

 in velocity, causing these deposits, are enormous, being on the Plum Point reach 

 as much as 6 feet per second (from 10 feet to 4 feet mean velocity). The remedy 

 is in contracting the channel in the wide places and not in building levees. 



