]VEATHER BEREA U RIVER AND FLOOD SYSTEM 305 
its tributaries from Evansville to Marietta ; Nashville : the Cum- 
berland, Chattanooga, and Tennessee rivers; Montgomeiy : the 
rivers in Alabama; Little Rock: the Arkansas; St. Paul: the 
INIississippi above Davenport; Harrisburg: the Susquehanna; 
Augusta : the Savannah ; Portland, Oregon : the Snake and Co- 
lumbia; San Francisco: the Sacramento and San Joaquin. 
A river bulletin-board has been placed on some of the prin- 
cipal steamboats leaving Cairo, so arranged that the river stages 
can lie read by people on shore and on passing steamers. Thus 
pilots ascending or descending the river get the latest informa- 
tion as to the height of the water at the places to which they are 
bound. 
The river-gauge is a graduated scale on which the height of 
the river is measured. The zero of the gauge is usually at or 
somewhere near the level of the lowest water known. A gauge 
is generall}' vertical, is usually fastened to a bridge, pier, or piling, 
and is of sufficient length to cover the greatest height of water 
likely to occur. ’When a river-gauge cannot be set vertically, it 
is laid on the bank according to the slope of the ground. The 
foot-marks on a gauge of this kind must be accurately located 
by means of a spirit-level, so as to agree with those on a vertical 
gauge. When a stage of water below the zero occurs, it is read 
as a minus stage. It is not desirable to change the zero point 
after readings made from that basis have continued for any 
length of time. 
It may be of interest to know that on account of the narrow- 
ne.ss of the valley and the precipitous shore line of the Ohio the 
water in this river must show a rise varying from 30 to 50 feet 
before the danger line is reached. At Cincinnati the danger line 
is 45 feet above the zero of the scale, and a height of 7 1 feet above 
zero lias been recorded. On the upper Mississi])pi the danger 
line averages about 15 feet above zero, but from St. Louis south- 
ward to Vicksburg it averages about 35 feet, while at New Orleans, 
with its great system of levees, the danger limit is but 13 feet 
above zero. 
In the early history of the river s\\stem the data received from 
the various river stations, tbougb meager, were sufficient to i>er- 
mit useful warning of marked changes in the river levels. In 
the spring of 1874 this branch of the Hureau bad its first expe- 
rience with destructive floods. In that year floods devastated 
the valleys of the lower Mississip])i, the Arkansas, White, Peil, 
and other rivers, causing crevasses in the levees and inundating 
