Rensselaer Union, Volume 7, Number 12, Rensselaer, Jasper County, 10 December 1874 — The “Probabilities” of Rivers. [ARTICLE]

The “Probabilities” of Rivers.

The utility of adapting the meteorological reports to switch and warn of the approach of floods in risers earU suggested itself to Gen Myer, as with the growth of the reports he was enabled to determine the route by which the witer in any section would seek the sea; and on New Year’s Day, 1873, observers stationed along the rivers which drain the country from the Rocky Mountains to the Alleghenies were instructed teiaelude in their reports a daily history of the river at. each point. At the present moment “ River Reports” are received from forty-seven stations along the hanks of the Monongahela, Youghiogheny, Allegheny. Ohio, Cumberland, Tennessee, Missouri, Arkansas, Red and Mississippi Rivers. Freshets are not caused by rain alone, but ofteh by the thawing of heavy snows. When thaws are accompanied by rain-fall the rise is rapid, and if the rivers are frozen the freshet becomes ■ ' a dangerous character by breaking and sweeping down the ice.' Such fresh - are usually accompanied by greater d. iiger than when the rise continues at-j great height from long-continu d rain-fall alone. As the results of i gorges along our Western rivers i reader will readily recall the yearly st< of steamers and barges crushed ana su. bridges carried away, and river bar. flooded or destroyed. At each river station careful reco have been made—as far as could be tained—of all former freshets, and a i tory of these has been compiled to ascertain the seasons when freshets may be expected, and to determine what may be called the danger lend along each river t. e., that height of water at which ex pe rience has proved that a river becomes liable to endanger not only commercial interests and property at cities and towns, but also to devastate the country between these by overflowing the river hanks and levees. To make these histories complete inspections have been made along each river by officers of the Signal Service, to ascertain not only the channel depth at which danger appears at different points, but when and where it will increase or expand itself, or where the river bed is going, and how fast. With the more extended information which the constant growth and enlarged experience of the weather report system must bring, the central office in coining time may not only predict heavy andcou■'“fihuous seasons OT rain-fall, nut when such is the case be able to warn the pboSie of river towns of the extent and uration of the resulting rise. This study has intimate and close relations to meteorology, for rivers are the best and most certain rain-gauges possible, and the study in effect resolves itself into measuring the amount of rain falling within the separate water sheds of the separate rivers, the rate of speed with which and the route by which the rain will seek its way to tlie sea. Thus, in a map representing the watersheds of the Western rivers—or the surface of country drained by each —it will be seen that if the central office receives information that heavy rain is falliug in Nebraska, Kansas and Western Missouri his knowledge of the number and capacity of the water-courses throughout that region enables the assistant in charge of river ports to decide when a freshet wave, great or small in extent,, will move down the .Missouri to the Mississippi; and if the rainfall has extended or promises to extend into lowa, Minnesota and Wisconsin to determine whether the wave from St. Paul to Keokuk will pass before or after that from the Missouri reaches its mouth, or whether they will meet, At each station the Observer Sergeant is required to prepare a “ bench-mark,” or gauge, set in the river bank, and marked in feet and inches above and below the point from which measurements are taken From April 1 to July 81, and from Oct. 1 to Nov. 80, in each year, observations must be made at three p. m, each day, and at such intermediate times as Gen. Myer may deem necessary for any sudden or unexpected change in the condition of a river, such as would result -from any portion of the country, or rapid melting of ice or deep snow. Besides these ordinary daily reports, during the seasons named, or when specially ordered, if the rise or fall in a river is sudden or unusual in its character, reports are required every three hours until The river resumes its normal condition. Most of these reports are made by telegraph, and a separate system of cipher writing is used, similar in character to the key used for the meteorological report*.. In the office study-room there is a large slab of slate with a profile of each of the rivers named engraved thereon. The assistant in charge receiving the various reports has on his desk a blank form, ruled, on which is printed a list of the rivers and the stations on each, and on this he writes the information received; turning to the slate he marks at each place on a scale, at each point on the profile, the height of water; then drawing a line on the slate which will connect these marks he has a profile map Ilf the position and extent of any Iresiiet wave which may then exist, and from this determines how he shall make the appropriate entries in the last four columns 'of his report sheet This sheet, thus filled, is then used to determine the “probabilities” in the! special river reports; and the general instructions require that, “ whenever the changes are greater than five inches, he must state, in the synopsis, ‘ the rivers have fallen [or risen] at [giving names- of stations], or decidedly fallen [or risen] ;’ or give the number of feet, when the change is remarkable;” and. following this, to state the probable condition based upon the facts given in the synopsis. This being the province of the officer in charge of the river report, the reader will see the use of the river profiles, and why a freshet following the course of a river has been called a “ wave.” In the profiles on the slate the grade of the river, or line of elevation above the sealevel, determines to a considerable extent the speed with which a freshet seeks its outlet. Let the reader, for example, take a profile of the Ohio River vnd mark the figures given below upon aertical scales; The reports upon a certain day gave the depth of water at various points as follows: Pittsburgh, 19 feet; Wheeling, 37.; Cincinnati, 17; Louisville, 7, and Cairo, 17; the latter being governed to some extent by the stage of water in the ] Mississippi. Now draw a line Which will connect these marks, and it i will be seen Oat the freshet resembles a j - huge wave, having its crest at Wheeling, j Three days later the depth of water was: Pittsburgh, 10 feet; Wheeling, 23; Cin- j cinnati, 30; Louisville, 8, and Cairo, 9; and another line drawn as before showg the crest of the wave to beat Cincinnati,

or, probably, a little above that city. Last Spring Gen. Myer discovered that large bodies of water were' gathering in the upper rivers, to such an «xtent that great, destruction of property would result along the river from Cairo to New Orleans, and telegraphed to Memphis, Natchez, and other places, giving warning that the rise would sweep away goods and vessels along the banks. The warning fairly astounded the “ river men,” and the editorial column of a local paper reviled and scoffed at the impudent assumption of a man sitting in his office at Washington who presumed to know more of tlieir river than they did. “ Why, the river was falling—fell ten inches yesterday, and fourteen the day before!" Within a few days, however, and within the time specified by the “probabilities of | rivers,’,’ the same journal contained colI umn after column telling the story of inundation and loss of life and property.— Scribner's Monthly.