1903 a total of $40,000,000; in 1912, $78,000,000; in 1922, $17,087,790; and in 1927 about $285,000,000 in losses. Such losses even though they be rough estimates cause one to ask: How often must these losses be borne?

FREQUENCY OF SEVERE FLOODS Attempts have been made to reduce the question of flood frequency to a mathematical basis. One set of calculations has been prepared for the Lower Mississippi River. Selecting New Orleans as typical it is illustrated by the number of ordinary floods per decade from 1871 to 1922, thus: 7, 10, 9, 6, 7, total 39. The frequency for severe floods at the same place and period is: 1, 1, 3, 3, 5, total 13. Vicksburg, Mississippi, and Memphis, Tennessee, show similar series. The expectancy or average interval in years between ordinary floods has been computed as 1.33 at New Orleans, 1.30 at Vicksburg, and 1.37 at Memphis. The similar expectancy for severe floods at the same places is respectively, 4.00, 3.06, and 5.20. The lack of correlation which is noticeable between the ordinary and severe floods is due to the fact that ordinary floods may be and frequently are caused by high waters in a single tributary, particularly the Ohio River, while severe floods are usually the result of high waters in two or more tributaries. The fact that the tributaries do not have high waters at the same time, except rarely, was shown by the data above for the years breaking records.

The flood frequencies of the major tributaries further show the lack of coincidence of high waters. This is shown for ordinary and severe floods (latter marked *) as follows: the Ohio River at Cairo, 1.33 and *2.08; the Upper Mississippi River at St. Louis, 2.74 and *10.40; the Arkansas River at Little Rock, 1.41 and *5.78; and the

Red River at Alexandria, 3.80 and *38.00. Thus it is evident that the chances of high waters occurring at the same time on all the major tributaries is rare. The last flood, 1927, was the nearest approach. Moreover it appears that there is a close relation between the floods of the Ohio and the Lower Mississippi rivers.

CAUSES OF FLOODS

Students of the floods assert that the Ohio River is by itself capable of producing severe floods in the Lower Mississippi River. And so another set of calculations has been made to determine the frequency of floods in the Ohio River. It appears from a study which correlates precipitation data and flood occurrence data in this basin that there is no evidence of increasing frequency of floods. It does demonstrate that there is a cause and effect relation between the precipitation features and floods. Thus, there was a rainfall deficiency in the Ohio Basin during the decade 1870-1880 which would account for the lack of floods of any noticeable size in that period. In 1881 to 1883 there was a large excess in rainfall which accounts for the great floods of those years, culminating in the record gage reading of 71.07 in 1884. Then followed a period of deficiency with no floods. In 1890 there was a local excess in the lower Ohio Basin which tallies with the flood in that part of the valley. Then drought followed, and no floods resulted until 1897; then a couple of years of heavy rains with corresponding floods; a term of dry years to 1906, then rains and floods in 1907. Similar studies concerning the Upper Mississippi River and lower Missouri River show conclusively that precipitation conditions are competent to produce the floods, and that the floods are as ir regular in occurrence as precipitation conditions are fickle. Hence a review

size in that period.

of the general conditions in the Mississippi Basin with regard to precipitation will aid in understanding the factors of flood frequency.

Normally there is scanty precipitation over the western and northern portions of the Mississippi Basin in January, February and March. At the same time rainy conditions prevail over the southern Appalachians. During April and May precipitation reaches its greatest amount over the West. In June two rainy centers appear: one in the Lower Mississippi, and the other in the lower Missouri basins. In July and August, rainfall diminishes in the West and becomes uniform over the Lower Mississippi Valley. September, October, November and December successively approach winter conditions with light precipitation over the West, and intense heavy downpours over the lower valley in December. The character of the ground, whether frozen or water soaked, has a great deal to do with the percentage of run-off from these precipitation conditions.

It has been estimated that about twenty-seven per cent of the precipitation in the Upper Mississippi Basin finds its way to the rivers and amounts to about 230,130,000,000 cubic yards of water. The early summer rains and winter scantiness result in a single swell reaching its height in June and declining to August, with marked low water levels to late January when the swell begins again.

In the Missouri Basin about fifteen per cent of the rainfall reaches the rivers and gives a normal discharge of about 131,230,000,000 cubic yards of water. The Missouri minimum occurs in December and rises to a minor swell in May which is followed by a major swell in June, after which the river level falls rapidly to a December minimum.

The Ohio Basin receives the most abundant and well distributed precipi

tation of all the component basins. This with its thirty per cent run-off totals about 230,130,000,000 cubic yards of water which makes it rank first in volume among the tributaries. The Ohio River normally because of winter rains in the Appalachians, has high water in March. Its low stages come in October.

The Mississippi River regimen below Cairo is the composite of the combined swells of its tributaries. The main swell of the Ohio River reaches Cairo about the middle of April, having risen rapidly. The ebbing of the swell is checked by the rising swells from the Upper Mississippi and Missouri rivers. Hence the swell below Cairo consists of one long sweeping rise for six months and one long decline of similar length. The heavy rains over the Lower Mississippi Basin at times aggravate the normally high waters into flood conditions.

The Arkansas River discharges about fifteen per cent of its precipitation amounting to about 74,070,000,000 cubic yards of water. The Arkansas River is low in August and high in May. Its swell normally has no effect upon the regimen of the Mississippi River.

The Red River with its annual discharge of 66,670,000,000 cubic yards of water, representing about twenty-two per cent of its rainfall, has a range similar to the Arkansas with similar lack of normal effects.

It may be noted again that the timing of these various swells from the major tributaries, considered from the standpoint also of their geographic location, gives a rhythmical succession of increments which normally results in harmless high waters. However, normal conditions do not always persist. In every case the floods can be traced to excess discharges from some one or more basins.

The actual discharges of water in a few of the great floods 1882, 1903, 1912,

1913, 1915-16, 1920 and 1922 according to calculation each exceeded 159,000,000,000 cubic yards. For example, the flood of 1882 was made up as follows: Ohio River, 107,868; Upper Mississippi River, 30,693; Lower Mississippi River, 68,005; Missouri River 25,826; and Red River 24,874 making a grand total of 272,137 in millions of cubic yards of water. This flood which is rated as an exceptionally severe one is typical of the kind produced by a great discharge from the Ohio River basin. The flood occurred early in 1882. During the months of January, February and March when the above discharges occurred, there was an excess precipitation over the southern half of the Ohio Basin and Lower Mississippi Basin, and over the lower Arkansas and Red basins ranging from 8 to 12 inches excess.

In 1927 all the rivers south of the Des Moines River were in excess discharge, with excesses ranging from six to nine inches in Iowa to twenty-three inches in the middle Arkansas Valley. The nearest approach to such conditions in the recorded past occurred in 1922 when there were excesses over the lower Ohio and Mississippi basins in February, with a spreading of excess conditions to the northward over the lower Missouri and lower Upper Mississippi basins by March. The total discharge of this 1922 flood is estimated at 265,146,000,000 cubic yards of water. The evenness of the distribution of excess is shown as follows: Ohio

River, 81,115; Upper Mississippi, 31,410; Lower Mississippi, 52,658; Missouri, 39,589; Arkansas, 31,410; and Red, 27,962 millions of cubic yards of water.

The flood discharges for the other floods listed (in millions of cubic yards) are: 1882, 272,137; 1903, 200,786; 1912, 239,774; 1913, 228,759; 1915-16, 170,049; 1920, 159,196; 1922, 365,146. These figures give some notion of the immense volumes of water which pass down the Mississippi River at flood times. As a measuring stick, the normal river flow past St. Louis, Missouri, is estimated at 225,000 cubic feet per second. It is stated by observers at Little Rock, Arkansas, that the Arkansas River ran at 813,000 cubic feet per second during the 1927 flood. CONCLUSIONS

It may be concluded:

I. That the basic factors of severe floods causation are uncontrollable.

II. That the frequency of severe flood occurrence is a function of precipitation and varies irregularly as the amount and distribution of precipitation varies.

III. That the engineering problem is to regulate the flow of flood waters and prevent the inundation of valuable lands.

IV. Supplementary, that such engineering works should be designed to conserve the features of the rivers adapted to waterpower, navigation, water supply, and sanitation.

WHEN Daniel Boone returned from one of his hunting and exploring expeditions, he was more than usually extravagant in his praises of the area he had just visited-that reached by passing westward through the famous Cumberland Gap. Here was a land described as rich in growth of all those hardwoods which show unusual fertility in the soil. The region he had seen was a part of the now well-known Blue Grass Region-a basin rich in agricultural development. But the Blue Grass Region, although one of the richest, is only a speck in that larger area of high fertility and gentle topography which reaches from the Alleghanies to the Rockies and is for the most part contained in the Mississippi Valley.

The Great Mississippi River and more than fifty navigable tributaries. furnish about 14,000 miles of waterways and border or traverse twentyseven states whose combined area is 1,935,952 square miles (65 per cent of U. S.). Of these twenty-seven states, seventeen are entirely or very largely within the Mississippi Drainage System. The importance of this great inland empire is unappreciated by most, only partly recognized by a considerable number and fully known to but few. Here is one of the best farming regions of the world, and when it was opened to the growth of the cereals New England and much of other Eastern areas went "down and out." In this area of the Mississippi Valley a little over half of the people of the United States live. Here is 65 per cent of the improved land of the nation.

Here is produced about 85 per cent of the country's crop of corn, 65 per cent of the wheat, 78 per cent of the oats, and almost 50 per cent of the cotton. Here also are raised about 65 per cent of the horses, 60 per cent of the dairy cattle, while 55 per cent of the beef cattle, 80 per cent of the hogs and 45 per cent of the sheep of the nation are made ready for the market. Here are obtained about 75 per cent of our bituminous coal, a considerable portion of the iron ore, over 50 per cent of the lead and over 50 per cent of the zinc. This area is also growing rapidly in manufactures and if the lake cities are included now produces almost 50 per cent of the country's manufactured articles.

TOPOGRAPHIC FEATURES

Most of this great area which is so rich in resources is without striking topographic features. It is generally level or gently rolling, occasionally hilly, but never mountainous. Much of it appears as a limitless expanse of grove-dotted, gently undulating country, here and there trenched by rivers and surmounted by low hills; or it stretches away as far as the eye can see without either of these relief featuresa grass-covered, farm-dotted, smoothly contoured prairie. North of the Missouri and Ohio Rivers it is glaciated. Morainic belts cross it in looped pattern, and between them are notably flat till plains. In that portion covered by glacial ice in the last (Wisconsin) glacial invasion, lakes, ponds, and undrained hollows in great numbers are scattered freely about, stream courses

are disorganized, falls and rapids abound and alternate with swampy depressions often of considerable extent. Most of the area, however, is well drained and well fitted for agriculture. This is shown by the great number of evenly spaced comfortable houses and big barns.

From north to south almost through the center of this area flows the mighty Father of Waters. This great stream, although at times a devastating curse to many inhabitants of the valley, has been of great importance in opening up the country to settlement and has borne many millions of tons of produce to market.

This great valley and its river system present a twofold problem. It has low-water difficulty as well as a highwater peril; it involves keeping navigable depths in the channel as well as keeping navigation off the riparian corn and cotton fields; it associates intimately the interests of navigation and conservation. It is, then, the problem of keeping the system in shape to carry river commerce and of controlling its disastrous floods.

RIVER COMMERCE

Although the lower river is still important as a commercial highway its value to the people of the valley was much greater in the past. New Orleans was established in 1718, but for a decade before this the river had been used as a carrier for furs and for lead from the easily worked mines along the river in Iowa and Wisconsin. By 1740 there were about 2000 farmers along the river in Illinois whose only outlet for their produce was the river. It is true that the early Western settlers could send over the mountain to the Eastern markets the valuable articles of little bulk, such as furs, ginseng or whiskey, or the livestock which could be driven to market. For carrying

their flour, pork, tallow, leather and lumber to market they used keel boats and barges.

The steamboat made its appearance on the Ohio River in 1811 and by 1817 · had been improved so that it could cope with the currents of the Mississippi and other interior rivers. With further improvements, the steamboat became important by 1822 and river traffic developed rapidly up to 1846 when the output of the lead mines began to decrease. The lead was beginning to go east via the Great Lakes and Erie Canal because the cost was less. The river boats had been having great difficulty especially at the rapids at Rock Island and at Keokuk, which at low-water stages in summer and fall were almost impassable and which often necessitated the reloading of cargoes into barges of light draft which were towed over the rapids with horses.

From 1840 to 1855, in spite of the difficulties of the rapids, etc., the boats reaped a rich harvest because of the large numbers of settlers going into Iowa, Wisconsin, and Minnesota.

The period 1858-1870 is the period of railroad competition, at first helping river commerce, later destroying it.

This period also saw the development of a new type of carrier, the grain barge, towed by steamboats. These were extensively used for about ten years, but about 1870 the railroads had penetrated the grain growing section, and the grain barges soon became almost useless.

Fifty years ago there were 470 steamboats plying regularly on the Mississippi. At the present time, you would have a hard time finding fortyseven, even if you were to count a few government snag and dredge boats to make up the total. In the spring a few big coal tows descend the stepping stones of the Ohio from Pittsburgh to Cairo, and then on down the main