 We have a potential danger that too often becomes more than a mere threat, so each fall of sleep leaves on the ground a fresh hit in suspension. Thus, when spring calls and warm spring rains come together, choice to bring about a concentration of runoff, we may look for destructive floods. It is the function of the United States Weather Bureau to gather information on such conditions, to make daily records of rainfall and snowfall and of river stages, and to give advance warning when human life and property are threatened by high water. The Weather Bureau has 66 district forecast centers as shown on this map, covering all the important rivers and most of their tributaries. Many rainfall and river gauges are strategically located in the various drainage basins throughout the country, and from each of these stations reports are sent daily to the forecast centers for use in making river staves and flood forecasts. Precipitation is caught in a rain gauge, but as we see here, and measured in inches or hundreds of an inch, when necessary, these measurements are telegraphed or telephoned to the district center. River gauge readings are made on various types of gauges. The recording gauge shown here is on the Sacramento River at Sacramento, California. The historic inclined river gauge at St. Louis has been used for many years to measure river stages there. Some memorable high water marks on adjacent waterfront buildings. The highest river stage of record was 41 and 3900 feet on June 27th, 1844. This is the more modern recording gauge now in use at St. Louis. At Cincinnati, we see a river gauge which automatically indicates and records the stage of the Ohio River at intervals of five minutes. This is the transmitter of the telerecorder. By means of a floating cable actuating the transmitter, the exact height of the river is electrically transmitted and recorded. Here, several miles away at the Weather Bureau office in the Abbey Observatory, we see the recording apparatus making a record of the river stage at the moment. These records are used in making forecasts of river stages, a service of vital importance to all persons or firms who have business along our rivers. Here at Sacramento, for example, river stage forecasts and flood warnings are a vital concern to the community. Sacramento River steamboat lines, of course, depend on river forecasts every day, no matter what the stage, while business interests and residents of the waterfront rely on flood warnings to enable them to safeguard their property and their persons. This view of the Sacramento River at flood stage will give some idea of how important a flood warning may be to ranchers who have livestock on lowland pasture. The Mississippi River Basin, of course, is of major concern in this regard. It is one of the largest in the world and embraces the world's richest agricultural region as well as scores of large riverside cities. The flood warning service of the Weather Bureau is of incalculable value to millions of farmers and waterfront city dwellers of this area. This is the familiar levee at St. Louis, the scene of many of the fastest overflow of the Mississippi. And an excursion steamer of that port. Owners and masters of such boats must depend daily on Weather Bureau reports. An Ohio River boat at Louisville, Kentucky. Except in periods of high water, the stage of the river here is controlled by dams and locks built and operated by the Corps of Engineers of the United States Army. This is true also of Cincinnati and elsewhere, from Pittsburgh to Cairo. There is close cooperation between the Weather Bureau and the U.S. engineers in the gathering of weather data. This animated map illustrates how river stage readings are relayed from lock to lock each morning to the Weather Bureau District Office at Cincinnati. For example, each morning the lockmaster at dam number 14 telephones the stage there to the lockmaster at the dam next below, who in turn telephones this report and his own to the next dam farther down, and so on. Meanwhile reports come down the Great Kanawa River in the same way. Reports from both rivers are received at dam number 28 at Huntington West Virginia, and at 8.5 each morning the lockmaster there relays the combined report to the District Office at Cincinnati. Similarly, reports come from the dams below Cincinnati, while other dams in the system report to Pittsburgh and Cairo. These reports are used in making river forecast and in preparing the daily river bulletin. When conditions are threatening, the switchboard in the Cincinnati Office of the Engineer Corps becomes a center for relaying reports of the advance of the flood test. While in the Weather Bureau Office in the same building, the work of collecting, coordinating and evaluating the reports goes forward day and night. It is continuous throughout the year, while the river reports are essential to navigation irrespective of flood dangers. Here we see the engineers preparing for a predicted rise by dropping the Great Watergate, or Bear Trap, an essential part of each dam and lock in the Ohio system. The Bear Trap are the most easily adjusted portion of the dam, and the rises of the river up to 5 or 6 feet can be taken care of without lowering the wickets of the dam proper. Now the Bear Trap is open. As the river continues to rise, the dam itself becomes unnecessary to maintenance of the pool level, and the work boat begins to lower the wickets of the dam. When the wickets are all down, the dam will not be any obstacle either to river navigation or stream flow. And now we see the reverse of these operations. As the river subsides in late spring or early summer, the wickets and bear taps are raised again. Raising the wickets is a slow and tedious job. Requiring great skill and physical endurance on the part of the operator, whose task it is to fish for and hook to submerged rings by which the wicket is raised. As the wicket comes up, a brace or prop on the downstream side of the framework catches in a notch, forming a support for the wicket. When the prop has been set, the pressure of the water on the lower part of the wicket is great enough to snap it down into its position in the dam. Raising the Bear Trap is relatively easy. Two men turn the lever that actuate the mechanism, and the barrier gradually rises. The bear trap consists of two leaves, hinted to an anchorage on the bottom of the river, and so arranged that the hydraulic pressure of the head of the water can be used to raise the gate. Each dam usually has two bear traps. And they are the last portion of the dam to be closed. Then the traffic that has hit the tube and going over the submerged wickets begins once more to pass through the lock, the gate of an Ohio River lock opening to commit the passage of downstream traffic. Here we see one of the modern diesel tow boats handling a string of barges with a shipment of steel pipe that would load perhaps miles of freight cars. And here is one of the famous Ohio River steam packets en route to Cincinnati. This is the type of boat that figures in the periodical Ohio River steamboat races we hear about. Indeed, if we mistake not, the sister of this particular boat holds, or at least has held, the Speed Championship of the Ohio. All this river traffic relies constantly on the reports and forecasts of the weather bureau as to the stages of the river along the river route. We have seen how the weather bureau gathers and disseminates information as to the normal rise and fall of rivers. And now let's talk about a flood. For example, the Great Potomac River flood of the spring of 1936. That flood began, potentially, with an almost unprecedented fall of snow on the watershed drained by the Potomac, where the accumulated depth averaged more than 15 inches over the entire drainage basin. This is not a glacier scene in some Arctic region, but a view of the great falls of the Potomac in February 1936. For the first time in 18 years, the Potomac River was frozen over with heavy ice throughout most of its length. And this, together with the heavy covering of snow on the watershed, caused grave fears that a flood would come with the inevitable spring break-up. And there was a solid sheet of all the Lincoln memorials. While snow lay deep over the whole Potomac basin, a period of mild weather beginning early in February caused a general thaw. The break-up was orderly. There was a sharp rise in the Potomac, but the water did not reach flood stage at any point. Came the heavy general rains of March 17th and 18th, and the greatest flood of record began to gather in the Shenandoah and Upper Potomac Valley. At Harper's Ferry, the business section was flooded and hundreds of persons driven from their homes. Great damage was done to property. Here we see the rescue of a maroon's mother and her baby from a home in Harper's Ferry. Clearly, at least one victim of this flood took it good-naturedly. The bridge at Harper's Ferry, before the flood leaked its crest. Shortly afterward, this bridge was carried away. Many buildings were under water, but no direct go washed away. Only one span of the bridge at Point of Rocks remained after the passage of the flood. Thus, for the first time since 1924, the nation's capital was threatened by a major flood. Soon as reports on heavy rainfall over the watershed were received, flood warnings were issued by the Weather Bureau. All interest were advised that a great flood was inevitable. Early on March 18th, a definite stage forecast of 19 feet was issued from Washington, D.C. A crest to occur on the afternoon of March 19th. Meanwhile, emergency labor, including CCC boys and others, under the direction of army engineers, worked night and day building a dike of sandbags, designed specifically to protect the government buildings on the mall from the flood. Thus, the great watertight wall was stretched across the only gap through which flood waters might reach the downtown section of the national capital. The crest of the flood passed over the great falls of the Potomac, a few miles above Washington during the afternoon of March 19th. At 7 p.m. on March 19th, 1936, the crest of the flood reached Washington, registering 19 and eight-tenths feet at the site of the old Aqueduct Bridge. This flood proved to be the greatest in the history of gauge records. It was several feet in excess of the record flood of 1889 in the reach above Harper's Ferry, but exceeded the previous record flood at Washington by only three-tenths of a foot. This is the John Paul Jones Monument in Potomac Park as it appeared during the passage of the flood. The water swept over the sea wall and flooded East Potomac Park. Many of the celebrated Japanese cherry trees there suffered serious damage. This is the same area as seen looking down the river from the top of the Washington Monument at the left, the harbor, Haynes Point in the middle distance. The beautiful memorial dedicated to the memory of the victims of the Titanic disaster as it appeared when the flood was nearing its crest. The damage to the park system, especially to the park way along the river, was heavy. Witness the effect of the swift current on the heavy flagstones in the vicinity of the Titanic memorial. The flood worked havoc here and elsewhere in Potomac Park, but did not reach the imposing new government buildings along them all. So much for the record-breaking Potomac flood of 1936. Now let's look at a record flood in another area caused by a wholly different combination of weather factors. At the beginning of January 1937, conditions in the Ohio Valley were set for disaster. Over the entire watershed, the ground had been saturated by unusually heavy December rain. The Wabash, the Cumberland, the Tennessee, and many lesser tributaries of the Ohio River were swollen. The Ohio was rising. At this juncture, the normal procession of barometric highs and lows across the continent was interrupted. For weeks, a high pressure area hung over the Atlantic near the Bermuda, while another high persisted over the northwestern states. A trough of low pressure lay between. Warm, moist air flowing northward from the gulf into this low pressure area met cold counterwinds from the Arctic, and it rained for 20 days in the Ohio River Basin and adjacent areas along the Mississippi. Heavy rains began on January 6th. Day after day, the downpour continued. During the period between January 6th and January 25th, rainfall over this area averaged about 14 inches. Fully one-third of the normal annual rainfall. In some places, it exceeded 20 inches. During the 21st and the 22nd, nearly 6 inches fell at Louisville, Kentucky. And thus, the great flood was on its way. Both were days and nights of terror at the age of thousands living in the flood plains of the Ohio and its tributaries. Practically every home and farm located on the low land bordering these rivers was under water. The streets of cities became watercourses and rescue and relief work became everybody's business. At Wheeling West Virginia, U.S. Route 40 looked like this. At Fort Smith, Ohio, the streets were swept by a raging torrent. Tributaries of the Ohio overflowed through the farmland. No, this is not the Mississippi, merely the Siota at flood stage. At Cincinnati, disaster was cumulative. Water rose to an all-time high of 80 feet. Sections of the city never before inundated were flooded, entailing evacuation of the residents and enormous property loss. Then fire heightened the horror of the flood and the great manufacturing plant was destroyed. While firefighters fought a losing battle waiting through flood to bring their hose to play on the fire. The loss in this fire alone was above one million dollars. At Louisville, Kentucky, a business section and many low-lying residential districts were flooded. Suffering among refugees was intense. Loss of life owing to exposure and privation was heavy because of the long persistence of the flood stage. For days, rescue boats directed by radio, evacuating Maroon residents and transferring them to hospitals or refugee camps. Similarly, to Evansville, Indiana, to Paducah, Kentucky and to scores of smaller river towns, the flood brought disaster unparalleled in the history of the valley. The loss attributable to flooding of farms was incalculable. Vast areas of rich bottom lands were seriously damaged. In many places, fields were literally washed away. Livestock that survived the flood suffered severely from starvation and exposure. These marooned animals found a haven of refuge on the top of a levee. Poor old chef put cold and precarious perch on the top of a submerged car while Tabbycat takes to a second-story window sill, high but not dry. Thus, convoyed by the Angel of Death and the specters of famine and disease, the crest of the greatest flood of record passed down the Ohio Valley to the Mississippi. The blasting of the so-called fuse plug in the levee below Carol on the Missouri side probably saved that city from complete inundation. Here, a part of the vast volume of water discharged into the Mississippi by the Ohio was allowed to spread over the adjacent lowlands, thus lowering the crest of the flood. To further safeguard Carol, all the levees surrounding the city were raised by emergency bulkheads. An army of workmen toiled night and day at this job, and they won the battle. But this picture of the water lapping over the top of the permanent seawall shows how narrowly disaster was averted here. Property loss entailed by this flood was certainly not less than half a billion dollars. 790 million dollars were appropriated for relief. A million persons were driven from their homes, and hundreds of human lives were lost. Much of this property loss, of course, was inevitable under the conditions. The usual gambling losses that man invites when he builds his home or shop on the slope of a volcano or in the flood plain of a river where floods have come periodically for ages. But at least the loss of life could have been largely prevented if residents and authorities of the threatened areas had paid due attention to the weather bureau warnings that were given them daily, both before and during the progress of the flood. Every foot of the rise in the Ohio from early in January to the all-time highest ages of the latter part of the month was forecast by the United States Weather Bureau day by day. These forecasts were printed in morning and evening newspapers. They were broadcast by radio. They were posted daily in every post office in the threatened area. Nevertheless, hundreds of human lives were lost. Man is a stubborn creature, inordinately wise in his own conceit and slow to learn that the cheap and simple way to avoid loss of life and property from great floods like this is to keep out of their way. Fortunately, the lower tributaries of the Mississippi, with the exception of the Yazoo, were not at dangerously high stages when the crest of the Ohio flood passed down the lower Mississippi. So from Memphis on, the flood did little damage, though it entailed a vast outlay of funds and labor. The water came perilously close to the tops of the levees, but they held. Above New Orleans, the floodwaters that threatened the Crescent City were safely bypassed through the new Bonaikare floodway. Here, 200,000 cubic feet of water per second was carried from the main channel to sea level through Lake Pontchartrain, over a floodway but a few miles in length. Thus passed the great flood of 1937. In 20 days, enough rain to cover the 207,000 square miles of the watershed, with water a foot deep, that's more than 176 billion tons. To impound all that water would take a reservoir almost as large as Lake Erie. A great flood and exceptionally disastrous flood with only one of many such flood. Don't forget the flood of 1927, of 1922, of 1913, of 1884, of 1844. Indeed, we can go back 400 years and find in print a description of a flood that fits this one fairly well. Here in this little moldy volume, printed in Lisbon in 1605 and now locked up in the Library of Congress among its rarest treasures, Garthilasa de la Vega tells of a flood that the Sotos men saw in 1543 somewhere below Memphis. Here on leaf 300, he says, on each side of the river the water extended over 20 leagues of land. They say that old Garthilasa was given to exaggeration. Perhaps. But the Yazoo backwater of 1937 stretched a long way. Again he says, nothing was seen but the tops of the trees. Well, and farther on, speaking of the homes of the Indians he continued, their houses are constructed on thick posts or pillars, thus they protect themselves from inundation. What intelligent people those aborigines. The houses we see here are the homes of people with the advantages of free schools, universal suffrage, 5 cent hot dogs and this and that. What holy wanting and aboriginal gumption. A great river the father of waters, a great river. A river worthy of wholesome respect. Certainly not a river to trifle with.