FARMING LAND DESTROYED BY FLOODS. MONONGAHELA RIVER.
WAGE-EARNERS' HOMES ABANDONED ON ACCOUNT OF FRESHET.
The river floods cannot be prevented by local effort. Their damage is by no means confined to Pittsburgh; it extends the entire course of the Ohio River and its most important tributaries; its causes originate in other states besides Pennsylvania. Although the state and even the cities might well co-operate in certain ways, the prevention of these floods is a problem for the Federal government to consider.
The cause of a flood lies partly in natural conditions. The run-off of the Allegheny and Monongahela Rivers is naturally concentrated and the highest floods occur when a deep snow on a frozen soil is suddenly melted by heavy warm rain. But their height has been accentuated by human agency; and this points to the two necessary phases of river flood control work. One is the re-establishment of normal forest conditions. This means not so much a great extension of the forest area, although there are many steep slopes now cleared which should be re-wooded; but it means the restocking as densely as possible of lands which have been cut or badly burned and are thinly or partially wooded. This is a means to an end. The forest produces a deep mat of leaves and mould, the humus which not only has a high water storage capacity itself but determines largely the porousness and absorptive power of the underlying soil. This function of the forest is not incompatible with the use of its timber. The most rapid growth of timber is secured by maintaining the deepest humus; but the cutting of it must be adjusted under skilled direction in order not to jeopardize the water storage function of the soil.
Furthermore, there is need of more evergreen forests. The pine and hemlock have been largely removed from the mountain sources of the Ohio. But these trees prolong the melting of deep snows, even under warm rains, for several days longer than deciduous trees. The re-establishment of forests of conifers will therefore contribute to lowering the crests of floods by distributing the flow over five or six days instead of two or three. This is one phase of the work of river control.
