Book Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 edition. Excerpt: ...ditches, and the discharge of waste weirs and overflow water from the canals. The drainage of swamps and marshes, and of agricultural lands, also modifies to a considerable extent the natural flow of a stream. Every means provided for the rapid removal of storm water from the land which formerly retained it will have a greater or less effect on the resulting flood heights and consequently on the regimen of the stream. Conditions Favorarle To Maximum Runoff And Torrential Flow In general, it may be concluded that the conditions most favorable to maximum runoff and irregular flow are as follows: On a bare rocky drainage area, with scant soil, the rainfall, unhindered by the soil, gravel, vegetation or forests, will flow rapidly into the stream, and except for a small amount of absorption and evaporation, the runoff will equal a large percentage of the rainfall. Under such conditions the stream will be torrential in character. The flow will gradually increase to a maximum just after the rainfall has reached its maximum, and as the rain ceases the flow will slowly decrease until nothing but a dry run is left, shortly after the rain has ceased, and the conditions will so remain until the next rainfall occurs. Conditions Favorarle To Maximum Runoff And Equalized Flow For conditions favorable to maximum runoff and equalized flow, consider this same rocky valley, filled deep with sand and gravel, with the stream meandering through the center of the pervious plain. Here different conditions will obtain. The rain, falling on this area, will sink rapidly into the pervious deposits and move slowly toward the river. Little of the water will be lost in evaporation, because the rainfall will immediately sink below the surface and reach the ground water, ..