DISTRIBUTION OF WATER. 143 



urements sbowing repeated high rises, which, as has been shown, predi- 

 cate disproportionate flow. The winter besides was warm, most of the 

 precipitation was rain, or, if snow, was qnickly melted and carried off. 

 We see then that, besides the h^cal and timely distribution of precipita- 

 tion, temperature, direction and strength of winds, condition of topog- 

 raphy and soil, other dynamic influences are exhibited in the river flow, 

 which make this as an immediate expression of condition of precipita- 

 tion uncertain. 



After water has reached the ground its distribution is determined, 

 first, by the character of the topography and, second, by the nature of 

 the soil and the surface conditions. 



Tlie topography determines the rapidity of run-off and of collection. 

 The more diversified the country — cut into dells, coves, rills, and fur- 

 rows, steeper and less steep slopes— the larger the number of runs of 

 unequal length in which the water is collected, while the less diversified 

 the contour the more water must be carried off in each run. Yet 

 where the diversity of configuration is accompanied by steep slopes 

 the run-oft' nmy be so rapid that the valley river is filled more rapidly 

 than the river of the open plains country with even slopes of moderate 

 inclination. 



Thus in some of the river valleys of West Virginia the watersheds 

 are scooped out into such an array of coves, gashes, and water courses 

 and minor watersheds, and so steep and rapid in descent that, in 

 spite of the forest cover, a rainfiill of a few days Avill induce a rapid 

 rise of the rivers, Avhile the same amount of rain will hardly wet the 

 ground in a prairie couutry like Iowa. 



The second of the above-mentioned conditions determining distribu- 

 tion — the nature of the soil and the surface conditions — comprises a 

 large number of separate, though related, factors. The composition, 

 structure, and stratification of the soil itself, its water capacity, its 

 permeability, and other physical properties; the nature of the under- 

 lying rock and its susceptibility to disintegration under the action of 

 erosion ; the surface conditions of the soil cover, whether frozen or 

 sunbaked, cultivated or uncultivated, barren or covered with grasses 

 or forests; these are a part of the factors which affect the distribution 

 of the water supply and determine the proportions of surface and 

 underground d r a i n a ge. 



On a given territory, then, with given geologic, topographic, and cli- 

 matic conditions, the only directly variable conditions influencing the 

 manner of di-aiuage are those of the u])per soil stratUi of the soil cover. 

 We are, then, ma inly concerned with the water capacity ol" soils and 

 soil covers, the inten.>ity of their water absorption and the amounts of 

 water which are drained through them in given times. We are inter- 

 ested in studying by what means the draining capacity of the soil is 

 increa.sed, and by what means altogether the run-oft" may be changed 

 in its nature from a superficial to a subterranean one and the reverse. 



