Abstract

Factors descriptive of a drainage‐basin as related to its hydrology may be classified broadly as: (1) Morphologic—These factors depend only on the topography of the land forms of which the drainage‐basin is composed and on the form and extent of the stream‐system or drainage‐net within it. ((2) Soil factors—This group includes factors descriptive of the materials forming the groundwork of the drainage‐basin, including all those physical properties involved in the moisture‐relations of soils. (3) Geologic‐structural factors—These factors relate to the depths and characteristics of the underlying rocks and the nature of the geologic structures in so far as they are related to ground‐water conditions or otherwise to the hydrology of the drainage‐basin. (4) Vegetational factors—These are factors which depend wholly or in part on the vegetation, natural or cultivated, growing within the drainage‐basin. (5) Climatic‐hydrologic factors—Climatic factors include: Temperature, humidity, rainfall, and evaporation, but as humidity, rainfall, and evaporation may also be considered as hydrologic, the two groups of factors have been combined. Hydrologic factors relate specially to conditions dependent on the operation of the hydrologic cycle, particularly with reference to runoff and ground‐water.