Effects of depth and gradient on soil moisture storage in a small agricultural watershed

Water supply has always exerted a major influence on the development of the economy of any community, state or nation. It has been observed through history that people frequently built homes, settlements and cities adjacent to waterways, though the divides between watersheds were often steep and heavily forested, and travel across them was difficult. As time advanced population increased, communication improved, and people started moving farther away from the streams or waterways. Recently the United States population and industrial and agricultural development have reached a stage of growth where local water supplies are failing to meet the demand (29,30). Individuals and organizations have frequently been enjoined from withdrawing water from upstream channels, because such withdrawals would have seriously impaired the activities of downstream water users. To improve public water supply is, therefore, the problem on which research is required. Consequently, efforts are being made to study the full life history of the waters of the earth, and in particular the factors affecting water yield of the watersheds.

Several aspects of water yield of a watershed are of concern to those engaged in the development of water supplies. These aspects are total quantity, fluctuations in quantity, and quality. Climate over a watershed,.and watershed characteristics are such that conditions varying from droughts to floods exist. Probably little can be done about the climate, consequently interest has centered on the effects of watershed characteristics upon water yield. Soil within the watershed is among the dominant factors causing variations in water yield. Hursh and Fletcher (15) state that an analogy of the storage function of the soil profile to the storage in an artificial reservoir is justifiable. Parks and Longwell (25) state that soil moisture is Tennessee's greatest water reservoir. Moisture storage in the soil profile, however, is not static; it is dynamic. The dynamic moisture conditions in the soil profile affect watershed hydrology to a considerable extent. Thus, a knowledge of moisture storage in the soil profile of a watershed is necessary.