Hydrology is the study of inter-relationships and interactions between water and its environment in the hydrological cycle. As water moves within a watershed, it carries sediment, chemicals, heat and biota. (Dunne and Leopold, 5). The movement of water in the hydrologic cycle drives the watershed system and affects all aspects of watershed health.
Groundwater and surface water sources are those most used by humans. Dependence on these limited sources creates vulnerability if they become impaired in quality or quantity (Adapted from Schlesinger 1991) (Annear, 2).
Water is central to human existence and life in general. Unless trapped as groundwater within closed basins, water is constantly in motion. It may be detained in glacial ice, under ground, or in lakes or reservoirs; but eventually it flows and melts, seeps, or evaporates. This movement of water is continuous, but irregular in space and time. Because of this, even areas that are typically well supplied can experience droughts or floods at various times (Satterlund and Adams 1992).