Hydrology is the study of water in the natural or disturbed environment. Another definition is the condition of a defined/limited environment (for example, a watershed) at any particular point in time and place. Hydrology integrates basic principles of meteorology (water and other substances in the atmosphere and their interactions), biology (especially ecology and plant physiology), and soils (the role of water, ice, and other factors in soil formation, classification, and use and their interaction with plants), along with the unusual characteristics of water itself: its physical, chemical, and biological characteristics and consequent behavior.

Hydraulics, in contrast to hydrology, is the science of water movement in confined pipes, pipe systems, and natural and artificial channels (such as canals and rivers).

Watershed hydrology is the science of surface and ground waters on a landscape scale where the unit of interest is the

Watershed, a natural or disturbed system that functions in a manner to collect, store, and discharge water to a common outlet, such as a larger stream, lake, or ocean. Between collection and runoff, water is stored. A watershed embraces all its natural and artificial (manmade) features, including its surface and subsurface features: climate and weather patterns, geologic and topographic history, soils and vegetation characteristics, and land use. A watershed may be as small as a house roof’s gutters and downspout, and as large as the Amazon, Mississippi, Nile, or St. Lawrence River basins. The science embraces a comprehensive understanding of the basic functions of a watershed and provides the basis for effective watershed management.

Watershed Functions are identified in three categories:

1. Hydrological Functions: Collection, Storage, and Discharge
2. Ecological Functions: Chemical reaction sites, and Habitat
3. Response Functions: Attentuation, and Flushing

The functions are described in detail in the autotutorial short course Concepts of Watershed Hydrology.

Concepts of Watershed Hydrology provides a fundamental – conceptual – approach to watershed hydrology and provides for the essential foundation of watershed management by showing context, meaning, and importance of environmental elements and processes that make up a watershed. Understanding basic concepts and effective communication constitute the starting point for successful watershed management. Click here for connection to an animated, narrated, autotutorial short course on CD/Workbook available at the linked website.

Infiltration is the movement of water across the interface between armosphere and soil. It is the single most important process in the hydrologic environment because it interacts with the rate of rainfall (or snowmelt) to divide surface and subsurface runoff. Impervious surfaces produce rapid and energy-laden runoff water that carries sediments and other pollutants directly to streams. That type of runoff is referred to as a nonpoint source of pollution, generally runoff that is diffused over the landscape. Such runoff requires restraints, called Best Management Practices and includes structures or processes that are designed, constructed, and maintained to prevent or control especially storm water runoff that typically carries dissolved and suspended materials. In contrast, point source pollutants are end-of-the-pipe outfalls generated by waste treatment and industrial plants.

Watershed management is the planned manipulation of one or more factors of the natural or disturbed drainage to effect a desired change in or maintain a desired condition of the water resource. Since the watershed includes the particular elements present, each is unique, and requires individual attention to the peculiarities of that particular unit of land. Watershed management begins with understanding basic concepts and the essential communication with all parties legitimately interested in the development or maintenance of watershed functions and values.

Organizations include government agencies (at all levels), professional societies, and non-government organizations (NGOs) that are involved in watershed management. They include people from all walks of life, including administrators, consultants, economists, farmers, politicians, regulators, scientists, and the lay public. All have a stake – a legitimate interest – in effective watershed management based on sound science and, consequently are called "stakeholders." (That term actually was originally used to define exactly the opposite, that is, persons who had no stake in the money that was entrusted to them while two or more contestants vitally interested in the outcome played for the pot in a poker game.)

Partnerships have developed widely at the watershed level and involve all stakeholders, individuals and representatives of organizations that have a legitimate stake in the management of the several watershed resources.

© 2005 Peter E. Black