Text A Hydrology

Hydrology is a scientific discipline concerned with the waters of the Earth, including their occurrence, distribution, circulation via the hydrologic cycle, and interactions with living things. It also deals with the chemical and physical properties of water in all its phases.

The world's supply of fresh water is obtained almost entirely as precipitation resulting from evaporation of sea water. The processes of moisture transfer from the sea to the land and back to the sea again are known to be called the hydrologic cycle. An understanding of these processes is considered very important to the water-resources engineer.

The first stage in the hydrologic cycle is the evaporation of water from the ocean. The heating of the ocean water by the sun is the key process that starts the hydrologic cycle (water cycle) in motion. The vapor is carried over the continents by moving air masses. If the vapor is cooled to its dew point, it condenses into visible water droplets which form cloud or fog. Under favourable conditions the tiny droplets grow large enough to fall to earth as precipitation. About two-thirds of the precipitation which reaches the land surface is returned to the atmosphere by evaporation from water surfaces, soil and vegetation and through transpiration by plants. The remaining part of precipitation returns to the ocean through surface or underground channels.

Precipitation includes all water which falls from the atmosphere to the earth's surface. Precipitation occurs in various forms. The hydrologist must be interested only in liquid precipitation / rainfall / and frozen precipitation / snow, hail, sleet, etc./. The amount of precipitation, however, can vary greatly from season to season in any location. Some regions experience very heavy precipitation in some seasons, and relatively little in others. The results of these variations mean that pipelines and large-scale dams must be used to supply some cities with water throughout the year.

Evaporation is the transfer of water from the liquid to the vapor state. Transpiration is the process by which plants remove moisture from the soil and release it to the air as vapor. More than half of the precipitation which reaches the surface of the earth is returned to the atmosphere by the combined process, evapotranspiration.

People tap the water cycle for their own uses. Water is diverted temporarily from one part of the cycle by pumping it from the ground or drawing it from a river or lake. It is used for a variety of activities such as households, businesses and industries; for transporting wastes through sewers; for irrigation of farms and parklands; and for production of electric power. After use, water is returned to another part of cycle: perhaps discharged downstream or allowed to soak into the ground. Used water normally is lower in quality, even after treatment, which often poses a problem for downstream users.

The engineering hydrologist, or water resources engineer, is involved in the planning, analysis, design, construction and operation of projects for the control, utilization and management of water resources. Water resources problems are also the concern of meteorologists, oceanographers, geologists, chemists, physicists, biologists, economists, specialists in applied mathematics and computer science, and engineers in several fields.

Hydrologists apply scientific knowledge to solve water-related problems in society: problems of quantity, quality and availability. They may be concerned with finding water supplies for cities or irrigated farms, or controlling river flooding, soil erosion, or in environmental protection.

Scientists and engineers in hydrology may be involved in both field investigations and office work. In the field, they may collect basic data, oversee testing of water quality, direct field crews and work with equipment. In the office, hydrologists do many things such as interpreting hydrologic data and performing analyses for determining possible water supplies.

The work of hydrologists is as varied as the uses of water and may range from planning multimillion dollar interstate water projects to advising homeowners about backyard drainage problems.