HYDROLOGY

• study of the spatial and temporal variations of water in the terrestrial, oceanic and atmospheric components of the global hydrologic cycle
• study of the movement and storage of water on and under the earth's land surface; of the physical and chemical processes and properties; of the biological processes that affect the storage and movement

Hydrologic Sciences

1. hydrometeorology: climatic processes that involve water (e.g. precipitation, snowmelt, evaporation)
2. limnology: lakes
3. cryology (glaciology): snow and ice
4. hydrogeology: groundwater
5. fluvial hydrology (potamology): streams

Approaches to the Study of Water

1. physical: physical basis of hydrology (chemistry and physics); physical processes; water as an element of the physical environment
2. theoretical: the mathematical basis; statistical models and methods
3. geographical: spatial aspects of the interactions between water and human activity
4. applied: application of physical and theoretical principles to water; water resource management (e.g. monitoring water supplies)

HISTORICAL NOTES

• Water is an essential resource and potential hazard and thus humans have always sought to understand and manage water.
• the first civilizations and densest populations have always developed on water, especially the banks of rivers: Egyptians (Nile), Romans (Tiber), Mesopotamia (Tigris and Euphrates), China (Huang Ho and Yangtze), Pakistan (Indus), India (Ganges)
• concept of a hydrologic cycle found millennia before present in writings of Greek philosophers (Aristotle explained the mechanics of precipitation) and of King Solomon (Ecclesiastes 1:7)
• Egyptians monitored the Nile around 3800 B.P.
• rainfall was measured in India before 2400 B.P. for tax assessment
• during the Renaissance (16th century), Leonardo da Vinci and Bernard Palissy linked stream flow to precipitation
• the first concrete theories and water balance studies were based onm experiments in the Seine basin and on the Mediterranean and surrounding and (Edmund Halley)
• first regular measurements of stream flow: the Rhine at Basel in 1809, the Tiber at Rome in 1825, the Ohio at Wheeling, W. Virginia in 1838
• current use of the term hydrology began around 1750
• in the 18th century the major advances were the mathematical basis of fluid mechanics and hydraulics (Chezy, Bernoulli), the nature of evaporation and the concept of the global hydrological cycle (Dalton)
• in 1856, Darcy laid the foundation of groundwater theory in a water supply report for Dijon, France
• first textbook: Manual of Hydrology by Nathaniel Beardmore (1851)
• in the 1930's the U.S. government heavily funded studies of irrigation, flood control and water conservation; in Canada PFRA was created in 1933
• detailed field experiments and experimental watersheds (e.g. Marmot basin) became a common approach to hydrologic research only since the 1960's

• three times more abundant than all other substances
• one of few inorganic liquids
• only substance that occurs naturally as a solid, liquid and gas
• the most universal solvent
• highest surface tension of all liquids except mercury
• expands upon freezing (by 9%), a property shared with few other substances
• expands with increasing temperature above 4 deg C
• greatest heat capacity of all liquids (1 cal/g/deg C)
• greatest latent heat of fusion and vaporization
• greatest thermal conductivity except for mercury
• high transparency
• like air, a highly mobile substance
• a dense liquid and therefore only slightly compressible