Chapter three

Hydrology involves the study of the occurrence, distribution, movement, and quality of the earth's waters in atmospheric, surface, and subsurface environments. Surface processes include precipitation, runoff, surface storage, surface water evaporation, and interception. Subsurface processes include infiltration, transpiration, soil water evaporation, and water movement in the vadose and saturated zones. Hydrologists and engineers generally are concerned with understanding the processes involving fluid flow, the dynamic interactions of fluids through earth materials, the chemical interactions between the fluid and solid phases, and, the transport of chemicals by flowing fluids. Although these areas are interconnected, each represents a separate science. Typically, these processes are observed and described (modeled) separately. Definitions and Terminology Watershed-The surface area that contributes runoff to a common point (known as the watershed outlet or outfall). Precipitation-Literally, water, in solid or liquid form falling from the atmosphere to earth. Forms of precipitation include: snow (crystalline), sleet (grains of ice), hail (balls of ice), and rain (liquid form). Types of precipitation include convective, orographic, frontal and cyclonic. Rainfall Depth-The total amount of rainfall that accumulates at-a-point (i.e., rain gage) during a storm event. Rainfall Intensity-The rate (velocity) of rainfall. Interception-Rainfall (precipitation) captured and stored on leaves, rooftops, etc. Depression Storage-Rain that becomes trapped in depressions (holes) in the land surface and subsequently evaporates or infiltrates. Evaporation-A diffusive process whereby water undergoes a change in state from liquid to vapor and rises from the land surface to the atmosphere. Evaporation occurs from water transpired by plants (evapotranspiration, ET), bare soil, and open water bodies. Infiltration-Water movement across the air-soil interface (ground surface) into the underlying soil. Represents the major loss or abstraction of rainfall. Runoff-Runoff is rainfall in excess of losses that retain the water within the watershed. Runoff is water that flows overland and through shallow and/or deep groundwater routes to exit the watershed at its outlet. Direct Runoff-Runoff that represents an immediate response of the watershed to a rainfall event.

Water Resources Research, 1970

In an area of low intensity rainfall and permeable soils, three hillside plots were instrumented for a study of runoff-producing mechanisms. Runoff from the plots was measured at the ground surface, the base of the root zone, and in the zone of perennial gro.undwater seepage. Data on soil moisture, water-table elevation, and piezometric head were also collected during natural and artificial storms. The data showed that, as the infiltration capacity of the soil exceeded the rainfall intensities that occurred and that were applied, overland flow generated by the mechanism described by Horton did not occur. Although soils and topography were those generally thought to be conducive to subsurface stormflow, the runoff produced by this mechanism was too small, too late, and too insensitive to fluctuations of rainfall intensity to add significantly to stormflow in the channel at the base of the hillside. When the water table rose to the surface of the ground, however, overland flow was generated on small areas of the hillside. Only when this overland flow occurred were significant amounts of stormflow contributed to the channel by the hillside. The return periods of storms that would produce such overland flow were found to be very large. face stormflow. Whipkey [1965, p. 74] defined subsurface stormflow as underground, storm-period flow that reaches the stream channel without entering the general groundwater zone. Kirkby and Chorley [1967, p. 7] used the term 'throughflow' to denote 'flow which takes place physically within the soil profile.' Hewlett and Hibbert [1965] described their concept of 'translatory flow.' They wrote, 'Above the zone of saturation, we may regard such movement as due to thickening of the water films surrounding soil particles and a resulting pulse in water flux as the saturated zone is approached.' AIMS OF THE PRESENT STUDY The magnitude and timing of subsurface contributions to channel runoff and the conditions under which significant amounts of subsurface stormflow are produced are generally unknown.

2016

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2013

Peatland Biogeochemistry and Watershed Hydrology at the Marcell Experimental Forest, 2011

2011

2005

A catchment is a basic unit of landscape particularly for investigations of hydrologic processes. Typically, the topographic boundary of a catchment coincides with the hydrologic boundary causing any precipitation falling on to the catchment to be routed to a stream where it is transported out of the catchment. Fundamental components of the hydrologic cycle, such as precipitation, runoff and evapotranspiration (computed by difference between precipitation and runoff over long periods), have been documented from water balance studies on small catchments. Observations and time series data collected from small catchments provide a basis for the development of hydrologic models, and many such models have been used for flood forecasting. However, one of the more recent goals of hydrologic investigations in small catchments is to understand better how streamflow is generated and how this process relates to water quality genesis. Prior to the last few decades, studies of the sources of str...

International Association of Scientific Hydrology. Bulletin, 1967

As communities grow, the need for diverting water increases. Storm water runoff overwhelms city sewers and can damage nearby streams and rivers through erosion. Handling the storm water near its source can save millions in costly repairs that would otherwise be directed at correcting erosion or controlling flooding. A common method for managing storm water is to build a basin. Basins are meant to collect the water, and release it at a rate the prevents flooding or erosion.