Environmental Engineering Reference
In-Depth Information
Horst An elevated, large-scale fault block, flanked by down-faulted graben .
Horton overland flow Surface water discharge in sheet rather than channel form,
occurring when rainfall intensity exceeds soil infiltration rates on non-vegetated
surfaces.
Hydration The incorporation of water into the chemical composition of a mineral,
converting it from an anhydrous to a hydrous form; the term is also applied to a form
of weathering in which hydration swelling creates tensile stress within a rock mass.
Hydraulic conductivity The rate at which water is able to move through a soil or rock.
Hydraulic drop An abrupt step over which a stream surface falls as the stream enters a
steeper segment.
Hydraulic efficiency The conservation of potential energy in stream flow, achieved by
minimizing friction losses against the channel, etc.
Hydraulic jump An abrupt step or standing wave over which a stream surface rises, as
the stream enters a less steep segment or encounters a submerged obstacle.
Hydraulic radius The relationship between the wetted perimeter to the cross-sectional
area of a stream; the higher the value, the more efficient the channel.
Hydrogenic The description of rocks formed at the sea bed by the hydrothermal
circulation of sea water through mid-ocean ridges.
Hydrogeology The study of the terrestrial part of the hydrological cycle and the
association between its vegetation, Earth materials and stream flow.
Hydrograph A plot of the variation of stream discharge with time at a selected point in a
catchment and capable of separation into estimates of the various components of flow.
Hydrological sequence The topographic sequence of soils, from ridge crest to adjoining
valley bottom, which reflects the changing soil-water regimes downslope.
Hydrolysis A form of chemical weathering in which the H + and OH ions of water react
with a mineral, with consequent loss of strength.
Hydrometeorology The study of the atmospheric part of the hydrological cycle and the
association between precipitation, evapotranspiration and the drainage basin .
Hydrophobic A soil structure or soil constituent which repels water.
Hydrophyte A plant adapted to growth in wet or waterlogged conditions.
Hydrosere The sequence of plant communities which, successively, occupy a silting-up
freshwater lake.
Hydrosphere Earth's outer, liquid envelope, concentrated almost entirely within the
oceans and its liquid, gaseous and solid derivatives on the land surface and in the
lower atmosphere.
Hydrothermal alteration The chemical weathering of minerals induced by exposure to
a different thermal and moisture environment from that in which they formed.
Hydrothermal circulation Sea-water circulation through mid-ocean ridges, entering
through extension faults and pumped back out through axial vents, and its associated
hydrothermal plume of new minerals formed by chemical reactions between the
heated water, oceanic crust and magma.
Hydrothermal plume The efflux of sea water and dissolved minerals from axial vents in
mid-ocean ridges.
Hygroscopic Said of water retained by or attracted to soil or dust particles and not
evaporated at ordinary temperatures and pressures.
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