alluvial Sedimentary material deposited by rivers, consisting of silt, sand, clay, gravel, and organic matter.
aquifer An underground geologic formation that acts as a natural catch basin for water; a water-bearing layer of earth.
arroyo Dry channel lying in a semiarid or desert area and subject to flash flooding during seasonal or irregular rainstorms.
cataract A waterfall, especially one containing great volumes of water rushing over a precipice.
clast A fragment of rock.
delta Low-lying plain composed of stream-borne sediments deposited by a river at its mouth.
ephemeral Short-lived.
estuary A section of coastal water that contains fresh and salt water, and is partly enclosed by land.
eutrophication The gradual accumulation of plant nutrients in a relatively sedentary body of water, such as a lake; the process by which a water body becomes enriched with nutrients that stimulate plant growth which leads to the depletion of dissolved oxygen.
evapotranspiration Loss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it.
fjord A long narrow arm of the sea, commonly extending far inland, that results from marine inundation of a glaciated valley.
gully Trench cut into land by the erosion of an accelerated stream of water.
hydroelectric power Electricity produced from generators driven by water turbines that convert the energy in falling or fast-flowing water to mechanical energy.
hydrology Scientific discipline concerned with the waters of the Earth, including their occurrence, distribution, circulation via the hydrologic cycle, and interactions with living things.
karst Irregular limestone with sinks, underground streams, and caverns.
khamsin Hot, dry, dusty wind in North Africa and the Arabian Peninsula that blows from the south or southeast in late winter and early spring.
levee Any low ridge or earthen embankment built along the edges of a stream or river channel to prevent flooding of the adjacent land.
lobate Resembling a lobe.
loess Unstratified, geologically recent deposit of silty or loamy material that is usually buff or yellowish brown and is deposited chiefly by the wind.
moraine Accumulation of rock debris (till) carried or deposited by a glacier.
pluviometric equator Imaginary east-west line indicating the region of heaviest rainfall.
rift valley Elongated trough formed by the subsidence of a segment of the Earth’s crust between dip-slip, or normal, faults.
rivulet A small stream.
silt Sediment particles 0.004–0.06 mm (0.00016—0.0024 inch) in diameter, regardless of mineral type.
taiga Open coniferous forest (conifer) growing on swampy ground that is commonly covered with lichens.
viscous Having the quality of a fluid and a semifluid that enables it to develop and maintain an amount of shearing stress depending on the velocity of the flow and then to offer continued resistance to the flow.
watershed Region or area bounded peripherally by a water parting and draining ultimately to a particular watercourse or body of water.