Geology Reference
In-Depth Information
Table 3.3 Springs
Type
Occurrence
Example
Waste cover
Dells and hollows where lower layers of soil or
bedrock is impervious
Common on hillslopes in humid
environments
Contact
Flat or gently dipping beds of differing
perviousness or permeability at the contact of
an aquifer and an aquiclude. Often occur as
a spring line
Junction of Totternhoe Sands and
underlying Chalk Marl,
Cambridgeshire, England
Fault
Fault boundaries between pervious and
impervious, or permeable and impermeable,
rocks
Delphi, Greece
Artesian
Synclinal basin with an aquifer sandwiched
between two aquicludes
Artois region of northern France
Karst
Karst landscapes
Orbe spring near Vallorbe, Switzerland
Vauclusian
U-shaped pipe in karst where water is under
pressure and one end opens on to the land
surface
Vaucluse, France; Blautopf near
Blaubeuren, Germany
Thermal
Hot springs
Many in Yellowstone National Park,
Wyoming, USA
Geyser
A thermal spring that spurts water into the air at
regular intervals
Old Faithful, Yellowstone National Park
Streamflow
Water flow may be turbulent or laminar. In
lami-
nar flow
, thin layers of water 'slide' over each other,
with resistance to flow arising from molecular viscosity
(Figure 3.8a). In
turbulent flow
, which is the pre-
dominant type of flow in stream channels, the chaotic
flow-velocity fluctuations are superimposed on the main
forward flow, and resistance is contributed by molec-
ular viscosity and eddy viscosity. In most channels, a
thin layer or laminar flow near the stream bed is sur-
mounted by a much thicker zone of turbulent flow
(Figure 3.8b). Mean flow velocity, molecular viscosity,
fluid density, and the size of the flow section deter-
mine the type of flow. The size of the flow section
may be measured as either the depth of flow or as
the hydraulic radius. The
hydraulic radius
,
R
, is the
cross-sectional area of flow divided by the wetted perime-
ter,
P
, which is the length of the boundary along
which water is in contact with the channel (Figure 3.9).
In broad, shallow channels, the flow depth can approx-
imate the hydraulic radius. The
Reynolds number
,
R
e
,
Rivers
are natural streams of water that flow from
higher to lower elevations across the land surface.
Their continued existence relies upon a supply of
water from overland flow, throughflow, interflow, base-
flow, and precipitation falling directly into the river.
Channelized rivers
are streams structurally engineered
to control floods, improve drainage, maintain naviga-
tion, and so on. In some lowland catchments of Europe,
more than 95 per cent of river channels have been
altered by channelization.
Water flowing in an open channel (
open channel
flow
) is subject to gravitational and frictional forces.
Gravity impels the water downslope, while friction from
within the water body (viscosity) and between the flow-
ing water and the channel surface resists movement.
Viscosity
arises through cohesion and collisions between
molecules (
molecular
or
dynamic viscosity
) and the
interchange of water adjacent to zones of flow within
eddies (
eddy viscosity
).
