Geoscience Reference
In-Depth Information
14
Water catalyses low-temperature melts and explosive
volcanic activity, essential to subduction orogeny and,
hence, tectonic uplift. It is also the principal agent in their
eventual destruction - and therefore Earth's 'proud setter
up and puller down of kings', borrowing Shakespeare's
reference to Warwick the 'Kingmaker' during the Wars of
the Roses. Nowhere is its ability to destroy, as well as create,
mountain systems and continents more obvious than in
running water at Earth's surface. Precipitation is widely
distributed over the land surface but markedly concen-
trated at points of
discharge
through
trunk
rivers. The
catchment
, or land surface unit generating river flow, is a
fundamental geomorphic and accounting unit. Catch-
ment slope processes are intimately linked with their
water and sediment transfers. Their collective yields then
drive fluvial processes in river channels, although
channel-slope links are rarely in equilibrium. Water-
sediment stores and fluxes are measured or estimated,
leading to calculation of
water
and
sediment balances
.
This is not done solely in the interests of geomorphology,
for the catchment also determines vital options for human
occupation and land use. Water is required simultaneously
for the essential but conflicting purposes of water supply
and waste stream disposal. Data gathered for both geo-
morphological investigation and hydrological manage-
ment considerably aid our appreciation of water flow
through the landscape.
We follow the cascade of water and sediment, from
precipitation to the generation of channel flow, the
behaviour of water and sediment in river channels and
their creation of
fluvial
landforms. At first sight the
terrestrial
component of the
global hydrological cycle
appears to be negligible. Surface freshwater rivers, lakes
and swamps account for only 110,000 km
3
or less than
0·01 per cent of the global water balance of approximately
amount is stored in terrestrial glaciers, ice sheets and
permafrost (see
Chapter 15).
However, high-energy, fast
river transfer over the land surface compensates for its
diminutive mass (
Figure 14.2
).
The turnover time of
surface waters is less than twenty days or 0·05 yr via rivers,
GLOBAL WATER
FRESH WATER
Rivers, Lakes
and Swamps
0.3%
Ice
1.79%
Global Ocean
96.5%
and
Saline
Groundwater
0.9%
Ice sheets,
Glaciers and
Permafrost
69.2%
Groundwater
30.4%
0.81%
Atmospheric
and Biological
0.01%
1350
w
10
6
km
3
35.1
w
10
6
km
3
