Geology Reference
In-Depth Information
Figure 3.7
The chief hydrological processes that influence the geomorphology of hillslopes and streams. Water flows over
and through landscapes in unconcentrated and concentrated forms.
Rill flow
is deeper and speedier than inter-rill flow and is
characteristically turbulent. It is a sporadic concentrated
flow that grades into streamflow.
during dry periods. Subsurface flow may take place as a
slow movement through rock and soil pores, sometimes
along distinct lines called
percolines
, or as a faster move-
ment in cracks, soil pipes (
pipe flow
), and underground
channels in caves.
Subsurface flow
Flow within a rock or soil body may take place under
unsaturated conditions, but faster
subsurface flow
is
associated with localized soil saturation. Where the
hydraulic conductivity of soil horizons decreases with
depth, and especially when hardpans or clay-rich sub-
strata are present in the soil, infiltrating water is deflected
downslope as
throughflow
. Engineering hydrologists use
the term
interflow
to refer to water arriving in the stream
towards the end of a storm after having followed a deep
subsurface route, typically through bedrock.
Baseflow
is
water entering the stream from the water table or delayed
interflow that keeps rivers in humid climates flowing
Springs
Springs
occur where the land surface and the water table
cross. Whereas saturation overland flow is the seepage
from a temporary saturation zone, springs arise where
the water table is almost permanent. Once a spring starts
to flow, it causes a dip in the water table that creates a pres-
sure gradient in the aquifer. The pressure gradient then
encourages water to move towards the spring. Several
types of spring are recognized, including waste cover
springs, contact springs, fault springs, artesian springs,
karst springs, vauclusian springs, and geysers (Table 3.3).
