Environmental Engineering Reference
In-Depth Information
Plate 14.4
Flume for stream gauging in a steep catchment on
Plynlimon, mid-Wales. Its height, and baffles to dissipate
stream energy, reflect the 'flashy' nature of upland stream
flow.
Photo: M. A. Fullen.
+ net onward transfer by percolation, groundwater recharge, seepage or abstraction
(output). This occurs as transient overland flow on slopes and
intermittent
,
ephemeral
or
permanent
channel flow
.
Horton overland flow
occurs when precipitation intensity
exceeds soil infiltration capacity on non-vegetated surfaces. Water moves away
downslope at 10
1-2
mm s
−1
, initially as
sheet flow
. This is simulated by impervious urban
surfaces when drain capacity is exceeded briefly during rainfall. Much water is detained
in surface
depression storage
, evaporates or drains by percolation. Some reaches
channels and contributes to
quickflow
- augmenting direct channel precipitation, riparian
vegetation drip and throughflow.
