Environmental Engineering Reference
In-Depth Information
Table 3.1
Pontbren subcatchment characteristics
Mean slope angle
(SD) (degrees)
Area under improved
pasture
a
(%)
HOST class
b
SPR
c
Site
Area (ha)
(%)
Hillslope
0.5
7.3 (0.57)
100
21.8
41.9
<
5
242
4.74 (2.93)
70
24.6
52.5
6
318
5.04 (3.08)
76
23.9
51.0
9
402
6.95 (6.36)
14
19.4
48.4
Source: Countryside Council for Wales phase 1 survey data.
a
Hydrology Of Soil Type Classi
cation (Boorman et al. 1995).
b
Standard Percentage Runoff.
c
SD, standard deviation.
pasture and openmoorland (see Table 3.1). There is
little difference in geomorphology between catch-
ments, and the potential dampening response of
the lake at the source of theMelin y grug appears to
have relatively little effect on flood peak. There are
differences in the soil types. Table 3.1 shows the
spatially averaged HOST (Hydrology Of Soil Type)
classification (Boorman et al. 1995) for each of the
subcatchments along with the estimated standard
percentage runoff (SPR) based on the HOST class
value. Results indicate that differences in runoff
response may arise from a combination of differ-
ences in soil type and land use, but the relative
contributions are difficult to disentangle.
In summary, the experimental results have
clearly demonstrated the dominant hillslope run-
off processes, and provided insight into the time-
varying nature of responses as soils respond to
seasonal wetting and drying and increases in bio-
logical activity. The plot experiments are ongoing,
but relatively rapid changes have been observed
in soil structure and biodiversity. Observations
of established tree shelter belts show significant
changes to soil hydraulic properties, with in-
creased infiltration capacity. Results are presented
in more detail in Wheater et al. (2008).
Multiscale Modelling
Modelling strategy
The modelling strategy has three elements. At
Pontbrenwe are concernedwith representing phys-
ical changes to soil structure, vegetation and field
drainage, and the associated effects on runoff pro-
cesses. A key element therefore is the establish-
ment of a detailed, physically based model, capable
Fig. 3.6
Standardized stream flow
response (Q) from gauging sites 6 and 9.
