Geoscience Reference
In-Depth Information
basins into five categories based on maximum
elevation within the hinterland: high mountain
(headwaters at elevations
sediment fluxes for 50 years ( Jäckli 1957,
Table 2.5). A sediment budget accounts for
the sources, transfers and storage of sediment
within a landscape unit. Constructing a contem-
porary sediment budget for a mountain catch-
ment is a time-consuming and labour intensive
endeavour and, therefore, most budgets tend
to be measured over short periods (typically
1-3 yr). Figure 2.9 shows a sediment budget
framework applied to a small glacier basin in
southern Switzerland in order to evaluate the
significance of the proglacial zone in contribut-
ing sediment to a glacier-fed stream (Warburton
1990). A measurement framework was set up
to determine the rates of sediment transport
of slope and channel processes and changes in
storage within the sediment system (Fig. 2.9a).
Results (Fig. 2.9b) clearly demonstrate the
importance of the glacier stream in terms of
sediment flux but there is still a significant addi-
tional load: approximately 23% of the total
catchment sediment yield is added by proglacial
sources (Warburton 1990). The overwhelming
proportion of the proglacial sediment (95%)
was eroded from the valley floor during a brief
meltwater flood.
This methodological approach is widely applied
in the study of mountain sediment systems
(Schlyter et al. 1993; Slaymaker et al. 2003). Two
further examples of mountain sediment budget
models are shown in Table 2.5. These are from
the Upper Rhine (area 4307 km
2
, relief 2800 m;
Jäckli 1957) and Kärkevagge in northern Sweden
(area 15 km
2
, relief 930 m; Rapp 1960). In terms
3000 m), mountain
(1000 -3000 m), upland (500 -1000 m), low-
land (100 -500 m) and coastal plain (
>
100 m).
Mountain rivers were further subdivided into:
Asia and Oceania (generally very high sediment
yield), the high Arctic and non-Alpine Europe
(low sediment yields) and the rest of the World.
The correlations between load and basin area
for the various topographic categories generally
range between 0.70 and 0.82. There is a distinct
pattern to the data dependent on topographic
setting. Mountain rivers have the greatest loads
followed by the uplands, lowlands and coastal
plains. There is some overlap in these general
relationships owing to exceptions within each of
the categories. For example, mountainous rivers
draining South Asia and Oceania have much
greater yields than (two to three times) other
mountainous areas and are generally an order
of magnitude greater than high Arctic and non-
Alpine European mountains. Although these
studies show some clear general patterns, such
data should be interpreted with caution owing
to the inherent errors in data collection and the
incommensurate nature of the measurements
(Harbor & Warburton 1993).
<
2.2.3 Sediment budget models of mountain
sediment systems
Sediment budgets have been used as a tool
for understanding sedimentary processes and
Table 2.5
Sediment fluxes from two high mountain environments: Upper Rhine (area 4307 km
2
, relief 2800 m; Jäckli 1957) and
Kärkevagge in northern Sweden (area 15 km
2
, relief 930 m; Rapp 1960). Units are in 10
6
Jkm
−
2
yr
−
1
. A joule ( J) is the unit of
work
(E),
which is generally defined by
E
=
mg
(
h
1
−
h
2
), where
m
is mass,
g
is acceleration due to gravity and
h
is elevation, with (
h
1
−
h
2
) being
the change in height between two points 1 and 2. (Source: Barsch & Caine 1984.)
Catchment details
Upper Rhine
Kärkevagge
Area (km
2
)
4307
15
Relief (m)
2800
930
Coarse debris bedrock slopes
729.2 (4.2%)
15.7 (58.4%)
Soil-fine sediment mantled slopes
53.5 (0.3%)
7.93 (29.5%)
Channel transport-lake sedimentation
13,798 (79.5%)
Not measured
Solute flux (output)
2781 (16.0%)
3.24 (12.1%)
Total
17,362
26.87
