WaterWare: a Water Resources |
Management Information System
Sediment yield, turbidity, and erosion
Specific erosion in a watershed and with it turbidity in the runoff vary widely
over several orders of magnitude, with physiographic and climatic conditions.
To give one of the more extreme examples:
As a very aggregate, average figure, USSCS estimates a national average for the continental US
of 4.8 tons/acre and year or 1,920 t/km²/y.
The highest yields from the North Island are towards the East Cape.
It is easy to see why erosion is so high here. Rainfall is moderately high.
The mudstone and sheared argillite rocks are easily eroded.
The area is prone to earthquakes, which tend to expose broken rock.
Finally, the native forest cover is almost completely removed.
These factors combine to give specific suspended sediment yields of up to 20,000 t/km²/y.
In the South Island, the highest SSYs are from the western flanks of the Southern Alps
in south Westland. There, a combination of steep slopes, heavy rainfall,
high uplift rates along the eastern side of the Alpine Fault,
and easily eroded schist result in specific yields up to 32,000 t/km²/y.
Source: http://www.niwa.co.nz/pubs/wa/11-4/estimates, model based estimates.
A large data collection on turbidity and specific sediment yield can be found on-line,
Specific sediment yields from this
global data base range from less than 0.5 t/km²/y to more than 35,000 t/km²/y
i.e., over more than five orders of magnitude.
Among the major world rivers, the Huanghe delivers the highest average
concentration of sediment load (22,000 g/m³) into the sea,
followed by the Nile which (before the construction of the Aswan Dam)
carried 3,700 g/m³ and the Ganges/Brahmaputra with 1,700 g/m³.
Amazonian rivers, as far as they drain old land
surfaces in the eastern Amazon basin, carry less than 5 g/m³ mineral
suspension, but in other parts of the lowland, where soft Tertiary
sediments crop out, the suspension load regionally exceeds 1,000 g/m³.
The suspended load of one single river, depending heavily on rainfall and thus floe levels,
may temporarily change in a wide range.
For example Pickup et al. (1979) published data on the Alice
River (Papua New Guinea) within a minimum of 1 g/m³ and a maximum of
The average concentrations of some other major rivers of the world are listed in the table on the right:
| River system
|| Catchment km²
|Purari River||Papua New Guinea||31,000
|| 1,040 ||2,600
|Fly River||Papua New Guinea||76,000
|| 390 ||1,500
|Mississippi||North America, USA||3,330,000
|| 360 ||120
|Mekong||SE Asia, Vietnam||790,000
|Danube||Europe, Romania ||810,000
|| 325|| 83
|Yukon||North America, USA||840,000
|Amazon||Latin America, Brazil||6,100,000
|Orinoco||Latin America, Venezuela||990,000
|Sao Francisco||Latin America, Brazil ||640,000