GLOBAL CHANGE AND THE SEDIMENT LOADS OF THE WORLD’S RIVERS
Department
of Geography,
The International Geosphere Biosphere Programme (IGBP) initiated by ICSU in 1987 (see Steffen et al., 2004), as well as a number of related initiatives, have focused increasing attention on the changes in the functioning of the Earth system caused by human activity and on the problems associated with the sustainable management of this changing system over the coming centuries. Much of this attention has been directed to the increased emission of greenhouse gases, leading to climate change. However, as recognized by the IGBP, anthropogenic pressure must be seen as the cause of many other facets of global change. These include major changes in vegetation cover and land use across the earth’s surface, wide ranging disturbance of that surface by infrastructure development and mineral exploitation and modification of the hydrological cycle caused by water resource exploitation. In the latter context it is estimated that dams currently intercept more than 40% of the annual water discharge from the continents (Vörösmarty et al., 2003). Such changes in the condition of the land surface of the earth and the flow of its rivers, as well as ongoing climate change, can be expected to have exerted a significant influence on the sediment loads of the world’s rivers. Sediment loads will be sensitive to both increases and reductions in land erosion caused by human activity, as well as changes in river flows and sediment transport caused by water resource exploitation, construction of dams and other human uses of river systems. The temporal trajectories of these anthropogenic impacts will have varied across the land surface of the globe in response to the history of human exploitation of the landscape. In some areas of the ‘old world’, for example, forest clearance and the expansion of agriculture can be expected to have resulted in changing sediment loads as far back as several millennia, whereas in areas of the ‘new world’ equivalent changes may have occurred within the last two centuries. Nevertheless, the accelerating pace of human impact in many areas of the world means that the changes in the sediment loads of its rivers are likely to be intensifying.
Fig. 1 emphasizes the acceleration of several likely drivers of changing sediment loads over the past century. Population growth can be viewed as a surrogate for many components of anthropogenic pressure, including land clearance, intensification of land use, mineral exploitation and infrastructure development, whilst the expansion of cropland and pasture and the destruction of tropical forests provide a more direct measure of changing land cover. The significance of recent change is particularly apparent in the case of water resource development, which itself links closely with population growth. Almost all of the world’s major reservoirs were, for example, constructed during the past 60 years.
The significance of potential changes in the sediment loads of the world’s rivers is wide ranging. From a global perspective, changes in land-ocean sediment transfer will result in changes in the global biogeochemical cycle, since sediment is important in the flux of many key elements and nutrients. Equally, this transfer will also reflect the intensity of soil erosion and land degradation and thus the longer-term sustainability of the global soil resource. At the regional and local scales, changes in the sediment load of a river can give rise to a range of problems. Excessive sediment loads can result in accelerated rates of sedimentation in reservoirs, river channels and water conveyance systems, causing problems for water resource development and in maintaining navigable waterways and harbours, as well as in adverse impacts on aquatic habitats and ecosystems, including offshore coral reefs Conversely, reduced sediment loads can result in the scouring of river channels and erosion of delta shorelines as well as reduced nutrient inputs to aquatic ecosytems, particularly lakes, river deltas and coastal seas.
Figure 1. Changes in world population, the global area of cropland and pasture, and the extent of the world’s tropical forest over the past 200 years. (Based Band C on Goldewijk, 2001 and D on Roper and Roberts, 1999)
This contribution provides a brief review of available empirical evidence of recent changes in the annual suspended sediment loads of the world’s rivers, with a view to evaluating recent trends and assessing their sensitivity to recent environmental change and other anthropogenic impacts, identifying the key drivers of change, highlighting some of the complexities associated with linking changes in the sediment output from a river basin to the changes occurring within that basin and evaluating the significance of the changes identified for global land-ocean sediment transfer.
A clear example of the non-stationary
nature of the recent record of suspended sediment transport by a major world
river and the potential importance of both human impact and climate change is
provided by the recent changes in the suspended sediment discharge of the lower
Huanghe or Yellow River in
Simple trend analysis applied to the records of water and suspended sediment discharge for the Yellow River at Lijin in fig. 2A, using linear regression to establish trend lines, provides clear evidence of a statistically significant (P >99.9%) reduction in both water and sediment load over the past 50 years. The lack of any clear break in the double mass plot (fig. 2Aiii), a tool frequently used to identify changes in the sediment response of a river (e.g. Walling, 1997), suggests that both the runoff and sediment response have responded to similar controls. The progressive reduction in both the water discharge and suspended sediment load of the Yellow River, demonstrated by Figure 2A, is in part a response to climate change, and, more particularly, reduced precipitation over the central region of the catchment , but it is primarily a reflection of human impact and, more particularly, increasing water abstraction (as evidenced by the greatly reduced flows in Figure 2Ai), sediment trapping by an increasing number of both large and small reservoirs and an extensive programme of soil and water conservation, aimed at both improving local agriculture and reducing sediment inputs to the river, where siltation poses major problems for effective flood control and water use in the lower reaches of the basin.
A
contrasting example of the recent trend of suspended sediment load is provided
by the Rio Magdalena in
Any
attempt to identify changes in the sediment fluxes of major rivers, such as
that attempted above, is heavily dependent on the availability of reliable
data. Long-term records stretching back over several decades are available for
relatively few of the world’s rivers.
Figure 2. Recent
changes in the suspended sediment loads of the Lower Yellow River, China (A)
and the Rio Magdalena, Colombia (B), as demonstrated by the time series of
annual water discharge (i) and annual sediment load
(ii) and the associated double mass plots (iii).
Furthermore,
for many rivers with sediment monitoring programmes,
the available data are inadequate for a rigorous assessment of trends in a
parameter that which can be expected to exhibit significant inter-annual
variability, even in the absence of a changing response For example, where only
a few sediment samples are collected each year, these data are frequently
aggregated over a long period, to construct a sediment rating curve that is
applied to the water discharge record for that period. Such temporally-lumped
sediment rating curves cannot represent non-stationarity
in the sediment concentration record, such as might occur due to sediment
trapping by upstream reservoirs or land use change within the catchment.
The literature contains a vast body of
empirical evidence derived from erosion plots and small catchments,
which demonstrates the impact of forest clearance and related land cover
change and land use activities on rates of soil loss and sediment yield. Order
of magnitude increases in both rates of soil loss and sediment yield have been
widely reported (e.g. Morgan, 1986) and these must clearly result in increased
sediment loads in rivers, whose basins have been widely affected by such
changes. However, when attempting to extrapolate the evidence provided by erosion
plots to larger river basins, it is important to recognise the need to take
account of the ‘connectivity’ of the landscape to the river system, since much
of the mobilised sediment may be deposited before reaching the channel network
and may therefore not be directly reflected by increased sediment loads.
Similar considerations apply when attempting to extrapolate the findings from
small catchments to larger river basins, since a significant proportion of the
increased sediment flux generated within small catchments may be deposited
downstream within the channel and floodplain system of the larger basin, before
reaching its outlet.
Two clear
examples of recent increases in river sediment loads associated with land
clearance and intensification of agricultural land use are provided in fig. 3.
Fig. 3A presents information for the 140.933 km2 basin of the
Upper Mekong or Lancang River in China where
extensive land clearance and land use change associated with rapid population
growth in the 1970s and 1980s are reflected by a significant (P>95%) trend
of increasing sediment loads over the period 1963 to 1990, whereas the annual
runoff record showed no statistically significant trend. The double mass plot
shows a clear shift towards increased sediment loads around 1980. Fig. 3B
presents data for the smaller 1.940 km2 basin of the
Land clearance for agriculture and
subsequent intensification of agricultural land use are only one of the many
ways in which human activity can change the natural vegetation cover and
disturb the catchment surface, thereby increasing
erosion and sediment yields.
Figure 3. Recent changes in the suspended sediment loads of the Lancang River, China (A) and the Yazgulem River, Tajikistan (B), as demonstrated by the time series of annual water discharge (i) and annual suspended sediment load (ii) and the associated double mass plots (iii)
The double mass plot (fig. 4Aiii) indicates
that the change in the sediment response of the basin dates from around 1956
and Bobrovitskaya (personal communication) has
indicated that the primary cause of this increase was the expansion of gold
mining activity within the basin, which caused major disturbance of river
channels and floodplains. The example presented in fig. 4B relates to the
smaller (1.584 km2) mountainous basin of the
Figure 4. Recent
changes in the suspended sediment loads of the
Although
land use impacts on sediment loads are commonly seen as resulting in increased
sediment loads, the implementation of soil and water conservation and sediment
control programmes in river basins can have the
reverse effect and result in reduced sediment loads, or at least reduce the
increases associated with land clearance and surface disturbance. By virtue of
the growing importance of soil and water conservation and sediment control programmes in many areas of the world, this component of
human impact on global sediment fluxes must be assuming increasing importance.
Quantitative evidence of that importance is, however, currently limited. As
with land use impacts considered above, the literature provides many examples
of plot and small catchment experiments, which
clearly demonstrate the success of soil and water conservation measures in
reducing local soil loss, but there is much less by way of quantitative
evidence, which can be used to demonstrate the effects of catchment-wide
soil and water conservation programmes and sediment
control measures in reducing sediment fluxes from larger drainage basins. Such
evidence is, however, now available for the loess region of the
Fig. 5
presents information for the 4.161 km2 basin of the
Similar catchment management strategies to that employed in the Sanchuanhe basin were implemented in many other areas of
the
Figure 5. Recent changes in the suspended sediment load of the Sanchuan River, China, as demonstrated by the time series of annual water discharge (i) and annual suspended sediment load (ii) and the associated double mass plots (iii)
Dams and their associated reservoirs now
represent a key component of water resource development in many areas of the
world and dams have been constructed on many of the world’s rivers, in order to
provide storage for water supply, irrigation, flood
control and power generation. Most dams are effective sediment traps and
therefore result in significant reduction in downstream sediment fluxes. Figure
6, which is based on world-wide data for the storage associated with ‘large’
dams, defined as those over 15m in height, provides information relating to the
growth of reservoir storage capacity over the past 100 years and currently
under construction (UC), and emphasizes that dam construction is a relatively
recent phenomenon. Most of the current storage was constructed between the
1950s and 1980s, with much of this being added during the 1970s and 1980s.
Figure 6B provides information on the cumulative volume of storage lost to
sediment deposition, and thus the total amount of sediment intercepted by dams,
in different areas of the world. Asia, and more
particularly,
Figure 6. The growth of reservoir storage capacity over the past century and that under construction and planned for the period 2000-2010 (A) and the global distribution of storage lost to sedimentation to date (B). Based on data from White (2001.2005) and Morris (2005).
Figure 7 provides two very clear, although somewhat different, examples of the impact of dam construction in reducing the sediment load of major world rivers, in this case the River Indus and the River Danube. As described by Milliman et al. (1984), exploitation and control of the River Indus for irrigation and water supply, flood control and hydropower generation commenced in the 1940s with the building of numerous barrages and irrigation channels and two major dams, the Mangla Dam on its tributary the Jhelum River, and the Tarbela Dam on the main Indus near Darband were completed in 1967 and 1974, respectively. The impact of these developments on the annual discharge and sediment load of the River Indus is clearly evident on Figure 7A. Both show a marked and progressive decline over the period of record, with recent annual suspended sediment loads being only about 15% of those in the 1930s. Most of the sediment load of the River Indus is generated in the upper part of its basin and the downstream diversion of water for irrigation and trapping of sediment behind dams and barrages causes the sediment load to progressively reduce through the middle and lower reaches of the river. In the case of the River Danube (ca. 800.000 km2), the time series of annual suspended sediment loads again shows a statistically significant reduction over the period of record, with current sediment loads being only approximately one third of those at the beginning of the period of record. Most of this reduction occurred since the 1960s and is linked with the construction of reservoirs and control structures on both the main river and its tributaries, including the closure of the Iron Gate Dam on the main river in the early 1970s. Although these dams have had an important effect in reducing sediment loads through sediment trapping, they have much less effect on the annual water discharge and in contrast to the River Indus, Figure 7(i) shows no evidence of a significant trend in the time series of annual runoff over the same period.
Figure 7. Recent
changes in the suspended sediment loads of the River Indus, Pakistan (A) and
the River Danube, Romania (B), as demonstrated by the time series of annual
water discharge (i) and annual suspended sediment
load (ii) and the associated double mass plots (iii). Data for the River
Indus compiled by Professor John Milliman, Virginia Institute
of Marine
The precise magnitude of the reduction in the sediment load cased by dam construction will reflect a number of factors, including the proportion of the river’s flow that is withdrawn for consumptive use and the nature of the water use. Where dams are used for flood control or hydropower production, a large proportion of the water stored will be subsequently released and the river’s ability to transport sediment will be maintained, at least partially, even though the sediment available for transport may be reduced, due to deposition in the upstream reservoir. Where, however, much of the stored water is diverted for irrigation or water supply, the flow in the river may decline markedly and its capacity to transport sediment will also be greatly reduced. It is also important to recognize that an estimate of the amount by which the downstream sediment load of a river is reduced due to sediment trapping behind the dam is not directly equivalent to the reduction in the sediment load at the basin outlet, particularly where the dam is a considerable distance from the sea. Under pre-dam conditions a significant proportion of the trapped sediment may not have reached the sea, but would have been deposited within the channel-floodplain system. Thus, although current estimates suggest that of the order of 25 Gt year-1 of sediment are trapped by large dams each year, the associated reduction in the land-ocean sediment flux will be very considerably less. Furthermore, in some rivers, the reduced sediment load below the dam could be, at least partly, offset by remobilisation of sediment from alluvial storage downstream (e.g. Phillips et al., 2004).
Although the trapping of sediment behind
dams and the loss of sediment associated with the diversion of flow for
irrigation and other water uses are likely to represent the main causes of
reduced sediment transport through river systems, it is important to recognise
that in many areas of the world, particularly in developing countries,
extraction of sand from river channels for use in the construction industry may
represent a significant component of the sediment budget. Marchetti
(2002), for example, suggests that as much as 2 Mt of sediment are extracted
each year from the central area of the Po Basin in
As in the case of sediment trapped behind
dams, it is difficult to relate the quantities of sand extracted to reductions
in the sediment load of the river, since not all of the sediment might have
been in active transport. However, there is increasing evidence that such ‘sand
mining’ could result in a significant reduction in the sediment load of the
rivers involved. In the case of the Yangtze River in China, Chen (2004)
suggests that along with sediment trapping by dams and the effects of soil
conservation and sediment control programmes, ‘sand mining’ was an important
cause of the recent reduction in the sediment load at the downstream measuring
station at Datong, where the mean annual sediment
load has reduced from ca. 500 Mt year-1 during the 1960s and 1970s
to ca. 350 Mt year-
Most of the examples of recent changes in
the annual sediment loads of the world’s rivers introduced above relate to
specific anthropogenic impacts, such as land clearance and dam construction.
However, the example of the
In many larger river basins, the key
drivers of changing sediment load identified above will interact and the
resultant signal, as reflected by the sediment load at the catchment
outlet, could provide limited evidence of the changes occurring in the upstream
basin. Thus, for example, increases in sediment load caused by land clearance
in some parts of a river basin could be balanced by reductions in sediment load
caused by dam construction on other tributaries or on the main river. Lu and Higgitt
(1998) suggest that this is the situation in the Upper Yangtze River, in
It is also important to recognise the
potential importance of river floodplains and other sediment sinks, such as
lakes, in more directly buffering the sediment response of large river basins
and attenuating increases in sediment transport caused by human activity within
the upstream catchment. A good example of changes in
the signal generated by human impact, as it is transmitted through the lower
reaches of a large river basin, is provided by the River Ob, which drains a
large 2.950.000 km2 catchment in Siberia
to the
The examples of the changing sediment loads
of various world rivers presented above must be seen as selective, aiming to
demonstrate the potential impact of the various drivers associated with global
change. There is no general or common trend, since in some cases loads are
increasing, whereas in others they are decreasing. Furthermore, it must be
recognised that the sediment loads of some, if not many, rivers will have been
stationary over the past few decades. Lack of reliable longer-term records of
suspended sediment flux for many of the world’s major rivers precludes detailed
analysis of the net impact of the various trends described on the global
land-ocean sediment flux. However, it is clear that change is an increasingly
significant feature of these records. Walling and Fang (2003) considered the
longer-term records of annual sediment load for 145 rivers, and reported that
ca. 70% were essentially stationary, whilst the remaining 30% provided evidence
of statistically significant trends. Of these, ca. one third (10%) were
increasing and ca. two thirds (20%) decreasing. The sample of rivers involved
was far from representative of the world’s rivers more generally, as it was
drawn exclusively from the northern hemisphere and included no rivers in Africa
or
In attempting to generate a preliminary, and necessarily tentative, assessment of the likely impact of the changes described above in producing a net change in the global land-ocean sediment flux, it is important to consider the extent to which the reductions in suspended sediment load associated with some rivers will be offset by increases in others. In undertaking this assessment, attention has focussed on the key drivers, namely the impact of dams in reducing sediment loads as a result of sediment trapping trapping and the various anthropogenic impacts leading to increased sediment loads. However, the contrasting temporal dimensions of these impacts complicates any simple balancing of the two opposing trends. Whereas Figure 6 emphasises that the impact of dams in reducing sediment loads is only likely to have been apparent since the 1950s, the main increases in sediment loads associated with land clearance and other facets of catchment disturbance may have occurred several centuries, and possibly several millennia ago in many river basins. To simplify any assessment of the two trends it is therefore convenient to compare the impact of the recent reduction in the land-ocean sediment flux associated with sediment trapping by dams with the longer-term increase in sediment loads associated with land clearance and catchment disturbance. Estimates of the magnitude of the latter increase are highly variable, ranging from the factor of 2.6 suggested by Dedkov and Mozzherin (2000) to a value of only 16% proposed by Syvitski et al. (2005). There is also considerable uncertainty as to the magnitude of the reduction in the land-ocean sediment flux caused by sediment trapping by dams. Syvitski et al. (2005) suggest that this trapping has reduced the global land-ocean sediment flux by 3.6 Gt year-1, but, based on the available evidence concerning the volumes of sediment currently being sequestered behind dams and an estimate of the proportion of that sediment that would have previously reached the oceans, Walling (2006) suggests that the reduction in the land-ocean sediment flux associated with reservoir trapping could be as much as 10 Gt year-1, and perhaps higher if the vast number of smaller dams are also taken into account.
Using, as a starting point, the estimate of the contemporary land-ocean sediment flux of 12.6 Gt year-1 provided by Syvistski et al. (2005) and combining this with the estimate on the current reduction of the land-ocean sediment flux caused by reservoir trapping of 10 Gt year-1, suggested by Walling (2006), it can be estimated that, in the absence of reservoir trapping, the current land-ocean sediment flux would be 22.6 Gt year-1. and that reservoir trapping has reduced this by 10 Gt year-1 or about 45%. In order to establish the extent to which this estimate of 22.6 Gt year-1 has been increased by anthropogenic activity, it is necessary to estimate the ‘natural’ or ‘pre-human’ flux. Syvitski et al. (2005) estimate that the ‘pristine’ land-ocean sediment flux was 14 Gt year-1, but Walling (2006) has suggested that this value may be an overestimate, since the model used by Syvitski et al. (2005) to predict the pristine flux was trained using data which may have included some signal (i.e. increase) from human impact. Taking account of this likely overestimation of the ‘pre-human’ sediment flux and other estimates of the factor of increase noted above, it would seem reasonable to suggest a` value of 12 Gt year-1 for the pre-human land-ocean sediment flux. Coupling this value with the estimates for the contemporary flux in the absence of reservoir trapping noted above, leads to the conclusion that human impact has increased the land-ocean sediment flux by 10.6 Gt year-1 and therefore by almost 90%. In absolute terms, this increase is very similar in magnitude to the current reduction in the land-ocean flux due to reservoir trapping. However, given that the estimate of the reduction in sediment flux relates only to sediment trapping behind dams and that the actual reduction could be greater, due to further reductions associated with water diversions for irrigation, soil conservation and sediment control programmes, sediment extraction from rivers by ‘sand mining’, and climate change leading to reduced annual precipitation (as in the case of the Yellow River), it seems probable that the contemporary reduction in the land-ocean sediment flux caused by human activity now exceeds the longer-term increase in the sediment flux caused by human activity.
Despite the several uncertainties
associated with identifying and interpreting recent trends in the suspended
sediment loads of the world’s rivers, it is clear that many of these rivers can
be expected to show evidence of changing sediment loads in response to recent
environmental change. For some rivers, loads will have increased due to human
activity, particularly land clearance and catchment
disturbance, whereas in others, loads will have decreased due to dam
construction and the widespread introduction of soil conservation and sediment
control programmes. In many river basins, the recent trend in sediment load
will reflect the resultant of these two opposing controls, with the trend
changing through time as the relative balance of the two controls shifts.
Furthermore, in some river basins anthropogenic impacts will be combined with
changes driven by recent climate change. A preliminary attempt to establish the
net effect of these changes on he global land-ocean sediment flux suggests that
the ‘natural’ or pre-human’ flux has been almost doubled by anthropogenic
impacts, but that this gross flux has in turn been reduced by almost 50% due to
reservoir trapping, meaning that the increases are balanced by the decreases.
However, when other causes of reduced sediment loads are considered, it seems
likely that net land-ocean flux may now be less than the ‘pre-human’ or
‘natural’ flux. It is important that the
sensitivity of the sediment loads of rivers to recent environmental change
should be recognised both in terms of the potential significance of these
changes to the functioning of the Earth system, for example via geochemical cycling, as well as in relation to
local and regional impacts and problems, such as the recession of delta
shorelines due to the reduced sediment supply and the destruction of coral
reefs due to increased sediment inputs to coastal seas.
This paper represents a contribution to the GEST (Global Evaluation of Sediment Transport) component of the UNESCO International Sedimentation Initiative (ISI). The help provided by Dr Don Fang with data analysis, and the generous assistance of many people and organisations, and particularly the International Research and Training Centre in Erosion and Sedimentation (IRTCES) in Beijing, China, Dr Nelly Bobrovitskaya from the State Hydrological Institute in St Petersburg, Russia, Professor John Milliman from the Virginia Institute of Marine Science, USA, Professor Juan Restrepo from EAFIT, Colombia and Professor Shuh-Ji Kao from the Research Center for Environmental Change, Academia Sinica, Taiwan, in providing sediment load data and background information, are very gratefully acknowledged.
Chen X., Zhou Q. and Zhang
E., 2006. In-channel sand extraction from the Mid-Lower Yangtze channels and
its manaqgement problems and challenges. J. Environmental Planning and Management,
49, pp. 309-320.
Chen X., 2004. Sand extraction from the
mid-lower
Dai D. and Tan Y., 1996. Soil erosion and sediment yield in the
Dedkov A.P. and Mozzherin V.I., 2000. Global river sediment discharge to the ocean: natural
and anthropogenic components. Erosionnye I Ruslovye
Processy. Vypusk, Vol. 3.
Goldewijk K.K., 2001. Estimating
global land use change over the past 300 years: the HYDE Database. Global Biogeochemical Cycles, 15, pp.
417-433.
Kao S-J., Lee, T-Y. and Milliman J.D., 2005. Calculating highly fluctuated
suspended sediment fluxes from mountainous rivers in
Lu X.X. and Higgitt D.L., 1998. Recent changes of sediment yield in the Upper Yangtze,
Marchetti M., 2002. Environmental changes in the
central Po Plain (northern
Milliman J.D., Quraishee
G.S. and Beg M.A.A., 1984. Sediment discharge from the
Milliman J.H. and Syvitski J.P.M., 1992. Geomorphic/Tectonic control of sediment discharge to
the ocean: The importance of small mountainous rivers. J. Geology, 100, pp. 325-344.
Morgan R.P.C., 1986. Soil Erosion and Conservation.
Longman, Harlow.
Morris G.L., 2003. Reservoir sedimentation
management: Worldwide status and prospects. Paper presented at the Third World
Water Forum, Otsu Siga,
Mou J., 1996. Recent studies of the role of
soil conservation in reducing erosion and sediment yield in the loess plateau
of the
Phillips J.D., Slattery
M.C. and Musselman Z.A., 2004. Dam-to-delta sediment
inputs and storage in the Lower Trinity River, Texas. Geomorphology, 62, pp. 17-34.
Restrepo J.D. and Kjerfve B., 2000.
Syvitski J.P.M., Vörösmarty
C.J., Kettner A.J. and Green P., 2005. Impact of humans on the flux of terrestrial sediment to the global
coastal ocean. Science,
308, pp.376-380.
Walling D.E., 2000. Linking land use, erosion
and sediment yields in river basins. Hydrobiol., 410, pp. 223-240.
Walling D.E. and Fang X.,
2003. Recent
trends in the suspended sediment loads of the world’s rivers. Global and Planetary Change, 39, pp.
111-126.
Wang Z., Li, Y and He Y.,
(in press). Sediment budget of the
White, W.R., 2001. Evacuation of Sediments from
Reservoirs. Thomas Telford Publishing,
White W. R., 2005. World Water Storage in Man-Made Reservoirs: Review of Current Knowledge. Foundation for Water
Research,
Xu J.X., 2003. Sediment flux to the sea as
influenced by changing human activities and precipitation: Example of the
Yellow River,
Zhao W., Jiao E., Wang G. and Meng X., 1992. Analysis on the variation of sediment yield in the Sanchuanhe river basin in 1980s. Internat. J. Sediment Res, 7, 1992, pp. 1-19.