Sediment loadings

Rivers transport suspended sediments derived from the disintegration of basin surface layers. With reduced velocity, sediment is deposited in the river channel. The finest material is carried to the sea. It has been estimated that the average mechanical denudation rate for continents is 0.056 mm year (35). This is based on a total suspended load of 13.5 x 10 metric tons year (S). Presently, about two-thirds of the world s total suspended sediment load derives from Southern Asia and large Pacific Islands. Berner has estimated the increase in sediment loss in the U.S. and world since prehuman times to be approximately 200% (35). Current estimated erosion rate from the major land forms is provided in Table I. The relatively recent construction of large sediment trapping dams that normally caused sediment to be deposited in river valleys or transported to the ocean has drastically reduced sediment yields in great rivers. 

The material transported by rivers consists of dissolved ions (dissolved load), sediment suspended in the flow (suspended load), and sediment transported along the bed of the river (bedload). The total load and the proportion of the load represented by these phases varies widely among rivers in different environments. In particular, climate, topography, and erosion influence the amount and composition of riverine sediment loads. 

The sediment load of a channel and the sediment yield of its drainage basin are expressed in different ways. The sediment load is the total mass of material moved by the river in a... 

Data on sediment transport in the Ebro basin is very scarce. Besides some historical studies in the lowermost reaches of the catchment (e.g. [21]), almost at the delta plain, and few others undertaken during the 1990s (see Table 1), only the work undertaken by the Fluvial Dynamics group of the University of Lleida (hereafter UdL) between 2002 and 2008 in the lower part of the river supply reliable data on the total sediment load and changes in sediment transport and channel morpho-sedimentary characteristics upstream and downstream from large dams. 

Reservoir sedimentation data allow estimating sediment loads of regulated catchments, although it is important to note that this sedimentation represents a fraction of the true yield since reservoir sediment trapping efficiency is usually... 

Sediment Load in the Lower Ebro 5.2.1 Suspended Load... 

Sediment load does not distribute uniformly through time. The transport of sediment is less constant and sporadic compared to the runoff, since floods typically... 

Fig. 7 Duration curves for (a) runoff, (b) suspended sediment load and (c) bedload in the lower Ebro River for the period 2002-2008...

Walling DE, Fang D (2003) Recent trends in the suspended sediment loads of the world s rivers. Glob Planet Change 39 111-126... 

Mobility and leachability of diflubenzuron in soils is low, and residues are usually not detectable after 7 days. In water, half-time persistence (Tb 1/2) is usually less than 8 days and lowest at elevated temperatures, alkaline pH, and high sediment loadings (Fischer and Hall 1992) (Table 17.2). Increased concentrations of diflubenzuron in soils and waters are associated with increased application frequency, flooding of treated supratidal areas, wind drift, and excessive rainfall (Cunningham 1986). 

Saturation ratios of CaCC>3 in Lake Constance and the corresponding sedimentation load. (From Sigg, Sturm, Davis and Stumm, 1982). 

River transport of clay minerals into the ocean is spatially and temporally variable. The global annual suspended load of river sediment into coastal waters currently averages 12.6 X 10 ton. This flux is approximately 10% less than was delivered before humans began damming rivers. (One notable exception is the Mississippi River, whose sediment load has increased due to very high rates of soil erosion. The riverine sediments deposited in the mouth of the Mississippi River form one of the world s largest deltas.)... 

Table 14.2 Discharge and Sediment Loads into the Ocean from the World s Twenty-Five Largest Rivers. ... 

Rank (Prehuman Sediment Load) River Name Continent Receiving Ocean Average annual discharge (kmVyr) Prehuman Sediment Load (MT/y) Modern Sediment Load (MT/y) Sediment Load Difference (Modern- Pre- human)... 

Loizeau JL, Dominik J (2000) Evolution of the upper Rhone river discharge and suspended sediment load during the last 80 years and some implications for Lake Geneva. Aquat Sci 62(l) 54-67... 

Historic records show how devastating intensive monsoon storms can be in the Middle Mountains. In 1993 a storm that produced 540 mm of rainfall over a 24 h period and with rainfall intensities exceeding 70 mm h hit the Kulekhani watershed [7-9]. This resulted in hundreds of landslides and a sediment load of up to 500 T ha per storm in the watershed (Fig. 1). This not only destroyed large tracks... 

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