Silt, deposition

High Water Velocities. The abiUty of high water velocities to minimize fouling depends on the nature of the foulant. Clay and silt deposits are more effectively removed by high water velocities than aluminum and iron deposits, which are more tacky and form interlocking networks with other precipitates. Operation at high water velocities is not always a viable solution to clay and silt deposition because of design limitations, economic considerations, and the potential for erosion corrosion. 

The more recent (Neonile) sediments in the area include the Masmas formation (clay and sandy silts deposited some 40,000 years ago). Neonile sediments called the Sahaba formation are younger (ca. 20,000 B.C.), and, as seen in Figure 1, these sediments cover much of the area bordering the modern flood plain on which most of the Predynastic sites are located. Some chemical differences are seen between these two Neonile sedimentary units... 

Hassan 16) suggested that grain size parameters of sediments could be used to differentiate among the Nile silts deposited over the last 90,000... 

Figure 3.8 Examples from the ferricrete alteration profile observed at outcrop at Palika Ba (13°28 N, 15°14 W), near the Gambia River, Gambia, West Africa. (A) Nodules of ferricrete developing within Quaternary alluvial sands and silts deposited by the Gambia River. Nodules consist of predominantly goethite with minor haematite (sample PG4 in Table 3.3). (B) Massive iron-cemented ferricrete horizon displaying characteristic tubes (i.e vermiform structure sample PG2 in Table 3.3). Importantly, the iron cement is entirely due to the introduction of allochthonous iron into the pore spaces of the sediment.

Singhvi, A.K. Wintle, A.G. (1999) Luminescence dating of aeolian and coastal sand and silt deposits applications and implications. In Goudie, A.S., Livingstone, I. Stokes, S. (Eds) Aeolian Environments, Sediments and Landforms. Chichester John Wiley Sons, pp. 293-317. 

The sediments in the Bohai Sea are generally fine (Fig. 1.12, Jiang et al., 2004). They consist of soft clay mud (sediment with sizes smaller than 0.01 mm amounts to a portion of more than 70%), fine silt mud (sediment with sizes smaller than 0.01 mm amounts to a portion of 50% 70%), coarse silt, and fine sand. In Liaodong Bay the coarse silt (0.1 0.05 mm) and fine sand (0.25 0.1 mm) dominate in the sediment. In Laizhou Bay the sediment consists of silt deposits, whereas in the central basin fine sand spreads widely. At the Laotieshan waterway (entrance to the Bohai Sea), the tidal flow is very strong, the area is often eroded and therefore the sediment particles are coarse there. The constituents of SPM in the Bohai Sea are mainly inorganic... 

Sometimes a combination of backwashing and air injection is used with good results. During backwashing, silt deposits may remain in the space between the back face of the tubesheet and the nozzle. Air can be injected through the lower tubesheet vent or drain connections to remove these deposits. 

Unfortunately, although a lot has been done to keep lead out of soil, the soil we will be living with for the foreseeable future still bears the contamination from years and years of accumulation. Lead does not degrade. Unless it is covered by new silt deposits or washed away by erosion, the lead deposited in our soil presents a permanent health hazard to those who may come in contact with it. So we had better learn to protect ourselves from it. 

Geopressurized zones— Areas formed by layers of clay that are deposited and compacted very quickly on the top of more porous, absorbent material such as sand or silt. Water and natural gas trapped within this clay are squeezed out by the rapid compression of the clay and enter the more porous sand or silt deposits. 

The soils of the eohan plains with dunes are often sandy Entisols with pH below 5.5 and low cation exchange capacity at the base of the sand dunes, where temporary flooding may occur during the rainy season, the predominant soil type is Ultisol with hardpan at <1.5 m of depth. Extensive wetlands or floodplains can usually be found in the aeohan plains with silt deposits, and Ultisols and Oxisols are again the most frequent soil types. 

Production rates of most types of dredgers are affected by the in-situ density, the friction angle, the grain size, the fines content and the permeabihty of the sand/ silt deposits. 

When dredging clay for reclamation purposes the work method is mostly aimed at limiting the disturbance of the material in order to preserve as much of the original strength as possible. The undrained shear strength, the Atterberg limits and the in-situ unit weight of the clay and/or silt deposits are the most important material properties. 

The disposed material will behave as any natural soil deposit, although it might be more homogeneous than a natural clay or silt deposit. 

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