Riverbed filtration? Is it, actual?

VLGYESI, Istvn www.volgyesi.uw.hu

Keywords: riverbank filtration, resistance of clogging, loss of curvature, partial penetration, cut bank.

The nature and process of bank filtration there are many locations disputed, and among the others water resources, for the bank filtration resources, a rather over-estimated data are known.

There are wells nearby rivers, where it is difficult to decide where they get the water. Frequently, however, that riverbank filtration talk. Therefore, it appears that within the underground water resources through over-estimated the proportion of bank filtration resources.

This can occur because they are often not taken into account the resistance at the river-aquifer interface phenomenon. Thus, most of the produced water - on paper - comes from the river, but the reality may be more water coming from the background. That is why it is produced in the nitrate in water is often many, while the river is tight. In calculating the actual processes, therefore, should be taken into account that the surface water groundwater interaction is one of the only the riverbed clogging and other inhibitory effects, (associated reduction in leakage on flow) may occur.

Actually, the riverbed-clogging is two things: above the riverbed the silting, and under the bottom the colmatation, created by the floating silts in the pores of the alluvial deposits (Figure 1). Moreover, there is some kind of hydraulic resistance at the riverbed and the aquifer boundary, if there is no riverbed-clogging, because whereas the surface water entering the pores there the velocity vectors (magnitude and direction) changes, this is the loss of curvature, Figure 2. This the subsurface hydraulic not accounted for, will always occur in the surface water-groundwater interaction, on the border of the two systems. (It is engaged in the development of well loss, plus the pipeline hydraulic turn reported it as a major factor. This is similar to the friction forces at work in pipe headloss, and provides for the head loss in river system.)

The riverbed-clogging and the loss of curvature are together with the concept of resistance at the river-aquifer interface.

Figure 1

Figure 2

Furthermore, the recharge from the river also depends on the extent to which intrude the river by the aquifer. If the aquifer is thick, the river only partially penetrating river, therefore, even under the river thick alluvial deposit is located. In this case, it may be that the coastal water wells less resistance to the far bank where there are, as from the river, and water could originate from the opposite bank of the river. And in this case it can be polluted from the other side. It can also occur in coastal filtration limited status.

There is still a factor, which often deceive ourselves: overestimate the possibilities cut banks. Today, it is everywhere these banks are protected with stone scattering or rock sills (Figure 3) to prevent undercutting of the bank. And very soon the gaps of stone scattering shall complete the same sludge, which is also charged the convex shores. For this reason, the old cut banks even in the convex revolving sections worse than will be the case, because the stones of stone scattering supplied the sludge worse. It is therefore concluded that cut banks in many river section is essentially gone, disappeared.

Figure 3

All in all, the potential for water production by bank filtration much smaller, as it is often assumed.