Hydraulic potential

It is suggested that the movement of the front by migration (electrical potential), diffusion (chemical potentials), and advection (hydraulic potentials) will cause desorption of cations and other species from clay surfaces and facilitate their release into the fluid.34... 

Transport in flowing groundwater is controlled primarily by the pattern and rate of flow, which are described by Darcy s law. Darcy s law says that groundwater migrates from high hydraulic potential to low, according to,... 

Hydraulic potential is the sum of the VdP work done on the water and its potential energy. The quantity is given by,... 

Changes in hydraulic head reflect variation in the hydraulic potential, according to d = pg dh, and hydraulic conductivity is proportional to permeability,... 

Physical Approaches. Groundwater-exchange rates with lakes are traditionally estimated by careful measurements of hydraulic potentials within the groundwater system, followed by application of Darcy s law in the form of flow-net analysis or numerical modeling. However, these measurements can be time-consuming and costly, and can require monthly to weekly measurements at many piezometers to examine the three-dimensional nature of the hydraulic-potential field. In addition, characterization of the hydraulic conductivity of the aquifer is critical to physical approaches and typically leads to results with large uncertainties (I, 2). 

Fig. 2.10 Rock beds in a subsidence basin. The part above the terminal base of drainage, for example, the sea, functions as a through-flow system (arrows). The deeper rock beds are fossil through-flow systems that host stagnant groundwater as they are (1) covered by impermeable rocks, (2) bisected by plastic impermeable rocks that have been squeezed into stretch joints in the competent rock beds and in between bedding plane thrusts, and (3) placed in a zone of zero hydraulic potential.

Terminal base of drainage (zero hydraulic potential)... 

Fig. 2.14 An entire groundwater system, from the water divide to the terminal base of drainage, built of permeable rocks. The following patterns of water motion are recognizable (1) a through-flow zone with vertical flow paths that join a lateral flow path toward the terminal base of drainage (2) a transition (mixing) zone and (3) a zone of stagnation occurring beneath the level of the terminal base of drainage (zero hydraulic potential).

Zone of groundwater stagnation. At depths below sea level all the rock systems of the continents are filled with water to their full capacity—they are saturated. Being below sea level, the water stored in these rocks is under no hydraulic potential difference, and therefore this water does not flow—it is static, or stagnant (Fig. 2.14). This situation is similar to that of water stored in a tub, it cannot flow out, and hence is stagnant. Additional water reaching the tub overflows. The same is observed in the sand-filled aquarium experiment (Fig. 2.13) after steady state is reached, all the new rainwater infiltrates down to the level of the rim and flows out, whereas the deeper water remains static. 

Subsidence structures often host traps of stagnant groundwater bodies. The groundwater entrapment is caused by several processes (1) burial to beneath sea level, that is, burial into a zone of zero hydraulic potential and hence a zone of stagnation (2) coverage by younger sediments... 

With glacial ice covering the discharge end of the flow system during much of the last 10 yr. and hydraulic potential available south of the ice-front to cause flow, it may be expected that groundwater would be forced to discharge in front of the ice in southern Alberta. These flow conditions would result in more pronounced cross-formational flow with deeper formation water moving into shallower units. 

Dorn, J.D., and Adams, L.D., "The Etch Rate of Portland Cement Clinkers as It Relates to Structure and Hydraulic Potential," Microscope, Vol. 31,1983, pp. 37-42. 

The flow processes, however, also depend on the interface between the geomembrane and its subgrade and on how intimate the contact is. The influence of overburden above the geomembrane on the hydraulic potential is neglected, their weight, however, very strongly influences this contact and interface properties. The load on the geomembrane is therefore another very important parameter. 

Using the physically correct approach, called Model II, the complete equation of motion is solved analytically or numerically for the hydraulic potential for the boundary eonditions described above and the tme flow rate is then calculated fi om this taking account of horizontal and vertical flow components (Fig. 7.7). Here, too, an intimate contact is assumed between the geomembrane and the subgrade. The details are described in (Walton and Sagar 1990). The potential and streamline pattern of water flow in the subgrade can formally be described as the potential and streamline pattern of an electric current in a condueting medium. Laplace s equation... 

Suction is the term describing the pressure state or hydraulic potential of water in soils, as the water content is decreased, for example, by evaporation (drying). Suction (or cryosuction) is also developed in the unfrozen water of a frozen soil. In this respect, the water which becomes ice in the freezing soil is analogous to that which evaporates in the drying soil. 

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