Head gradient

Two hydraulic head gradients determined from wells or piezometers are shown in Figure 3.15. Piezometers are basically pipes or wells put in the ground which are... 

Porosity and hydraulic conductivity are both properties of the porous medium. Hydraulic heads, and the hydraulic head gradient, may be determined by solving the equations of flow, with appropriate initial and boundary conditions [2]. 

Flow of groundwater in confined aquifers is determined by the water head gradient and by the degree to which the system is drained. In extreme cases water may be trapped in confined aquifers. The topic of water movement in confined aquifers is best studied by means of chemical and isotopic parameters (section 6.5). 

At a held site, head gradients and K both can be measured, allowing one to estimate specific discharge by using Darcy s law. To fully describe the... 

In the stream tube labeled A, there are 14 intervals defined by isopotentials between the two boundaries of known head (2 and 4.9 m). In square B, the head gradient is the head change, 0.2 m, divided by the spacing between isopotentials, 20 m. By using Eq. [3-2], the specific discharge in square B can... 

To characterize flow in the subsurface environment, groundwater wells often are installed. Wells can be used to measure hydraulic head gradients, and thus to determine the direction of groundwater flow to conduct aquifer tests to... 

When water is pumped from a production or remediation well, water from the surrounding aquifer enters the well in response to the head gradient created by the water removal. This leads to a lowering of the hydraulic head around the well, forming a cone of depression (Fig. 3-10). It takes some time for this cone of depression to fully develop while it is developing, the flow of water must be analyzed by transient techniques that account for flow changes over time (see Section 3.2.4). Ultimately, the water removed by a well must be replaced—in an unconhned aquifer, this is usually by rainwater percolation or by inflow from a river—or else the well will go dry. Wells often are... 

Fair has published a refinement of the Souders-Brown correlation for bubble cap tray capacity, while Glitsch has provided a vapor flooding relationship for valve trays, which also seems to represent bubble cap tray capacity for 3 or 4 in. bubble caps at low pressure.f In the latter, originally developed for valve trays and called equation (13) by Glitsch, the effect of hydraulic liquid head gradient is expressed as an equivalent added vapor load ... 

Large liquid head gradients reduce tray capacity and may damage separation by causing maldistribution of vapor flow across the tray. In fact, an extremely large head gradient can cause some caps to dump the liquid to the tray below. 

Cai J and Wu Y. 2001. Analysis of one-dimensional seepage model by coupling hydraulic head gradient, temperature gradient and stress. Chinese J. Rock Mech. Engng., 20(suppl), pp. 1026-1028. 

Figure 8 shows a snapshot of hydraulic heads at 19 ka, for the permafrost distribution at the same time shown in figure 7. The main flow is horizontal, being driven to the left by the leftward pressure gradient generated by the ice load shown in figure 4. Head gradients increase leftwards... 

Figure 2.35 Modeling of channel forms in gypsum formed by water flow with head gradient 0.2 and temperature 10 °C in fractures with the initial width 0.2 to 1 mm (A) and their dependence on flow rate (B). The numbers are initial fracture width and flow duration (Klimchouk, 1996 James, 1992).

Open models of local chemical equilibrium are object balanced only chemically. That is why they accept groimd water flow, may be nonuniform but ignore processes of mass transfer between water and rock. Their main assumption is that the relaxation time At = 0 and flow time At > 0. These models consider hydrochemical processes relative to time, distance and events scales, which characterize change of rock properties and composition, head gradient, etc. However, they do not consider kinetics of chemical processes. 

If in the larger gap strata or the water head gradient higher, the water move subjects to the turbulent motion laws which is as the follow ... 

Gas filtration through a porous medium is often described mathematically in the form of the Darcy equation u = KI, where is a filtration rate, / is a head gradient, and permeability coefficient K is the main characteristics of the medium. To model gas reservoirs, it is necessary to know permeability coefficients for both gas and liquid phases and to have a model to calculate reservoir liquid saturation [1,2]. The equilibrium liquid saturation depends only on the thermodynamic functions of the fluids and reservoir walls. 

A one-dimensional form of Darcy s law (Darcy, 1856), which expresses the relationship between groundwater flow and head gradient, may be written as... 

Darcy s law is equally applicable in three dimensions, where, assuming K is independent of direction, the specific discharge is proportional to, and in the same direction as, the head gradient ... 

Superposition in phreatic aquifers is more problematic than superposition in confined aquifers, because changes in saturated thickness affect aquifer transmissivity and thereby create a nonlinear relationship between head gradient and total flow. However, for imconfined aquifers in which drawdovm is a sufficiently small fraction of aquifer thickness, the technique of superposition can be a useful approximation. The reader is referred to Strack (1989) for further details on superposition in imconfined aquifers. 

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