a List all the methods that can be used to determine hydraul

(a) List all the methods that can be used to determine hydraulic conductivity.

(b) Define the term “transient flow (or unsteady flow)”.

(c) If petroleum hydrocarbon is spilled into the unsaturated zone, describe its migration pattern.

(d) Describe the cause of mechanical dispersion.

(e) What is Peclet number? When Peclet number is < 1, what kind of transport mechanism would be dominant?

Solution

a)Hydraulic conductivity, represented as K, is property , soils and rocks, that describes the ease with which a fluid (usually water) can move through pore spaces or fractures. It depends on intrinsic permeability of the material, saturaton , and on the density and viscosity of the fluid. Saturated hydraulic conductivity   describes water movement through saturated media.

here are two broad categories of determining hydraulic conductivity:

EMPIRICAL approach - the hydraulic conductivity is correlated to soil properties like pore size and particle size distributions, and texture of soil.

EXPERIMENTAL approach by which the hydraulic conductivity is determined from hydraulic experiments using DARCY LAW

The experimental approach is classified into:

LABORATORY tests using soil samples subjected to hydraulic experiment

FIELD TEST

Field test is further   differentiated into:

1) small scale field tests, using observations of the water level in cavities in the soil

2) large scale field tests, like pump test in well or by observing the existing horizontal drainage systems.

The small scale field tests are further subdivided into:

INFILTRATION tests in cavities above the water table

       SLUG TEST in cavities below the water table.

b)TRANSIENT FLOW -> It is the flow where the flow velocity and pressure are changing with time.

c)

Fluid volume increases the retention capacity of unsaturated zone . The hetero generity of unsaturated zone reduces the penetration effect iof the oil. The hetero generity of unsaturated zone and the degree of water saturation of the individual layers results in lateral component of percolation process and consequently broadening of oil body with increasing depth.

d)mechanical dispersion is caused by different flow paths water particles take in a geological medium. Some of the flow paths are faster because they follow a more direct path or because they are going through larger pores in which water flows faster as less friction is involved. Other flow paths may be slower because they are closer to grain boundaries , thus being exposed to more friction in the pore thoat slowing down water particles. The different flow parts of water particles cause the mechanical dispersion, a mechanical mixing and dilution of the solute within bulk movement of ground water.