2
General Overview
The class of problems involving flow of water through permeable media has a wide
range and is of considerable importance to engineers and scientists. The Armfield
Drainage and Seepage Tank, Model S1, facilitates a detailed study of the movement
of water through permeable media.
The engineer is probably the one who faces such problems most frequently and
whose success or failure will often depend on his knowledge and understanding of
phenomena related to the movement of the water in soils. This is one of the most
important aspects in the design of almost all hydraulic structures. Consider an earth
or rock fill dam, for instance. Water flows directly through the engineering structure
itself. Obviously, it is important to know how much water we can expect to lose from
the reservoir by seepage through the dam. We also need to know whether a certain
kind of soil can be used to construct the dam without running the risk that the
reservoir will run dry after filling. The safety and the very existence of the dam
depends on the flow pattern of the penetrating water and on the balance of the
hydraulic and static forces. Many earth dams have collapsed because of improper
design with respect to the movement of water through their bodies. In fact, the
conditions of seepage are vital, not only for earth dams, but for any dams having
permeable materials in the foundations. A dam can collapse or be badly damaged as
a result of seepage underneath its bottom, or because of hydrostatic forces exerted
by the penetrating waters. These forces cannot be determined without prior
determination of the flow pattern underneath the structure. Once known, they can be
altered using drains, cut-offs, sheet pile walls and other means to change the flow
pattern.
Similar problems arise in other engineering structures built from, or on, soil. As
examples, we can mention levees, road and railway embankments, canals,
navigation locks, foundations of buildings, bridges, harbour walls and similar
structures.
Another engineering field where good understanding of water movement in soil is
essential is water supply and drainage. In both we are concerned with extracting
water from saturated strata by using wells, horizontal galleries, tile lines, or trenches.
In this type of problem, we usually deal only with the flow pattern and quantity of the
water traversing the strata. The forces exerted by seepage remain of secondary
importance.
Mining is an area where both seepage and ground water flow is fundamentally
important. The design of an effective drainage system for a mine must be based on
profound knowledge of permeability, of the degree of water saturation of the various
geological layers, of seepage rates and of the effect of pumping or draining the water
on the balance of forces.
Ground water hydrology and hydrogeology are the main non-engineering fields
dealing with flow of water through permeable media and require the study of
problems such as salt water intrusion into fresh water basins, underground
movement of water towards inner channels, discharge of ground water into surface
run-offs, recharge of water from rivers to underground storage, artificial recharge of
ground water.
Generally speaking, the movement of water through soil under natural conditions is
very complex and cannot be reproduced in full in the laboratory. This complexity is
caused by the non-uniformity of natural soils over large areas, the stratified and the
tectonic structures of geological layers, and by the fact that water movement in
