Characteristics of the Environment - Field Sampling: Principles and Practices in Environmental Analysis - page 46

FIGURE 2.11 Soil moving down a bank under the influence of gravity
(colluvial). Note the tree (A), which has moved with the soil.
In addition to moving over the surface of the soil, water percolates down through the soil
into the underlying loose material and rock. Salts, amendments, and spills will tend to
move down through the soil and underlying material with the water. Horizons in soil,
their texture, structure, and density, will be important in determining how the water and
material it is carrying moves. If at any place in the soil profile or in underlying material
there is a change, water will stop and move laterally along the boundary. (See Figure
2.8.)
In Figure 2.12 there is a sand layer overlain by a gravel layer (gravel does not pass a
#10 sieve), which in turn is overlain by a sand layer. Water moves into the upper sand
layer and fills this upper layer before it moves through the gravel layer. Sand has finer
pores or capillaries than the gravel. Water can move from large into smaller pores or
capillaries, but without an