Soil Profile

Graphic showing the different basic characteristics of a soil profile.

The soil profile provides information about the depth to bedrock as well as discontinuities in soil characteristics. Discontinuities include, among other things, vertical changes in soil properties and permeability.

Depth to bedrock can vary widely across even small areas. In river valleys with rich soil, the depth to bedrock may be at least 200 centimeters. By contrast, soil depth in other areas, such as mountainous regions, can be less than 25 centimeters.

Graphic showing the influences of depth-to-bedrock on runoff.

In general, areas with greater soil depth will have greater capacity to absorb and store water. These areas will likely have more interflow as well. By contrast, shallow soil areas typically saturate faster and produce more runoff given the same soil and rainfall conditions.

Graphic showing the influence on runoff and groundwater caused by layers of low permeability within the soil profile.

Another important characteristic of the soil profile is whether there are impermeable or low-permeable layers within the profile (also known as a fragipan). For example, consider a low-permeable layer of clay and rock beneath a surface layer of sandy soil. Rainfall or snowmelt in this area may rapidly infiltrate into the top sand layer, but only very slowly percolate through the more impermeable layer in the profile. This can result in both enhanced runoff and interflow in this area. Some areas may also contain impermeable mineral layers, such as calcium carbonate deposits.

Graphic showing the location of a caliche in a desert soil profile.

Finally, biologic and chemical activity in the soil can leave macropores. Recall that these natural pipes and void spaces enhance both the speed and the volume of water that can move vertically and horizontally through the soil profile.

Animation showing how tranmissivity feedback through macropore networks can enhance storm runoff beneath the soil surface.