Soil in the Calgary area may be defined in a broad sense as either organic or mineral. Black Chernozemic is the dominant type of organic soil found in and around Calgary. This soil is most associated with grasslands. It has a surface horizon that is black in color and contains 12 to 20 cm in thick organic material that is up to ten percent of the entire soil. Mineral soils are also quite common. From colloidal clays that are quite small up to the glacial erratics that are upwards of three meters in width and larger. For those digging in the area, they might come across the following mineral soils.
- Clays
- Gravels
- Loess
- Sands
- Silts
The characteristics of a soil will help determine its erodibility. There are currently four classifications of mineral soils. Such soils are defined by their clays, cobbles, gravels, sands, and silts. The differentiation of the types of soils comes down to the size of the particles.
Soil Classification Systems
There are different systems used depending on the location that helps classify specific soils. The RUSLE equation is used for agricultural purposes. This equation subscribes to the USDA soil system in terms of soil characteristics and its erodibility.
For construction purposes, the ASTM International standards are most often used. Which means that ASTM looks at the same soil as USDA, but the viewpoint of how the soil is classified is different. The USDA is more towards the agricultural prospective while the ATSM is more along the lines of building a structure or construction on the soil.
For the ESC designer, the classification of the soil should translate the ATSM information to the USDA information so that the RUSLEFAC formula can be used. A key variable in soil erodibility is the amount of very fine sand that is present. Understanding the amount of fine sand in the soil is crucial to employing the proper erosion protection measures.
K-Value Determination
The makeup of the soil determines the probabilities of erosion rate. Since soil consists of particles that are of different sizes, understanding the size and substance difference in the particles will help make erosion determinations possible.
- Particle Size
- Soil Structure
- Soil Permeability
- Recording K-Value
Particle size starts with determining the amount of clay, organic matter, sand, very fine sand, and silt by weight. The soil texture class can be determined by the ESC designer when they have this information. The soil structure is determined by the gaps in the aggregate peds of the soil. The greater the size of the crevices and cracks, the more likely that water will flow through. This is helped by the description of the soil that runs from very fine granular to blocky or platy.
Permeability is the description of how easily water will flow through the soil. This is rated from 1 to 6 on a scale that starts with rapid and ends with very slow. At this point the K-Value of the soil can be determined based on particle size distribution of different organic and mineral factors.
Tag: soil, Calgary
