Hydraulic Conductivity in Soils - Essay Example

Hydraulic Conductivity in Soils Hydraulic Conductivity in Soils Bi-modal soils are the soils that have structural and matrix porosity (Dexter & Richard, 2009). In these bi-modal soils there is a model for water retention which is developed into other models such as the tri-modal soils (Dexter & Richard, 2009). Such a change ensures there is an incorporation of the existing effects of macro-pores. Additionally, the bi-modal soil model has its basis on the idea of water retention function of the exponential Boltzmann.

Researchers also believe that the model can also extend to include other numbers such as the “n” of the modes of porosity. These modes exist because the soil structure is usually hierarchical. It is also used together with other models to produce a model that promotes a saturated hydraulic conductivity. These are the hydraulic conductivity models such as the Marshall’s pore model. It also produces a K-sat and that of the n-modal soils (Dexter & Richard, 2009). For such reasons, the n-modal soils tend to give a simple equation.

Hence, with a simple K-sat expression, it is easy to come up with a scale for the soil’s porosity and its pore size distribution. A Polish data set is useful in illustrating this model (Dexter & Richard, 2009). To make an estimate of the limit of a macro-pore term, it is essential to use the measure values of curves obtained when there is water retention. It also involves using other measured values obtained from identifying the bulk density and K-sat. Additionally, for the 42 Polish arable soils there are distributions and mean values of macro pore limits (Dexter & Richard, 2009).

However, having such macro pore limits does not guarantee there will be hydraulic conductivity in the soil. For example, these parameters are usually found in fields during a harvest and in most cases they do not lead to hydraulic conductivity. In the field, water movement occurs through the use of structural pores. The flow of water also goes through macro-pore spaces which are prevalent in soil that is freshly plowed. To determine the value of saturated hydraulic conductivity in soils, there are different scenarios to look at.

One of the scenarios is that in theory it is known that soil tends to become dense when there is a decrease in structural pores (Dexter & Richard, 2009). However, this is not determined during observations. This leads to the conclusion that it is the number of structural pores in the soil that determines the density and not their size. The multi-modal nature of the soil’s pore size distribution is the key determining factor of the soil’s water retention levels and the value of saturated hydraulic conductivity.

Therefore, this improves our understanding of the soil’s structure and function because of the ability to make physical predictions of its hydraulic characteristics. Reference Dexter, A., & Richard, G. (2009). The saturated hydraulic conductivity of soils with n-modal pore size distributions. Journal of Geoderma, 154(1-2), 76-85 doi:10.1016/j.geoderma.2009.09.015