Modeling - Field Sampling: Principles and Practices in Environmental Analysis - page 173

TABLE 7.1 Common Constants and Variables Used in Modeling the Environment

Quantity/constant Units Common abbreviation

Water solubility g/ml C

cm 2 /s

Diffusion coefficient D

Soil hydraulic conductivity cm/s θ

erg cm −2 s −1

Solar radiation R

Temperature °C or °K C or K

erg g −1 d −1

Heat capacity c

m/s 2

Acceleration due to gravity g

cm 3 /cm 3

Soil porosity n

cm 3 /cm 3

Volumetric water content θ

Ψ m

Soil matrix potential kPa

cm 3 /cm 3

θ s

Saturated soil water content

cm 3 /cm 3

Volumetric air content Φ

g/cm 3

Air density ρ

Mg/m 3

Soil bulk density B.D.

Note: Not an exhaustive list.

7.1. PHYSICAL MODELS

A physical model may be constructed in a number of different ways and may represent
one or several characteristics of the environment. The model may be static and only be a
scale model of the actual area, or it might be dynamic but qualitative in that several
components interact and the interactions are observed. In this case the model is used only
for visualization. The most sophisticated models will be both dynamic and quantitative,
allowing the calculation of the amount of change taking place over time. All of these
models may be valuable, depending on the system and the situation being investigated.

7.1.1. Static
The static model typically has all its components represented by various constructed
structures. Soil might be represented by fine sand. The sand might be colored to represent
various horizons. Fractured rock can be represented by gravel and consolidated rock by
colored clay. Water could be represented by water, colored clay, and the like. Such a
representation might also show caves, trees, and so forth. Often such a model is
constructed to scale. Such a scale might be something like 1:10,000 meaning 1 cm in the