Glossary of Terms

Diffusion:

The process where molecules spread out to form an even concentration.

Hydrological Soil Group:

Soil groups which are classified according to their drainage potential. Group A soils absorb a lot of water and are deep, well-drained, and composed of sand or gravel. Conversely, Group D soils do not absorb as much water and have a high run-off potential, and have a layer of high clay content near the surface or are shallow soils over bedrock or other material which does not absorb water. For more info, visit the Penn State Earth System Science Center Database page on HSG percent

Hydrologic Condition:

A rating (good, fair, poor) that is based on a combination of factors that affect infiltration and runoff, including:

1. density and canopy of vegetative areas
2. amount of year-round ground cover
3. amount of grass or close-seeded legumes in rotations
4. percent of residue cover on the land surface (good is more than 20%)
5. degree of surface roughness

The Explanations page gives a more complete breakdown of good, fair, and poor ratings for different groups of land types.

Infiltration:

process of water moving into the soil/ground

Linearized Rainfall Frequency:

The likelihood in years that a rainfall with a given intensity and duration will occur. This is also called the "return period" or "recurrence interval".

Nitrogen:

The 14th of the 107 elements. Nitrogen is important for plant growth and is found in many commercial fertilizers. It also is found in the environment in different forms (sometimes as a gas, sometimes as a compound with Oxygen or Hydrogen), from both natural and man-made sources. Because of this, it is often washed through a watershed into a stream or river. If there is too much Nitrogen in the water, it is a pollutant.

Percolation:

water movement through the soil.

Pollutant: A pollutant is anything which has a bad effect on the environment.

Runoff:

Water which is not absorbed by the soil and flows to lower ground, eventually draining into a stream, river, or other body of water.

Tributary:

A stream or river whose water flows into a larger stream or river.

Watershed:

The sum total of all the land and smaller bodies of water which drains into a particular stream or river.

Water-soluble:

capable of being dissolved in water