Glossary:Hydrologic soil groups

Refers to soils grouped according to their runoff-producing charac teristics. The chief consideration is the inherent capacity of soil devoid of vegetation to permit infiltration. The slope and the kind of plant cover are not considered but are separate factors in predicting runoff. Soils are assigned to four groups. In group A are soils having a high infiltration rate when thoroughly wet and having a low runoff potential. They are mainly deep, well drained, and sandy or gravelly. In group D, at the other extreme, are soils having a very slow infiltration rate, and thus, a high runoff potential. They have (a) a claypan or clay layer at or near the sur face, (b) have a permanent high water table, or (c) are shallow over nearly impervious bedrock or other material. A soil is assigned to two hydrologic groups if part of the acreage is artificially drained and part is undrained.