Soils of the - Agriculture and Agri-Food Canada

APPENDIX G
SURFACE RUNOFF CLASSES *
Very rapid runoff-A very large part of the water moves rapidly over the surface of the soil and a ver y
small part passes through the profile . Surface water runs off as fast as it is added . Soils with very rapid rates of
runoff are usually steep or very steep and have low infiltration capacities . The erosion hazard is commonly hig h
or very high .
Rapid runoff-A large proportion of the precipitation moves rapidly over the surface of the soil and a
small part moves through the soil profile . Surface water runs off nearly as fast as it is added . Soils with rapid
runoff are usually moderately steep to steep and have low infiltration capacities . The erosion hazard i s
commonly moderate to high .
Medium (moderate) runoff-Surface water flows away at such a rate that a moderate proportion of th e
water enters the soil profile and free water lies on the surface for only short periods . A large part of th e
precipitation is absorbed by the soil and used for plant growth, is lost by evaporation, or moves downward int o
underground channels . With medium runoff, the loss of water over the surface does not seriously reduce th e
supply available for plant growth . The erosion hazard may be slight to moderate if soils of this class ar e
cultivated .
Slow runoff-Surface water flows away so slowly that free water covers the soil for significant periods o r
enters the soil rapidly and a large part of the water passes through the profile or evaporates into the air . Soils wit h
a slow rate of surface runoff are either nearly level or very gently sloping, or they absorb precipitation ver y
rapidly. Normally there is little or no erosion hazard .
Very slow runoff-Surface water flows away so very slowly that free water lies on the surface for lon g
periods or enters immediately into the soil . Much of the water either passes through the soil or evaporates int o
the air. Soils with very slow surface runoff are commonly level .
Ponded-None of the water added to the soil as precipitation or by flow from surrounding higher lan d
escapes as runoff . The total amount of water that must be removed from ponded areas by movement through th e
soil or by evaporation is usually greater than the total rainfall . Ponding normally occurs in depressed areas an d
may fluctuate seasonally .
APPENDIX H
TOPOGRAPHIC CLASSES
Simple Topography Complex Topography Slop e
Single Slopes Multiple Slopes %
(Regular Surface)
(Irregular Surface)
A depressional to level a nearly level 0 to 0 . 5
B very gently sloping b gently undulating 0.5+ to 2
C gently sloping c undulating 2 + to 5
D moderately sloping d gently rolling 5+ to 9
E strongly sloping e moderately rolling 9+ to 1 5
F steeply sloping f strongly rolling 15+ to 30
G . very steeply sloping g hilly 30+ to 60
H extremely sloping h very hilly over 60
Dumanski, J., editor. 1978, revised . The Canada Soil Information 1System (CANSIS) . Manual for Describing Soils in the Field . Lan d
Resource Research Institute, Agriculture Canada, Ottawa, Ont .
226