A typical ground slope for new construction can range from one percent to 50 percent. A minimum slope of one percent allows for proper drainage of stormwater during rainfall events and a maximum of 50 percent is usually used for safety issues. Any slopes above 50 percent would most likely require a retaining wall.
The actual range of slopes that would be used for a proposed land development plan would depend on the requirements of the local ordinances. The requirements would probably be listed under a section referring to grading or construction standards.
Related: Land Development Regulations (A Simple Guide)
How Ground Slope Is Represented on a Plan
A proposed ground slope is represented on a plan through proposed contours. For steeper slopes such as 25% or 33%, you might see labels on the plan for these slopes so that it is easier for someone reviewing the plan to recognize these areas.
Without labels, you would have to take some measurements off of the plan before calculating slopes.
Related: The Parts of a Land Development Plan
What Determines Proposed Ground Slopes
There are many factors that go into the design of a proposed grading plan and in determining what ground slopes to use. In addition to local requirements, the following are some other things that go toward determining ground slopes.
1) Local regulations.
2) The stormwater management system design.
3) The storm drainage system design.
4) Preference of the land developer.
5) Wanting the site earth cuts and fills to balance better.
A Part of the Land Development Design
As a part of the overall land development design, determining proper ground slopes is important to creating a grading plan that ties together the parts of the project.
Related: 7 Ways to Find the Slope of Land
Related: Site Grading Design (A Guide for the Non-Professional)
Related: How to Create a Land Development Design (In 12 Steps)