Technical information

136 | Chapter 9 Using Grading Commands
Working with Ponds
The Grading menu contains commands to design and define ponds. You can
use these commands with Hydrology commands to create and edit ponds or
any type of water-retention structure.
The first step in a detention design is to use Runoff commands from the
Hydrology menu to calculate the runoff from the watershed and to create the
inflow hydrograph for the design storms. For more information, see
Chapter 4, “Hydrology and Hydraulics.” You can estimate the size of a
detention pond by using the Detention Basin Storage method. Based on the
inflow runoff and the allowable peak discharge, this method calculates the
size needed for a detention pond.
You can then establish the preliminary pond location and size by drawing
and editing the pond perimeter until the shape and size are satisfactory. The
pond perimeter is a polyline. You can then calculate subsequent slopes from
each vertex in the polyline.
The next step in pond design is a preliminary design of the outflow
structures. You can then calculate routed hydrographs using the Storage
Indication Method. For more information, see Chapter 4, “Hydrology and
Hydraulics.”
The following illustration shows a shaped pond with normal and highlight
contours.