When should a grass waterway be placed according to the site conditions?

A grass waterway should be placed where it is specifically needed to manage water runoff and reduce soil erosion. Choosing to implement a grass waterway in an area that crosses into land requiring it indicates that there are existing issues with water flow or erosion in that specific area. The placement of the grass waterway in such locations ensures that water is channeled correctly, reducing potential damage to the surrounding agricultural land and improving soil health.

In contrast, the other options do not appropriately address the necessity of a grass waterway based on landscape and environmental conditions. For example, simply having a flat area does not automatically necessitate a grass waterway if water flow issues are not present. Similarly, claiming that a waterway is needed solely because land is slope-free or that there are no existing waterways does not take into account the hydrology of the site and the potential for erosion or water management needs. The most effective placement is determined by assessing specific site conditions related to water movement and erosion risk.