What is the maximum allowable vertical to horizontal slope ratio for embankments above the water line?

The maximum allowable vertical to horizontal slope ratio for embankments above the water line is established based on the principles of stability and erosion control. A slope ratio of 1 foot vertical to 3 feet horizontal is widely accepted in various engineering standards because it provides a balance between structural integrity and water management.

This ratio helps ensure that the embankment is stable enough to support its weight and resist erosion from water flow, while also accommodating settling and expanding soil conditions. A steeper slope could lead to instability, while a flatter slope might not properly manage the runoff, leading to erosion.

In this context, the other ratios presented may either be too steep or too flat. A steeper slope (like 1 foot vertical to 2 feet horizontal) increases the risk of collapse, while a flatter slope (like 1 foot vertical to 4 feet horizontal or beyond) may struggle to adequately direct runoff and maintain soil structure. Thus, the 1 vertical to 3 horizontal ratio represents a practical compromise that enhances both safety and functionality in septic system design.