Any water moving the wrong way through an irrigation system is referred to as backflow. Backflow can lead to contaminants in the water - or debris from the surface - infiltrating and damaging your irrigation system. Backflow prevention involves equipping a system with devices such as valves that only allow water to move in one direction.
When backflow (a reversal of flow) happens because of a reduction in system pressure and this in turn causes a negative or sub-atmospheric pressure to exist at any location in a system, back siphonage can occur.
An increase in pressure in the downstream piping of an irrigation system that causes it to be greater than the supply pressure is known as back pressure. It can result in many and varied problems including a reversal in the normal direction of water flow.
When irrigating a field, soil pores fill with water. When this water drains away, smaller pores remain filled with water, while larger (macro) pores end up filled with a mixture of water and air. This state is referred to as field capacity (Cc). Aeration capacity is simply a volume fraction of air-filled pores in soil at field capacity.
