What is the effect of a broken mainline?

A broken mainline disrupts the integrity of the irrigation system, leading to significant drops in pressure. When the mainline is compromised, water begins to escape at the break, which reduces the volume of water that can effectively be distributed throughout the system. This loss of pressure can result in insufficient watering of the areas that the irrigation system is intended to cover. Consequently, plants may receive inadequate moisture, leading to stress and poor growth.

In contrast, while one might assume that a broken mainline could result in increased water flow, the actuality is that the water is lost through the break, which means that the overall flow available to the designated irrigation zones is diminished. The other options regarding runoff and water quality issues could occur in different contexts but are not the most direct effects of a broken mainline. Thus, low pressure is the most immediate and relevant consequence.