The goal of an irrigation system is to evenly apply water in a desired manner on a scheduled basis. Areas that are continuously wet or excessively wet after or between watering cycles should be addressed immediately. Several factors can result in "wet spots", here are a few common causes:
Leaking Zone Control Valves: The individual valves in your system are essentially like faucets, they turn on and they turn off. Like a faucet, they can leak. Leakage can be caused by something caught in the mechanism that operates the valve or it can also be a sign that the valve is old and may need a replacement part installed. The most visible symptom of a leaking valve is water continuously coming out of a head long after the system has shut off. (Be careful, this can also be a symptom of low head drainage, which is described below.)
SYSTEM ZONE CONTROL VALVES SHOULD ONLY BE SERVICED BY A LICENSED IRRIGATION TECHNICIAN.
Low-Head Drainage: This problem is caused by water siphoning out of the lowest head in a sprinkler zone after watering is completed. When the water flow to the zone has been shut off at the end of its cycle, the remaining water in the lines will drain downhill to the lowest point. If a sprinkler head is located in the lowest part of the system, water will flow out of that head until an equilibrium has been reached or all of the water has emptied out of that zone’s pipes.
Low head drainage can be a problem if the water collects in a low area of the yard and makes a puddle, or if it flows across a walk or driveway.
This normal process is caused by gravity flow and water attempting to reach its own level and is typically not considered a problem. If it becomes a problem it can usually be corrected by adjustments to the system or installation of devices, called drain check valves, that can prevent low head drainage.
CONTACT A LICENSED IRRIGATION CONTRACTOR IF
LOW HEAD DRAINAGE BECOMES A NUISANCE.
Broken Pipes: "Wet Spots" can also be caused by broken pipes in the system. There are two types of lines in irrigation systems where pipe breaks can occur: Main (Constant Pressure) Lines and Lateral (Zone) Lines. In order to assess your situation, you will best be served by determining which type of line is broken.
Main (Constant Pressure) Line: This pipe that leads from the back-flow prevention device to the individual zone control valves and supplies the system with continuous water pressure. If you break or have a leak in a main line, the water will flow continuously whether the system is running or not. The flow may be large enough to erode a hole in the soil or cause a continuous leak or wet spot.
IF YOU HAVE A MAIN LINE LEAK YOU WILL NEED TO TURN THE WATER OFF IMMEDIATELY
Lateral (Zone) Lines: These pipes feed the various individual zones of the sprinkler system that are under pressure only when the system is actually running. A lateral line break can be hard to spot because it only leaks while that particular zone or station of the system is active. No matter whether it is a small leak or a large break, it will eventually erode the soil and create a hole in the lawn or bed.
Line breaks waste water and can cause damage by erosion or over watering. Both Main Line and Lateral Line breaks should be repaired by an irrigation professional. Contaminants (dirt, rocks or mulch) could enter the line during repairs and clog or permanently damage downstream sprinklers and other components.
IF YOU HAVE A LATERAL LINE BREAK, YOU CAN CONTINUE TO OPERATE THE SYSTEM BY TURNING OFF THE ZONE THAT CONTAINS THE BREAK UNTIL THE REPAIR IS MADE. THIS WILL LIMIT DAMAGE TO THE LANDSCAPE.