Many sewer systems are built to take advantage of gravity. Sewer lines sloping down to carry waste through a series of pipes and ultimately to a treatment plant. Although lift stations and force mains can be used when water must be moved uphill, slope is a critical consideration for the design and maintenance of a sewer system. Sewer pipe slope refers to the angle the pipe is laid to allow for wastewater run-off. Sewer slope keeps liquids and solids moving at an appropriate speed. In a gravity system, pipes must slope downhill to drain properly. If the slope is not steep enough, the sewage slows down, resulting in clogs. If it’s too steep, liquid and solids can separate, causing solids to accumulate in the pipe.

What is Pipe Slope or Pitch

The term slope is also frequently used and has the same meaning as pitch. It is generally accepted that 1/4″ per foot of pipe run is the minimum for proper pitch on a sewer line. Larger lines such as 8″ pipe require less pitch due to the larger circumference of the pipe. But there are other issues concerning pitch to keep in mind. Large sewer lines require calculations to determine the proper pitch. Sewer mains are designed to have a flow rate of 2 feet-per-second during peak dry-weather conditions. Flow rates are kept below 10 feet per second. To prevent shifting pipes with flow rates greater than 10 feet-per-second are designed with anchors to keep them in place.

Why is Pipe Slope Important

Why go to all the trouble of these intricate calculations? Is anything really going to drastically change the sewage system if the pipe slope is a little less or a little more than the existing parameters? Even a small variation in the rate of the slope from the established norms can disrupt the normal operation of the sewage system. Sloppy plumbing work is another common factor leading to a incorrectly pitched sewer line.  It is common for a general contractor to install the sewer line when building a new house however, the proper installation of a sewer line requires a sewer specialist. There is a great deal of experience and attention to detail required in each aspect of the sewer installation, everything from the excavation process to the back-fill and tampering of the soil upon completion.

What Can Happen if Sewer Slope is Wrong

Backups can occur if the slope is too steep or not steep enough. A backup prevents liquids and solids from draining. A pipe blockage can prevent water or solids from draining. Types of debris that can cause blockages include plastic bags, solidified grease (FOG), detergents, or the pipe can break itself. When pipes become clogged due to an improper slope water can be forced around the pipe. The force of this water then causes extreme erosion to the surrounding soil and pipe bedding. If this pipe bedding is not properly prepared a pipe can sag. This settling bedding and soil can cause a sag in a pipe where water, waste and debris accumulate. This accumulation will result in backups and clogs and collecting bacteria.

Whether we realize it or not, keeping our sewers clean and unblocked is very important for ensuring that our water is clean and that our rivers remain unpolluted. A working sewerage system is vital for a clean environment. Making it important that we understand what causes blocked sewers and act to prevent problems before they happen. Regular pipe inspections can locate and prevent a lot of these issues that block and break sewer pipes.

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