Slope

The key to a great drain

Slope refers to the angle that the pipe slopes downward to allow gravity to pull the water toward the disposal point. We measure slope very carefully whenever we install a drain. Using a laser level we grade the bottom of the trench as we excavate it. We measure slope in percentage. A percentage slope is measured by the number of inches the level falls every hundred inches of distance. It is important to remember that a french drain will not drop the water table any lower than the level of the discharge point. This is one reason a core thought he curb can be very helpful in a french drain. The extra 6” of drop to the discharge point can make a big difference in the water table.

We start at the top of the drain and shoot our way down to the discharge location. The bed of the trench is carefully graded at an even level of slope. This is important because dips or valleys in the trench can create water holding spots which will collect debris, hold water, and attract roots which can clog your drain. Our drains are engineered to achieve a 2.5 foot per second water velocity when full. This is important because it is the velocity of the water in the pipe that will keep it clean and clear of debris. One of the great advantages to using PVC in our installations is that this velocity can be achieved at much lower slopes than it can with corrugated pipes. This allows us to install gravity drains in lawns with less slope while still creating a drain that will work effectively for many years.

See Manning’s Formula to see how we calculate water velocity.