Pond drainage and the low-flow orifice

Exact Stormwater Management is a stormwater-centered business handling all aspects of the stormwater world.  While providing maintenance services for stormwater BMPs since 2013, we have encountered some of the same challenges over and over.  One of the most common issue with ponds is blockage of the low-flow orifice.

The low-flow orifice is typically a 1-inch to 6-inch opening in the outlet structure that is placed near the bottom of the pond.  During a rainn event, the water level will rise until it reaches this opening.  Once the water rises above the opening, it will begin to drain out of the pond at a rate restricted by the opening size.  The purpose of the low-flow orifice is to mimic pre-development hydrology.  In other words, water flowing off of a site after development should closely match water flowing off the site before development.  The opening size is calculated by engineers based on studies performed during the design phase of the project.  When this opening gets clogged, the pond is no longer functioning as designed and all downstream property is at an increased risk of damage (typically flooding and/or erosion).

We have seen many different methods of protecting these orifices, but they continuously get clogged with leaves, sticks, trash, and straw.  Many of the protection methods have opening large enough to allow floatables to bypass and cover the orifice.  

So what's the answer?  We use a shield with over 100 openings making it extremely more difficult to block all of them.  Water flows through one of the many openings of the DebriShield, and then passes through the design opening unobstructed.

Do you want to learn more about DebriShield?  Call or email us now.