First, The problem
You go take a look at your storm drain system and, lo and behold, the pipes and catch basins are full of water even though it hasn't rained in a long time. The water isn't moving - there must be a major problem, right? Not necessarily. Read on.
Next, Some Background
Pipes that are always full (we engineers would call them "surcharged") do not necessarily point to a major problem - some systems were designed to do that. I have designed several storm drainage systems over the years that included pipes that would always be surcharged - I actually designed it to do that. Why? The reason is simple - there isn't enough topography on the site for the stormwater to drain away. Pipes are put in with gravity flow, but each foot the pipes drop brings them a little lower in elevation. The pipes flow to the low spot, but once there the water is significantly lower than the outflow elevation. So the system has to flood to get the water elevation high enough to actually discharge. You see this all the time in ponds and rivers. In fact, think of a dam. The water builds up behind a higher grade until it gets so high that it can actually overflow the obstruction. The same thing happens with designed storm drain systems.
Sometimes, the pond that results is a water quality or quantity pond. This is a common situation, because many projects required a pond anyway, so the water impounded by insufficient topography has another purpose - clean the stormwater before it is released. In other situations, however, the water may seemingly be just impounded, maybe in a vault, a pond, or just in the pipes. Why?
Enter the pump
When you have impounded water, it is a good time to start looking for the pump. However, even in the case of a pump, there will typically be impounded water contributing to backed-up pipes. Why? Stupid Engineers? Nope.
A correctly installed pump requires a constant supply of water behind it. You could imagine that if a pump turned on every time a little water came to it, it would turn on and off every few seconds and quickly burn out. For that reason, we back water up before a pump so that there is a decent volume there before the pump starts. The backed-up water you see may just be the water waiting for the pump to turn on.
Even when the pump does turn on, it won't pump the system dry. It can't, because it is typically that water pool that is required to remain to cool the pump motor. Pump floats (the floating mechanisms designed to turn pumps on and off) are put at elevations so that water will always remain to keep the pump cool.
So Now What?
If you see surcharged water in your storm drainage system, you may have discovered a big problem OR you may be looking at a system operating as it was designed to operate. There is no substitute for calling out a credentialed professional to take a look. Surcharged water may be a sign of a huge downstream obstruction, possibly a broken pipe, or it may just be operating perfectly.
Call out the professionals who can actually diagnose your stormwater system and help you to make sure it remains in good working condition. Click here to put in a request to have a CatchAll Environmental professional come and take a look.
Jeff McInnis is an engineer who knew there had to be a better way to help owners keep their systems in compliance.