Click Below to Hear This Blog as Narrated by the Author, John Cruikshank, PE
If your project’s storm water runoff discharges through a “point source” to the waters of the United States, then you’ll need a National Pollution Discharge Elimination System NPDES permit – “Clean Water Act”. A point source is a discrete conveyance system such as a pipe, tunnel, channel, or ditch. The permit works to ensure that storm water discharges do not hurt water quality or people’s health.
An efficient storm drainage system design starts with site visits and a topographic survey. Then, a civil engineer prepares a Hydrology Report that includes the study of drainage patterns, contributing watersheds, rainfall amounts, site slopes, the amount of hardscape, and soil characteristics. This report is the basis for the design of both grading and drainage, and is submitted to the local jurisdiction so they can confirm that the designer is following their approved methodologies.
It has been suggested to always “follow the water” when developing a drainage system. Since water flows with gravity, it is best to start at the highest point with an end game in mind. For example, if you are working on a building project, typically the highest point and largest area is the roof. Roof drainage is prepared by a mechanical engineer, but a civil engineer can suggest that more of the roof drains flow to a certain side of the building. If the site typically flows from north to south, and the goal is to connect the drainage system to a City storm drainage system within a street to the south, then the civil engineer needs to work with the architect and mechanical engineer to have as much of the roof draining to the south building edge as possible.
Roof drains and drainage inlets usually connect with underground pipes. These pipes flow with gravity and need to have certain minimum slopes to be ‘self-cleaning’ when they get more than half-full. The reality is that these out of sight drainage devices are typically neglected, so an experienced engineer will develop their drainage system to be as maintenance free as possible.
Finally, the overall system needs to be large enough to handle all expected water spreading out over flatter (ADA compliant) sites. Assuming there will be less future maintenance, there will be a greater chance of failure. If your storm drainage system is efficient and relatively maintenance free, then you can rest easy and tout this site feature in your real estate prospectus.