Let’s be honest, stormwater professionals love to use confusing terms, big words and funny acronyms. If you’re not in the know, you could find yourself looking for a translator! Here are a few key terms that might help you speak their language.
Stormwater Runoff: The water from rain, melting snow or other precipitation that “runs off” across the land instead of seeping into the ground. This runoff usually flows into the nearest stream, creek, river, lake or ocean and is not treated in any way.
Pervious/Impervious Surfaces: A pervious surface is one that is permeable or allows water to pass through such as grass, sand, mulch or even pavers which are specifically designed to allow water to infiltrate into the ground. Impervious surfaces (such as driveways, sidewalks, roads or roofs) do not allow water to pass through. When it comes to managing stormwater, pervious surfaces are preferred because they limit runoff which can cause flooding and carry pollutants to our waterways.
Nonpoint source pollution: Stormwater runoff that cannot be directly traced to a specific origin but comes from a variety of areas such as farms, roads, construction sites and yards. This is the opposite of point source pollution which comes directly from a single identifiable source.
ERU (Equivalent Residential Unit): An ERU is equal to the average impervious area determined from an evaluation of all residential parcels within a locality. ERUs are used to determine stormwater fees. (All localities are a little different, though, so be sure to check with your local stormwater folks to get the details!)
BMP (Best Management Practice): A device used to reduce pollution in stormwater runoff. Examples include ponds, grassed swales, ditches and infiltration trenches. BMPs are often installed by municipalities and require maintenance to function efficiently.
TMDL (Total Maximum Daily Load): The amount of pollutants a body of water can handle while still able to support beneficial uses (aquatic life, fishing, drinking water, recreation, etc.). The term is being used more often these days because of state and federal regulations requiring localities reduce the amount of nitrogen, phosphorous and sediment that goes into local waterways.