Have you ever driven past a construction site and wondered:
Why is there a black fabric fence around the dirt?
Why are storm drains covered up?
Why is there a pile of rocks at the entrance?
Why is there a giant container labeled “Concrete Washout”?
Those features are not random. They are temporary stormwater controls designed to keep soil, sediment, and other pollutants from leaving the site and entering local waterways.
Construction sites expose large areas of bare soil. Without proper controls, rain can wash that soil into streets, storm drains, lakes, streams, and rivers.
Let’s take a closer look at some of the most common stormwater controls you may see around construction projects.
The Black Fabric Fence
One of the most recognizable stormwater controls is the black fabric fence installed around disturbed soil.
This is called a silt fence.
Silt fences help slow stormwater runoff and capture sediment before it leaves the site. They are designed to hold back soil while allowing water to pass through.
Without these barriers, a heavy rain can carry large amounts of sediment off-site.
Why Is Dirt Such a Big Deal?
It may seem surprising, but sediment is one of the most common pollutants found in stormwater runoff.
When soil enters waterways, it can:
- Cloud the water
- Cover fish habitat
- Fill drainage channels
- Carry other pollutants attached to soil particles
Keeping soil in place is one of the most important goals of construction stormwater management.
Why Are Storm Drains Covered?
You may occasionally notice fabric, gravel bags, or other materials placed around storm drains near construction sites.
This is called inlet protection.
Storm drains are designed to move water. They are not designed to remove sediment.
Inlet protection helps keep soil and debris from entering the storm sewer system where it can clog pipes, reduce drainage capacity, and eventually reach local waterways.
What’s the Purpose of the Rock Entrance?
Many construction sites have a pad of large rock where vehicles enter and leave the site.
This is called a stabilized construction entrance.
The rock helps remove mud from vehicle tires before they reach public streets.
This prevents a problem known as trackout.
What Is Trackout?
Trackout occurs when vehicles carry dirt and mud from a construction site onto nearby roads.
Once mud reaches the street, traffic can spread it throughout the neighborhood. Rain can then wash that sediment into storm drains and waterways.
Construction sites are expected to minimize trackout. If large amounts of mud are leaving the site, additional controls or cleanup may be needed.
Ideally, you should never see trackout leaving a construction site.
What Is a Concrete Washout?
Concrete trucks, tools, and equipment must be cleaned after use.
That wash water cannot simply be dumped onto the ground or into a storm drain.
Concrete wash water is highly alkaline and can be harmful to aquatic life if it reaches streams, lakes, or rivers.
That’s why many construction sites use designated concrete washout areas.
These temporary containment areas collect wash water and concrete residue so they can be managed properly.
Why Are Some Areas Surrounded by Orange Fence?
Orange fencing is often used to protect sensitive areas during construction.
It may be installed around:
- Existing trees
- Natural vegetation
- Drainage features
- Areas that should not be disturbed
Protecting established vegetation helps reduce erosion and preserve natural stormwater functions.
Construction Sites and Stormwater Rules
Construction projects are temporary, but the impacts of uncontrolled erosion can last much longer.
That’s why construction sites are required to use stormwater controls that help prevent pollution and protect local waterways.
The goal isn’t to stop rainwater from leaving the site. The goal is to keep soil and pollutants from leaving with it.
Why It Matters
Most people don’t think about stormwater when they pass a construction site.
But those black fences, covered storm drains, rock entrances, and concrete washout areas are all working toward the same goal: keeping dirt and pollutants out of our water.
The next time you drive by a construction project, take a closer look. What may seem like a collection of temporary barriers is actually a system designed to protect streams, rivers, groundwater, and the community’s stormwater infrastructure.
Our Water. Our Responsibility.