Did you know the Hawaiʻi Department of Transportation operates and maintains over 8,000 storm drain inlets along more than 350 miles of roadway across Oʻahu? These inlets connect over 950 outfall locations, forming a vital network that helps reduce flooding during heavy rains to keep the entire community safe. The City and County of Honolulu also manages thousands of additional storm drains along streets within its jurisdiction.

While this extensive system plays a crucial role in managing stormwater, it can also carry pollutants into our oceans if not properly maintained. Trash, debris, chemicals, and other waste that enter the storm drains can clog the system or end up in the ocean, harming our marine ecosystems. By understanding where storm drain inlets and outfall locations are, we can take steps to protect these critical waterways.

To see Oʻahu’s storm drain system in action, check out this interactive map, which shows the drainage system under the City and County of Honolulu’s jurisdiction. Their storm drain system also connects with HDOT’s system along state roads and highways creating a network of storm water infrastructure designed to accommodate both urban and roadway storm water runoff. Learn more about how this interconnected storm water network works through this map, which shows both systems and the relationship between them within the Ala Wai watershed.

You likely walk or drive by storm drains everyday and might not even notice them. To locate the storm drains present in your community, start by looking for roadside curb inlets or grates. They might even have placards or signs that say “No Dumping, Drains to Ocean”. If you suspect that someone might be polluting or dumping into a storm drain, you can report it to HDOT or CCH to help protect the health of our local waterways and ocean.

On top of reporting suspicious activity, you can also help keep our storm drain systems clean and reduce pollution by adopting simple practices, such as recycling, picking up pet waste, composting, disposing of chemical products properly, and participating in neighborhood cleanups. Our oceans and marine life will thank you!

For more tips on protecting Oʻahu’s stormwater system, visit our website.

Sources: Stormwater System Map, Storm Water Hawaii \