Secondary Floods … of Plastics

3/11/26 – After every street flood, we often see floods of another sort: plastics littering our shorelines.

Today, a peaceful walk by the San Jacinto West Fork turned into a horror show when I saw thousands of plastic bottles, cups and food containers littering the shoreline. So, I did some research to see how it typically gets there.

Spoiler alert: it doesn’t all come from boaters or fishermen. And lest you think I’m anti-plastic, let me say upfront that I’m not.

Benefits of Plastics

Plastics have many benefits. For instance, they reduce food waste. According to the UN Food and Agriculture Organization, about one-third of all food produced globally is lost or wasted (~1.3 billion tons annually).

However, plastic packaging plays a significant role in reducing losses in:

• Transportation
• Storage
• Retail display
• Household storage.

Think how much worse our hunger problems would be without plastics.

Thin, lightweight plastics also reduce packaging and transportation costs.

If Not Recycled…

But if not recycled, plastics can also have a downside. They can persist hundreds of years in the environment.

River systems like the San Jacinto act as plastic transport corridors.

They carry urban litter to estuaries and the Gulf of Mexico. Instead of decomposing biologically, plastics fragment into smaller pieces due to UV light and mechanical abrasion. These fragments accumulate in:

• Oceans
• River sediments
• Floodplains
• Agricultural soils
• Groundwater systems

From there, they can enter the food chain via fish, birds, and other animals.

Runoff Flushes Plastic Litter into Rivers

The best available evidence indicates that urban runoff and storm-drain systems are among the dominant pathways for plastics to enter the food chain, especially in developed watersheds.

A 2024 review of stormwater microplastics concluded: 

• Urban runoff is “one of the main sources of microplastics in aquatic systems.” 
• Stormwater samples contained up to 15,499 microplastic particles per liter in some urban runoff events. 

Episodic Nature of Plastic Discharges

Because municipal storm-drain systems discharge directly to rivers or streams without treatment, they function as a direct transport pathway. Up to 80% of plastic entering urban rivers occurs during stormwater runoff events, when neighborhood litter gets flushed into streams and bayous.

Floods dominate plastic transport. Hydrologic studies suggest plastic movement is extremely episodic.

One recent river monitoring study found that 90% of the annual plastic load moved during only 43 high-flow days in a year. Because storm drains generally bypass treatment, plastic moves directly from streets to rivers within minutes to hours of rainfall.

Problem All Over Houston

Houston City Council Member Fred Flickinger says the problem is serious all over Houston. He sent me an article about two men who clean the trash out of Buffalo Bayou using a small barge and a giant vacuum. “It’s a misconception,” says the article’s author, “that the trash comes from people littering directly into the bayou. The vast majority comes from more than 200 square miles of Houston streets that drain into Buffalo Bayou. … Some masses of plastic are so thick, they can be walked on.”

There’s a very simple answer to this problem:

Don’t throw your plastics in the gutter; recycle them.

Posted by Bob Rehak on 3/11/26

3116 Days since Hurricane Harvey