That's an excellent and practical question! It gets to the heart of why litter often ends up around public bins. The short answer is that depth alone isn't the sole solution; it's a combination of depth, design, and features.
To directly address your question: a bin needs to be deep enough that an animal (like a raccoon, dog, or bird) cannot easily reach the bottom or get a stable foothold to pull items out. From municipal guidelines and practical observations, a depth of at least 30 to 36 inches (about 75 to 90 cm) for the main body is often considered a minimum starting point to be effective. This puts the contents out of easy reach for most common urban scavengers.
However, depth is just one part of the equation. A very deep bin with a wide opening is still vulnerable. Here’s what truly makes a bin resistant to scavenging:
1. Secure Lid Design: This is arguably more critical than depth. A heavy, close-fitting lid that requires a hand lever or foot pedal to open is ideal. Smooth, rounded tops also prevent animals from gaining leverage to pry it open.
2. Narrow Openings: The aperture (the hole where trash goes) should be just wide enough for common waste items but too small for an animal to crawl into. Slotted openings for bottles/cans or mail-slot styles are very effective.
3. Animal-Proof Latches: Some advanced public bins feature locking mechanisms that automatically engage when the lid closes.
4. Material and Stability: The bin should be heavy (or securely anchored) so it cannot be tipped over. Durable, smooth materials like metal prevent claws from gaining traction.
So, while a sufficient depth creates a crucial physical barrier, the most effective "scavenge-proof" urban bin integrates a deep body (30+ inches), a secure locking or weighted lid, and a narrow, targeted opening. Municipalities aiming to reduce litter often prioritize these designed features over simply installing deeper bins. Proper maintenance and regular emptying are also essential, as overflowing bins are an open invitation regardless of depth. Ultimately, preventing scavenged litter is about smart design that outsmarts the animal, not just out-depths it.