Culvert or ford? Telling stream crossings apart in satellite imagery
A new track running up to a stream edge and continuing on the other side means someone built a crossing. Whether it's a culvert or a ford changes what you're looking at, legally and ecologically, and the two don't look the same from above even at modest resolution.
What separates the two on the ground
A culvert crossing buries a pipe under a fill pad and lets the road surface run continuous across it. From a plan-view image, you'll see a straight or gently curved road segment that doesn't break stride at the stream, often with a slight bulge where the fill was compacted wider than the running surface on either side. The channel itself stays mostly intact upstream and downstream of the crossing, though you may see a narrow dark line (the pipe outlet) and a small apron of disturbed soil or rock at the discharge end.
A ford crossing, by contrast, is where the vehicle just drives through the water. There's no fill pad and no pipe. What you get instead is a visible break in the vegetation line right at the channel, often with braided or widened wet tracks on both banks where tires have chewed through saturated soil over repeated passes. The streambed itself frequently shows disruption, lighter-toned gravel or sediment fanning downstream of the crossing point, sometimes a pool scoured out on the downstream side from runoff concentrating through the gap.
Reading it in high-res RGB
At sub-meter resolution, the tell isn't the water itself, it's the margins. Look at the road's cross-section as it approaches the bank. A culvert approach tends to be engineered: consistent width, a visible grade change as the road climbs onto the fill, and often a slight shadow line where the fill shoulder drops off to the original ground level. A ford approach is rawer. The track widens and frays as it nears the water, sometimes splitting into two or three parallel ruts where drivers have hunted for firmer footing, and the vegetation disturbance extends further along the bank than the road's working width would explain.
Shadow angle matters more than people expect. A culvert's fill pad casts a short, even shadow along its edge because it's a built structure with a consistent slope. A ford crossing casts an irregular shadow because the disturbance follows the bank's natural contour instead of an engineered grade. If you're working from a single date of imagery and the lighting is low-angle, that shadow difference is often your fastest read before you even look at the channel.
Why the distinction drives the compliance call
This matters because the permit question is different for each. A lot of jurisdictions require a stream crossing permit before a culvert goes in, precisely because it's a permanent structure that changes hydrology. A ford, done right, is sometimes treated as a temporary low-impact crossing under bmp guidance and doesn't trigger the same permit threshold, but only if it's used during low-flow periods and the operator stabilizes the banks afterward. An auditor who mistakes a scoured ford for an unpermitted culvert failure, or vice versa, is chasing the wrong violation.
The other thing worth checking every time: riparian buffer incursion on either side of the crossing. Even a properly permitted crossing can come with buffer cuts that extend beyond the approach width, cleared wider than the road needs to be because it was easier to skid logs through than route around standing timber. That buffer encroachment often shows up as a lighter, more irregular patch adjacent to the crossing rather than the crossing itself, and it's a separate compliance question from the crossing type.
Both crossing types are downstream of the real tell for enforcement work: the new track appearing in the first place. By the time a crossing is built and visible in a quarterly or annual pass, the operator has already committed to the route. A monthly scan that catches the spur road before it reaches the bank gives a field team time to pull the permit file and check it against what's on paper, rather than documenting a crossing that's already been driven through for weeks. If that's the gap in your current monitoring, Logging Road Detection is built around exactly that window.