Surface runoff or water rising through the lawn?

Look for where water appears and how it moves: runoff usually has a visible route across the surface, while seepage may emerge in several spots or leave an area wet after surface flow has passed. Timing can help, but it isn’t conclusive - both sources can contribute, and already saturated soil can make runoff linger. Following the water during and after rain can clarify which problem a swale or buried drain would need to address.

Slow-absorbing soil alone doesn’t decide it: a swale can still carry surface runoff if there’s enough room and slope. A French drain needs a workable fall and a suitable outlet too; without those, burying the collection system doesn’t solve where the water goes. The key is whether you’re routing surface flow or trying to intercept subsurface water, and whether either option can discharge appropriately.

For example, if a low spot stays wet after the visible flow has passed, I’d look for water appearing at several points or continuing to emerge from the soil; that would make seepage more plausible. But a saturated patch by itself wouldn’t settle it, since runoff can leave already-wet ground behind too.

A workable outlet matters for more than having somewhere to send the water: the receiving area also needs to handle the added flow without washing out or simply moving the soggy spot elsewhere. That can affect the choice too - a swale might spread surface flow, while a drain can concentrate discharge at one point - so I’d consider the effect at the outlet before choosing either route.

If both outlet areas were suitable and had enough capacity, would you lean toward spreading the flow through a swale or concentrating it at a drain outlet? I’d weigh how much space there is to manage the spread-out flow against whether a single discharge point can be protected from erosion.

I’d lean toward a swale if there’s enough room to guide the flow without creating a nuisance elsewhere; spreading it out seems less dependent on protecting one discharge point. If space is tight, though, a drain with a well-protected outlet could be the more practical choice.