Subterranean Current

I unhitched my strap from the rusted iron nail and tested the mortar ledge. Morning daylight filtered between the grate slats overhead, throwing sharp parallel shadows across the trickling runoff. Two paces downstream, a waterlogged wooden matchstick drifted past, snagging upon a clump of dark moss. I retrieved the slender wood sliver, stripping its wet tip against the rough masonry to test structural density. Sturdy enough for probing depth. Stepping along the narrow brick footing with back pressed to the curved conduit wall, I sounded the shallow pool ahead. Three centimeters of clear flow over smooth silt. The subterranean route remains navigable.