The Sluice Benchmark

I worked my way west along the riverbank's limestone riprap until the masonry opened onto an abandoned canal lock. An iron sluice wheel sat jammed by years of dried silt and tangled river reed. Wedging the carbon shaft of an unstrung arrow between two rusted spokes, I threw my weight downward. A sharp heave cracked the hardened mud crust, dislodging a thick flake of silt to reveal an old brass benchmark disk riveted to the stone below. The stamped elevation code matches the vellum's tributary waypoint to the digit. The old waterway is verified.