You may also want to ensure you have enough freeboard above the spillway to account for wind & wave action or a heavy rainstorm event. The water color is beautiful.

Cool video, well done!

I’d take the walnut out, if it was me. I’d also bring that swale farther up hill or make a terrace up hill. Either way I’d make it much larger, I’d put it on contour, and give it a large, level spillway away from the dam. If your spring seepage is slow, a contour swale up hill would charge the ground water flow. I’d make the emergency spillway substantial in size just in case. Did the primary spillway have an anti seep collars around it?