Cemetary Storm Channel

I'd still like to call this one something like the Laser Beam or the Twin Beam drain, but I never actually got around to thinking up a creative name. This drain is essentially a long culvert, which takes the North Storm Channel (NSC) underground from Broad to Albert Streets, and runs along the north boundary of a cemetary. It's about 12 blocks long, though I wasn't inclined to traverse the entire length.
It begins as an 1800 RCP, and remains this way for much of its length. The outfall is the site of a beaver dam, built just inside the concrete structure's walls. Thanks to this dam, the water level in the ditch is about two feet higher than the trickle entering the actual pipe. About 50m inside lies what I assume are the leftovers of the infall grate; which is now a twisted wreckage entangled with tumbleweeds and debris. I wonder what kind of force was sufficient to slam a heavy iron grate from its anchor bolts and carry it this far up the pipe? Surely it wasn't the family of beavers.
Further along, the water level rises, and the pipe becomes corrugated for about 20m. The water, about knee deep here, finally dropped down inside the first manhole room, and the drain changed back into RCP. The first two manhole rooms I passed through didn't actually have manhole lids- instead, they were covered by large metal plates. Presumably, these were hinged on the surface, although possibly locked down- I didn't try opening them.
The water level fluctuated quite a bit in this drain- from just a trickle to knee-deep, then up and down some more. In one of the deeper sections, the RCP entered a large, rectangular junction room. Straight ahead were two identical 1800 duct pipes, and on the right was a smaller 1500 RCP. The ceiling of this chamber was made of the metal plates, and each of these had a pair of holes in them. These holes allowed for the most amazing feature of this drain- the "Laser Beams".
Bright midday sunlight, entering at and agle through the holes, made matching bright dots on the surface of the water. The slight fog underground drifted through the beams, lighting up where it was hit by the light. The result was a pair of laser beams; which I spent much time examing, playing with, and photographing.
After getting my fill of the beams, I took a closer look at the other pipes leaving the junction. The RCP was small, and half-full of water, so I didn't bother with it. The ducts looked to be much more appealing, but they also had their share of obstacles. The duct on the right was half-full of sediment, with poor air quality. The duct on the left had about six inches of that soft, black sediment mud underneath the water's surface- after going only twenty meters inside, my steps churning up the mud released so much gas I decided to turn back.
With no appealing options left, I rationalized that I'd explored far enough into this pipe. It probably only gets worse near the outfall, which I know for a fact is quite small.