Bell-Mouth Spillway exploration.
April 19, 2010 by Eli

Before I get into this story, let me give you a little background.  There is an entire group of people out there (I happen to be one of them) who call themselves “Urban Explorers.”  We get a thrill from checking out the hidden-away, man-made structures that most people never get the chance to see.  From abandoned buildings, to storm drains, and everything in between, we enjoy finding out more about what is and what once was by exploring the remains of forgotten human accomplishments.  Now don’t get us confused with the punks that vandalise abandoned building.  Sure, what we do might be viewed by some as trespassing, but our purpose is simply one of innocent exploration, and once we leave, we leave with everything the same as when we arrived.  Just like in other outdoor sports that I participate in such as hiking, kayaking, or caving, real Urban Explorers try to practice responsible Leave No Trace Ethics. As we say “Take nothing but pictures, leave nothing but footprints, & kill nothing but time.”  We do it purely for the exploration and discovery that comes from seeking out such places.  With that said, please read on.

I should have posted this some time ago, but I have been pretty overwhelmed with work and not gotten a chance to finish editing the pictures until now.  A while back, me and a group of other Urban Explorers ventured into the depths of a bell-mouth spillway.  What is a bell-mouth spillway you might ask?  It’s a giant concrete structure forming a hole in the ground.  Check it out on the good old Wikipedia here:

Bell-Mouth Spillways on Wikipedia

So after meeting up that morning and driving out to the location (and no, I’m not going to tell you where it is), we got all geared up and made our way to the edge of this behemoth.  most people just decided to use a boat and paddle into it from the bottom, but three of us with vertical experience decided to rappel into it from the top.  After rigging ropes, we got over the lip and started rappelling in from opposite sides.  I of course took my camera with me, locking off my rappel rack and taking pictures every 50′ or so.   How deep was this thing?  Well, my rope is 360′ long and there was only about 30′ of rope at the bottom.  After taking into account some rope length for rigging and going over the lip, I would estimate it was right around 300′ deep.  Not too shabby.    We were clearly not the first people to rappel into this thing… not only were there bolt anchors in both sides of the spillway, but there were also rope grooves worn into the concrete lip just above the bottom.  I see these types of grooves pretty often in caves where the rope has widdled its way through the stone, but I think this was my first time seeing them in concrete.

So we get to the bottom, get off rope, and start exploring this huge tunnel in the earth.  I would estimate the diameter of the tube at right around 30′ in most places.  This thing is seriously huge!  Somewhere near the middle of the tunnel, there is a junction where the auxiliary dam release comes in from the side.  After taking some pictures at the junction, we head up the junction tunnel about 100′ to where the auxiliary release tubes are.  There is a massive 15′ tall concrete barricade between us and the release tubes, so we go about trying to find a way to get over.  We agree that using any kind of grappling hook risks damaging something (which would both be against our ethic, and pretty stupid when in front of release valves at the bottom of a 250′ lake), so we set about trying to make some sort of rigid structure to climb over with.  We find some metal pipes (they look like hand rails) within the debris in the main tunnel and bring them back to the barricade.  After several failed attempts, we put together a Dr. Seuss looking ladder-type-thing, and using my spider-monkey skills, I manage to climb to the top.  After getting some rope and vertical gear thrown up to me, we get a few more people up top and take some pictures.  The scene is just spooky with water hissing out of the rivets of the release tubes from every angle due to the immense pressure it’s holding back (a quick calculation reveals over eight atmospheres of pressure!).

After getting some good pictures near the release tubes, we head back out to the main chamber to facilitate our exit.  Before we go, I decide to take some pictures of the tunnel in both directions to later process using HDR (high dynamic range).  Everyone else (including my dog Taro) decides to takes the boat out the bottom and walk up to the top.  Not wanting to pass up the opportunity to climb a perfectly good rope, I decide to climb back out the way I came in.  The drip-line was brutal and by the time I got up the first 80′ or so, I was already soaking wet.  Whatever, I don’t believe in misadventure… only adventure 🙂   After 300′ of rope climbing, I was at the top and ready to de-rig.  All in a good day’s work.

Here are some of the pictures from that day:

Peace, Eli

read comments (29)
  • Nicole Gray

    These are all wonderful photographs! You have a great eye for composition. The spillway tunnels look like something out of a science fiction novel! Thanks for sharing your art.


  • Curious one

    Incredible photos! I found this searching around about bellmouth spillways. I was really curious what one looked like all the through. Hats off to you for roping back up the gateway to hell, I mean spillway.

  • I came in from a redirect from this page w/ a photo of a “Hole In The Water” also, UR pics are great! From the first link post#68: ” Someone has drowned in the glory hole spillway of the Monticello Dam in CA.

    Emily T. Schwalen (November 28, 1955 – March 9, 1997) of Davis drowned when she was pulled into the Glory Hole spillway at the Monticello Dam at Lake Berryessa. She held onto the edge of the hole for 20 minutes, but could not be safely approached by witnesses. (San Francisco Chronicle, March 12, 1997) ” What did you tie into at top? How did you approach w/o fear of falling before being tied in? That anchor must give you great faith to repel into this structure. How’s an item like this built? I live near Liberty Dam between Randallstown & Sykesville a little west of Baltimore that supplies a portion of their drinking water. I’ve heard stories of explores like yourself w/ tales of pipes so big you could drive an 18 wheeler in them & that these go all the way to town via gravity, but to see them is like seeing behind the curtain in Oz. Was UR adventure at a time when water wasn’t up to the bell? You mentioned getting soaked, was it wind driven waves or normal intake rate? Not nearly as cool but the 2 tunnels in this link have cool galleries, also look at Raystown Lake pics of power-station. Do you have blog? Where can we see more from UR group? Have you seen the History Channel show about secrets of the underground?

  • Mitch

    I like reading these ‘urban-explorer’ ventures on the internet, especially with the photos. These are great photos and just really wicked in a way. There is just something inherently scary about these huge holes that water flows through. Niagara Falls spooks me for some reason.

    Speaking of Niagara Falls, have you read about the group of urban explorers that documented their exploration of going through the Tail Race’s that go underneath the falls from an old abandoned power station up river. This one is just really freaky and they took some wonderful photos of the entire trip. It is really spooky thinking of the risks that they went through and the chance of getting stranded down there.

    Cheers and thanks for an interesting story with photos.

  • Pingback: It’s a giant hole or whirlpool in a lake – How a morning glory spillway works – The Blogs at HowStuffWorks()

  • KillHour

    You’re insane. I would never rappel down that thing. Hell, I would never go in there in the first place. Just look at the water trying to escape from those pipes and drown you. Dams are seriously dangerous and scary places. Gives me nightmares just thinking about it.

  • Eli

    The water was no where near the spillway, so there was literally no danger of water pouring in on top of us. At the top it was dry concrete. The water that was soaking us was seeping through the seams between layers of concrete once we were below the level of the lake. Not much water can seep through the concrete at any given seam, but over the course of 300′ there are allot of seams for water to find its way in.

  • Eli

    There was no water dumping into the spillway other than small leaks in the concrete, so we were not too concerned. I’m an experienced caver with allot of experience dropping into natural pits very similar to this one, so this actually felt pretty comfortable. The rope was attached to 3 climbing anchors in concrete and there was little or no concern about wall failure like there is in a natural cave.

  • Nigel H

    We have these ‘plugholes’ in Ladybower in Derbyshire. I have always been terrified just looking at them and seeing the water just swirl in, but have always wondered what’s down one so I found this page very interesting! Maybe your lack of fear just comes with all your experience but my legs were turning to jelly just looking at the photos (which are stunning by the way!) and I could never justify doing it myself.
    Is there really that much light down there or was it just a long exposure? Didn’t expect it to look like that at all.

  • Sayan

    Hats off Eli!

    Bumped into this page while searching for bellmouth spillways in google. As a civil engineer, I have had my share of dams too and saw things that very few commoners can see in a lifetime. What I regretted most was that I didn’t have a good digital camera to capture those moments. This page, kind of made my heart jump up! Thanks for putting up such a rare (and artistic) collection of pics, and a damn good story! Hope to see more from Urban Explorers. Really glad to know there are people who’d share such uncommon tastes and follow them with strict ethics.





  • Alex

    Like others that have posted here, I salute you for going where the rest of us have hardly even dared to imagine, but been fascinated with nonetheless. I’ve done a bit of caving myself, but these bellmouth spillways seem to instill a real ‘point of no return’ kind of dread in you. Must’ve been an amazing mixture of excitement and at last some fear, knowing you were standing where so few had been, or dare to venture. The pics are awesome. Keep up the urban exploring

  • stuart

    Scares the bejeezus out of me these glory holes yet I still find them strangely compelling to look at. how weird is that? im also a sucker for hydro power station head and tail races and lock culverts and sluices (you can thank Dirty Jobs’ Mike Rowe for that as he is another one of the few people to venture into these strange worlds when they are dry!) Think Soo Locks and youll get the eeby jeebies. Mike even voiceovers “as we descend further into the locks i get the feeling we are entering an ever increasing series of death traps”.

    Boy you wouldnt want to be swimming into one of these hole or near a hydro head race……these photos are superb and give a real eye opening glimpse into what is along the bottom of these structures. From most normal viewing levels all you get to see are the steps or curves as they disappear into darkness but you cant see the very bottom unless you hired a helicopter and hovered over one (again id be too scared to do that). Interesting that this one joins up with a larger tunnel coming from the dams huge valves. I wonder what it would be like to stand behind the valve gates as they open? Is it possible or do they shut that area off? The pressure would probably cut through steel. Check sluice testing out on you tube and see some gates open millimetres to see the devastating forces at work. scary but just mesmorising.

  • ItsLeeOwen

    That is amazing! How huge it is!

  • Vatin

    You are brave to make such adventure and thank you for sharing your amazing story.
    Since I first learned of this horrific structure from youtube, I was fascinated and have been searching for more information and photos ever since. Your’s are the most fascinated so far!!! Unbelievable trip!!!!

  • Philip

    Its amazing, mazzive. Where is this, somewhere in UK?

  • Jennifer Jones

    This is old, but heck, I bet you still check once the notion strikes on a boring sunday afternoon…I also share the wierd fascintion with Stuart up there in the comments . Dams, spillways, creepy industrial waterways…ewwwwwww scary and fascinating. I do wish they didn’t call the overflows gloryholes after doing a google image search with safe-searching off. lol.

    Now, your pictures and bravery are awesome…thank you so much for posting the views so many of us dam junkies dream of (but are too scared to venture near)! I was a happy camper to get to see them! Very very nice.

  • Epic Photos, Looks like it could be a fun day of climbing along with some killer skateboarding.

  • sue davies

    Hi Wow what awesome pics, great job, ive often wondered what a spillway looks like inside. Ive just stumbled on to this site, now I know, it took guts to go down there i couldnt. I hope to visit the Ladybower dam in Derbyshire this year, i love walking around reservoirs, i find them fascinating and how they work. Great job

  • There have been at least 2 people killed in the Glory Hole in Lake Berryessa. Supposing under the best conditions, with water going in, not in the totally dry season and water coming out but not in the wet season, is it possible for a human being to survive a fall into it? I mean there have been miracles before right? It’s just that there are no documented survivors. If someone physically survived wouldn’t they be driven insane? Not everybody is a daredevil. It would be pretty hard to handle because you’d be wondering who threw you in.

  • Eli

    No, if you fell into one of these, you would die, water or no water. The vertical distance you would fall is simply too great.

  • Scott

    Wow, awesome photos! What are the light sources in photos 6-9? Is it legal to do this? When water is flowing into the spillway, how much of the cavern your group is standing in would be underwater?

  • charlie

    Ive always had a fear of large, man made lakes, spillways, dams etc. They just give me nightmares but at the same time Im sooo fascinated. Amazing pictures. Ive always wanted to know what the inside looked like. Great job!

  • Eli

    6 and 7 are a combination natural light and strobes in background. 8 and 9 are from a very warm light that was installed in the tunnel, but with the long exposure it brought out the warm color. As for the 2nd part of your question, no comment.

  • Joel

    Eli, I know EXACTLY which dam this is (and, yes, your secret is safe with me). I sent an e-mail to you on this particular blog subject a year or two ago, but I forgot to ask this: Does this particular bellmouth spillway have a 90° elbow turn where the inlet/vertical part of the tunnel meets the outlet/horizontal part, or is the transition from vertical to horizontal a gradual slope? I can’t tell 100% from your absolutely boss photos.

    I would think that a high volume of falling water in such a spillway would absolutely wreck the concrete at a sharp 90° elbow. (Do a Google search on the extensive spillway tunnel damage at both Hoover Dam and Glen Canyon Dam caused by record floods in the Southwestern U.S. back in 1983–both of those dams’ spillway tunnels are angled on a gradual downward slope, yet they suffered extreme damage.)

    Thanks again for posting this particular adventure; “fascinating” doesn’t even begin to describe getting to see that which few people ever get to see in a lifetime. I have this particular blog in my bookmarks and return to it from time to time to experience the vicarious thrill of it.

  • Eli

    The tube turns 90 degrees, but it is a gradual transition in the bottom 50 ft or so (so the outside of the curvature is on a radius of about 50′). You can see the curvature of the chamber in the 3rd, 4th, and especially 5th photo. Being a wet and slippery slope certainly made getting some of those images tricky. Thank you for your kind words. Knowing people use and enjoy my site certainly helps motivate me to keep it going. I can get prints made in any size up to 4’x6′, so let me know if there is a particular image you really like and I can get you hooked up.

  • Lawrence

    Eli, I never knew anything like this existed and I am grateful to you that you gave me a chance to see something I would have never had the chance to see on my own. Thank you. And yes it is an awesome sight! It reminds me of something from Arthur C. Clarke. Anyway, Beautiful Photos! Thanks Again! Please post more Adventure Photos!

  • nah

    THIS IS DOPE i wanna go too

  • coby scheldt

    Stunning images. Thanks. (and be careful!) As a kid my friends and I would enter the 10 or 12 foot diameter storm drains in Wichita and keep going as the tunnels grew smaller and smaller. Finally, we could crawl up very narrow tubes that opened in the street gutter drains. When the feet of a an unwary pedestrian appeared, they would hear a voice seemingly out of nowhere. Such choice phrases as “hey, where do you think you’re going?!” In a storm the ubiquitous drainage canals of the city could truly flood in a very short time. At that time of year we were thankfully wise enough to stay out of the tunnels. Instead, we’d surf along the roaring flood on flotsam, like old doors. Somehow, we all survived.