M
melvinp
Member
- Joined
- May 29, 2009
- Messages
- 549
How long has California been in a drought seems like plenty of time to fix things that needed to be fixed.
Oroville Dam – If this goes south it could change the course of dam management immediately.
Swattie87
Well-known member
- Joined
- May 3, 2011
- Messages
- 5,831
100% capacity would be the actual top of the dam. Meaning the threshold at which the water level begins to top the dam uncontrolled over its entire length. Any time this happens a dam is in imminent danger of total failure as the top will begin to be eroded across its entire length. The longer this is allowed (or forced) to happen, the greater the danger. The “emergency” spillway is a few feet below the height of the top of the dam but is only a fraction of the length of the dam. Apparently at Oroville, this level represents 97% capacity. The idea behind the emergency spillway is that when the water gets to that level it spills out the emergency spillway in an uncontrolled fashion, but prevents the level behind the dam from getting any higher and keeps it from spilling over the actual top of the dam. The “regular” spillway allows for a top release from the dam, in addition to the powerhouse release, and is controllable.
The issue at Oroville is that the emergency spillway was poorly designed and/or not updated to modern standards and will suffer from severe erosion if used. Couple this with the main spillway being poorly maintained. As it sits, any top release from the dam will lead to severe erosion on whichever spillway is used. There may be some degree of poor water level management in the weeks/months preceding the event as kray mentioned too…I haven’t kept up on that piece of things. Right now, until proper repairs can be undertaken, their choices are, in order of preference with the least damage occurring:
1. As long as inflows allow, just use the power house release, and neither spillway. Feasible perhaps as long as no MAJOR rain events.
2. If needed, use the regular spillway. It will continue to erode and be further damaged, but it will keep the level of the lake lower (below the emergency spillway) and allow at least some level of control over what is released.
3. Allow (or be forced by major rain) the lake to fill to the level of the emergency spillway and spill out the emergency spillway. There is some concern of the emergency spillway failing via severe erosion if this happens. This is the “30 foot wall of water” scenario they’re talking about. The main dam likely would not fail, but the emergency spillway erosion would allow approximately 30 vertical feet of water out of the lake if this happens.
Beyond Oroville, the concern of course is that there are many many dams across the country that would probably be in this same predicament, or worse. Many of PA’s dams, especially the smaller ones, only have one spillway a few feet below the top of the dam, with no other safety mechanisms or ways to lower the water level if needed. Johnstown Flood was caused in part by the removal of the bottom release pipes from the dam. Poor maintenance and poor decision making regarding the single spillway (putting mesh over the opening to keep fish from escaping, which over time became clogged with debris), coupled with a massive rain caused the ultimate failure.
The issue at Oroville is that the emergency spillway was poorly designed and/or not updated to modern standards and will suffer from severe erosion if used. Couple this with the main spillway being poorly maintained. As it sits, any top release from the dam will lead to severe erosion on whichever spillway is used. There may be some degree of poor water level management in the weeks/months preceding the event as kray mentioned too…I haven’t kept up on that piece of things. Right now, until proper repairs can be undertaken, their choices are, in order of preference with the least damage occurring:
1. As long as inflows allow, just use the power house release, and neither spillway. Feasible perhaps as long as no MAJOR rain events.
2. If needed, use the regular spillway. It will continue to erode and be further damaged, but it will keep the level of the lake lower (below the emergency spillway) and allow at least some level of control over what is released.
3. Allow (or be forced by major rain) the lake to fill to the level of the emergency spillway and spill out the emergency spillway. There is some concern of the emergency spillway failing via severe erosion if this happens. This is the “30 foot wall of water” scenario they’re talking about. The main dam likely would not fail, but the emergency spillway erosion would allow approximately 30 vertical feet of water out of the lake if this happens.
Beyond Oroville, the concern of course is that there are many many dams across the country that would probably be in this same predicament, or worse. Many of PA’s dams, especially the smaller ones, only have one spillway a few feet below the top of the dam, with no other safety mechanisms or ways to lower the water level if needed. Johnstown Flood was caused in part by the removal of the bottom release pipes from the dam. Poor maintenance and poor decision making regarding the single spillway (putting mesh over the opening to keep fish from escaping, which over time became clogged with debris), coupled with a massive rain caused the ultimate failure.
T
timmyt
Member
- Joined
- Jun 20, 2007
- Messages
- 724
We need to wake up and quit giving all our money away to other countries and spend it here.
What you saw onTV yesterday was the BIGGEST example of the problem. How many dams you think we could fix for 36 billion over a years time?
What you saw onTV yesterday was the BIGGEST example of the problem. How many dams you think we could fix for 36 billion over a years time?
M
mkerr
Member
- Joined
- Jun 20, 2012
- Messages
- 57
There are lots of dams that have untested emergency spillways in the state of PA. However, they should not be the primary concern in our state. There are countless earthen dams in PA that only have a primary, and in lots of cases undersized, spillways.
wildtrout2
Well-known member
Those folks out there are in for some serious issues, they're talking about a bunch more rain coming in the next 3-4 days. Some areas in that drainage are expecting 3"-5", and possibly up to 8" of rain!! THAT would be a game changer.
franklin
Active member
- Joined
- Feb 10, 2009
- Messages
- 4,660
If you look at that dam on Google maps it wouldn't be hard to add an additional spillway in the future.
It does appear the emergency spillway is build over the original hillside. Not on fill. So it may hold up a bit better.
Back when my daughter went to IUP I stopped by the dam that caused the Johnstown flood. Didn't look very big. Amazing the energy behind even a small dam with a steep stream incline has.
It does appear the emergency spillway is build over the original hillside. Not on fill. So it may hold up a bit better.
Back when my daughter went to IUP I stopped by the dam that caused the Johnstown flood. Didn't look very big. Amazing the energy behind even a small dam with a steep stream incline has.
pcray1231
Well-known member
Again, part of the issue is that when it was designed, it was done so based on the belief that the Marysville dam would be built upstream before the lake was even filled. This incoming water during wet periods would never be as high (and never as low during dry periods either, so they could keep the lake lower).
Marysville was never built.
Farmer, I did not know there was a third spillage.
Marysville was never built.
Farmer, I did not know there was a third spillage.
