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WxWatcher007

Harvey - Main Thread

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Just now, NCBlizzard said:

Threw together a quick chart showing the reservoir level change per hour. They both look to be averaging roughly 2.5" - 3" an hour now...

 

59a4ca8304047_ReservoirLevelChange.thumb.jpg.33786894f20582e46dffa3db0e8ff438.jpg

Don't forget it is also covering more and more surface area. Would be interesting to see volume, not height.

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5 minutes ago, stockmanjr said:

They specifically mentioned the gauges along brays bayou, but said that they believed most of the Harris County gauges have been washed away as evidenced by the lack of updates. Of course now we can't even tell as the Harris County Flood Control website is down.

That's a pretty bold and foolish assumption that "all" gauges have been washed away.  The main site is working and it is updating.  However the links to the individual gauges are not working.  Those links and the site itself has been up and down through out the event.  Like the flood control system the data flow has been stressed also.  Not pointing fingers but I'm smelling conspiracy theory rearing it's ugly head.  No place for that now.  Where ever or whomever you heard that from can go post in the flat earth chat room.

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1 minute ago, TellicoWx said:

The precinct they told them to move to was on Ley Rd.

The one thing no one has really talked about is Lake Houston over topping.   Or the fact that Lake Conroe up stream is pumping out something like 80k CFS as of this afternoon.   It's full too, so they likely don't have much option but to mirror inflow at this point.

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So I'm confused. Is 108 ft the height of the auxiliary spillway at Addicks? Anyone know what the maximum flow rate is for it? I saw someone mention the inflow is 6x the outflow rate right now so if the spillway balances inflow and outflow then we'd go from 4000 cfs to 24000 cfs rushing down the bayou right?

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From a Reddit livethread:

 

Addicks Reservoir Update

There's been a lot of misinformation flowing around re: the fill rate of Addicks Reservoir. Below, I've provided some information that should clarify the issue for people. As a caveat, I'm not a pro by any means... I just like to read. So take this for what its worth, which is maybe very little.

First, background detail: Addicks Reservoir is an earthen dam, with concrete outlet works and rolled compacted concrete uncontrolled auxiliary spillways. The shape and function of the dam may be confusing to some, as Addicks is not your typical "dam up a canyon" structure. Importantly, the ground at either end of Addicks Dam (referred to as an abutment) is lower than the top of the dam. The abutment at the northern end of the dam has an elevation of 108.0 feet. The abutment at the southern end of the dam has an elevation of 111.0 feet. Further, the northern abutment interfaces with the spillway crest at 112.5 feet, while the southern abutment interfaces with the spillway crest at 115.5 feet. Finally, ACE documents state that both ends Addicks Dam have been "armored with roller-compacted concrete that serve uncontrolled spillways."

So, what does this mean? A couple things.

First, there are multiple stages at which water will begin to flow out from the dam in places other than the concrete control structures:

At 108 feet, water will begin to flow out and over land at the northern end of the dam (but not the spillway).

At 111 feet, water will begin to flow out and over land at the southern end of the dam (but not the spillway).

At 112.5 feet, water will begin to flow over the spillway at the northern end of the dam.

At 115.5 feet, water will begin to flow over the spillway at the southern end of the dam.

Second, this means that after each of these thresholds are met, the amount of water needed to reach the next threshold will be raised quite a bit. I haven't been able to find documents stating what the flowrates of the spillways are, but I assume they're substantial.

Third, due to the thresholds listed above, I find it highly, highly unlikely that water will overtop the dam (which has been a recurring statement in the comments). However, I believe that the water will reach the 108 feet threshold tonight. Once that occurs, we'll have to wait and see what the flows look like to determine whether the next threshold will be met tonight or tomorrow morning.

 

This seems to make it sound like the officials actually knew what they were talking about and not maliciously keeping info from the masses. Who'd've thunk it.

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Just now, Ralph Wiggum said:

NAM says lets do this all over again tomorrow night for the final(?) act. 

 

It aligns the heaviest rain along and west of the longitude of IAH as well. It seems like the initialization might be a bit too far west though, with respect to the convection. The HIRES Nam suggests the heaviest rain is near the longitude of IAH. It will be a nowcast, but latest radar trends don't look positive to me.

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Just now, bdgwx said:

So I'm confused. Is 108 ft the height of the auxiliary spillway at Addicks? Anyone know what the maximum flow rate is for it? I saw someone mention the inflow is 6x the outflow rate right now so if the spillway balances inflow and outflow then we'd go from 4000 cfs to 24000 cfs rushing down the bayou right?

Yes, Aux spillway.   Or in this case more an armored overflow at the ends of the dam.   I would say it's max is whatever those overflows could flow before the main dam is over topped.   However, looking at how large they are and that it seems the dam height is significantly higher it doesn't seem like it's realistic that they couldn't flow whatever is needed.

Slightly tricky in they don't flow to a normal watershed directly. They flow to smaller drainages and neighborhoods.

But yeah, all of that will end up somewhere and eventually in the bayou.

 

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Great information guys. I was specifically wondering if the 108 ft height represented an unfortified earthern levee or a fortified spillway. That answers my question. And yes, assuming that information is correct it would be incredibly unlikely that a catastrophic failure would occur...if I'm understanding the design correctly that is.

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6 minutes ago, Upper Level LOL said:

From a Reddit livethread:

 

Addicks Reservoir Update

There's been a lot of misinformation flowing around re: the fill rate of Addicks Reservoir. Below, I've provided some information that should clarify the issue for people. As a caveat, I'm not a pro by any means... I just like to read. So take this for what its worth, which is maybe very little.

First, background detail: Addicks Reservoir is an earthen dam, with concrete outlet works and rolled compacted concrete uncontrolled auxiliary spillways. The shape and function of the dam may be confusing to some, as Addicks is not your typical "dam up a canyon" structure. Importantly, the ground at either end of Addicks Dam (referred to as an abutment) is lower than the top of the dam. The abutment at the northern end of the dam has an elevation of 108.0 feet. The abutment at the southern end of the dam has an elevation of 111.0 feet. Further, the northern abutment interfaces with the spillway crest at 112.5 feet, while the southern abutment interfaces with the spillway crest at 115.5 feet. Finally, ACE documents state that both ends Addicks Dam have been "armored with roller-compacted concrete that serve uncontrolled spillways."

So, what does this mean? A couple things.

First, there are multiple stages at which water will begin to flow out from the dam in places other than the concrete control structures:

At 108 feet, water will begin to flow out and over land at the northern end of the dam (but not the spillway).

At 111 feet, water will begin to flow out and over land at the southern end of the dam (but not the spillway).

At 112.5 feet, water will begin to flow over the spillway at the northern end of the dam.

At 115.5 feet, water will begin to flow over the spillway at the southern end of the dam.

Second, this means that after each of these thresholds are met, the amount of water needed to reach the next threshold will be raised quite a bit. I haven't been able to find documents stating what the flowrates of the spillways are, but I assume they're substantial.

Third, due to the thresholds listed above, I find it highly, highly unlikely that water will overtop the dam (which has been a recurring statement in the comments). However, I believe that the water will reach the 108 feet threshold tonight. Once that occurs, we'll have to wait and see what the flows look like to determine whether the next threshold will be met tonight or tomorrow morning.

 

This seems to make it sound like the officials actually knew what they were talking about and not maliciously keeping info from the masses. Who'd've thunk it.

Exactly.

What I would like answered is where does that water go from each stage?  Potential major issue.  Going out the NE corner at 108 it looks to go right into a neighborhood.   The NE overflow "spillway" does have a drainage that runs down near the face of the dam towards the gate then out to the bayou.   But does that capture all the flow?   It certainly seems small on the map.

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Whoever this man is that is speaking on abc13 is so clear, concise and calm. He is doing an incredible job of informing people. There are no mixing the words at all, and there is no way they can confuse what he is saying. Everyone should take notes from him.

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4 minutes ago, bdgwx said:

So I'm confused. Is 108 ft the height of the auxiliary spillway at Addicks? Anyone know what the maximum flow rate is for it? I saw someone mention the inflow is 6x the outflow rate right now so if the spillway balances inflow and outflow then we'd go from 4000 cfs to 24000 cfs rushing down the bayou right?

From what I understand and from what was quoted at the press conference, releases become uncontrolled at 108' pool level. Whether that's overtopping or via an auxillary, I'm not sure as they didn't specify and I'm having trouble finding specifics. Either way, I'm not sure an auxillary is going to handle 35kcfs as the main spill is only discharging at 5kcfs.

From what I've been able to gather is that these two reservoirs were built after the 1935 event to buffer the system and prevent a repeat. Well, if they're reaching capacity, then what's stopping a repeat?

The fact of the matter is that the reservoir is taking on water at 3000 acre feet per hour. That's 35kcfs that has to go somewhere. I'm assuming that goes into Buffalo Bayou since they said the combined controlled releases were accounting for 20% of the flow in the Bayou at the moment.

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4 minutes ago, Amped said:

NAM is a lot drier everywhere than last run at least. 

Im not sure any model has been really "good" with QPF depictions this whole event. My takeway from this run is a slower moving more stalled out Harvey. Hopefully not a trend. Some guidance had this outta there by tomorrow evening (Houston proper).

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Just now, Polka1 said:

Exactly.

What I would like answered is where does that water go from each stage?  Potential major issue.  Going out the NE corner at 108 it looks to go right into a neighborhood.   The NE overflow "spillway" does have a drainage that runs down near the face of the dam towards the gate then out to the bayou.   But does that capture all the flow?   It certainly seems small on the map.

It goes into neighborhoods around the reservoir, yeah.  Most of these neighborhoods are recent developments which were built there despite the objections of the ACOE. Now the people who bought there are suffering the consequences.

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just went over 30.5" storm total at my house. getting creamed now. looks like an awful night with no breaks to drain.  i'll be shocked if brays doesn't exceed its banks along here again

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