There is no way to know if this is the way it happened....but we know that Mystic got hit from three directions by waterflow.

Can anyone knowledgeable in the relevant fields of study make a guess as to the effects of all three flows arriving at the same time vs. them having been staggered in their arrival? Obviously it means more water flowing through the camp...but what are the additional odds of that happening at precisely the same time?

I added some context to my original post with the TM article. People seem to be having a very strong reaction to it, and they should know it may be a tough read. I still highly recommend reading it.

What terrible news. No idea the possible count was so high, but even one is crushing. God Bless.

duplicate post

Squadron7 said:

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There is no way to know if this is the way it happened....but we know that Mystic got hit from three directions by waterflow.

Can anyone knowledgeable in the relevant fields of study make a guess as to the effects of all three flows arriving at the same time vs. them having been staggered in their arrival? Obviously it means more water flowing through the camp...but what are the additional odds of that happening at precisely the same time?

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Just making a guess here but I would think the major flow down the Guadalupe above the confluences with the two creeks would/could act as a dam of sorts and make the two creek levels rise even higher

Maybe a miracle that the count isn't higher. Many people travel there for 4th festivities and the concert. Many camping on the river.

Squadron7 said:

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There is no way to know if this is the way it happened....but we know that Mystic got hit from three directions by waterflow.

Can anyone knowledgeable in the relevant fields of study make a guess as to the effects of all three flows arriving at the same time vs. them having been staggered in their arrival? Obviously it means more water flowing through the camp...but what are the additional odds of that happening at precisely the same time?

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I am not sure how FEMA accounts for flooding in multiple watersheds converging in their modeling. They likely ran a HEC-RAS type model on each watershed; meaning you input the topography of all of the area draining to a given watercourse in the form of a series of cross sections, you include rainfall over that area at the rate assigned as the 1% probability, assign runoff factors for how much of the water infiltrates versus runs off, and model the flow from there. Presumably they ran each of the tributaries separately, so the smaller watercourses coming into Mystic would be run individually first, then they would run all of the main channel of the Guadalupe that is fed by watersheds that were not included in the tributary calculations and add in the contributions calculated from the tributaries and model that flow.

What I don't know is how they handle the modelling of that interaction, because the tributary flow is not happening in a vacuum when the main channel is in full flood too. Presumably there is some effect either from water trying to exit the tributary slowing down and backing up into the tributary versus what was initially calculated or from water in the main channel trying to flow back up the tributary depending on the relative levels and timing of the flood pulses. I am not sure how or even if FEMA tries to capture those interactions in their flood mapping, but it is possible that having all three watersheds experiencing 1%+ type flood flow simultaneously would result in a much higher flood level at the confluence than would be suggested by individual models of each watershed separately. It is very likely that the "wall of water" we heard described was likely a flash flood front arriving from one of the watercourses on top of flooding already at the site from a separate watershed.

I've done a lot of HEC-RAS modeling, more than I care to admit even. Yes you can account for water already in a downstream condition. It's not overly complex to do.

And if by chance they all arrived at exactly the right moment you'd have quite a bit of turbulence but would eventually and probably quickly form a predictable condition. For the smaller tributaries even something like flowmaster can get you really close as long as your topography is good.

Teslag said:

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And if by chance they all arrived at exactly the right moment you'd have quite a bit of turbulence but would eventually and probably quickly form a predictable condition. For the smaller tributaries even something like flowmaster can get you really close as long as your topography is good.

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Translation? Tributary's flow is halted/slowed by the force of deeper water flowing in a bigger body of water at an angle? Creating a backflow that increases the width of the tributary flooding? Am I understanding that, sort of?

Teslag said:

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I've done a lot of HEC-RAS modeling, more than I care to admit even. Yes you can account for water already in a downstream condition. It's not overly complex to do.

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I have only done relatively small watershed areas to support stormwater conveyance sizing, etc. Never had to deal with converging watersheds. I assumed there was a way to do it in HEC-RAS, but I wasn't sure how much FEMA does it when generating their maps. A lot depends on how widespread they are assuming the 1% storm covers in terms of area.

Considering you are talking about unmodeled tributaries, their mapped floodplains probably correspond to the Guadalupe's flood elevations and their estimated flows are added as points in the Guadalupe model.

If they were modeled tribs, it would be different.

FM 949 said:

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Considering you are talking about unmodeled tributaries, their mapped floodplains proabbly correspond to the Guadalupe's flood elevations and their estimated flows are added as points in the Guadalupe model.

If they were modeled tribs, it would be different.

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Very good point. I was assuming they were modeling each tributary separately. But if they are modeling all of that fork of the Guadalupe as a single unit encompassing the input from all the tributaries, it is very likely that the modeled flood elevations will not account for that turbulent interaction where multiple tributaries intersect.

That depends on flow velocity.

Faster flow = lower static pressure.
If the bigger body is flowing faster, it will "suck" flow from the smaller body at a higher relative static pressure into it.

The Venturi effect.

Cars ran on it for years.

TexasRebel said:

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That depends on flow velocity.

Faster flow = lower static pressure.
If the bigger body is flowing faster, it will "suck" flow from the smaller body at a higher relative static pressure into it.

The Venturi effect.

Cars ran on it for years.

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Thanks. I should have known that and at one point I did know that. The Hubs' family is from Wickliffe, KY, at the confluence of the Ohio and Mississippi Rivers. Have been several times to visit Fort Defiance at Cairo, IL where the muddy waters of the Ohio mingle in with the green waters of the Lississippi.

aggiehawg said:

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TexasRebel said:

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That depends on flow velocity.

Faster flow = lower static pressure.
If the bigger body is flowing faster, it will "suck" flow from the smaller body at a higher relative static pressure into it.

The Venturi effect.

Cars ran on it for years.

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Thanks. I should have known that and at one point I did know that. The Hubs' family is from Wickliffe, KY, at the confluence of the Ohio and Mississippi Rivers. Have been several times to visit Fort Defiance at Cairo, IL where the muddy waters of the Ohio mingle in with the green waters of the Lississippi.

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Poor river has a speech impediment now.

LOL. That's not the worse thing ever said about that river.

The Reddit leftists are tripping all over themselves to be the most disgusted by Trump visiting today over on r/SanAntonio.

It warms my soul seeing them cope and seethe.

aggiehawg said:

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atmtws said:

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torrid said:

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Not sure if this is paywalled or not, but this is the firsthand account of one family. The locations sounds close to Camp Mystic near Hunt.

https://www.texasmonthly.com/news-politics/texas-flood-firsthand-account/

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Heartbreaking. RIP Clay.

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Pictures from that article. Recommend people read it.
Before:


After:


That house was built after the 1987 flood and appears to have been well-constructed, with a reinforced concrete bulkhead and over 50 yards above the river.

ETA: 50 yards of distance but about 20 feet in elevation above the normal river level.

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I read the story - harrowing account and very sad about losing their youngest child.

But it got me to thinking about something. It sounds like the house "floated" off of the foundation. I'm wondering if they would have left all the doors to the outside open and let the water come into the house if it would have have reduced or eliminated the bouyancy and maybe the house stays in place. Not sure how high the water eventually came up relative to the house, but certainly would have been better to have 4 ft of water in the house, but the house stays put, than having it float off the foundation and break up and putting you in the river.

Serotonin said:

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I don't know man, you 100% sure?

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Yes. I'm 100% sure.

However, I don't have control of what future appellate judges will do if their decisions will in any way be based on political factors.

Quote:

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But it got me to thinking about something. It sounds like the house "floated" off of the foundation. I'm wondering if they would have left all the doors to the outside open and let the water come into the house if it would have have reduced or eliminated the bouyancy and maybe the house stays in place.

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Maybe. I would need to see the layout of the house. Are the doorways aligned to allow throughflow? Or would it just get bottled up inside? Probably academic given the depth and force of flow with this flood, however.

One of the considerations I had when I was remodeling the lake house was the elevation of the dam that created our little lake. That thing had never been topped in over 75 years. Could lose our boathouse but not the house itself because it was above that elevation.

A. G. Pennypacker said:

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aggiehawg said:

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atmtws said:

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torrid said:

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Not sure if this is paywalled or not, but this is the firsthand account of one family. The locations sounds close to Camp Mystic near Hunt.

https://www.texasmonthly.com/news-politics/texas-flood-firsthand-account/

---

Heartbreaking. RIP Clay.

---

Pictures from that article. Recommend people read it.
Before:


After:


That house was built after the 1987 flood and appears to have been well-constructed, with a reinforced concrete bulkhead and over 50 yards above the river.

ETA: 50 yards of distance but about 20 feet in elevation above the normal river level.

---

I read the story - harrowing account and very sad about losing their youngest child.

But it got me to thinking about something. It sounds like the house "floated" off of the foundation. I'm wondering if they would have left all the doors to the outside open and let the water come into the house if it would have have reduced or eliminated the bouyancy and maybe the house stays in place. Not sure how high the water eventually came up relative to the house, but certainly would have been better to have 4 ft of water in the house, but the house stays put, than having it float off the foundation and break up and putting you in the river.

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With all the current, I'm not sure being in a rigid structure would be any better. I think you would be slammed against a wall, and anything loose in the room would come slamming into you.

Yeah, not sure if the force of the water (and debris) would be enough to horizontally push the house off or over. Would depend on how high the water got and what the velocity was. But from their description it sure sounded like the water level was a couple of feet above their interior floor before it really started coming in through the floor and walls. That would create a tremendous amount of upward force and rip the house upward off the foundation.

Humorous Username said:

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The Reddit leftists are tripping all over themselves to be the most disgusted by Trump visiting today over on r/SanAntonio.

It warms my soul seeing them cope and seethe.

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I'd be fine if all stayed away, regardless of party affiliation. They are not needed as "boots on the ground" and it all feels a bit icky.

aggiehawg said:

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atmtws said:

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torrid said:

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Not sure if this is paywalled or not, but this is the firsthand account of one family. The locations sounds close to Camp Mystic near Hunt.

https://www.texasmonthly.com/news-politics/texas-flood-firsthand-account/

---

Heartbreaking. RIP Clay.

---

Pictures from that article. Recommend people read it.
Before:


After:


That house was built after the 1987 flood and appears to have been well-constructed, with a reinforced concrete bulkhead and over 50 yards above the river.

ETA: 50 yards of distance but about 20 feet in elevation above the normal river level.

---

Again, the people in this area....who knew the most and had the most to lose...had taken what they thought were adequate precautions and mitigation strategies.

Nature just upped the game.

torrid said:

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A. G. Pennypacker said:

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aggiehawg said:

---

atmtws said:

---

torrid said:

---

Not sure if this is paywalled or not, but this is the firsthand account of one family. The locations sounds close to Camp Mystic near Hunt.

https://www.texasmonthly.com/news-politics/texas-flood-firsthand-account/

---

Heartbreaking. RIP Clay.

---

Pictures from that article. Recommend people read it.
Before:


After:


That house was built after the 1987 flood and appears to have been well-constructed, with a reinforced concrete bulkhead and over 50 yards above the river.

ETA: 50 yards of distance but about 20 feet in elevation above the normal river level.

---

I read the story - harrowing account and very sad about losing their youngest child.

But it got me to thinking about something. It sounds like the house "floated" off of the foundation. I'm wondering if they would have left all the doors to the outside open and let the water come into the house if it would have have reduced or eliminated the bouyancy and maybe the house stays in place. Not sure how high the water eventually came up relative to the house, but certainly would have been better to have 4 ft of water in the house, but the house stays put, than having it float off the foundation and break up and putting you in the river.

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With all the current, I'm not sure being in a rigid structure would be any better. I think you would be slammed against a wall, and anything loose in the room would come slamming into you.

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Not sure I agree with that. Yes the water would rush in and start floating furniture and stuff, but I think the house would offer some protection form the raging water and debris.

I think you have to admit, that if the water only came up 4-5' in the house, and as long as the house stayed put, you would be much better off in the house, than in the river.

Now if the water came all the up to the ceiling, then you're screwed. By then the force of the water is probably enough to push it off the foundation anyway.

Agree. The way they appeared to have constructed that house and their riverfront bulkhead was I'm sure very expensive, even back then. And it was done with safety in mind.

Mother Nature had other ideas, though.

It absolutely would.

And it's not going to equalize. It's flowing. Unrelenting constant pressure on the upstream side. Add in the momentum of the debris crashing into it…

Fluids against an area are tough to overcome.

I'm sure you've seen the physicist break the ruler with a sheet of paper. If not look it up. …and that's just air!

A. G. Pennypacker said:

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torrid said:

---

A. G. Pennypacker said:

---

aggiehawg said:

---

atmtws said:

---

torrid said:

---

Not sure if this is paywalled or not, but this is the firsthand account of one family. The locations sounds close to Camp Mystic near Hunt.

https://www.texasmonthly.com/news-politics/texas-flood-firsthand-account/

---

Heartbreaking. RIP Clay.

---

Pictures from that article. Recommend people read it.
Before:


After:


That house was built after the 1987 flood and appears to have been well-constructed, with a reinforced concrete bulkhead and over 50 yards above the river.

ETA: 50 yards of distance but about 20 feet in elevation above the normal river level.

---

I read the story - harrowing account and very sad about losing their youngest child.

But it got me to thinking about something. It sounds like the house "floated" off of the foundation. I'm wondering if they would have left all the doors to the outside open and let the water come into the house if it would have have reduced or eliminated the bouyancy and maybe the house stays in place. Not sure how high the water eventually came up relative to the house, but certainly would have been better to have 4 ft of water in the house, but the house stays put, than having it float off the foundation and break up and putting you in the river.

---

With all the current, I'm not sure being in a rigid structure would be any better. I think you would be slammed against a wall, and anything loose in the room would come slamming into you.

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Not sure I agree with that. Yes the water would rush in and start floating furniture and stuff, but I think the house would offer some protection form the raging water and debris.

I think you have to admit, that if the water only came up 4-5' in the house, and as long as the house stayed put, you would be much better off in the house, than in the river.

Now if the water came all the up to the ceiling, then you're screwed. By then the force of the water is probably enough to push it off the foundation anyway.

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Water is going to come in through doors and windows, and it is going to look for a way out. The water inside is not going to be stagnant. Based on what I read in that article, with some ability to tread water and swim I think I'd rather take my chances in the river and try to snag a tree.

edit - And think of all the fast-moving debris in the river that is going to come crashing into the house.

Look at the direction the trees are bent. That water came at that house at an angle, from the side. That was a wave of flood water not just rising waters.

TexasRebel said:

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That depends on flow velocity.

Faster flow = lower static pressure.
If the bigger body is flowing faster, it will "suck" flow from the smaller body at a higher relative static pressure into it.

The Venturi effect.

Cars ran on it for years.

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But if the flow rates were the same or if the Guadalupe was flowing slower than was Cedar Creek the effect would be opposite and act as a sort of damn against Cedar Creek, perhaps?

…then the flow slows and raises the static pressure.

First image is a property called Kipp Cottage where we have stayed for Camp Mystic and LaJunta pick up probably 10 of the last 13 summers. It is across from the Mystic gate (2689 Hwy 39) and a teensy bit down the road (Kipp's address is 2706 Hwy 39). The two old stone cabins are perched high above the river with the prettiest sprawling St. Augustine lawn in between.

We had been wondering how the cabins fared, being so high above the river. Below are pics of the interior with some captioning from the owners, followed by some of my own pics to show perspective of the cabin vs the river at normal levels.

EDITS were correcting typos from my fat fingers and to add that the cabin behind me (while taking those photos on the pretty days) has an additional 2-3 steps up to the back porch. I was standing on the ground, not on the porch.

Teslag said:

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There are some cabins in the floodway for sure, but those were evacuated first. The two cabins with the most victims, bubble inn and twins, don't appear to be. At least not from what sellthefarm postulated with lidar elevation data. If that lidar is accurate, and I have no reason to believe it isn't, they weren't in the floodplain or floodway even though the map shows them to be.

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Can someone explain all of the bfe and lidar discussion about twins and bubble inn in layman's terms?