Llano River flooding. (Brownwood, Lake Brownwood, Buchanan Dam: closing, live, electric)

[afterdark80]

That's exactly how it works, I've been watching this lake rise and fall for 25 years. Saw it rise in 1997 and in 2007. This is a different situation. Those events came and went, the lake rose then began to fall with releases and that was it, in 2007 the hot sun was shining on the full lake days after it rose.



This time it is different. Rain continues, lake continues to rise, and significant rain is in the forecast before the lake may or may not lose any significant volume before inflows increase again.


The lake should be drawn down to avoid potential increase to the spillway (714') which would result in uncontrolled releases. Sounds crazy, but if heavy rains dump in the upper basin again, the lake could rise to those levels in less than a day.

Originally Posted by cBach

That's not the way it works. Think of Lake Travis as a water storage tank. You wait until it's full before you start dumping out water.

There are published guidelines on how to handle the releases based on lake level. There is still a good 8 feet (currently 702) before they can increase the release. No other water body has the capacity that Travis does, so we have to use it.

Originally Posted by Trainwreck20

They have the gates open. If they open more, then there is guaranteed significant damage ($$) downstream - Lake Austin (property), Town Lake (road closures and HnB trail damage) and some damage all the way through Bastrop, La Grange, and Columbus. Buchanan is gaining capacity slowly and Travis is losing it slowly. If the rain falls upstream of Buchanan, then it is easier to deal with as the days go by until then. If it falls on the Travis watershed, then they may have to open more gates to deal with it. But they have some breathing space for the moment and you don't want to contribute to flooding downstream, either - if a bunch of rain falls on the coastal area in addition to large releases from Travis, the flooding could be compounded.

They CAN release it now if they PROJECT that the level will exceed 710 (even if it is well below). I think they are projecting right under 710 for now and will wait a bit longer to see if the rain develops. There was significant rain projected for today over Llano/Brady, and it never happened. Also, the 4" of rain is localized, the average across the watershed is <2". The news guys only talk the exciting numbers :/.

Controlled releases now to prevent future catastrophe. They can ONLY project based on current inflows.
If the rain starts, the rise in the lake levels will be quicker than they can release.

[cBach]

Originally Posted by Trainwreck20

Try to build a bigger lake on the plains...it is tough. A huge footprint to get that much water - and a long dam - because they can't manage to make it deep (no real 'valleys' to dam up).

That's not the question I had.

The reservoir is 40k acre feet. They say they can constantly "swap" the volume out by draining and refilling but that the limit is 90k. To me you could swap more often and get a higher acre feet out of it.

[Austin97]

Originally Posted by cBach

Can you explain why it's only 90K acre-feet per year?

Let's say we get rain early in the year, say Jan/Feb and Arbuckle is filled. Then say Mar/Apr is dry and they need water, they could drain 40k out for that. Then let's say it rains in May and they fill it back. That's 80k already. Now say it is drained out Jun/Jul/Aug during the summer heat. Then let's say Sep is rainy and they fill it back, it's now 120k acre feet that has been stored.

Or is there a minimum level in the reservoir that has to be kept? If they have 40k in there and the rice farmers need it (let's say in the summer), can the rice farmers fully drain Arbuckle or will they only let them draw a portion.

I don't see how they get to 90K, seems like it should be far greater than that.

I think the 90 is probably just their guesstimate based on typical rainfall patterns. Im sure some years it will be 120K and some 40, maybe averaging to 90k

[Trainwreck20]

Originally Posted by cBach

That's not the question I had.

The reservoir is 40k acre feet. They say they can constantly "swap" the volume out by draining and refilling but that the limit is 90k. To me you could swap more often and get a higher acre feet out of it.

Ah, sorry, misunderstood. I am guessing that is an estimate based on when they need the water (for farming) - if the farmers need 100k, maybe they are estimating that they will be able to provide 90k of that at the needed times? After the 100k for farming, there just isn't a lot of need for that water, I guess. I suspect the evaporation will be a killer on a wide, shallow reservoir...

[ScoPro]

Guess it's flushing a lot of those Zebra Mussels downstream to contaminate the rest of the Colorado River basin.

[Trainwreck20]

Originally Posted by afterdark80

That's exactly how it works, I've been watching this lake rise and fall for 25 years. Saw it rise in 1997 and in 2007. This is a different situation. Those events came and went, the lake rose then began to fall with releases and that was it, in 2007 the hot sun was shining on the full lake days after it rose.



This time it is different. Rain continues, lake continues to rise, and significant rain is in the forecast before the lake may or may not lose any significant volume before inflows increase again.


The lake should be drawn down to avoid potential increase to the spillway (714') which would result in uncontrolled releases. Sounds crazy, but if heavy rains dump in the upper basin again, the lake could rise to those levels in less than a day.


Controlled releases now to prevent future catastrophe. They can ONLY project based on current inflows.
If the rain starts, the rise in the lake levels will be quicker than they can release.

The can (and do) include projected rainfall in their planning, not just current flows. They aren't going to panic and cause millions of dollars of certain damage to avoid a very small risk (based on rainfall projections) of over-topping the spillway.

You say 'significant rain' is forecast, but it is ~1.2" in the Llano basin (into Travis) over the next 5 days and <1" over the San Saba basin (into Buchanan) during the same time, and almost all of that is four and five days out. The next three days from now are <0.25". After that, a clearing period is forecast. The current situation is not dire. If the forecast changes, then of course, they need to make adjustments to their plan. But they cannot just decide the 1" of rain may turn into 6" in a day and start flooding Lake Austin, Downtown Austin, and La Grange. It almost completely defeats the purpose of the lakes.

Based on current conditions, LCRA now projects that Lake Travis will rise within a range of 704 to 706 feet above mean level today and Saturday. Those projections could change if additional rain falls in the lower Colorado River basin.

Two floodgates are open at Buchanan Dam. Flood releases from Lake Buchanan are being gradually reduced as inflows to Lake Buchanan have declined. Based on current conditions, LCRA projects that Lake Buchanan will gradually rise within a range of 1,108 to 1,020 feet msl today and Saturday. Forecasts for Lake Buchanan and gate operations at Buchanan Dam may change with additional rainfall.

With only two gates open on Buchanan (14k cfs), Travis will start to fall sometime mid- to late-day tomorrow, probably at a rate of about 1" per hour or a little less depending on rainfall. The increase is almost stalled currently at about 0.6" per hour. I wouldn't be surprised to see it zero out before the day is done.

They are definitely trying to get Travis down, as they have reduced the gates on Buchanan to the point that it is rising again. It is less painful to dump Buchanan in an emergency, though, as there isn't the concentration of housing/urban area directly downstream of the dam.

[cBach]

In 16 hours it raised 1 foot to 704. However it's been slowing drastically. Only .01" in an hour.

[mhudson78641]

Originally Posted by ashbeeigh

Well tried. You didn't make it.

Ha I made it had to 183 to 45 to Mopac to 360 to 35. Super fun day.

[cBach]

The traffic didn't clear on 620 until 7:30 PM tonight.

Bullick Hollow closed until Oct 26. 2769 closed until Nov 2.

It's gonna be a long few weeks...

[cBach]

Lake Travis is now on the decline. It peaked at
10/20/18 12:15 PM 704.39

is now at
10/20/18 2:00 PM 704.31

Today is cloudy but dry so today is the day that they can finally drain down the lake a bit.