Small Llano River Flash Flood into Lake LBJ.

[oliver2-44 10,077]

I live in a Neighborhood on Lake LBJ, and have lake access through a dredged channel in my back yard.  I've lived here 30 years.

LBJ is a constant level (+/-6") lake built for Hydro-Electric Generation, Recreation, and later as a cooling pond for a steam electric plant. 

It is about an hour North of Austin, Tx. 

It is formed by the joining of the Texas Colorado River (not the Grand Canyon Colorado)  and the 105 mile long Llano river.

The area above Austin - San Antonio is known as the Texas Hill Country. 

The semi-arid somewhat desert looking limestone and granite hills also make it the most flash flood prone area in the US.   

Working at the 6 dams for 40 years, I'm still amazed at how fast a flood can build on the Llano river.

After all those years working numerous floods, its just part of me to arm chair them now.

Thanks to modern internet access to rain, streamflow and lake level gages. 

Last Monday the upper area of the Llano river at Junction and Mason had 5" to 11" of rain on top of 1-2" the previous 3 days. 

They are about 35 miles apart, and their gages peaked about the same time.

The Mason gage rose from roughly 300 cfs to 58,000 cfs, 17 ft,  in 2 hours and fifteen minutes.  It rose 1 foot every 8 minutes.

 

 

The Llano gage is about 30 miles below Mason and 10 miles from where the river enters lake LBJ.  

The area above the lake is ranch land.

This flow entered lake LBJ Tuesday morning.  The river bed and subsequent lake is quite wide.  So the lake level never rose, but flow increased from standstill to a brisk walking speed. 

Two of ten floodgates were partially opened  to pass this into a large storage lake (Travis). The majority of this water passed in about a day.

Lake Travis is an 80 mile long 190 ft deep storage lake.  It was 47 ft down and rose 7 ft.  So this water was appreciated as it supplies drinking and agricultural irrigation water to central and lower central Texas.

While 58,000cfs is a significant flow, back in October 2018 Lake LBJ peaked at 375,000 cfs discharge coming from both the Llano and Colorado. 

All 10 floodgates on LBJ were open for that one. That was the 3rd highest flow on record. 

 

 

[953 nut 56,742]

              Without those man made lakes there probably would have been significant flooding and property damage.           

[Handy Don 13,085]

So would the folks engineering the electrical power grid be open to asking for advice from the folks who engineered the water management system? 

[oliver2-44 10,077]

46 minutes ago, Handy Don said:

So would the folks engineering the electrical power grid be open to asking for advice from the folks who engineered the water management system? 

How dare you make such an implication. You need more than a chair to hide under on that one