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Sounds plausible to me. Which Amite gauge compared to which Manchac gauge?
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The reason I asked is cause the Amite is dropping pretty fast. Bout 1.5"/hr
Because tonight's rain will push more water down Ward Creek, that new water will reinforce pressure toward Spanish Lake. If Spanish Lake continues to fill for hours longer than it would have because of the extra pressure from Ward Creek, water will get into more houses in Ascension. If water from Bayou Fountain is prevented from crossing I-10 for another day because of that Bayou Manchac backflow, and we have another storm like tonight, then more upstream areas around Bayou Fountain will be affected.
Most of the water will exit through the Amite eventually, but the time it takes and the rain events that can happen during that time are important to the people who haven't been hit yet. For example, the upper Bayou Fountain area has dodged a bullet so far. If Spanish Lake is full and Ward Creek keeps getting replenished by daily rains, Bayou Fountain is going to go higher than it is now.
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Why are Ward & Dawson still rising when everything else is falling back to pre-rain pace? And I mean RISING DC up 9", WC up almost 1.5 FEET since the rain. Is it still raining there?
We're seeing this because Dawson and Ward are headwater/upstream gauges. They are much more sensitive to the effects of flash flooding. The downstream gauges are many miles away and will not show flash flooding effects because they measure the stage of a much larger body of water.
The effects of the rain tonight will be to prolong the backflow of bayou manchac across I-10 into the Alligator Bayou/Bluff Swamp/Spanish Lake area. That extra water on that side of I-10, will also cause more Bayou Fountain flooding.
re: The Great Flood of 2016: Fill Out Disaster Forms NOW. Link Inside!
Posted by p15r on 8/17/16 at 7:19 pm to KamaCausey_LSU
The flood prone areas around Bayou Fountain are definitely still in danger of flooding. Use this LINK to see if different areas around there are in the blue flood zone. Most of these areas have been safe because of the water overtopping manchac road and flowing into Spanish lake swamp.
The Bluebonnet gauge has only moved down 3 inches since yesterday afternoon's rain. New rain is falling in that watershed right now. In fact, a flash flood warning is in effect. After this rain has had some time to move down Bayou Fountain, the gauge will probably show a new high at that gauge.
Normal (heavy and short) rains that usually just drain off into ditches now have no where to go. The ditches and bayous and swamps are full. So the flat areas near Bayou Fountain are much more likely to flood simply because the NEW water has nowhere else to go.
Add to the above the fact that the Spanish Lake swamp is filling up. Once that happens any new rainwater on this side of I-10 will not be able to go there. Over the last couple of days the water flowing from Bayou Manchac into Spanish Lake swamp has been the only reason that these low areas around Bayou Fountain have not already flooded.
Eventually the water will all go to the Amite. But it may be days before it gets down to safe levels, and if we get a lot of new rain in that time, things will get worse.
The Bluebonnet gauge has only moved down 3 inches since yesterday afternoon's rain. New rain is falling in that watershed right now. In fact, a flash flood warning is in effect. After this rain has had some time to move down Bayou Fountain, the gauge will probably show a new high at that gauge.
Normal (heavy and short) rains that usually just drain off into ditches now have no where to go. The ditches and bayous and swamps are full. So the flat areas near Bayou Fountain are much more likely to flood simply because the NEW water has nowhere else to go.
Add to the above the fact that the Spanish Lake swamp is filling up. Once that happens any new rainwater on this side of I-10 will not be able to go there. Over the last couple of days the water flowing from Bayou Manchac into Spanish Lake swamp has been the only reason that these low areas around Bayou Fountain have not already flooded.
Eventually the water will all go to the Amite. But it may be days before it gets down to safe levels, and if we get a lot of new rain in that time, things will get worse.
re: The Great Flood of 2016: Fill Out Disaster Forms NOW. Link Inside!
Posted by p15r on 8/16/16 at 9:40 am to LSUweights
This Bluebonnet gauge (if it is to be believed) shows a drop of only 5/100s of a foot since early Monday morning. That is a good sign, but I would still be watching it closely if I lived in that area.
LINK
LINK
re: The Great Flood of 2016: Fill Out Disaster Forms NOW. Link Inside!
Posted by p15r on 8/16/16 at 9:28 am to TigahFan4Life
This depends on a number of factors: 1) how fast the Amite at Manchac Point recedes; 2) how fast the water can get under the I-10 bridge; and 3) how much more water the Spanish lake basin can hold.
My guess is that the Spanish Lake basin can handle most of the water. But the water in BF really doesn't have to rise much more to cause flood problems for some people (those between Highland and Burbank, for instance.) The gauge at Bluebonnet is already over 15 ft. And that water and the water above it will have no where to go for a while.
My guess is that the Spanish Lake basin can handle most of the water. But the water in BF really doesn't have to rise much more to cause flood problems for some people (those between Highland and Burbank, for instance.) The gauge at Bluebonnet is already over 15 ft. And that water and the water above it will have no where to go for a while.
LSUJuice you are correct. The Spanish Lake swamp "is hydraulically connected to Bayou Manchac," but the natural flow of water is controlled by the Alligator Bayou gate and Manchac levee system. The gate is set at a certain level by Iberville parish. My guess is that it was fully closed for this flood event.
And, yes, the gauges make perfect sense. You have a huge amount of water on the east side of I-10, because of the Amite and Ward Creek, and much less on the west side (Bayou Fountain, Spanish Lake). The most important pinch point for the whole system is the narrow canyon that the water has to go through under the I-10 bridge. The water from the east side wants to go west but the volume is slowed by the lack of space in that canyon.
And, yes, the gauges make perfect sense. You have a huge amount of water on the east side of I-10, because of the Amite and Ward Creek, and much less on the west side (Bayou Fountain, Spanish Lake). The most important pinch point for the whole system is the narrow canyon that the water has to go through under the I-10 bridge. The water from the east side wants to go west but the volume is slowed by the lack of space in that canyon.
Spanish Lake is separated from the Bayou Manchac system by the lock/gate system at Alligator Bayou and the Manchac Road levee. That levee system is controlled by Iberville Parish. Iberville Parish (St. Gabriel/Bayou Paul area) wants to keep as much Baton Rouge water out of Spanish Lake as possible. In this flood, their system failed because their levee was overtopped. Otherwise, they would have been happy to keep the flood gate closed, which would keep the EBR water out of Iberville.
Once the water recedes on the Bayou Manchac side, you will see the Iberville authorities open the gate and let the water back out of the lake into Bayou Manchac.
There was a recent controversy over the proper lake levels a few years ago. The Alligator Bayou swamp tour people wanted high water in the lake for their boat tours. Other landowners in Iberville wanted low water in the lake for flood control and a wetland mitigation bank. The "other landowners" won, which is great for Bayou Fountain in this flood because the lake was almost empty before the rains came and it could hold more water after the overtopping.
Having said all of that, there is still danger of more flooding in the Bayou Fountain basin. The water elevation at the I-10 bridge is around 20ft right now. The gauge at Alligator bayou is 11.65. The water is moving slowing through the narrow channel/canyon created when the interstate bridge was built. There is an 8ft+ elevation differential between the two sides of Bayou Manchac separated by I-10. Only when that balances out will the flood risk be completely over for the Bayou Fountain side of things.
Once the water recedes on the Bayou Manchac side, you will see the Iberville authorities open the gate and let the water back out of the lake into Bayou Manchac.
There was a recent controversy over the proper lake levels a few years ago. The Alligator Bayou swamp tour people wanted high water in the lake for their boat tours. Other landowners in Iberville wanted low water in the lake for flood control and a wetland mitigation bank. The "other landowners" won, which is great for Bayou Fountain in this flood because the lake was almost empty before the rains came and it could hold more water after the overtopping.
Having said all of that, there is still danger of more flooding in the Bayou Fountain basin. The water elevation at the I-10 bridge is around 20ft right now. The gauge at Alligator bayou is 11.65. The water is moving slowing through the narrow channel/canyon created when the interstate bridge was built. There is an 8ft+ elevation differential between the two sides of Bayou Manchac separated by I-10. Only when that balances out will the flood risk be completely over for the Bayou Fountain side of things.
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