Question on basin erosion

[Ken123]

Sketch shows an example of the South Amite River in Louisiana.

Flood waters flowed down this basin (1 mile wide) and the river during the Baton Rouge flood a few months ago. Near Baton Rouge level was 17 ft above sea level and near the lake 26 miles downstream it was 4.5 ft ASL. The basin is 1 ft ASL from Baton Rouge to the lake and all the housing is 10 ft or higher ASL and essentially there is no housing in the basin.

I am looking at select removal of trees (10-20% ?) in the forested area of the basin between the river meanders but not along the river banks and this will minimize river erosion because most trees will remain and major floods are few. Seems like there will be minimum erosion of the basin and river thus of no concern.

Is my concept a concern for erosion of the basin or river? And what concerns would there be?

Google Maps

https://www.google.com/maps/@30.3324,-90.79567,10z

https://www.google.com/maps/@30.3939841,-90.9605319,84018m/data=!3m1!1e3

[studiot]

I'm having a little trouble reconciling the left hand picture with the satellite view.

 

The intention on the left hand sketch is clear enough.

 

But where are these meanders on the sat view?

What is the wiggly river on the left half of the sat view ?west? of Baton Rouge?

Which way are the rivers flowing?

Why is it necessary to remove natural berms and levees? Surely that makes a greater flood risk than removing trees?

 

Is the intention to create a new waterway?

[Ken123]

But where are these meanders on the sat view?

Ken: Telescope in the sat view and they will appear.

 

What is the wiggly river on the left half of the sat view ?

Ken: It is the Amite River. It splits into the south Amite River and the Diversion Canal going south and the South Amite River which is north of the diversion canal. It is essentially a dead river because the diversion canal has taken most of the flow.

 

west?

Yes

of Baton Rouge?

South west

 

Which way are the rivers flowing?

South east to Lake Maurepas.

 

Why is it necessary to remove natural berms and levees?

Ken: The berm held back water flooding Baton Rouge and Congress gave 500 million dollars for the flood victims Actual cos ti 2 billion.

 

Surely that makes a greater flood risk than removing trees?

Ken: Removing the berm which is at the lower end of the basin will relieve levels and flow a few miles further into Lake Maurepas,

 

Is the intention to create a new waterway?

Ken No, but to prevent another disaster flood.

 

Thanks for reviewing.

 

 

 

[studiot]

Thanks for the answers Ken.

 

I will have to think about what you said.

 

Have you read Brian Fagan "The attacking Ocean" on the subject?

[Ken123]

No, I have not read it but looked at a review of the book and seems very interesting. Lately I have been working with Mississippi River Morphology and diversions. Found a concern and sent my calculations to the CORPS and they did not respond. Then Sent to a private university and the professor does the calcs for the corps. He agreed with me and below is a summary.

 

Wetlands Restoration Engineers have not considered Mississippi River hydraulics for a future possible diversion, the Third Delta Conveyance Channel and I have performed necessary calculation showing a grave concern with the diversion and reviewed results with University discussions. Also a west Third Delta conveyance channel may be considered because of a need for depositing sediment west of Bayou Lafourche. Please Contact Coastal Protection and Restoration Authority (CPRA) asking about this concern.

 

Third Delta Diversion will result in an unstable Mississippi River because river slope will increase when the diversion is added and this increased slope will add levee undercutting capability. The First Law of Thermodynamics (Conservation of Energy) was applied for calculating Mississippi River power associated with the diversion. USGS river discharge/stages were used for the calculations giving sobering results and our Government is listing this diversion in recent publications.

 

The Concern: When the diversion is operated a large increase in Mississippi River power upstream of the diversion will be generated increasing scouring of river peak meander points causing levee failures.

 

Calculations are performed associated with the Mississippi River/Third Delta Diversion location based on height of river change when the diversion added. One third (1/3) river flow will be diverted and 2/3 will continue in the normal channel. Height associated with river flow minus historical river height associated with 2/3 river flow is height change with the diversion addition. This height change causes a need for river length to increase upstream of diversion and generates large power increases upstream of the diversion.

 

River length increase

River slope post-addition of the diversion is 0.223 feet/mile. When the diversion is added river length upstream of the diversion would need to increase 34 miles to keep this slope and is based on river draw down (Height drop) of 8 feet when the diversion is added (8 feet/(0.223 feet/mile) = 34 miles).

Thanks for the answers Ken.

 

I will have to think about what you said.

 

Have you read Brian Fagan "The attacking Ocean" on the subject?

I want to mention I sent my flood drainage concept to a professor of civil engineering and he said the erosion would be a concern.

 

Seems like the professor may have read my statement too fast and did not understand it giving a reply that is not based on my statement. The confusion of basin and channel seems very unclear. The statement and reply:

My statement:
Two solutions for flooding near Baton Rouge, La. are to remove trees restricting flow in the Lower Amite River Basin and remove man-made HW 22 flow restriction which is located on the basin's outlet thus increasing basin's velocity. Select, remove and sell trees in the basin from the river's mouth to north Baton Rouge and this will reduce flood crests with flow moving quickly along the 36+ mile basin. Because this is a public flood drainage concept hopefully tree removal would not need to meet wetlands mitigation cost. Water elevation will not build at an existing 5 ft high earthen HW 22 restriction because it will be removed and replaced with a HW 22-0.5 mile long elevated open bottom highway allowing flood water to flow underneath quickly releasing into Lake Maurepas.

Reply:
River systems do not work in a way similar to pipes. So, cutting trees would not necessarily lead to the reduction of channel roughness. The removal of trees would cause more channel bank erosion, resulting wider, shallower, or more sinuous channels. Therefore, channel roughness would not necessarily decrease following the removal of trees. 3. My overall conclusion about your concepts is that they would not work in the way you envisioned.

FYI, I have added to my statement for detail clarity:Select removal of trees (10-20% ?) in the forested area of the basin between the river meanders but not along the river banks will minimize erosion because most trees will remain and major floods are few.

[studiot]

The geologically recent (holocene) history of the whole area has been one of shifting channels.

 

 

Looking at the level/gradient figures you gave, along with some have from elsewhere I note how low and how flat everything is.

 

In these circumstances European experience, both in Holland and where I live in Somerset has been that the level of forestation makes little difference to the disposition of water, especially in flood conditions. Unlike the Mississippi, the Rhine delta has been stable for a long time.

 

Manual control is essential in the form of drainage channels and flood protection works in the form of levees and berms.

Somerset has suffered over the last couple of decades from failure to dredge the channels, leading to the substantial floods in 2015.

Approximately 30% of Somerset is at or near sea level, as is a greater % of Holland.

In both areas the both the main and minor river channels are artificial and sometimes above local ground level.

Water has been pumped into them since Roman times.

 

A big difference from the Gulf is the outlet conditions.

Both the North Sea and the Irish Sea have exceptionally large tidal ranges, so the drainage channels are gated and drained at low tide in normal circumstances.

 

The incoming water must have somewhere to go.

 

In exceptionally high tide conditions, with a strong westerly wind also piling water, the draining rivers cannot drain to the sea so incoming water backs upstream and inland and floods occur.

Because of the large swath of low lying land the floodwater spreads out unless constrained by defences.

 

I fear that in the case of Baton Rouge, local drainage measures will be subsumed in the regional situation so you are left with protection defences as we are.

[Ken123]

Please see updated sk and wording. Essentially list with whole basin 10-20 % select cut trees and the velocities will be less.

 

Nine (9) locations with trees along the South Amite River, without roads, can be select cut (10 - 20%) for a 5,000+ Ft wide path. When the river is overflowing its banks there will be a wide path for flood waters to travel. Flow will stay in the river banks during low floods but for high floods over the banks, this path will quickly flow flood waters to Lake Maurepas. A hydraulics review needs to determine if a channel will be cut and if so what will be the effects on the river. In short the river will achieve drop per foot before a flood by flowing along its winding banks with land build up at channel intersections. Please see below video where steam channelization simulation was done and it returned back to its winding path. Note: Video has the meander stream completely blocked but the South Amite River may be slightly blocked and if(?) a shallow channel is cut then after a flood the river meander should not be cut off thus giving way for quick recovery of the meander to the same location with drop per foot as before a flood. The sketch should prevent a premature meander cutoff because the entire basin has an even distribution of trees removed. When a meander cutoff happens it will be a natural cutoff and acceptable.

 

Stream Simulation Tables

BYU Stream Table

REF: Emriver channelization, large meanders, packed sediment

Emriver channelization, large meanders, packed sediment

...This is a time-lapsed Emriver channelization demonstration in which a meander loop is cut off. In this case the channel length between two points is more than halved, so slope would increase by a factor of 2+..

Edited December 13, 2016 by Ken123

[Ken123]

The geologically recent (holocene) history of the whole area has been one of shifting channels.

 

amite1.jpg

 

Looking at the level/gradient figures you gave, along with some have from elsewhere I note how low and how flat everything is.

 

In these circumstances European experience, both in Holland and where I live in Somerset has been that the level of forestation makes little difference to the disposition of water, especially in flood conditions. Unlike the Mississippi, the Rhine delta has been stable for a long time.

 

Manual control is essential in the form of drainage channels and flood protection works in the form of levees and berms.

Somerset has suffered over the last couple of decades from failure to dredge the channels, leading to the substantial floods in 2015.

Approximately 30% of Somerset is at or near sea level, as is a greater % of Holland.

In both areas the both the main and minor river channels are artificial and sometimes above local ground level.

Water has been pumped into them since Roman times.

 

A big difference from the Gulf is the outlet conditions.

Both the North Sea and the Irish Sea have exceptionally large tidal ranges, so the drainage channels are gated and drained at low tide in normal circumstances.

 

The incoming water must have somewhere to go.

 

In exceptionally high tide conditions, with a strong westerly wind also piling water, the draining rivers cannot drain to the sea so incoming water backs upstream and inland and floods occur.

Because of the large swath of low lying land the floodwater spreads out unless constrained by defences.

 

I fear that in the case of Baton Rouge, local drainage measures will be subsumed in the regional situation so you are left with protection defences as we are.

 

Flood size threat is growing by the year. For the Amite River basin tree diameter is growing yearly and I need to review further. If the trees doubled in diameter in the last 10 years then resistance of the basin has doubled or more preventing flood waters from draining as quick as needed. The next 10 years would bring a doubling of tree resistance again and Baton Rouge flooding will become more frequent and greater crest heights will be realized. Will review tree diameter growth and share more.

 

Concept example:

Also please see below USGS graphs showing 40 hours for the flood crest to travel from Port Vincent to Maurepas. The resistances to water flow is air, land, and trees and trees is the only variable that can be changed. Removing trees to have a tree area similar to 10 years ago would help drainage greatly because of less tree area in the basin than present and there will be no added erosion than was 10 years ago.

 

Below picture of river levels are at Port Vincent, French Sediment and near Maurepas. This shows a spillway "only" may not help drainage and select removal of trees will be needed. It took about 40 hours for the crest to arrive at Maurepas from Port Vincent, April 15, 0:20 to April 17, 0:12 traveling 115K ft is 0.8 ft/s

Please see below two replies with graphs.

Ken

Please see two replies with USGS graphs.

The geologically recent (holocene) history of the whole area has been one of shifting channels.

 

amite1.jpg

 

Looking at the level/gradient figures you gave, along with some have from elsewhere I note how low and how flat everything is.

 

In these circumstances European experience, both in Holland and where I live in Somerset has been that the level of forestation makes little difference to the disposition of water, especially in flood conditions. Unlike the Mississippi, the Rhine delta has been stable for a long time.

 

Manual control is essential in the form of drainage channels and flood protection works in the form of levees and berms.

Somerset has suffered over the last couple of decades from failure to dredge the channels, leading to the substantial floods in 2015.

Approximately 30% of Somerset is at or near sea level, as is a greater % of Holland.

In both areas the both the main and minor river channels are artificial and sometimes above local ground level.

Water has been pumped into them since Roman times.

 

A big difference from the Gulf is the outlet conditions.

Both the North Sea and the Irish Sea have exceptionally large tidal ranges, so the drainage channels are gated and drained at low tide in normal circumstances.

 

The incoming water must have somewhere to go.

 

In exceptionally high tide conditions, with a strong westerly wind also piling water, the draining rivers cannot drain to the sea so incoming water backs upstream and inland and floods occur.

Because of the large swath of low lying land the floodwater spreads out unless constrained by defences.

 

I fear that in the case of Baton Rouge, local drainage measures will be subsumed in the regional situation so you are left with protection defences as we are.

Please see two recent replies with USGS graphs.

Edited December 13, 2016 by Ken123

[studiot]

Where does the flood water come from?

[Ken123]

Where does the flood water come from?

Most from north of Baton Rouge and south Mississippi. USGS flow was at 52 KCFS but river natural levee was topped and flow could have been greater than 80K CFS?

[studiot]

Most from north of Baton Rouge and south Mississippi. USGS flow was at 52 KCFS but river natural levee was topped and flow could have been greater than 80K CFS?

 

Sorry, I really meant what are the circumstances leading to sufficient water to cause flooding?

 

Remember I noted this to be a regional rather than a local problem and I still think this.

 

These are some typical UK local solutions.

 

[Ken123]

 

Sorry, I really meant what are the circumstances leading to sufficient water to cause flooding?

 

Remember I noted this to be a regional rather than a local problem and I still think this.

 

These are some typical UK local solutions.

 

amite2.jpg

The circumstances were mostly an air flow from the Gulf of Mexico with moist air but I do not know the exact reason for the high rainfall. This was an 500 year flood event.

 

Yes, it is a regional concern. Please see basin map link.

https://la.water.usgs.gov/images/AmiteBasinFloodMap.gif

 

Solution C is being used with a diversion canal below the Amite River but the flood was much greater than the diversion. Solution B seems like what I am suggesting with removing tree area back to same tree area 30 years ago. Because of wetlands laws the trees have not been logged in 30+ Years. Will send this concept to the professor.

Edited December 14, 2016 by Ken123

[Ken123]

Wetlands Law has allowed trees to grow in the Amite Basin for more than 30 years and brought a $2 billion disaster to our country.

Graph shows:
If tree diameter growth is 0.5 inches per year for 30 years and the basin width is 4,000 ft, then tree area has increased 325 ft in the basin for 1.5 tree/ 20 ft of basin width or 500 ft for 2 trees/ 20ft.

This growth has greatly restricted flood drainage in the basin and will generate more floods in Baton Rouge as the trees grow in diameter. Removing and selling enough trees to eliminate this increase will help flood drainage and there will be no extra erosion as compared to tree area 30 years ago.

Anything I missed or incorrect?

Edited December 14, 2016 by Ken123