Proposed flood defences - Rivelin allotments at risk?

[Annie Bynnol]

Warping was a large scale method of draining and fertilizing land used for centuries in Yorkshire and the World before the import and manufacture of artificial fertilizers.

 

The process involved the periodic blocking of river and drains to deliberately flood surrounding land. The silt is rich in nutrients and is absorbed into the soil.

 

Flooding is made worse by human activities such as making parks, footpaths, car parks, roads, cafes, allotments etc., in valley sides and bottoms causing increased damage downstream. Therefore if we try to "beautify" by destroying the natural habitat we have a responsibility to alleviate the problems we cause.

 

Perhaps we should build structures to pound water during flooding - "Dams in our valleys! Never!" I here people say -well they are already there.

 

Two thing learnt from our last big flood:

Don't ever let "environmentalists" play God nature with rivers.

One day another natural dam will be created during a flood at a bottleneck built by humans at a point chosen by physics. If not released quickly the damage by the backup will be slow and expensive while the downstream damage caused by the quick release could be catastrophic.

[Parvo]

 

Two thing learnt from our last big flood:

Don't ever let "environmentalists" play God nature with rivers.

One day another natural dam will be created during a flood at a bottleneck built by humans at a point chosen by physics. If not released quickly the damage by the backup will be slow and expensive while the downstream damage caused by the quick release could be catastrophic.

 

I'm confused

its not the environmentalists playing god here but the council - its not a natural dam if its manmade. and yes it will damage the valley when it floods and if it fails it will devastate downstream. especially all the houses they want to build on the flood plain but it is the council plus ARUP the dam builders who want this. The environmentalists want a lot of small softer options that are sustainable, plus upland and riverside management that is in part replacing what was originally there.

Edited April 12, 2017 by Parvo

[Annie Bynnol]

I'm confused

its not the environmentalists playing god here but the council - its not a natural dam if its manmade. and yes it will damage the valley when it floods and if it fails it will devastate downstream. especially all the houses they want to build on the flood plain but it is the council plus ARUP the dam builders who want this. The environmentalists want a lot of small softer options that are sustainable, plus upland and riverside management that is in part replacing what was originally there.

 

Natural dams are created during floods at bottlenecks from materials brought downstream. In Sheffield they were created at several points and were initially composed of trees and vegetation. These would often break under pressure and release a high energy flow which would sweep riverside furniture and break retaining walls into roads and businesses gathering even more material.

 

The valleys in question have had man made dams for centuries which indirectly and unexpectedly did exactly what the council are planning the new ones to do. Unfortunately most of these dams are now silted up or broken but in the eyes of environmentalists are some form of natural habitat so cannot be touched to provide temporary storage as they did.

Unfortunately we have created a very artificial and unsustainable series of habitats. Lack of money and direction from the new private water companies, councils and the EA and its predecessors made it very easy for the environmentalists to forge ahead with a series of incredibly stupid ideas which prevented river management from scouring out river beds, creating natural flood plains and natural silt banks which the rivers did for free and for thousands of years and with which natural habitats dealt with. When the storm did come what happened to the benches, the duck hotels, the planted reeds and protected trees in the river and on the river bank etc., etc.? They became the avalanche of material that destroyed swathes of natural habitat with their thousands of fish, birds and mammals all the way down to Thorne.

 

Rivers in flood are high energy systems that need to be calmed, nature did it, so why cannot environmentalists learn from their mistakes and work with people to manage things. A hundred tons of silt on Endcliffe Park is not a problem that environmentalists, people and the council cannot deal with to their advantage and at the same time protect wildlife and habitats downstream.

 

Some day in the future we will have to pay to dredge or break the dam at Forge Dam. Why not pay a bit more once to use it as an amenity and a functional temporary storage as it was always intended to be.

Edited April 12, 2017 by Annie Bynnol

[Eater Sundae]

Natural dams are created during floods at bottlenecks from materials brought downstream. In Sheffield they were created at several points and were initially composed of trees and vegetation. These would often break under pressure and release a high energy flow which would sweep riverside furniture and break retaining walls into roads and businesses gathering even more material.

 

The valleys in question have had man made dams for centuries which indirectly and unexpectedly did exactly what the council are planning the new ones to do. Unfortunately most of these dams are now silted up or broken but in the eyes of environmentalists are some form of natural habitat so cannot be touched to provide temporary storage as they did.

Unfortunately we have created a very artificial and unsustainable series of habitats. Lack of money and direction from the new private water companies, councils and the EA and its predecessors made it very easy for the environmentalists to forge ahead with a series of incredibly stupid ideas which prevented river management from scouring out river beds, creating natural flood plains and natural silt banks which the rivers did for free and for thousands of years and with which natural habitats dealt with. When the storm did come what happened to the benches, the duck hotels, the planted reeds and protected trees in the river and on the river bank etc., etc.? They became the avalanche of material that destroyed swathes of natural habitat with their thousands of fish, birds and mammals all the way down to Thorne.

 

Rivers in flood are high energy systems that need to be calmed, nature did it, so why cannot environmentalists learn from their mistakes and work with people to manage things. A hundred tons of silt on Endcliffe Park is not a problem that environmentalists, people and the council cannot deal with to their advantage and at the same time protect wildlife and habitats downstream.

 

Some day in the future we will have to pay to dredge or break the dam at Forge Dam. Why not pay a bit more once to use it as an amenity and a functional temporary storage as it was always intended to be.

 

Forge dam (and all of the other dams on the valley) were built to remain as full as possible to provide a water pressure and flow every day. To act as flood protection the levels would need to be lowered pretty much all the time (although there might be some opportunity to lower the level in readiness for an expected flood event, but only if the rivers were not already at high flow). The current amenity value would be lost if the levels were lowered by much. The issue would be whether or not the required storage volume could be provided by a series of small buffer volumes in each dam.

 

Also, re bib, nature is not guaranteed to calm rivers if left to its own devices. Natural rivers, unaffected by man-made structures, can and do still flood.

[Parvo]

annie your posts seem to be a mass of contradictions and you seem to have a bit of a down on environmentalists.....anyway:

The dams were originally for industry not flood control, but could help now.

They are Sheffields unique history/heritage dating back centuries.

You don't Create a natural flood plain- there aren't natural flood plains in the valleys. its when the rivers slow on flatter land you get flood plains. ie where the developers intend to build. the storage areas are for the benefit of business not wildlife or nature, public protection isn't top either.

Also this thread is not about Endcliffe park - the system suggested there works differently to the system proposed for Rivelin. and is less than a fifth of the size.

Personally I don't have a problem with parks being used for flood storage dams when they are just grassed areas, nor for fields nor on concreted areas (like in Rotterdam )- its what will be lost in rivelin that matters.

Edited April 12, 2017 by Parvo

[Annie Bynnol]

Forge dam (and all of the other dams on the valley) were built to remain as full as possible to provide a water pressure and flow every day. To act as flood protection the levels would need to be lowered pretty much all the time (although there might be some opportunity to lower the level in readiness for an expected flood event, but only if the rivers were not already at high flow). The current amenity value would be lost if the levels were lowered by much. The issue would be whether or not the required storage volume could be provided by a series of small buffer volumes in each dam.

 

Also, re bib, nature is not guaranteed to calm rivers if left to its own devices. Natural rivers, unaffected by man-made structures, can and do still flood.

 

I do not want to be dragged into having to justify isolated examples when the principle is to manage a system - but I stupidly did so here goes.

 

What is the current amenity value of Forge Dam? What will it be in 10 years?

Where have the boats gone?

Where are the anglers?

Where are the fish?

The water is shallow, warm and de-oxygenated.

Something will need to be done soon before it becomes a toxic bog.

 

In practice water level management can be dynamic with early release from the dams as upstream water levels rate rise is detected on saturated uplands.

Repeated downstream this would contribute to reduction in peak flow. These measure repeated in other valleys would be used to contribute to reducing flow- a method already used on a much larger scale in catchments such as the Dee. In Sheffield there would at least be a reduction in the duration and volume of peak flow.

Other measure like using a flood plain for what its for would also contribute.

 

The concerns for catastrophic flooding in Sheffield are real. One scenario is a heavy rain storm after a heavy snowfall on saturated moorland. All of which happen individually, occasionally two events overlap and sooner than later all three (absolutely nothing to do with Global Warming- this about weather, hydrology and statistics in a dynamic system).

 

The storm of 2007 caused flood damage in Sheffield that was largely avoidable had those responsible been so strapped for cash and expertise and had such an easy way out as that provided by the environmentalists. A similar storm today would not cause anywhere near as much damage.

 

Sheffield has the clear responsibility of having to do something and yes they must be challenged at each step, but so do those who claim that controlling 56km² of moorland area is plausible.

[dutch]

Sheffield don is already flowing much better than it did pre 2007 and can handle large volumes of water a lot better.

Flooding is only a risk when soaked moorlands + sudden rare peak rainstorm happen.

 

Like others have said here this is something that can be predicted fairly well and existing reservoirs can be reduced in advance to eliminate risk of flooding free of charge.

[Eater Sundae]

Sheffield don is already flowing much better than it did pre 2007 and can handle large volumes of water a lot better.

Flooding is only a risk when soaked moorlands + sudden rare peak rainstorm happen.

 

Like others have said here this is something that can be predicted fairly well and existing reservoirs can be reduced in advance to eliminate risk of flooding free of charge.

 

But if the moorlands are already soaked, aren't the downstream rivers already likely to be at or near capacity. Would it be possible to then lower the dam levels quickly enough to provide the capacity ready for the peak rainstorm?

 

Edit. I think the reality is more likely to be that the dams will need to be kept part full all the time, ready to cope at a moments notice.

Edited April 13, 2017 by Eater Sundae

[markfor]

If you look at the street gullies most of them are blocked

Where Amey have resurfaced roads they are blocked with tarmac

 

No wonder Sheffield floods:rant:

 

---------- Post added 13-04-2017 at 11:43 ----------

 

If you look at the street gullies most of them are blocked

Where Amey have resurfaced roads they are blocked with tarmac

 

No wonder Sheffield floods:rant:

[Eater Sundae]

If you look at the street gullies most of them are blocked

Where Amey have resurfaced roads they are blocked with tarmac

 

No wonder Sheffield floods:rant:

 

---------- Post added 13-04-2017 at 11:43 ----------

 

If you look at the street gullies most of them are blocked

Where Amey have resurfaced roads they are blocked with tarmac

 

No wonder Sheffield floods:rant:

 

I think that's a good point. I reported such a blocked grating soon after the roads near us were resurfaced. I forgot to go back later to check if they had been cleared.

 

I remember during the floods in 2007 (I didn't realise how long ago it was until people quoted on here) I travelled along the section of the A61, near the turn off towards Huddersfield, where the road collapsed. At the time, there was a river of water running across the road at that point. That part of the road is, in effect, a bridge across a valley - there is an obvious valley in the adjacent land to the north side of the road, which must be funnelling water towards the road. So the road must be on a bridge, or more probably an infilled section, with a culvert piped through.

 

On the day of the flood, for the water to be running across the road the culvert must have been overloaded. That was either because the culvert wasn't big enough for the unusually high flow, or debris had been brought down by the unusually high flow and had blocked the culvert, or the culvert had not been maintained and was already blocked or partially blocked by debris. I hope it was not the last option.