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Proposed flood defences - Rivelin allotments at risk?

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All of the rivers except the Sheaf are supplied by reservoir water upstream; a quick look on a map will highlight this quite starkly.

Yes. Of course, this is no coincidence. Reservoirs are almost always constructed where it's possible to accumulate rainfall or ground water springs on ground higher than the residential areas which they serve.

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I don't understand what you're trying to say.

 

Where does the water treatment work's reservoir get it's water from?

 

Clearly it gets it from the rivers but you seemed to be implying that the reservoirs are there to supply water only when the river levels have got so low that you can't take water direct from the rivers anymore. Apologies if this wasn't what you were saying.

 

You are proposing that the reservoir level be dropped by a metre. If this is done, then at dry times the treatment works will run out of water earlier.

 

Did you not read my last comment when I specifically stated this was not the case and asked why would spare capacity in the reservoir be needed in a dry spell?

 

 

Now, what do you propose to do in times of heavy rain which would currently result in so much water flowing down the rivelin valley that it would flood further downstream? Do you propose to store some of this excess water in the existing reservoir at the water treatment works? If so, how would you get it into the reservoir?

 

I also dealt with this in my last post to some extent. There is no reason why all of the city's reservoirs, when they've filled to within a metre of the brim after a dry summer, can't be held at that level under normal climatic conditions throughout the autumn, winter and spring. The city is in the very fortunate position that all the rivers flow west to east and we get most of our heavy rain from the west (the Atlantic). This means you can release excess water into the rivers well in advance of a storm coming and the water will be out in the Humber before the weather system arrives. Even during longer intense periods of rain, if you make sure you keep dropping the reservoir levels during any drier interlude then you're continually providing spare capacity............and on a level that makes the proposed dam building's water retention look insignificant.

 

---------- Post added 10-10-2016 at 17:51 ----------

 

Yes. Of course, this is no coincidence. Reservoirs are almost always constructed where it's possible to accumulate rainfall or ground water springs on ground higher than the residential areas which they serve.

 

Yes, so we already have an impressive and extensive system of flood defences sitting there already.

Edited by six45ive

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Clearly it gets it from the rivers but you seemed to be implying that the reservoirs are there to supply water only when the river levels have got so low that you can't take water direct from the rivers anymore. Apologies if this wasn't what you were saying.

 

 

 

Did you not read my last comment when I specifically stated this was not the case and asked why would spare capacity in the reservoir be needed in a dry spell?

 

 

 

 

I also dealt with this in my last post to some extent. There is no reason why all of the city's reservoirs, when they've filled to within a metre of the brim after a dry summer, can't be held at that level under normal climatic conditions throughout the autumn, winter and spring. The city is in the very fortunate position that all the rivers flow west to east and we get most of our heavy rain from the west (the Atlantic). This means you can release excess water into the rivers well in advance of a storm coming and the water will be out in the Humber before the weather system arrives. Even during longer intense periods of rain, if you make sure you keep dropping the reservoir levels during any drier interlude then you're continually providing spare capacity............and on a level that makes the proposed dam building's water retention look insignificant.

 

---------- Post added 10-10-2016 at 17:51 ----------

 

 

Yes, so we already have an impressive and extensive system of flood defences sitting there already.

 

I missed the second paragraph of your earlier post, as I was responding to the first paragraph as you added the second paragraph.

 

I now understand what you mean regarding emptying the reservoir just before the storm arrives. Yes, that makes sense, assuming it can be emptied quickly enough, and provided that the river levels are not already too high. Extended periods of heavy rain may mean that there's no opportunity to drop the level - but I suppose the same could be said of the proposed barriers.

 

However, I still think that it is likely to be necessary to fill the reservoir (to avoid flooding) much faster than the current design allows it to be filled. The two new flood areas would be able to be filled as quickly as the flow arrives.

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I missed the second paragraph of your earlier post, as I was responding to the first paragraph as you added the second paragraph.

 

Ok. Cheers.

 

I now understand what you mean regarding emptying the reservoir just before the storm arrives. Yes, that makes sense, assuming it can be emptied quickly enough, and provided that the river levels are not already too high. Extended periods of heavy rain may mean that there's no opportunity to drop the level - but I suppose the same could be said of the proposed barriers.

 

Yes precisely. Don't forget that the June 2007 event came after one of the wettest winters on record and then there was intense heavy rain which caused heavy flooding in Barnsley during May further saturating the ground and then a similar intense system hit the area causing the devastation in Sheffield (and Barnsley again) on June 25th.

Since then there has been extensive work to clear the rivers of debris and to increase the flow rate of the rivers to move the water away quicker as well as de-silting. For example, Malin Bridge where the Rivelin meets the Loxley, has had much of the river bed lowered by over a metre and water now flows freely under all the arches of the bridges rather than just one which was the case in 2007. Compare the two photos. The first taken just after the vegetation had been cleared but before the river bed had been scraped.

http://www.sheffieldhistory.co.uk/forums/uploads/monthly_08_2009/post-1014-1251205405_thumb.jpg

 

This one taken just after. You can clearly see how the bed level has dropped and the de-silting has created more capacity at the sides with a mill pond on the left revealed.

http://s0.geograph.org.uk/geophotos/01/54/00/1540057_74b59fbc.jpg

 

It's arguable that, if this had been the state of the rivers in 2007, then large parts of the city centre and the Lower Don Valley wouldn't have flooded to anywhere near the extent they did....and that's without any other defences being built in the meantime. A better and more nuanced management of all the reservoirs upstream combined with more tree planting further up the valleys and the re-creation of thousands of acres of peat bogs on the moors should make it a near impossibility that flooding on the scale of 2007 could ever happen again in Sheffield.

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Yes precisely. Don't forget that the June 2007 event came after one of the wettest winters on record

Coo, do you have a fortune-telling business?

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Have said it before but Don runs much more efficient faster better now. Lots of flood risk has been sorted already.

Some of the expensive extras done and suggested are unnecessary panicky worry actions done by people who will never feel safe or secure even if they concreted every valley of Sheffield off.

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Reading this government report, it's clear that Sheffield is, once again, being used as a testing ground to see what works and what doesn't for other, er............shall we say............more important cities - surreptitiously under the guise of regeneration.

Page 25 of this document highlights Sheffield as the testing ground.

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/551137/national-flood-resilience-review.pdf

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Reading this government report, it's clear that Sheffield is, once again, being used as a testing ground to see what works and what doesn't for other, er............shall we say............more important cities - surreptitiously under the guise of regeneration.

Page 25 of this document highlights Sheffield as the testing ground.

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/551137/national-flood-resilience-review.pdf

 

You don't need to read page 25 of the report to find that out; it was in the second paragraph of the Star's big story about it: http://www.thestar.co.uk/news/sheffield-to-get-the-same-level-of-flood-defences-as-london-by-2021-1-8116388 and in any case, there's nothing wrong with being involved in a pilot. The point of any pilot is that you do a small initial roll-out, paying lots of attention to what works easily and what is more difficult to implement; it's not an experiment to see whether the flood defences work at all, they know the proposed defences will work, the pilot is about finding out how practical they are to put in.

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The following information is from the website and the public consultation events:

 

Flood storage areas have been widely used around the country. They would not require the removal of all the trees in the area that could temporarily be flooded. Trees would have to be removed under where the grassy earth embankment would be built. Footpaths would remain, but may need rerouting around or over the embankment. The area would not be fenced off and would be designed for safe access under normal conditions.

 

Particularly for the parkland ones, like at Endcliffe Park, they would include improved land drainage so that the rest of the time the parks have a better surface and condition for normal uses, like cricket, festivals, play areas. Examples of this include at Todmorden flood scheme.

 

Information about all the many options being proposed at this stage are on the website: http://floodprotectionsheffield.com/pages/consultation. Find the options maps, and click on the option icons to get more information about each one.

 

Please be sure to give your responses - even if just for the sites that interest you - to the online questionnaire by 31st October. https://sheffield.citizenspace.com/place-business-strategy/upper-don-and-sheaf-flood-defence-consultation

 

I asked, above, what would be done to the area which would be subject to flooding. I presume it would need to be cleared of trees, walls, hedges, allotment stuff such as huts, greenhouses etc, otherwise this would become entangled with river borne debris each time it floods. I expect they would need to leave it with a smoothish finish, such as grass or bare earth or some other compacted surface.

 

Once flooded and then drained, the area would become wet and muddy/slippery. Is seems likely that they would have to detour all the paths to put them above the top flood level. From a H&S viewpoint, I wonder if they would feel it necessary to remove all lower, riverside paths to avoid having situations where paths just disappear under floodwater and where people might slip.

 

There is a gate at Rother Valley which can operate to hold back water (to prevent flooding downstream towards Rotherham), but that just increases the area and depth of existing lakes (wild life and fishing lakes, I think). I doubt that the depth increases by much, and certainly not by 10m. The sluice gate is under an access bridge, IIRC, and would probably only add around 1 to 2 metres upstream depth, at most. Does anyone know how they manage lakeside/riverside paths in that case?

 

The more I think about this idea for Rivelin, and now I understand how deep it would be, the impact would be large. As noted above, this would be a full blown dam. It's a pity they couldn't use lots of small impounding dams such as all the little dams which were/are already there from its old industrial days, by keeping them all just a few metres lower, each, but allowing for extra depth and volume during heavier river flow.

 

---------- Post added 10-10-2016 at 06:43 ----------

 

 

The link above leads to another link which shows more detail for the two Rivelin dams. I don't want to derail this thread about Rivelin, but I am interested in also looking at other rivers (in particular the Porter, which is part of the Sheaf proposals). Can anyone point me towards more details on the other schemes ie something similar to the Rivelin document posted by WalkeyIan.

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and in any case, there's nothing wrong with being involved in a pilot. The point of any pilot is that you do a small initial roll-out, paying lots of attention to what works easily and what is more difficult to implement; it's not an experiment to see whether the flood defences work at all, they know the proposed defences will work, the pilot is about finding out how practical they are to put in.

 

There is when a large part of what's being proposed will have such a major impact on large areas of the city.

Historically this is one of the main reasons why Sheffield is the disjointed place it is; the crass result of being the test bed for many an architect or urban planner that wants to foist something new on the city and it's people. Hey, after all they're only Sheffielders - thick working class people who'll accept anything you'll throw at them that has the key words 'jobs' and 'regeneration' attached.

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There appears to be very little understanding of:

a) How Sheffield is supplied with drinking water.

Practically none comes from Derbyshire, although some is available from Derwent and Howden via Rivelin most of the is sold to the cities of the east Midlands at a premium.

Some of the moorland reservoirs used to directly supply a considerable minority of our water some are used to control summer flow in the Don.

Most are now used to store "clean" and "treated" water and because the peaty, acidic and limited in supply of moorland water which is therefore high in metallic content, is not as economic to treat except at times of low water supply from our main supply source which is the North Yorkshire river Derwent.

 

b)How we have created the problem and how we manage it.

Before and during the industrial revolution the western valleys provided natural storage during flooding. The original wooded valleys became very absorbent as natural temporary ponding took place because of fallen trees and collapsing banks. Works and their later abandonment during the industrial revolution created a man made equivalent.

In modern times, many of these valleys have become "hard" surfaces with run-off increasing in "speed" and volume.

These "hard" surfaces range from houses, roads, paths, car parks, cafes, pools, play areas and grassland. The associated drainage work has also lead to more run off.

 

 

We all want to enjoy or valleys but we can't bring back the water buffalo, the beavers and the water meadows neither can we allow the ignorant environmentalists to contribute to another flood like they did in 2007.

 

For those of us who have lived in western Britain where sacrificial flooding has always been the norm, taking steps like the current plan do not appear too drastic.

There is a real opportunity here to create environments within this plan that will enrich our surroundings -even with buffalos, water meadows and beavers helping to manage a floodable wetland.

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I have just seen this information and not quite sure how many others have seen it,

 

Rivelin Valley Conservation Group

6 October at 14:15 ·

 

In response to your front page article on Wednesday and the comment included on page 11 by Cllr Bryan Lodge I feel it necessary to state that it was never the intention of The Rivelin Valley Conservation Group to be alarmist but simply to ensure that because the consultation was started in August when most people

are on holiday that Sheffielders were fully acquainted with the facts.

 

If the councillor had attended one of the consultation meetings and asked the pertinent questions our representatives did he would know that the computer model used by the Council's consultants indicated that in Rivelin's case the 2 impounding

reservoirs would need to hold back a volume of water that would mean a depth of some 10 metres at the embankments, 80 metres wide and running back up the river and Nature trail for several hundred yards Holding back this pressure of water will involve the engineering construction of a full reservoir dam and with a safety element to ensure no overtopping this would mean an 11 metre

embankment.

 

This water would be held until the flood risk had subsided when it would be released gradually to allow for re-use. Should the Rivelin scheme proceed we are faced with a massive obstruction to people being able to walk freely up the most accessible easy-going countryside walk in the City, but with the safety hazard of a 10 metre deep unfenced reservoir. The impact on the landscape of

these structures and the drowned debris strewn areas where the impounded water had been will be enormous.

 

Although the scheme may be funded through government grant I would question whether the Council has any contingency plans for the subsequent maintenance of reservoir dams, the complicated sluices and their gates and the reinstatement of footpaths and retaining walls after each flood.

 

The wildlife corridor so vital to the movement and interaction of the

valley's wildlife would be severed by the dams and sluices and significant areas temporarily inundated by the impounded waters. The wildlife of a pennine river and its banksides is very special and unique to that particular habitat.

 

To suggest days, if not weeks, of interrupting the flow and drowning of areas irrespective of nesting seasons for birds and small mammals, the sequence of insect development which is specific to different water conditions and the flowering times of our native flora is nothing short of criminal. There has to be an alternative to a complete obstruction of the river and Nature trail.

 

Alternatives include better maintenance of the river systems, particularly at confluences and bridges, the repair of some of the existing mill dams, construction of new impounding dams which do not interrupt the river and footpath networks and a conversation with Yorkshire Water regarding the use of Rivelin reservoirs.

 

The drawing down of the Lower Dam by 1 metre would more than compensate for the volume of the scheme being suggested and would have minimal impact on the supply to the treatment Works.

 

The facts put together by our professional experts cannot be disputed by councillors and we hope Sheffielders will use the consultation process to make their views on the value of each affected valley known. The viability of alternative schemes does need to take full account of the Value, even if unquantifiable, of our ability to access and enjoy the wild and industrial heritage that makes Sheffield the unique City it is.

 

Roger Kite M.B.E.

Ex Chairman and currently Conservation Adviser to Rivelin Valley Conservation Group

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