The mission statement of the Trust is to conserve, protect, rehabilitate and improve the Rivers Don, Dearne and Rother and the associated non-tidal and tidal systems that might influence their fauna, flora, water quality and hydrology. Beyond this we aim to promote these rivers as assets that enrich people’s lives, whether through experience of their rich natural and built heritage, or as a pleasant environment that enhances recreational or everyday activities. We recognise the need to protect people from flooding and also to foster a vibrant economy in the catchment. The 2007 floods dealt a blow to many businesses in Sheffield and it is essential that similar events do not occur in the future. We are keen for flood risk to be reduced through the implementation of sustainable solutions that not only protect against flooding but also provide multiple additional environmental, economic and social benefits.
The Trust is pleased with the initiative being taken by SCC in developing the Sheffield Flood Protection Programme, and also that individuals and organisations have been given opportunity to contribute their views on potential options. Given the scale of the challenge flood prevention poses we realise that difficult decisions may need to be made. However, we are concerned that the programme has prematurely decided on orthodox hard engineering solutions, and is considering what we believe to be some major retrograde measures. In addition we feel that the proposed measures fail to address the Government’s requirement to provide multiple benefits in association with flood management capital expenditure. We are troubled by the urgency of the programme’s timetable, and fear that the Council is placed in the position of having to rush through decisions without being able to fully explore alternative options. Going forward the Trust wishes to work constructively with SCC, Arup and other stakeholders to arrive at the best outcome for the catchment and its people.
As was requested, this position statement sets out the Trust’s views following the structure of the Sheffield Flood Alleviation Scheme Consultation Questionnaire. Questions applicable to individuals rather than organisations are omitted.
Do we agree with the objectives of the Sheffield Flood Protection Programme?
The Trust strongly agrees with the objectives of ‘protecting our communities’, ‘growing our economy’ and ‘transforming our waterways’.
Which aspects of Sheffield’s rivers do you value most?
While our primary interest in ‘supporting a wide variety of plants and wildlife’ and ‘walking and cycling alongside the river’, we strongly value ‘enjoying the river’s heritage and history’, and ‘improving the quality of environment for homes and businesses near to the river’.
Overall, do you agree with the range of flood protection options that are being considered?
The Trust strongly disagrees with the range of flood protection options that have been identified for consideration. While we do agree with the focus on ‘slowing the flow’, which usually helps prevent the exacerbation of flooding further downstream, we are disappointed by the seemingly premature limiting of options to floodwalls and on-river flood storage schemes. There has been little explanation of why land management measures (such as moorland restoration, agricultural soil management practices and afforestation of upper catchments) that slow the rate of runoff and make more space for water have largely been discounted (as was announced in the consultation meetings). Such measures are desirable not only because they have a softer impact on the environment and landscape, but also because they can often provide a suite of additional benefits such as improved water quality, reduced soil erosion, increased carbon sequestration, and the creation of valuable new habitats.
We understand that SCC has commissioned high level investigations into the effectiveness and potential contribution of natural flood management (NFM) measures – to be precise the study only looked at the storage of runoff in the upper catchments. The consideration of using NFM measures has been driven by recommendations made in the Pitt Review of the 2007 floods and subsequent legislation and published flood reviews. These have all given weight to the requirement to integrate NFM approaches with more orthodox, and expensive, flood defence measures. The Trust appreciates that the criteria and requirements set for capital investment through grant-in-aid for flood risk management proposals make the use of most NFM approaches ineligible. However, we feel that SCC should challenge these requirements in order to use more sustainable and multiple benefits options which have been recommended in numerous government and statutory agency reports since 2007 (see Flooding: Cooperation Across Government inquiry http://bit.ly/1UFlWw2).
The Trust understands from the investigations commissioned by SCC that the results of modelling multiple small scale flood storage options in the upper catchments indicate that their flood risk benefits rapidly decline once the tributary streams enter the urbanised sectors of the catchment. As mentioned above these investigations should not discount the adoption of other, sustainable land management approaches. However, we are also aware that rapid urban runoff is a critical factor in flood risk, and that little strategic thought has gone into developing more sustainable ways of managing these flows within the built environment. SCC has invested huge sums in road and pavement repair and improvement but seemed to ignore the opportunity these works presented for better runoff management. In many other cities, and particularly London, the use of soakage and filtration zones is becoming an integral part of the street scene, but not it seems in Sheffield.
Another flood management approach that the Trust fears may not have been fully investigated is the storage of floodwater within existing compensation reservoirs such as Damflask on the Loxley and Scout Dike in the Upper Don catchment. Using reservoirs for flood storage has local precedent in the Ladybower/Derwent/Howden complex which belongs to Severn Trent. Within the Don Catchment there are a number of compensation reservoirs, the role of which is to ensure a constant flow of water in rivers impounded by water supply reservoirs further upstream. There is much more scope with such reservoirs to draw down water levels in advance of heavy rainfall as compared to water supply reservoirs. It is unclear if there has been a serious discussion with YW on the use of reservoirs for flood storage, though we are aware that there has been a national dialogue between DEFRA and the Water Utilities on the matter.
Lastly, while improving flood resilience is raised in the consultation materials, there has been little explanation of the role that these flood resilience measures will play, other than to say they are not the main approach being considered. We do not know, for example, the extent to which flood resilience is being incorporated into plans for the 46 hectares of land earmarked for development e.g. as could be achieved by running infrastructure and access along elevated routes. If flood resilience measures have not yet been considered for this land, could their implementation enable the planned level of flood protection to be relaxed?
Our current work is showing that due to the nature of the Upper Don and Sheaf catchments, the most appropriate options are focused on the balance between flood storage areas and flood defences. Do you agree in principle that we should try to find spaces to temporarily store flood water in areas of existing flood plains along the rivers, in order to reduce flood risk and potentially minimise the impact of flood defences downstream within the city?
The flood storage embankments would represent the most significant engineering of the catchment’s rivers in recent decades. Their large footprints will require significant areas of land, and once built the difficulty in removing them means they will probably remain indefinitely. Recovery from some of the resultant ecological damage will take hundreds of years. It is saddening that after the deculverting gains recently achieved in Sheffield that sections of some of the finest rivers in the catchment now face being buried under the embankments. Furthermore the embankments are so tall they will mar the character of the picturesque Pennine valleys and woodlands that are well loved by the people of Sheffield. If the on-river flood storage approach is to be taken then the consultation process would benefit from a full explanation of why all alternatives measures to reduce flood risk have been discounted.
7 & 8. Do you agree with the flood storage options presented on the consultation website?
Whilst the Trust believes that the assessment of specific flood storage options is at this stage best left to local groups and individuals who know the areas well, we wish to make general comments on the potential ecological impacts of the schemes that apply to a number of sites. We do not agree as is suggested in the consultation materials that the ecological impact within the flood storage areas will be temporary, and in particular we fear the schemes will be especially damaging in woodland, which is why we believe they should only be placed in such areas as a measure of last resort.
On the consultation maps it appears that schemes coincident with woodland will require a significant amount of tree felling and loss of habitat during embankment construction, which would be a great shame given that many of the woods are unusually old and biodiverse – for example Gillfield Wood, Totley is designated as an Ancient Woodland, and as such is irreplaceable. It is simply not possible to mitigate much of the damage inflicted on such woodlands.
Post construction we expect that in the heavily wooded catchments such as the Rivelin and Loxley, woody debris will mobilise during flood events and collect at the mouth of the culverts. The potential for this material to block the culvert is high and it is difficult to see how blockages will be cleared effectively when the culvert is at the bottom of a high embankment. We suspect that floodwaters will be left to dissipate through the debris, meaning that the flooded area may well remain inundated for much longer than is suggested in the consultation document.
Where woodland is periodically inundated the environmental conditions will to some extent change e.g. the enrichment of the soils due to deposition of silts, extirpation of species that cannot survive inundation etc. When biodiversity is low, as in most places in the UK, such flooding can be a good thing in terms of conservation. It is, however, more of a concern in species rich locations like the woodlands in question. The specialist flora, fauna and fungi that have over centuries found niches in the woodland often require remarkably specific environmental conditions e.g. low soil fertility, a certain soil structure etc. The change to long standing environmental conditions could have serious consequences for many species. In addition there are two specific issues we suggest need considering; the possibility that the inundations will cause large scale mortality of nesting birds, and the potential proliferation of Himalayan balsam due to the deposition of silt and seeds within the flood storage area.
Looking at the fish populations, the Rivelin and Loxley populations consist of brown trout and bullhead, with a small and vulnerable population of brook lamprey in the Rivelin. We have two principal concerns. Firstly, culverting is known to inhibit fish movement, and generally fish will only move through a culvert when light can be seen at the exit. It needs to be recognised that if the embankments are created, the culverts should be as short as possible so to limit their impact on movement, particularly on fish seeking spawning sites. If we get it wrong they could have a significant impact on the future viability of fish populations, particularly relevant if we are to be successful in re-establishing Atlantic salmon populations in these rivers.
The second concern relates to the impact flood storage will have on eggs and fry of brown trout (and Atlantic salmon in the future). The eggs of salmonids require a constant flow of well oxygenated water passing through the gravels in which they have been laid to remain viable, and so they will almost certainly perish in the ponded conditions created during floods. Fry (and adult fish) will move out of the river channel into adjacent areas during inundations, and there is potential for high levels of mortality if stranded in unsuitable habitats such as goits and mill ponds when the water recedes.
On the basis of ecological considerations the Trust has less of an objection to the construction of flood storage schemes on areas of grassland such as at Millhouses and Endcliffe Parks, as mown grass has limited ecological value.
9 & 10. We would like your views on the height of walls that could be acceptable for various sites along the Sheaf, Porter, Upper Don and Loxley.
It is difficult to answer this question without further information. Of course we would prefer the floodwalls to be as low as possible, but it depends on the degree of protection that a wall provides and the benefits that result from this protection
We would like your views on which of these options you believe should be used as part of our programme.
As stated earlier the Trust strongly feels that NFM measures such as ‘Planting trees in upland areas’, ‘Restoring peatland’ and ‘Working with farmers and communities to pilot land management techniques’ are preferable to the construction of flood storage schemes and floodwalls.
Do you agree that flood corridor options should be considered for further investigation?
We know little about this type of intervention, but in principle it sounds a very good idea and worth investigating.
Do you agree that the following resilience options should be considered for further investigation?
The Trust strongly agrees that ‘Better emergency planning’, ‘Householder resilience advice’, ‘Establish a network of flood action/support groups’, and ‘Improved flood warning systems’ are worth further investigation.
14. Please share any alternative options you believe should be considered:
As stated in the answer to Q5 the Trust firmly believes that considerable extra effort needs to go into investigating the potential for NFM measures to contribute towards flood risk reduction. As an example of what can be achieved, at Holnicote in Somerset a change to the land management of only 2% of the catchment resulted in a 10% reduction in flood peak during a 1:75 year flood event. The Trust also believes that there may be potential for a substantial reduction in flood risk through the use of existing YW compensation reservoirs as flood storage. The water levels in these reservoirs already fluctuate widely, and towards the end of the season may be down to less than one third of capacity. If water levels are already high when heavy rain is forecast then levels can be drawn down in advance of the rain. We see that there is a risk that the forecast rain may sometimes not be sufficient to replenish water released during the draw down. However this could be mitigated by a temporary reduction in the compensation flows, which would not be such an issue as river ecosystems are resilient to low flows. The situation on the Loxley and Rivelin is unusual in that while both rivers are fed by compensation reservoirs, there is only a single compensation flow target. This means there is the extra option of implementing a greater level of draw down at a single reservoir, thereby focussing flood risk reduction on a single river, while reserving water in the other reservoir to ensure the compensation flow target is met.
A further strategy that the Trust feels might be worth investigating is the adoption of flood resilience measures at the 46 hectares of land earmarked for development. As the land is yet to be built on there is significant scope to for flood resilience techniques to be incorporated into designs, which means the measures could be particularly effective as compared to at existing urban areas. If these areas were to be developed using flood resilience designs and principles, could the level of flood protection currently being planned for be relaxed?
