9. CaBA Conference 2017 NFM Modelling - Dave Johnson
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Overview of the NFM benefits modelling work in Merseyside
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9. CaBA Conference 2017 NFM Modelling - Dave Johnson
- 1. David Johnson. C Eng, MICE Paul Wisse Sefton Council Natural Flood Management : Merseyside FCERM Partnership
- 2. Catchment based approach to NFM. Local delivery of NFM to deal with localised issues remains 1. At a catchment scale we can change: Storage, Roughness & Permeability/losses 2. Based on the outputs from a fully distributed model (SW Flood maps) & recent research. Tier 2! 3. Improved by local expertise and data to produce maps, a User Guide and improved understanding. 4. Requires more local knowledge to refine, achieve consensus and be accepted...in a few weeks time! 5. NFM can make a significant contribution but need to be realistic about time/uncertainty and that engineering will still do the ‘heavy lifting’.
- 3. Large scale NFM could deliver significant flood benefits even in extreme events. (Dadson Report) Flow Time Abigail Desmond
- 4. 4 How confident should we be? Barney Abigail Desmond
- 5. NFM storage: Top three. 1) River Birket corridor, NIA 16. Wirral. 2) Ditton & Netherley Brooks, especially in NIA - 7 3) Upper Alt and Tue Brook, especially NIA – 04 4) Pumped catchments...caution require
- 6. #/NFM storage: Detail in the Birket 1) High NFM benefits 2) WFD 3) Water resources 4) Sewer flooding 5) NIRS 6) Ecology 7) C@R 8) SgZ 9) Climate Change
- 7. NFM roughness top three. 1) Don’t do it! 2) Trees increase flood risk....but.......... 3) That it not what the modelling is saying.....more later...
- 8. NFM Permeability or SuDs top three/four. 1) River Birket, damages avoided > £2M (1:100 event) 2) Liverpool and Tue Brook, damages avoided of >£5M (1:100 event) 3) Three Pools Waterway, for rural soil improvement, but beware pumping!
- 9. NFM urban trees top four. 1) Liverpool, damages avoided of >£5M (1:100 event) for target tree coverage 2) Upper Alt including Fazakerlay and Tue Brooks. Especially NIA – 03 3) River Birket, damages avoided > £2M (1:100 event) 4) Sefton target is 40% already have 12% look what you could lose?
- 10. Stage 1: Initial modelling: All opportunities. Storage & permeability/SuDS
- 11. Stage 1: Initial modelling: Benefits Permeability Urban trees Storage
- 12. Stage 2: Collaborative modelling Allow experts to modify opportunities based on local knowledge X X Remove opportunities that are not possible Add in opportunities that have been missed
- 13. Stage 3: Collaborative NFM maps: Which incorporate local knowledge: Outputs=>PDF, GIS and User Guide
- 14. What next? AGOL? AGOL. Share the data, to realise multiple benefits. Is this where you might go? Look at what they did in Cumbria
- 15. What next? AGOL? AGOL. Share the data, to realise multiple benefits. Is this where you might go? Look at what they did in Cumbria
- 16. Using the data and progressing the business cases Opportunities for NFM identified Freely available dataset Partners engaged and skilled Mutual benefits Maintenance of NFM datasets Flood risk Management Partnerships Skeleton Business cases Background evidence Framework
- 17. NFM and spatial planning Consenting NFM on ordinary water courses. You must let water flow through your land without any obstruction, pollution or diversion which affects the rights of others. Others also have the right to receive water in its natural quantity and quality You should be aware that all riparian owners have the same rights and responsibilities. Planning applications Local plans
- 18. Barriers to overcome Understanding and buy-in Identifying viable schemes that deliver multiple benefits Issues with securing funding Cross boundary issues Ownership and future maintenance of NFM schemes
- 19. Other opportunities Day-lighting watercourses and public sewers To reduce flood risk Create new habitat Urban trees Does cutting them down potentially increases flood risk? Can NFM modelling provide evidence to their value?
Editor's Notes
- Explain that benefits quantified in losses avoided rather than change in peak flow.
- Explain: Urban trees designed to increase losses not roughness Value of existing tree coverage Value of increasing tree coverage What could the target tree coverage mean
- Stage 1: Identify all the opportunities First for storage using SWfM to find out where water accumulates Then landuse to find out where opportunities for Soil improvement. Arable land SuDs urban lanuse
- Initial benefits map: Assessed in terms of damages avoided Because the catchment is so flat we cant define outlet hydrographs very well So we use damages avoided, based on approved methodology The inside colour of a sub-catchment tells you the damages avoided The outside colour tells you the amount of opportunity you need to take What you want is a blue catchment with a yellow surround (lots of benefit but little effort Can’t do anything with sycroisation in this catchment but can normally
- Local knowledge gets rid of some opportunities And adds in new opportunities that we have not identified
- Then the model is re-run and we get to see the benefits of the opportunities that local experts think are realistic
- The NFM modelling has created an additional piece of evidence that is necessary if we are to deliver sustainable flood risk management. It has added another layer to our understanding and given us many more options to consider. It is vital for this to be used correctly and as such users must have a good understanding of the concepts of NFM, catchment scale working and the dataset itself but also any limitations associated with it. To help achieve this we must ensure the dataset is freely available and partners are identified and engaged early on. I know Dave is working on training days for staff asking questions about what else people need to help them use the datasets more effectively. There is a fundamental need to change the way flood risk managers, wildlife and conservation organisations and funding bodies think. For many years we worked in isolation and often competed against each other to deliver our own outcomes at the expense of others. Nowadays there are very few opportunities, especially in urban areas, to deliver schemes that make a significant difference, any that would have have already been done or don’t achieve a suitable cost benefit . By looking at a variety of methods for NFM in these models it clearly demonstrates the need to work together. We can only achieve this by identifying mutual benefits. The only way we will be able to deliver flood risk management outcomes is by packaging a number of smaller schemes together that achieve the these multiple benefits. This is actually quite a challenge and requires partners to work together in an way they previously haven’t. Being better coordinated, honest about funding and even taking a risk to get things delivered. Another challenge working at catchment scales is the separation between where the works take place and where the benefits accrue, this can be difficult for some to understand and subsequently approve. For example the river alt flows from Knowsley into Sefton before it discharges into the sea. There is flood risk associated with the alt in Sefton, however, some of the best NFM opportunities are in Knowsley. It is going to be a very interesting discussion if I ask the Sefton Council for money to spend in another authority to deliver a scheme and also then have to maintain it. The ownership and future maintenance of the data could potentially be an issue, we received local levy funding from the RFCC to undertake this modelling. However, we don’t have additional funding to update the modelling as new data and information becomes available. There are potential issue with the longevity of the data as it was a cross boundary catchment based exercise and it works best in this manner, how this dataset is maintained in the future and who takes responsibility needs to be addressed. I can’t see one authority taking responsibility for the whole dataset unless there is an incentive. Also the ability to use the dataset effectively may vary from one authority to another and we may end up with some disparity between organisations. The flood risk partnerships and catchment partnership are key to ensure assessments are may on a system or catchment basis. To try and help us along the way we have had skeleton business case developed. The help identify the multiple benefits in terms of flood risk management, water frame directive, spatial planning, countryside stewardship and bio-diversity. However, as they stand, are unlikely to secure funding for any one of the funding sources pot but do provide a great deal of the background evidence and also the framework in which a bidding package can be developed. This isn’t about the quality of information on he form but more around how the funding is awarded. I talk a bit more about this later.
- Role of LLFA comes from the flood and water management act and land drainage act and amongst other stuff it is responsible for Consenting works on ordinary watercourses, normally this would be culverts, bridges or temporary works, rarely, if at all, have we had NFM schemes come through. So we would be going into a new areas. Essentially when we assess consent what we need to understand is will this increase flood risk elsewhere on the system. The modelling may help us address that question. However, the legislation states that You must let water flow through your land without any obstruction, pollution or diversion which affects the rights of others. Others also have the right to receive water in its natural quantity and quality as explained in the Your Rights Section. You should be aware that all riparian owners have the same rights and responsibilities. This potentially causes us a problem if a nfm scheme on an ordinary watercourse is reducing or changing flows. Only just realised this as putting the presentation together. So in effect we may need to get the permission of the all the owners along the whole length of the watercouse before we can consent work. The other issue is its maintenance and how it may affect the maintenance regime of the wider system. Linked to this is a power of Enforcement on ordinary watercourses, if the responsible person/organisation isn’t maintaining the flow of water in the watercourse the LLFA has powers to enforce them to. So if we have approved something that then causes a knock on effect we could be in a difficult position The LLFA is a Statutory consultee on major planning applications and more commonly these are coming through on sites that were greenbelt land, many of which have been identified a suitable for NFM. The role as a consultee is actually quite simple in that we assess their application to see if it is consistent with the national planning policy and any local policies. And we tell them yes or no, we are avoiding telling them why it is wrong as this could put a liability on the LLFA/local authority in the future. So there is an element of work for us to make sure this information is freely and easily available and our planning colleagues are aware and understand it so we can influence the design without compromising our position as a consultee Linked to this is the development of local plans which identify areas for development for a period of roughly 15yrs. Targets are given for the number of houses, businesses , schools etc that need to be delivered during this time period. In the urban areas, such as Merseyside, we have seen more and more green belt being reallocated for development. In Sefton the majority of these had some degree of flood risk. Any future allocations needed will be using land that is currently at flood risk and foreseeably this risk will increase. This NFM modelling can help us in two ways, firstly we could deliver schemes that reduce risk to some of those sites making them more viable for development, and if we are really clever we can link the maintenance of the NFM scheme to the development, secondly it can help us identify sites that we could reserve for future schemes where NFM will derive benefits.
- There is a fundamental need to change the way flood risk managers and funding bodies think about reducing flood risk. For this to work we need buy-in and understanding, NFM is a large step away from the ordinary for some but does offer some significant potential gains. Individuals and organisations need to understand the concept, and the opportunities of NFM. It would be very easy for us to go off and think that the modelling we have done provides answers to all our questions and gives us all the solutions, unfortunately we cannot take that approach. It is a massive step forward in our understanding and has identified a number of opportunities but it is only part of the puzzle. We need to ensure this dataset is used along side other datasets, from a variety of organisations, to ensure we fully understand the system, the risks, opportunities and the benefits and then the effect any scheme could have on the system or catchment as a whole. There are very few opportunities, especially in urban areas to deliver schemes that make a significant difference, most of them have already been done or don’t achieve a suitable cost benefit to secure funding. These NFM opportunities only really deliver some small benefits on an individual basis and are therefore unlikely to attract grant funding for flood risk management or be able to be funded by local authorities due to their budget reductions and their competing priorities. The only way we will be able to deliver flood risk management outcomes is by packaging a number of smaller schemes together that achieve multiple benefits This is actually quite a challenging this to achieve when you are working with engineers who like to see straight forward solutions that they can quantify the benefits. But this really requires the understanding and buy in to allow effective partnerships to be established Something else that needs to be considered is land ownership, most of these schemes are in rural land or greenspace, much of which is farmed, so there will be an additional cost to use this land unless we can identify a benefit to the land owner. Unfortunately, the funding process isn’t as easy as it could be. Funding sources to deliver are different with different criteria and timescales, and schemes may need all of the funding sources to be approved and aligned before they can proceed. For example the Environment agency’s funding for flood risk management is separate to the water frame directive grant, with no clear link between them. As a flood risk manager I’m not allowed to bid into the WFD funding. To overcome this we are working closely with the Rivers trust and we are effectively having two separate bids going in with no clear link in their consideration. So there needs to be a look at the funding mechanisms to try and simplify the process. Another challenge is working at wider scales separation between where the works take place and where the benefits accrue can be difficult for some to understand and if it goes across authority boundaries can add a further complication. There are potential issue with the longevity of the data as it was a cross boundary catchment based exercise and it works best in this manner, how this dataset is maintained in the future and who takes responsibility needs to be addressed. I can’t see one authority taking responsibility for the whole dataset unless there is an incentive. Also the ability to use the dataset effectively may vary from one authority to another and we may end up with some disparity between organisations. The flood risk partnerships and catchment partnership are key to ensure assessments are made on a system or catchment basis. Once we have overcome all of these challenges and delivered a scheme. As part of the scheme a very clear, funded maintenance programme needs to be identified. I can foresee issues arising where multiple partners who have contributed to a scheme to achieve their own outcomes, potentially can’t support future maintenance and as a result the schemes functionality decreases over time. Its clear if we are going deliver good flood risk management, deliver water framework objectives, create habitats and avoid inappropriate development that we do need to work together The funding mechanisms and packages need to be reviewed and simplified. I know this has come across as quite a negative review of nfm but I do believe it will deliver significant benefits to all parties but we do need to be mindful that it isn’t always straight forward process especially in urban areas where opportunities are limited and benefits difficult to demonstrate.
- Thames Water are identifying sewers that are really streams and highlighting them to partnerships for daylighting?