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Assessing The Role Of Runoff Attenuation Features In Managing Flood Runoff For Multiple Benefits

Congress: 2015
Author(s): Mark Wilkinson, Paul Quinn, Steve Addy, Nicholas Barber, Sohan Ghimire, Marc Stutter
The James Hutton Institute1, Newcastle University2, Durham University 3

Keyword(s): Sub-theme 11: Key vulnerabilities and security risks,
AbstractIntensive farming practices have the potential to increase local runoff rates, resulting in various water quality issues and local flooding problems (O'Connell et al. 2004, O'Connell et al. 2007, Parrott et al. 2009, Hess et al. 2010, McIntyre and Marshall 2010, Wilkinson et al. 2013). There is great potential for agriculture to become part of the solution, rather than being part of the problem (e.g. Kenyon et al. 2008). Many European Union policies attempt to reduce flooding and improve water quality through preserving, enhancing or reinstating natural processes and features (e.g. Water Framework Directive and Floods Directive). However, methodologies for mitigating water quantity and quality issues share many commonalities and these aspects should be considered together in order to maximise benefits and persuade local actions. This idea is embraced in policy within the Blueprint to safeguard Europe's waters document (European Commission 2012); however, it is rarely applied in practice (Wilkinson et al. 2014). Runoff Attenuation Features (RAFs) are based on the concept of promoting the storage, slowing, filtering and infiltration of runoff on farms, at source, by targeting surface flow pathways in fields and farm ditches to achieve multiple environmental benefits (Quinn et al. 2007, Wilkinson et al. 2010, Wilby and Keenan 2012, Wilkinson et al. 2014). Here we focus on the placement, management and effectiveness of RAFs (edge of field disconnection bunds, offline ponds, riparian management and wetlands) in the rural landscape.

Two UK case study headwater catchments where RAFs have been implemented by local agencies, landowners and rivers trusts are presented. These are; (i) Tarland Catchment (50 km2), a mixed grazing and arable catchment in Aberdeenshire where infield storage ponds, wetlands and riparian management have been implemented, and (2); Belford Burn catchment (6 km2), a mixed pasture and arable rotation catchment in Northumberland where over 40 offline ponds, in field storage ponds and have been installed. These catchments are known for their rapid runoff generation and have downstream local communities at risk of flash flooding. The use of novel GIS tools (FARM Pond Location Tool) and stakeholder site meetings were used in order to place measures in the optimal locations. The study catchments have unusually dense, multiscale hydrometric networks. Using the data derived from these monitoring networks, the multiple functions of the measures during high and flood flows are assessed. Evidence from these measures is used in hydrological and hydraulic modelling approaches to upscale predictions of their effects.

Results in Belford have shown that through a modelling study, using data from an intense summer storm suggests that 30 small scale pond features (500 m3) used in sequence could reduce the flood peak by approximately 35% (3 km2 scale). By placing sediment traps and filters into small ditches, suspended sediment loads have been reduced during moderate events. For example, Barber (2014) found that relatively small RAFs, principally sediment traps, constructed in farm ditches (<1 km2 sub-catchment area) can reduce mean SS, TP, SRP and NO3 loads during storm events by 30-49%, 23-37%, 12-27% and 8-14%, respectively. Knowledge from this study was transferred to local stakeholders in the Tarland catchment which resulted in a field storage pond being constructed. Initial results show that this feature is storing 250m3 of surface runoff during intensive storm events, potentially reducing the risk of muddy flooding to the local village. The pond has been designed to hold water for around 8-12 hours in order to protect the crop behind it. The multiple functions of that feature and a nearby wetland are currently being assessed. At both sites, there is a need to remove sediments collected behind the bunds and in the offline ponds in order to preserve storage volume and to protect nearby (in some cases adjoining) wetlands. By integrating a sediment storage trap upstream of a wetland, the life of the wetland could be extended. Therefore a network of RAFs, where each measure plays a role in delivering a certain environmental benefit, can deliver a range of multiple benefits at the local scale.

When assessing the larger scale impacts of these measures, continued long term data collection from multiple scales and measures will help to improve our understanding (through the use of empirical data driven models) of how they function to reduce flood peaks and improve water quality. Catchment stakeholder engagement has been vital for the sucessful implementation of these measures. It has been demostrated that by transferring knowledge and lessons learnt from the Belford catchment to the Tarland catchment, confidence in the implementation of pilot disconnection bund within an arable field system has increased. By holding and attenuating runoff in rural landscapes, benefits for local flood peak reduction, water quality improvement and sediment management can be achieved. Hence this presentation aims to demonstrate that using networks of RAFs in the rural landscape could potentially provide a cost effective means for managing local flood runoff for multiple environmental objectives. However, there is still a need to examine the sustainability of such measures through long term environmental payment schemes and to montior these measures over longer timescales and in multiple settings. Barber, N., 2014. Sediment, nutrient and runoff management and mitigation in rural catchments. (PhD thesis). Newcastle University.
European Commission, 2012. A Blueprint to Safeguard Europe's Water Resources. Brussels.
Hess, T. M., Holman, I. P., Rose, S. C., Rosolova, Z. and Parrott, A. 2010. Estimating the impact of rural land management changes on catchment runoff generation in England and Wales. Hydrological Processes, 24, 1357-1368.
Kenyon, W., Hill, G. and Shannon, P. 2008. Scoping the role of agriculture in sustainable flood management. Land use policy, 25, 351-360.
McIntyre, N. and Marshall, M. 2010. Identification of rural land management signals in runoff response. Hydrological Processes, 24, 3521-3534.
O'Connell, P. E., Beven, K. J., Carney, J. N., Clements, R. O., Ewen, J., Fowler, H., Harris, G. L., Hollis, J., Morris, J., O'Donnell, G., Packman, J. C., Parkin, A., Quinn, P. F., Rose, S. C. and Shepard, M. A., 2004. Review of impacts of rural and land use and management on flood generation. Defra, London.
O'Connell, P. E., Ewen, J., O'Donnell, G. and Quinn, P. F. 2007. Is there a link between agricultural land-use management and flooding? Hydrol. Earth Syst. Sci., 11(1), 96-107.
Parrott, A., Brooks, W., Harmar, O. and Pygott, K. 2009. Role of land use management in flood and coastal risk management. Journal of Flood Risk Management, 2, 272-284.
Quinn, P. F., Hewett, C. J. M., Jonczyk, J. and Glenis, V., 2007. The PROACTIVE approach to Farm Integrated Runoff Management (FIRM) plans: Flood storage on farms. Newcastle University.
Wilby, R. L. and Keenan, R. 2012. Adapting to flood risk under climate change. Progress in Physical Geography, 36(3), 348-378.
Wilkinson, M. E., Quinn, P. F., Barber, N. J. and Jonczyk, J. 2014. A framework for managing runoff and pollution in the rural landscape using a Catchment Systems Engineering approach. Science of the Total Environment, 468, 1245-1254.
Wilkinson, M. E., Quinn, P. F., & Hewett, C. J. (2013). The Floods and Agriculture Risk Matrix: a decision support tool for effectively communicating flood risk from farmed landscapes. International Journal of River Basin Management, 11(3), 237-252.
Wilkinson, M. E., Quinn, P. F. and Welton, P. 2010. Runoff management during the September 2008 floods in the Belford catchment, Northumberland. Journal of Flood Risk Management, 3(4), 285-295.

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