Rural runoff attenuation in the Belford catchment, UK

General

National Id:

United Kingdom_01

Site name:

Belford Burn catchment, Northumberland

Summary:

Measures to attenuate runoff were installed in the small Belford catchment, in northeast England, in order to reduce the risk of flooding to the village downstream. The installations involved a network of small measures to capture and delay runoff from the rural catchment, including detention basins and overland flow features, as well as sediment capture measures to improve water quality.

The in-depth description of the case study:

cs-uk-03-final_version.pdf

NUTS Code:

Northumberland and Tyne and Wear

RBD code:

UK03

Transboundary:

Data provider:

Katie Hill and Heather Williams, AMEC

Source(s):

Potential Use of Runoff Attenuation Features in small Rural Catchments for Flood Mitigation

A framework for managing runoff and pollution in the rural landscape using a Catchment Systems Engineering approach

Belford catchment proactive flood soutions: storing and attenuating runoff on farms

Runoff management: Mitigation measures for disconnecting flow pathways in the Belford Burn catchmen to reduce flood Risk

Runoff Attenuation Features - A guide for all those working in catchment Management

NWRM(s) implemented in the case study:

Basins and ponds

Coarse woody debris

Peak flow control structures

Sediment capture ponds

Longitude:

-1.83175794041

Latitude:

55.5986067185

Site information

Climate zone:

cool temperate moist

Mean rainfall:

750

Mean rainfall unit:

mm/year

Average temperature:

Mean runoff:

400

Mean runoff unit:

450 - 600 mm

Average runoff coefficient:

0,4

Type:

Case Study Info

Light or indepth?:

In-depth

Average slope range:

5-10%

Vegetation class:

Rural with predominantly pasture and cultivated grasslands.

Monitoring maintenance

Monitoring impacts effects:

Monitoring location:

In-Stream

Administrative annual cost information:

Up to 2013 monitoring was funded by the Environment Agency. Now Newcastle University continue to provide skeletal monitoring at the site through student research projects.

Monitoring parameters:

At the start of the project there was no hydrometry present within the catchment. The Environment Agency has installed a telemetered gauging station within Belford village for Flood warning purposes. In addition they have installed a tipping bucket rain gauge at a farm to help with flood warning predictions. Alongside this Newcastle university installed a raingauge and three flow gauging stations, which will help understand the impact of the features on the flood peak hydrograph as a flood moves through the catchment. A grab sampling campaign began in 2009 to characterize the sediment and nutrient regime and identify locations contributing to elevated levels of agricultural diffuse pollution. Four auto samplers were deployed at two online pond features, one upstream and one downstream of each feature. This was to understand if they were retaining sediments and nutrients during storm events.

Monitoring upstream station:

Monitoring was undertaken at locations directly upstream and downstream of some NWRM features.

Monitoring downstream station:

Monitoring was undertaken at locations directly upstream and downstream of some NWRM features. There is a WFD monitoring location on the Belford Burn.

Performance

Performance impact estimation method:

Laboratory

Performance impact estimation information:

For some NWRM features direct comparisons were made pre and post implementation, and also upstream and downstream of individual measures. Impact assessments were undertaken at a number of the indivdiual measures using available observed data. Model interpolation was used to understand the effects of multiple measures using hydraulic modelling.

Biophysical impacts

Information on retained water:

The estimated total for the suite of NWRMs is around 10,000 cubic metres in total.

Information on increased water storage:

There was no storage previously.The estimated total for the suite of NWRMs is around 10,000 cubic metres in total.

Information on runoff reduction:

Little net change in total runoff

Peak flow rate reduction:

Peak flow rate reduction unit:

Information on Peak flow rate reduction:

An individual NWRM may only provide a very small reduction in the peak flow, but in combination larger peak flow reductions can be observed. This value is for a MODELLED system representative of Belford with total storage of 19,250 cubic metres, for the reduction of peak flow at the downstream end of the network of measures: 15-30% peak flow reduction.

Maintenance baseflow:

Information on Increased infiltration:

Possible increases in infiltration due to water being retained within the upper catchment for longer before flowing downstream.

Information on Increased Evapotranspiration:

There is an increased extent of open water, but effects on evapotranspiration are likely to be insignificant since the retention times are low.

Water quality overall improvements:

Positive impact-WQ improvement

Information on Water quality overall improvements:

An investigation was begun in 2009 to assess effectiveness of features to reduce losses of sediment and nutrients. Parts of the catchment already had high concentrations of SS, P and NO3. The overall, cumulative impact of all the NWRMs has been found to be difficult to prove, and to require extensive monitoring. However some findings included: - It was identified that online ponds were not retaining pollutants during the rising limb and peak of flood events. - Overall conclusion was that online features are functioning to reduce chronic losses of Suspended solids but are less effective in storm events. - Different features operate to retain pollutants under contrasting flow conditions. The study area covers the upper 50% (approximate) of the associated WFD waterbody. Therefore it is likely that the improvements identified in water quality (e.g. phosphate) due the NWRMs will contribute to overall improvements in the Ecological status of the waterbody. - A multi stage NWRM (constructed following findings of initial NWRMs) that included a sediment trap and willow barriers works effectively to reduce sediment and nutrient losses from the catchment during storms

Water quality Improvements Phosphorus (P):

Water quality Improvements (P) unit:

% reduction pf pollutant

Information on Water quality Improvements (P):

Multi stage NWRM measured over a 24hour storm event. 26% TP reduction, 25% soluble RP reduction

Water quality Improvements Nitrogen (N):

Wq Improvements n unit:

% reduction pf pollutant

Information on Water quality Improvements (N):

Multi stage NWRM measured over a 24hour storm event. 15% NO3 reduction

Water quality Improvements Total Suspended Solid (TSS):

Water quality Improvements (TSS) unit:

% reduction pf pollutant

Water quality Improvements (TSS):

After a large runoff event a retention bund. Estimated 0.99 tonnes of sediment captured (retention bund) Multi stage NWRM over a 24hour storm event. 40% SS reduction (multi stage NWRM)

Soil quality overall soil improvements:

N/A info

Information on Soil quality overall soil improvements:

No information available. Unlikely to be significant changes

Information on Effect delaying peak:

Per NWRM the influence is small, but in combination the effects are significant

Lessons, risks, implications...

Key lessons:

The implementation of the suite of 35 NWRM features within the Belford Burn has shown how a catchment plan was created that was effective at providing multi purpose benefits (including flooding prevention and water quality improvements). A variety of stakeholders were engaged in the work from identification of the problem to be addressed to the siting and implementation of the individual NWRMs. A challenge is to remain adaptable and flexible, changing materials or NWRMs used to suit specific site conditions, in some cases using existing natural features within the channel such as large boulders, trees and bends to assist with stream control without the need for in-channel structures. Although developed for Belford the approach has generic applicability to many other catchments. Key lessons identified are that: - A number of NWRMs can be used together, with the materials, location and choice of feature being dependant on local factors including land owner/farmer preferences and local terrain. - One single NWRM feature only has a small benefit and it is likely that a number may be required together, but this should not ignore the fact that other structural measures may also be beneficial. - Online features are best suited to smaller channels. - The effectiveness of networks of NWRMs to attenuate flood depends upon the shape of the hydrograph, often being more effective for flashy short duration flood events. - Ongoing maintenance and the potential need to recover trapped sediment, which could be of value to famers. - It is essential to engage stakeholders, as this will encourage uptake by farmers. - It is crucial to build up the trust of farmers and residents from the earliest opportunity and maintain it throughout. One important finding has been that different types of measures may be more effective for flood and water quality benefits. At this site, a range of measures has been incorporated in to the overall scheme and hence provides effectiveness for both flood management and water quality improvements (nutrients and sediment). However only using a single type of measure, rather than a range, may not have been so successful in this regard. The need to consider a range of measures distributed through the catchment, to meet multiple objectives, is clear.

Success factor(s):

Type	Role	Comments
Attitude of relevant stakeholders	main factor	Identification of a combined approach that was flexible and adapted to the local factors, and the willingness of the regulator to explore new approaches.
Available support tools	main factor	Availability of the tools for non-expert stakeholders to appreciate and inform solutions
Communication activities	secondary factor	Crucial in getting "buy -in" from land owners and famers to allow these features on the land
Conducted assessments (incl. economic)	secondary factor	Interest in a catchment based approach and the requirement for monitoring and modeling investigations did not prevent the work going ahead, but ensured confidence in the outcomes of the work and further understanding of effectiveness of the NWRM approach.
Attitude of the public	secondary factor	It helps greatly when there is good relationship between the community and farmers.

Financing:

Type	Comments
National funds	Environment Agency
Sub-national funds	Northumbrian Regional Flood Defence Committee

Barrier:

Type	Role	Comments
Attitude of the public	secondary barrier	In the early stages the new concept meant that time was required to build the trust with Farmers and the community, to confirm benefits and effectiveness of the approach. This became less of a problem as more measures were implemented.
Attitude of relevant stakeholders	secondary barrier	Being a new concept there were delays in early measure implementation due to the need to consult everyone on the appropriate approach to use. All departments within the Environment Agency were consulted from Fisheries through to the Archaeology department. (For example placing barriers in channels required consultation with Fisheries experts to ensure adequate fish passage.)
Legal obligations / restrictions	secondary barrier	On all watercourses, in stream channel structures (e.g. Online flow storage) that interrupt normal flow will require a consent from the Environment Agency for works in a watercourse.

Driver:

Type	Role	Comments
Past flooding events	main driver	Severe flood events in small settlements downstream caused this to be considered. The Environment Agency were the main driver behind this measure being implemented, looking for lower-cost solutions to enable protection of small communities where high capital expenditure could not be justified. Other 'normal'flood defence approaches failed cost benefit criteria for support, and would not be suitable within Belford due to shortage of space between the channel and nearby houses. The 'natural' approaches were financially viable for the site, and enabled storing and attenuating flows in the upstream area.
Other	secondary driver	Unsuitability of 'structural' measures in the area.

Socio-economic

Direct benefits information:

There is no quantified information on the socio-economic benefits. The use of a network of NWRMs in a rural landscape has provided a cost effective means to reduce flood risk downstream. Additional benefits include: - Storing water in ponds on the fields removes sediment picked up by overland flow which can be returned to the farmer's field. - Creating wetlands on some of the ponds provides new habitat for wildlife. - The increased habitat and improved water quality is leading to an increase in the biodiversity in the catchment.

Costs investment:

120000

Costs investment information:

Construction costs only. 85,000 - 120,000 euros Approximate costs per feature: Barriers: €900-2,000 per m (dependent on material) Woody debris: €120-1,200 per feature Offline Ponds: €6,000 per feature (less if multiple ponds in close proximity)

Costs land acquisition information:

No land aquisition was required as all measures were in-channel or on buffer strips, causing minimal disturbance to farmers' land.

Costs operation maintenance:

Due to the nature of the NWRM, operational costs will be minimal, but there are maintenance requirements. There is also some additional cost associated with optimisation following implementation, e.g. Raising the outflow from a pond to increase its capacity

Costs operational information:

Small costs are envisaged, but no quantative indication available. Management of features is done by combination of Environment Agency, Northumberland Rivers Trust and Natural England.

Costs maintenance information:

Sediment clearance is important e.g. At sediment traps. Maintenance is also required of log/debris dams, which may need repairing or replacing over time

Costs disposal decommissioning information:

Minimal costs

Compensations annual information:

A one-off payment was made by the Environment Agency to famers for having access to the site for measure installation.

Information on Economic costs - income loss:

There is some minor land loss associated with the construction of ponds. However any costs associated with this could be offset in part by benefits of sediment recovery and re-use. No quantification is avaialble

Ecosystem improved biodiversity:

Information on Ecosystem improved biodiversity:

Overall there is increased habitat for wildlife (water features), however the overall ecological performance is difficult to quantify and required further evidence.

Ecosystem provisioning services:

Information on Ecosystem provisioning services:

Minor loss of agricultural land for ponds, however in most cases these are usually located on field margins, in corners or in buffer strips to minimise impact. Some benefits from re use of sediments that are removed from the NWRMs as part of the maintenance, although further investigation is required on the effectiveness and benefits of this.

Ecosystem impact climate regulation:

Not relevant for the specific application

Ecosystem erosion control:

Information on Ecosystem erosion control:

Does not directly affect erosion, but does allow sediment to be captured and re-applied to fields, resulting in lower net loss

Policy, general governance and design targets

Policy description:

Belford village has a long history of flooding, often causing damage to properties. An Environment Agency flood defence pre-feasibility study concluded that traditional flood defences were not suitable for Belford because of the high cost, lack of space for flood walls and banks, and the small number of properties at risk, resulting in an unfavourable cost-benefit assessment. There was a desire to deliver an alternative catchment based and more cost-effective solution to the problem. In addition to this, the waterbody is not at Good Ecological Status, and sediment retention and nutrient management as part of the NWRM programme will help to address this.

Quantified objectives:

The main objective is to reduce flood risk to Belford village downstream. Some of the measures also contribute to sediment retention, which has the potential to contribute to the waterbody achieving good ecological status, and help towards maintaining the quality of the downstream SPA.

Part of wider plan:

Policy pressure:

Policy requirement directive:

Policy impact:

Policy wider plan:

Wider plan type	Wider plan focus	Name	Comments
Local	Water	Defence strengthening in Belford Village	This strategy was 1 of 3 strategies (including the NWRM measures implementation) where the Environment Agency funded investigation and strengthening wirk to be undertaken at the existing 'structural' flood defences within Belford Village.
Local	Urban	Sewer upgrade	This strategy was 1 of the 3 strategies (including the NWRM implementation) where Northumbrian Water upgraded sewers to improve the resiliance and prevent surface water flooding.

Policy area:

Policy target:

Target purpose
Runoff control
Peak-flow reduction
Increase Water Storage
Pollutants Removal

Design & implementations

Application scale:

River

Installation date:

2011

Performance timescale:

< 1 year

Area (ha):

570

Design capacity description:

For this site a suite of small NWRMs are operating in combination, with a total storage of 9-10,000 m3. The following are approximate maximum storage capacities used on the Belford site, per individual feature: Overland flow interception: 1000 m3 Online ditch features: 150 m3 Offline ponds: 3000 m3 Large woody debris: 150 m3 Opportunistic measure sites: 3000 m3 As an example, one of the off line ponds implemented (approximately equivalent to 60x20m rectangle) stores approximately 3mm of runoff for 0.74km2 (however it is noted that in some cases the storage capacity reduced over time due to sediment buildup, which is an important consideration for maintenance). A further example was a small 1.2m dam that stores 500m3 of flow.

Max water retention capacity:

10000

Max water retention capacity unit:

m3/day

Basis of design:

Relatively short, high-intensity rainfall events. 5-17 year return period

Constraints:

These types of measures are most suited for rural headwater catchments. The benefits can most directly be seen in terms of flood protection for small settlements a short distance downstream, although will continue to have a cumulative benefit in the whole downstream catchment. Modelling has indicated that the measures are most effective for short, high intensity rainfall events, which suggests that they could also be applicable in drier climates, where intense rainfall events are experienced. They are effective for managing overland flow runoff, so may be less suitable in groundwater-dominated areas (although even in those situations could still have benefit for high intensity events that generate overland flow). Fish passage requirements can pose a constraint to the type of NWRM applied. Fish passage can be restricted by online structures (e.g. in stream dams) so they are more suited to small watercourses and ditches where fish passage is not important or the watercourse runs dry during the summer months.

Favourable preconditions:

The upstream characteristics of the watercourse (small channels) are ideal for implementation to these types of NWRM features as the scale of flows to be retained is not large and the size of the feature can be kept small, resulting in little loss of agricultural land

Crop rotation:

n/a. Mainly pasture

Public consultation:

Design contractual arrangement:

Arrangement type	Role	Responsibility	Name	Comments
		No information available

Design consultation activity:

Activity stage	Name	Key issues
Design phase	meetings	Decision support tools were made availalble to the famers to understand the underlying issues and provide them with adequate knowledge to participate in formulating a solution
Other	Effectiveness understanding	Famers were taking photographs and videos during flood events of the NWRM during flood conditions.
Implementation phase	Field trips	Field trips were organised for villagers to see the wrok being undertaken

Design land use change:

Land use change type
Land principally occupied by agriculture, with significant areas of natural vegetation

Design authority:

Authority type	Role	Name	Comments
	Monitoring	Newcastle University	Design and implementation of features; Monitoring; hydrological analyses and support tool generation
	Financing	Northumbrian Regional Flood Defence Committee	Financial; co- ordination
	Other	Northumberland Rivers Trust	Implimentation of more recent measures and maintenance
Farmers	Other	Famers and Residents of Belford	Provision of land; support for scheme
National water authority	Implementation	Environment Agency	Implementation; co-ordination; financial

Last updated: 18 Jun 2015 | Top

Miscellanous

Main menu

Rural runoff attenuation in the Belford catchment, UK

Partners