The Nature of Millbrook Exploring environmental issues in a community workshop 1Â
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Contents Introduction……………………………………………….. 4 Flooding in Millbrook…………….………………………. 6 The Millbrook Floods of 2012:
- Why did it happen?.....................................................9 - Solutions: infrastructure…………………………………. 10 - Solutions: Slow the Flow……......................................11 Water quality in Millbrook……………………………….. 14
- Solutions: Water Quality………………………………... 16 Millbrook Lake…………………………………………….. 18 Amenity in Millbrook……….……………………………..20
- Solutions: Millbrook Lake...…………………………….. 22 - Solutions: Amenity in Millbrook...……………………...23
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Westcountry Rivers Trust We are a charity working to restore and protect the rivers, lakes, estuaries and coastal areas for the benefit of people, wildlife and the local economy. By working with local communities, businesses and other environmental organisations we work to bring our lost and forgotten rivers back to life so that they can once again play their vital role in all of our lives. 4
Introduction Nestled in the rolling hills of East Cornwall, the village of Millbrook is surrounded by beautiful countryside and boasts a fantastic array of greenspace within the village itself. Millbrook also has a rich and eclectic environmental history and its well informed and committed community are very keen to take actions that will protect and enhance the natural and cultural assets they have in their surrounding landscape. In 2016, the Westcountry Rivers Trust (WRT) were engaged by the local community in Millbrook to help them identify and take‐up the opportunities available to them and to ensure that the environmental issues experienced in the village do not begin to overshadow the many wonderful things about living in Millbrook.
Millbrook Lake from the North
In September 2016, WRT and some local residents hosted a drop‐in information session in Millbrook’s Scout Hall, during which members of the community could learn more about the flooding risks to them, discuss the various environmental challenges faced in the area and to explain how they saw the Millbrook landscape being managed in the future. The day culminated with a presentation and discussion workshop in the evening and, with over 60 people attending throughout the course of the day, WRT were overwhelmed by the commitment of the Millbrook residents, their engagement with the local environmental issues and their eagerness to build on the wealth of natural resources on their doorstep. During the workshop, four key environmental issues were discussed and are explored further in this summary report: the management of Millbrook Lake, the natural amenity spaces in Millbrook, flood risk management and protecting water quality.
Millbrook lake—from the south bank
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Millbrook landscape from the South
Flooding Flooding in Millbrook Millbrook has a long history of being flooded. The location of the village, being so close to the estuary, has always made it vulnerable to tidal surges and, before the 1970s, it used to be flooded as often as four or five times a year—whenever spring tides coincided with low pressure weather systems. Following repeated severe flooding in the 1970s a tidal barrage was constructed across the estuary, significantly reducing the risk of tidal flooding. It was during the construction of the tidal barrage that the Millbrook Lake was created, designed as a storage area to hold water from the freshwater streams and overland flow and prevent it from backing up in the village. Millbrook has not suffered from tidal flooding since 1981 and the Environment Agency have estimated that the tidal barrage has prevented over 100 floods from the estuary during this time. Unfortunately, in 2012 Millbrook was affected by two rainfall‐related flood events in November and December of that year. Unlike the regular flooding of the past, the flooding of 2012 was derived from river (fluvial) and surface (pluvial) sources. 6
River (fluvial) Flood Risk Flood Risk 1970s
1978-1981
Regular coastal flooding in Millbrook ~4‐5 times a year.
Flood alleviation scheme constructed & Millbrook Lake created.
1981-2012
2012
No major flooding ‐ tidal barrier protects Millbrook over 100 times.
Millbrook has severe floods in November & December.
2015-2016
2016
2‐phase flood defence improvements by EA & Cornwall Council.
WRT host a Millbrook Community Workshop to discuss flooding.
There are significant areas of flood risk in Millbrook, but most of these are defended against by the infrastructure that drains water away from the village centre.
Surface (pluvial) Flood Risk
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Flooding
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The Flooding of 2012: Why did it happen? The two severe flooding events that occurred in Millbrook in November and December 2012 were caused by a number of factors that coincided and combined to exacerbate the problems experienced. These factors can broadly be put into two main categories; 1. Problems related to water management infrastructure in the village, which included a blockage in the main drainage culvert under the village and another culvert being unable to cope with the volume of water entering it. 2. The unprecedented volume and flow‐rate of water running off from the land surface of the catchment via fields, gateways, roads, and the watercourses and into the heart of the village. A huge volume of surface runoff flowed down from the steep valley slopes and into the Millpool Stream. This runoff exceeded the capacity of the 30cm culvert at Millpool Head (1) designed to channel the water under the southern part of the village and into the main stream (‐‐‐). All the excess water therefore flowed down the road and was delivered into the village centre (), which lies in a depression above the head of the lake. At the same time there was a 50% debris blockage (2) in the large old culvert that takes stream flow and surface drainage water into the lake (‐‐‐), which led to the increased accumulation of rainwater in the village centre. The blockage also caused the excess flood water from the Mill Brook to back‐ up at the entrance to the two culverts that drain into the lake (3) and this both created pressure back up towards Millpool Head, making this problem even worse, and put huge pressure on the flood defence wall, which fortunately did not fail and saved many additional homes from flooding. The pressure from (3) not only exacerbated the problem at (1), but it also caused a large volume of water to accumulate at the end of the culvert at (4), which then rapidly and catastrophically spilled over into the top of the village centre (). 9
Flooding
Solutions to the flooding problem: Improvements to infrastructure In the aftermath of the 2012 flooding, the Environment Agency carried out extensive research into why Millbrook flooded and, as a result, the infrastructure within the village has been significantly upgraded. The risk of debris blocking the culverts has been reduced through the construction of new brash screens at the main culvert entrances (see below). In addition new flood banks and a new flood wall have been constructed to ensure that water does not escape from the flood storage areas (also shown below and right). In order to reduce the risk of another failure of the Millpool Head culvert system, Cornwall Country Council have also drawn up plans to increase the size of this culvert. This will ensure that water from Millpool Head remains in culvert system and is rapidly diverted into the lake, rather than flowing down the road and into the village centre.
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Solutions to the flooding problem: slow the flow While the Environment Agency and Cornwall Council are making great improvements to the flood risk management infrastructure within the village, the question of why the infrastructure was placed under so much pressure by such a huge volume of water remains largely unanswered. What is clear is that water does run‐off too quickly from the land around Millbrook during rainfall events and that this is happening much more than it has done previously. This is clearly shown by the speed at which the streams rise after rainfall, by the water that can be seen flowing down roads and from gateways around the catchment and by reports of water seeping into people’s homes due to the high level of the water table. It is even more important to consider this in light of the growing risk of high rainfall and flood events that are expected to occur in the future as a result of climate change. We can map areas where run‐off is most likely to occur (see below) and use natural measures and improvement of soil condition to slow‐the‐flow and reduce the severity of these rapid response events.
The network index gives an indication of where in the catchment there is greatest risk of the rainfall reaching the river channel, rather than permeating into the ground
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Flooding
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Solutions to the flooding problem: slow the flow continued... Increasingly, the condition of our soils, the way we use land and our water management approaches mean that rainfall runs and accumulates too rapidly over the land surface and into our river channels, rather than seeping slowly through the landscape as would be the case with less human influence. Urban Areas: Sustainable Drainage Systems (SuDS)
Rural Solutions: Natural Flood Management
Urban areas tend to speed the movement of water through the landscape, causing it to accumulate in certain places. One of the main reasons for this is the lack of trees and other greenspaces in our towns and villages as these naturally slow the flow of water and allow water to permeate into the soils or be removed via evapotranspiration.
Broadly speaking, rural areas are much better equipped to slow the flow of water through the environment. However, disturbance to the natural flow of water in rural areas, such as compaction of soils through intensive farming practices, reduces the soil’s permeability and so encourages water to flow rapidly over the surface rather than being stored in the soil.
Instead, the impermeable surfaces that dominate urban areas (e.g. buildings, roads and pavements) cause surface water to cause floods locally and flow rapidly into rivers. With so much water arriving into the river within a short period of time, the channel may not be able to store the volume of water and so may burst its banks. This effect is exacerbated where the channel has been straightened as the length of the channel (and therefore its capacity) is reduced.
Furthermore, features, such as hedgerows, buffer zones and trees, that would naturally impede flow and encourage surface water to permeate into the soils have been removed as agriculture has become more intensive. The resulting unregulated movement of water can have huge implications for flood risk management.
Sustainable Drainage Systems (SuDS) are designed to transport, slow or store rainfall in a more natural way. These systems reduce the risk of large volumes of rainfall causing flooding locally or reaching the river channel in a short space of time, as this is when the river may burst its banks and flood people’s homes. SuDS provide a whole range of opportunities, not just for flood risk, but also for water quality, biodiversity and amenities. There are a range of different interventions that constitute SuDS, from trees and rain gardens to permeable paving and green roofs. A toolkit of these interventions, their multifunctional benefits and approximate costs can be found at: www.urbanwater‐eco.services/toolbox
In contrast to the traditional engineered approach to flood risk management, natural flood management schemes aim to work with nature. By restoring or enhancing natural processes, the movement of water around the catchment can be better regulated, reducing the risk of water accumulating in areas where flooding can cause significant damage, such as Millbrook village centre. Examples of natural flood management approaches include woodland planting, creating buffer strips on agricultural land and wetland creation. In fact, SuDS can be equally effective in rural or urban landscapes. For more information about natural flood management, SEPA’s Natural Flood Management Handbook and the Natural Water Retention Measures catalogue provide comprehensive guides: www.sepa.org.uk/media/163560/sepa‐natural‐flood‐ management‐handbook1.pdf www.nwrm.eu/measures‐catalogue
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Water Quality
Water quality in Millbrook Keeping our rivers clean is a major challenge in river management. In the Westcountry we often see evidence of sediment, nutrients and other chemicals entering our rivers, estuaries and other waterbodies. Ensuring that the rivers in the Millbrook catchment are healthy is hugely important, since this will also have implications for the health of the ecosystems living in and around the rivers, Millbrook Lake and the estuary below the tidal barrier. In addition, reducing sediment inputs may also have additional benefits in terms of the need for dredging the lake. River pollution sources within a catchment generally fall under two categories: point source and diffuse. Point source pollution is pollution that can be traced to a single point within the landscape whereas diffuse pollution derives from large areas of a catchment
Point source pollution: rural
Diffuse pollution: rural
The most common forms of rural point source pollution in the Westcountry are slurry and septic tank systems. In heavy rainfall these systems may overflow, causing material to enter the watercourse. This is often the case where slurry and septic tank systems have not been emptied or maintained according to best practice guidelines.
Diffuse pollution is the most significant water quality issue we face in the Westcountry and generally derives from agricultural or forestry activities.
Other examples of rural point source pollution include the disposal of chemicals and other pollutants in specific areas of the landscape. Pesticide wash‐down areas are one example of this.
Point source pollution: urban There are a range of point sources in urban areas. Pollution from domestic and commercial activity may be transported along pipes and drains directly into the watercourse. Misconnections in the sewage system can also contribute to pollution, allowing sewage to leak out into the river. A potential source of pollution in the Millbrook catchment is the former landfill site. There have been concerns raised over the proximity of this landfill site, which lies beneath the park, to Millbrook Lake. The landfill site is uncapped and, since the bank on that side of the lake is showing signs of erosion, there is potential for leachate from the landfill to reach the lake. 14
Agriculture is the major contributor to diffuse pollution since rainfall moving across the land transports sediment and other pollutants (e.g. pesticides, nutrients) from the fields and into the river. As well as impacting water quality and ecological health in the river, this can lead to a loss of agricultural productivity on the land. Reports of brown water flowing through the Millbrook stream after rainfall and of silty runoff seen flowing from fields entrances suggest that diffuse pollution is an issue in the catchment.
Diffuse pollution: urban Diffuse urban sources can also pollute the river. As water flows across roads and constructed areas it mobilises a range of pollutants such as oil, petrol, diesel, nutrients and toxic chemicals. These are then transported into the watercourse.
Erosion risk gives an indication of where in the catchment there is greatest risk of rainfall eroding the soils. Where these high erosion risk areas coincide with a high network index, it is likely that eroded material will reach the river.
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Water Quality
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Solutions to the Water Quality Problem Monitoring & surveys Diffuse pollution derives from sources across wide areas of the catchment. Since we cannot make interventions over this whole area, monitoring can help to identify and target key sources or pollution or the pathways that polluted water is moving along. Wet weather walkovers and chemical monitoring of stream water are used to gain a detailed understand of how water moves through a catchment during rainfall events. Since surface water is the major transporter of pollution into our rivers, we are planning to carry out a wet weather walkover survey to identify pollution sources in the Millbrook catchment. The Westcountry Rivers Trust has also set up a citizen science scheme, Westcountry CSI. Through the scheme, citizen scientists are able to record observations of their local rivers and gain knowledge of signs of healthy and polluted rivers. The data recorded allows us to understand how pollution is moving through the catchment and which areas are being most affected. It also empowers the local community to look after their own environment.
Farmer advice & investment The Westcountry Rivers Trust has a team of farm advisors who are hugely experienced in developing tailored and targeted catchment management interventions to remove pollution sources and disconnect their pollution pathways. Working with the farmers in the Millbrook catchment, our farm advisors will be able to identify where changes to the land management can help to reduce soil loss from the fields and so reduce pollution.
Other solutions Another source of water pollution which needs to be addressed is that of misconnections and septic tanks—there was clear evidence of misconnections in Millbrook during the workshop. Homeowners in the Millbrook catchment can learn more about preventing misconnections and ensuring their septic tanks comply with the new general binding rules at the following addresses: www.connectright.org.uk www.gov.uk/government/publications/small‐sewage‐discharges‐in‐england‐general‐binding‐rules Another solution to water quality that arose during the Millbrook Community Workshop was the potential to access funding for water quality improvement from the Landfill Communities Fund (LCF). If the community were interested in reducing pollution or improving amenity value and biodiversity on Millbrook’s former landfill site, this may be eligible for LCF funding. www.entrust.org.uk 17
Millbrook Lake
Millbrook Park (formerly Millbrook Pond and landfill site)
Estuary
Millbrook Village Centre
Sluice gate
Millbrook Lake Freshwater input from culvert 18Â
The Millbrook Lake The Millbrook Lake, which was formed by the construction of the tidal barrage, is an important and well loved feature within the village. The lake provides a popular recreational area and is home to an array of wildlife. There has, however, been some debate over the optimal future management of the lake. The conversation about Millbrook Lake focussed on two main areas: 1. Should the lake be managed as a fresh- or saltwater habitat
2. Water level and the need to dredge the lake
Currently the Millbrook Lake is managed by the Environment Agency as a brackish (slightly salty) environment. By occasionally opening the sluice gates, the lake receives regular inputs of saline (salty) water from the estuary below the tidal bank, in addition to the continuous supply of freshwater from rainfall and the Millbrook stream.
The Environment Agency periodically dredges Millbrook Lake, both for aesthetic reasons (which many support) and to ensure that it retains the capacity required to store water entering it from the catchment streams and from overland flow when the tidal flood defence is closed. However, in addition to the costs associated with dredging the lake and disposing of the dredged sediment, many have concerns about the disturbance this causes to the lake’s ecosystem. There are also doubts over whether dredging is necessary, since the extra capacity above the current water level should provide sufficient additional storage, even during high flow events.
Several people have proposed that, by adjusting the management of the lake, such that it became more decisively a fresh– or saltwater habitat, it would support a greater variety of aquatic species and birdlife. While some are in favour of allowing the lake to become a freshwater environment with freshwater habitats such as reedbeds, others are concerned about the midges this would attract. They believe that managing the lake as a properly brackish environment would allow natural saltmarsh vegetation to establish around the lakeside and prevent the midge problem. There were also suggestions that the lake might have economic potential, for example if it was used to produce seaweed, shellfish or hydropower.
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Greenspaces & Amenity
Amenity in Millbrook Having access to the natural spaces, often called ‘greenspace’, where we live makes a vital contribution to our health and well‐ being and the Millbrook community are very fortunate to be surrounded by a great variety of green (and blue) spaces in their immediate landscape and across the Rame Peninsula more widely. These natural assets are a source of great pride for the Millbrook residents and there is a drive in the community to incorporate additional greenspace within the village itself, creating an even better environment for both residents and wildlife. This ambition is illustrated by established schemes such as ‘Get Millbrook Buzzing’, the community orchard and the volunteer group. These schemes have created a wealth of local experience and enthusiasm that can be drawn on going forward to find new ways to regenerate neglected space around the village and to develop volunteer groups. At the Millbrook Community Workshop, a number of ideas for greenspace creation and enhancement were discussed. For example, the creation of wetland areas in the upper catchment, green corridors in agricultural areas, a local nature reserve and a community sustainable drainage scheme were all suggested on the day. 20
Mowing regimes in the ‘Millbrook Park’ Members of the Millbrook Community have been working to influence the mowing regime in the Millbrook Park (created by the landscaping of the landfill site to the north of Millbrook Lake) and have succeeded in having the field margin left un‐ mown for certain periods to encourage flowers and pollinators to thrive.
Playing fields Re-wilded field margins
Community orchard
The management of lakeside vegetation The various banks around Millbrook Lake are regularly strimmed by Environment Agency contractors to ensure that any damage to the tidal barrage would be easily visible and maintenance easily performed.
Millbrook Lake
However there may be potential to limit the practice of removing vegetation and so provide habitat for wildlife residing in and around the lake, creating a more natural lakeside environment. There are also concerns over the use of glyphosate (e.g. Roundup) and other weed‐killers to remove vegetation due to their potential impact on the ecosystems in and around the lake, and also to human health through coming into contact with the chemicals in the environment.
Footpaths to open country 21
Millbrook Lake
Solutions: Millbrook Lake 1. Lake Habitat Management
2. Dredging Millbrook Lake
Making a decision about whether Millbrook lake should be managed as a freshwater or saltwater habitat will allow its biodiversity and amenity value to be increased in a way not posible in its current, brackish state.
Dredging has been carried out in the Millbrook Lake as part of the flood mitigation efforts. By reducing the volume of sediment in the lake, the lake has a greater capacity to store water. An additional benefit of dredging is aesthetic: without altering the level of the lake’s surface, there is a greater depth of water and the lake bed is invisible.
There is no clear advantage of managing the lake as one of these two environments over the other; the decision will depend on the preference of the community as a whole. However there are some additional considerations that require further investigation: would a freshwater lake attract midges and would a saltwater lake hold economic potential? When the Millbrook community have reached a decision over the future of the lake, a conversation needs to be opened with the Environment Agency to look into alternative management regimes.
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However, dredging is both cost and energy intensive and causes disturbance both to the ecosystem within the lake, and to that at the sediment disposal site. There is also debate about whether dredging is necessary in terms of flood risk mitigation. Above the current water level, there is already sufficient storage volume available. Discussions with the Environment Agency will give the Millbrook community the opportunity to learn more about the necessity of the practice and to voice their opinion of future lake management.
Millbrook already has an excellent variety of amenity areas, much helped by the enthusiasm and dedication of the local community. While creating amenity spaces in Millbrook is no longer a priority, it is important that any further changes to the Millbrook catchment continue to build on its amenity value. Many of potential schemes to mitigate other issues in the catchment, for example sustainable drainage systems (SuDS) and natural flood management schemes to reduce flood risk, can have multifunctional benefits, also adding to the village’s amenity value. Having said that, there remain concerns over the regime of removing vegetation on the dam and around the lake. This was an issue identified during the Millbrook Community Workshop and we suggest that the village open discussion with the Environment Agency to ascertain whether there is any flexibility or alternative options regarding vegetation removal.
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Greenspaces & Amenity
Solutions: Greenspaces & Amenity
The Nature of Millbrook Exploring environmental issues in a community workshop On the 30th November, Westcountry Rivers Trust held a Community Drop‐In Session & Workshop in the Cornish village of Millbrook, during which the local community discussed the environmental challenges they are facing and the opportunities they have for meeting them. We also discussed how they saw the Millbrook catchment landscape being managed in the future. The day culminated with a presentation and workshop in the evening, with over 60 people attending throughout the course of the day. We were overwhelmed by the community spirit shown by the Millbrook residents, their engagement in their local environment and willingness to continue to build on the wealth of natural resources on their doorstep. Millbrook is a stunning place to live and we are looking forward to continuing to work with the local community to help them make the most of the opportunities available to them and ensure that the environmental issues faced by the village do not overshadow the many wonderful things about living in Millbrook.
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