Priority Areas and Drivers

Flooding has the potential to negatively affect people and communities. By considering both the vulnerability of communities and the opportunities for land management interventions, actions can be targeted to have a positive impact on communities most at risk. Flooding is one of a number of natural hazards which can cause harm to people, the environment and the economy. The primary driver for targeting this catchment is flooding. However, there are other priority areas and drivers which will be affected by NFM and can determine the most appropriate type of NFM for the catchment. These are mapped in the following pages.

Priority Areas and Drivers

Flooding

The Neighbourhood Flood Vulnerability Index (NFVI) characterises vulnerability as communities likely to experience losses in wellbeing during flood events. This is based on their susceptibility, preparedness, responsiveness, and ability to recover, all without significant support from emergency services. Roughly half of the Honiton buildings in the catchment are classed as Average in the NFVI, meaning that they are moderately vulnerable to losses in wellbeing from a flood event and generally equivalent with the UK average. However, the centre of Honiton around the railway line is classed as “Relatively High”, meaning communities are highly vulnerable to flooding compared to the rest of the UK. The rest of the catchment is classed as “relatively low”, meaning they are slightly less vulnerable.

Priority Areas and Drivers

Flooding

The Social Flood Risk Index (SFRI) is a geographic measure of flood disadvantage. It identifies communities who are both exposed to flood risk by living on a flood plain and who are more vulnerable to the effects of flooding, due to factors such as health, preparedness and the availability of community support. Higher numbers of people living in a flood plain coinciding with high social vulnerability result in higher index values. The map highlights neighbourhoods identified as at risk of fluvial flooding higher than the national average. Please note that this is based on flood

risk from rivers and the sea, so coastal areas may not be affected by changes in land management upstream.

At present, most of the catchment within the valley is classed as “Low” in the SFRI for river and coastal flooding, and this decreases to “No exposed population” in future predicted scenarios of 2 and 4 degree temperature increases by the 2050s. However, the centre of Honiton (as identified on the previous page as Relatively High on the NFVI) increases from “Low” to “Moderate” in a 2 degree temperature increase by the 2050s scenario, and increases further still to “High” in a 4 degree increase scenario. The tops of the plateau remain at “Exposed” but the NFVI stays below the UK mean in all scenarios.

Priority Areas and Drivers

Flooding

When considering flooding, it is necessary to investigate records of previous flood events and combine this with modelled scenarios of what could happen, particularly in the face of the uncertainty of climate change affecting weather patterns. The Gissage has previously flooded in 2 places in July 1968 where channel capacity was exceeded with no raised defences and there is a single building overlapping the recorded flood outline in the south, but multiple buildings overlap with the flood outline in the north. There are currently no flood defences along The Gissage in the southern flood outline. In Honiton itself, but there are a series of contiguous artificial walls, embankments, and natural high grounds along the The Gissage on both sides in the northern flood outline. These continue further up the watercourse and end shortly before it reaches the River Otter. These are owned by a mix of private individuals and the Environment Agency. All were previously inspected in May 2021 and their next inspection is due in February or March 2023. The EA’s modelled fluvial Flood Zone 2 dataset show areas predicted to flood from rivers in a storm event so severe it is likely to occur only once every 1000 years. This is also known as a 0.1% Annual Exceedance Probability. Flood Zone 2 was used to identify buildings potentially at flood risk as shown previously on page 8. There are 108 properties in flood zone 2. Here, this extends the entire length of The Gissage and its floodplain closely matches the recorded flood outlines. The EA’s Risk of Flooding from Surface Water (RoFSW) dataset shows the extent of flooding caused by rainwater flowing across the ground towards the nearest water course in a 1 in 1000 year storm event. This overlaps frequently with Flood Zone 2, but also shows depressions in the ground where surface water will accumulate. There are 122 properties at Risk of Flooding from Surface Water. It is the only modelled risk of flooding around the smaller watercourses that feed into The Gissage. Furthermore, it identifies several depressions on the southeast top of the plateau and an area in Honiton south and adjacent to the railway line that is only at risk of flooding from surface water.

Priority Areas and Drivers

Flooding

The upstream rural part of the catchment appears to have a floodplain that is connected to the river and experiences wetting events. This would suggest the modelling is correct and there is flooding in times of high water.

The flooding pinch-point in the rural area appears to be the road bridge which has been repaired in the past and reinforced to mange throughput of water.

The majority of the Gissage surface water from upstream passes this point and so may present an opportunity to hold back water.

The town would appear to be at risk from large volumes of surface water as the valley, slopes, and impermeable surfaces such as roads are all very steep.

Key infrastructure such as the hospital and railway station don’t have problems with flooding towards the Eastern side off the town, further away from the Gissage, although they are elevated and still experience a lot of surface water flowing past on hard surfaces. The Gissage watercourse is heavily channelised through Honiton although the extent of historic flooding wasn’t determined at the time of survey. Surface water runoff and standing water was reported as a problem, as well as observed when a mobility vehicle on the pavement was soaked by a passing vehicle on the road. Picture taken from the road bridge acting as the pinchpoint for ~2/3 of the catchment surface flow.

Priority Areas and Drivers

Flooding

The parish council does have a flooding plan which falls under the Town Emergency Response Group plan (TERG). The TERG is comprised of town councillors and may include other key members of the community. The main body of the plan is contacting appropriate emergency services and people within the town. The National Flood Forum could be used to further identify any groups and to provide support.

Just upstream of Honiton with The Gissage flowing through it, there is the Honiton Bottom Community Nature Reserve.

Priority Areas and Drivers

Water Quality

Clean and plentiful water is vital for a huge variety of our activities, and for supporting healthy ecosystems. Good water quality supports an efficient water supply, healthy natural habitats and cultural ecosystem services. A plentiful water supply is important for drinking water and household use, irrigation, industrial use and for maintaining habitats. Water quality is a key underpinning for the Water Framework Directive. There are no Water Framework Directive monitoring sites, priority wetlands, or aquatic habitats in the catchment. The southern edge of the catchment however borders the Branscombe Nitrate Vulnerable Zone (NVZ) designated for Ground Water, also containing a historic landfill site just outside of the catchment boundary. For more information on water quality go to slide 26.

Priority Areas and Drivers

Water Quantity and Drought Risk

The amount of water available for abstraction is an indicator of how much drinking water is available for people. The catchment sits within an area not currently available for licensed water abstraction (left map) but is bordered to the east and south by areas where water is available for licensed abstraction. In the context of NFM, it is also necessary to consider water availability for plants and wildlife. Drought can cause vegetation to die back, leaving bare soil exposed and more vulnerable to erosion and runoff when it eventually rains. The Vegetation Health Index (VHI) uses satellite data to combine temperature and vegetation condition to characterise vegetation health. Areas are scored between 0 and 1 with lower values indicating low drought risk to plant health and higher values indicating higher risk. Most of the catchment is ranked relatively low at 0.35 on the VHI (right map), indicating low risk to plant life from drought stress, and the southern edge is ranked even lower at 0.295.

Priority Areas and Drivers

Designated Sites

Designated habitat sites, from small local nature reserves all the way up to large national parks, need to be protected for the wealth of benefits they provide to people and the environment, including already providing some degree of NFM. A site being designated can be an indicator of habitat health.

The majority of the catchment, aside form the urban area of Honiton, falls within the East Devon AONB. Just outside the southern tip of the catchment boundary is Knapp Copse Local Nature Reserve. Aside from this, there are no other designated sites for habitats present.

Priority Areas and Drivers

Air Quality

Clean air is important for people’s health and for healthy ecosystems. Air quality is the term used to describe the levels of pollution in the air. When air quality is poor, pollutants in the air may be hazardous to people, particularly those with lung or heart conditions. In the past, the main air pollution problem was smoke and sulphur dioxide from fossil fuels such as coal. Now, the major threat to clean air is from traffic emissions. Petrol and diesel motor vehicles emit a variety of pollutants, principally carbon monoxide (CO), oxides of nitrogen (NOx), volatile organic compounds (VOCs) and particulate matter (PMx). A growing body of research suggested that smaller particles, in particular PM less than 2.5μm in diameter (PM2.5), is a metric for air pollution which is closely associated with the adverse health effects of poor air quality. Therefore, this section will use data relating to PM2.5 where relevant. Improvements to the soil and surrounding environment have the potential to also deliver improvements to air quality through natural filtering processes. The Honiton area has a relatively high concentration of air particulate matter of 7.67PM2.5 from emissions, but this falls in the centre and south of the catchment to the lowest value of 6.56PM2.5, possibly due to the sparse roads and lack of proximity to urban areas. It is important to note that the High Street running through Honiton is an Air Quality Management Area.

Priority Areas and Drivers

Tourism and Recreation

Areas and features important for tourism and recreation may also be at flood risk and it is necessary to protect them for a healthy society and environment.

The catchment exhibits several greenspaces in the north in Honiton, 8 of which are play spaces. The large greenspace north of the railway line at the confluence of The Gissage and the Glen Brook contains a playing field and a bowling green belonging to Honiton Bowling Club. Another playing field can be found south of the railway line with a small section adjacent to The Gissage. To the east on the edge of the urban area are religious grounds belonging to St Michael And All Angels Church. The large greenspace on the eastern edge of the catchment is a golf course on top of the plateau belonging to Honiton Golf Club. A network of Public Rights of Way (PRoW) run through Honiton, one of which connects the religious grounds to the golf course. Another PRoW intersects the southeastern tip of the catchment. The southwestern top of the plateau, identified in the land cover map as both heather and arable, is Countryside Right of Way (CRoW) Access Land.