Flood Risk Assessment

to support Planning Applications at Watts Folly Arkesden CB11 4HB

Ian Abrams Architect Ltd 5 The Maltings Station Road Newport . CB11 3RN

Telephone: 01799 543533

E-mail: [email protected]

1. BACKGROUND

This flood risk assessment is provided in support of a planning application (Planning Portal Reference – UTT/20/3266/HHF & UTT/20/3267/LB) for the proposed garden room extension that lie within Flood Zone 3 as defined by the Environment Agency. It is intended to be an assessment of flood risk for the planning proposals that is appropriate to the scale and nature of the development.

It is understood that development areas at risk of flooding will only be permitted where the development will not cause or exacerbate flooding in other areas and where flood protection or mitigation measures are incorporated into the application.

The planning and listed building application seeks approval for the extensions and alterations at the property known as Watts Folly, Arkesden. This property is Grade II Listed and the breakdown of the proposals are listed below: i. Single storey glazed Oak frame extension to provide new Garden Room to the rear of the property. ii. Form a link between the existing Rear Hall and proposed new Garden Room, forming new Boot Room and alterations to existing Shower Room.

2. LOCATION DETAILS

The site lies to in the center of Arkesden – 3miles West of Newport and 4.3 miles South-West of Saffron Walden. Arkesden is a and Civil in Essex in the District of . The property fronts the East side of the junction between Hampit Road & Royston Road. Watts Folly is set back from the highway on the other side of Wicken Water, which runs through the village. Watts Folly is Grade II Listed. For more details on the site and historic surroundings, please refer to the attached Heritage Statement prepared by Brighter Planning Ltd.

2.1 Location Plan

The figure below illustrates the location of the property and is taken from the OS Block plans included as part of the planning application. (not to scale – please refer to architectural drawings including within this application for scaled drawings)

2.2 Block Plan

The figure below shows the site of the development and illustrates the proposed extension hatched in red. (not to scale – please refer to architectural drawings including within this application for scaled drawings)

3. FLOOD RISK ASSESSMENT

3.01 Flood Risk

The Environment Agency classifies the site as being partly within Flood Zone 3.

Many of the settlements across Uttlesford have experienced flooding in the past, including (but not limited to) Arkesden, , Berden, Birchanger, Clavering, Debden, Elsenham, Great Chesterford, , Great Sampford, Hadstock, , Hazelend, Hempstead, Henham, Howe Green, Littlebury, Little Hallingbury, Little Walden, Manuden, Newport, Quendon, Radwinter, Saffron Walden, Sewards End, Stansted Mountfitchet, Stebbing, Takeley, , Wendens Ambo, Ugley, White Roding, Wicken Bonhunt and Wimbish. Sources of past flooding have been predominantly from main rivers, ordinary watercourses and surface water.

Flood Zone Definition

Zone 1 Low Land having a less than 1 in 1,000 annual probability of river or sea flooding. (Shown as ‘clear’ on the Probability Flood Map – all land outside Zones 2 and 3)

Zone 2 Medium Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding; or land having Probability between a 1 in 200 and 1 in 1,000 annual probability of sea flooding. (Land shown in light blue on the Flood Map)

Zone 3a High Land having a 1 in 100 or greater annual probability of river flooding; or Land having a 1 in 200 or Probability greater annual probability of sea flooding. (Land shown in dark blue on the Flood Map)

Zone 3b The This zone comprises land where water has to flow or be stored in times of flood. Local planning Functional authorities should identify in their Strategic Flood Risk Assessments areas of functional floodplain Floodplain and its boundaries accordingly, in agreement with the Environment Agency. (Not separately distinguished from Zone 3a on the Flood Map)

3.02 Surface Water Risk

‘Surface water flooding is a problem throughout the District with reported incidents referring to runoff from fields and drains being unable to cope with the storm water. Saffron Walden has been identified as a Tier 2 area of local flood risk due to its surface water risk and flood history’.

The Surface water flooding risk for Arkesden is labelled as “high risk”. High risk means that each year this area has a chance of flooding of greater than 3.3%. Surface water flooding, sometimes known as flash flooding is caused by the following:

• happens when heavy rain cannot drain away • is difficult to predict as it depends on rainfall volume and location • can happen up hills and away from rivers and other bodies of water • is more widespread in areas with harder surfaces like concrete

The risk scenario for the site shows the risk being below 300-900mm. As you can see from the location of the site in relation to the architectural drawings submitted. The flood risk area is to the North of the site. It is unknown if this site risk is from data linked to Wicken Water that runs to the front of the property. As shown on the topographical survey, the site areas to the rear garden are much higher than the front of the property adjacent to Wicken Water.

3.03 Sewer / Ground Water Flooding

There is little or no risk of sewer or ground water flooding reported in this area.

3.04 Fluvial Flooding

The main risk to flooding at the site is Fluvial Flooding from the Wicken Water. The site may be affected by a stretch of Wicken Water which runs below the junction of Hampit Road and Royston Road.

Flows northwest to southeast from Upper Pond Street to its confluence with the (or Granta) at Newport. Mostly Ordinary Watercourse with the 1.5km section downstream of M11 classified as Main River. Flows through Arkesden and Wicken Bonhunt.

The location identifies the level of risk placed upon the site. (The flood map is indicative only and does not provide information regarding levels.)

From the below map taken from flood-warning-information.service.gov.uk you can see that this river risk identification does not follow Wicken Water at the Junction of Hampit Road. It is therefore understood, although the site is within an area at risk of flooding, the potential flooding cause is identified as Wicken Water which is to the front of the site. We do not believe that the extension location at Watts Folly is within this risk area or the adjacent watercourse is not susceptible to flooding in this location.

3.05 The Impact of Climate Change

The impact of climate change has been identified in the Uttlesford Strategical Flood Risk Assessment;

Fluvial flooding

‘The effect of climate change on the fluvial flood extents tends to be small in the district because Uttlesford covers the upper reaches of three river basins. This means the topography is relatively steep resulting in a confined floodplain. The largest increase in flood extent is on the River Cam in Newport, The Slade system in Saffron Walden and in Clavering on the . However, climate change does not just affect the extent of flooding. It is important to remember that even where extent does not significantly increase; flooding is likely to become more frequent under a climate change scenario. For example, what is currently an event with a 2% probability of occurring in any one year, may increase to say a 5% probability under climate change. The impact of an event with a given probability is also likely to become more severe. For example as water depths, velocities and flood hazard increase, so will the risk to people and property. Although qualitative statements can be made as to whether extreme events are likely to increase or decrease over the UK in the future, there is still considerable uncertainty regarding the magnitude of the localised impact of these changes.’

Surface water

‘Climate change is predicted to increase rainfall intensity in the future by up to 30% (the recommended national precautionary sensitive range for 2085 to 2115). This will increase the likelihood and frequency of surface water flooding across catchments, but particularly in impermeable urban areas that are already susceptible such as Clavering, Great Dunmow, Manuden, Radwinter, Takeley, Thaxted, Stansted Mountfitchet, Little Hallingbury and Little Dunmow.’ – Arkesden is not mentioned.

3.0 Conclusion

Although part of the site is identified as been in high risk of the surface waterflood risk area, the risk is low for fluvial flood. Due to the topographical levels on the site believe the reality of this risk is relatively low.

The client is not aware of any history of site flooding to the property during their ownership.

Watts Folly is set back from the Wicken Water and the topographical survey shows that the finish floor level of the ground floor of the property is approx. 1400mm higher than the pavement level which sits adjacent to the watercourse. This is well above the max. 300-900mm depth for the low risk flood scenario for the area.

The application provides for a small single storey extension, (which does not increase the area of surface water drainage) the proposals make use of the existing building and its floor levels. The building has undergone many changes in the past, without the need of a flood risk assessment.

Source information Environment Agency – flood maps Uttlesford’s Strategic Flood Risk Assessment