The Lower Sheering SWMP is within the administrative area of Epping Forest District Council and is ranked tenth within the county in terms of properties at risk of surface water flooding. The study area is approximately 12.45km2 and spans the administrative boundary into Sawbridgeworth, Hertfordshire.

The study area is characterised by valley topography with areas of high elevation in the North-east, and North-west, falling to the South  onto the floodplain of the River Stort. The catchment is underlain by solid and drift geology of Clayey Loams, Sandy Loams and Clay to Silt, which vary from relatively freely draining (Sandy Loams) to soils that impede flows (Clayey Loams).

The River Stort and the Sawbridgeworth Brook run through parts of the study area. The River Stort is the largest watercourse, and it begins to the North of the townships before travelling South, dividing Sawbridgeworth and Lower Sheering until its confluence with the River Lea. The Sawbridgeworth Brook is a designated main river and flows through Sawbridgeworth from West Road, along Chalk Farms and then Brook Lane. Various other ordinary watercourses drain from Lower Sheering and Sawbridgeworth into the River Stort.

3 CDA’s have been identified within the study area and around 170 residential properties identified as being at risk of surface water flooding during a 1 in 100 year storm, or 1% Annual Exceedance Probability (AEP). This has potential to increase to around 270 residential properties should the upper limit of 40% be considered to account be considered to account for future climate change. There is a history of surface water flooding within the area that reinforces the LLFA’s decision to conduct a more detailed study here.

Map of Lower Sheering Study Area

1) The SWMP Study Area represents the extent of the LLFA’s hydraulic modelling and detailed modelling data can be made available within this area. The Risk of Flooding from Surface Water (RoFfSW) mapping should continue to be referenced for an indication of surface water flood risk outside of the SWMP Study Area boundary.

2) A Critical Drainage Area (CDA) is a discrete geographic area (usually a hydrological catchment), within the SWMP Study Area where multiple or interlinked sources of flood risk cause flooding during a severe rainfall event thereby affecting people, property, or local infrastructure.

Summary of Flood Risk across the Study Area

Table 1

AEP*	Residential †	Non-Residential ‡	Critical Service §	Total
10%	77	3	0	80
5%	-	-	-	-
3.33%	110	4	0	114
1.33%	152	11	0	163
1%	174	12	0	186
0.50%	236	12	0	248
1% CCL**	232	12	0	244
1% CCU***	267	15	0	282

* Annual Exceedance Probability (AEP) = Chance of a rainfall event occuring, or being exceeded in any one year.
** Climate Change Lower (CCL) = Lower Climate Change increase, taken as 20% additional rainfall.
*** Climate Change Upper (CCU) = Upper Climate Change increase, taken as 40% additional rainfall.

† Residential Property = a building used, or is suitable for use as, a dwelling.
‡ Non-Residential Property = property other than residential, such as office buildings, shopping centres, businesses, churches, hotels, hospitals, schools or government buildings.
§ Critical Service = includes services such as power, water, sewer, wastewater treatment, communications, education and emergency medical care.

Table 2

			Residential Properties
No.	CDA Ref.	CDA Name.	1% AEP	1% AEP+CCU
1	LSH_003	Lower Sheering	94	150
2	LSH_001****	Sawbridgeworth Brook	59	83
3	LSH_002****	April Place	18	24

**** Critical Drainage Area (CDA) is located in the Hertfordshire County Council administrative area. Refer to the Hertfordshire LLFA for Sawbridgeworth Surface Water Study - Technical Report (June 2020), containing further details.