The Braintree and Witham SWMP is within the administrative area of Braintree District Council and is ranked seventh within the county in terms of properties at risk of surface water flooding. The wider urban area of Braintree, that encompasses Great Notley and Rayne to the south, has a population of over 50,000, whilst Witham’s population is approximately 25,000.

There are Two notable main rivers that flow through Braintree; the River Blackwater flows in a South-easterly direction through the north of Braintree, and the River Brain, which similarly flows in a South-easterly direction to the south of the main built-up areas of Braintree. Downstream of Braintree, the River Brain continues to flow South-eastwards towards Witham, less than 10km away. The river flows through the centre of Witham before joining the River Blackwater east of Witham and the A12.

5 CDA’s have been identified within the study area and around 460 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 830 residential properties should the upper limit of 40% be considered to account be considered to account for future climate change. There is a recorded history of flooding incidents within the area that corroborates the LLFA’s decision to conduct a more detailed study.

Map of Braintree and Witham 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%	94	48	2	144
5%	235	78	2	315
3.33%	305	91	2	398
1.33%	387	111	2	500
1%	457	128	2	587
0.50%	616	169	2	787
1% CCL**	628	172	2	802
1% CCU***	831	223	5	1059

* 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	BTR_001	Bradford Street	62	142
2	WTH_001	Maltings Lane	29	42
3	WTH_002	Blunts Hall Road	17	19
4	WTH_003	Spa Road	15	25
5	WTH_004	Elderberry Gardens	22	39