The South Essex SWMP spans the administrative areas of Basildon, Castle Point and Rochford District Councils. The study area is ranked highest within the county in terms of properties at risk of surface water flooding and is also recognised nationally as a Flood Risk Area (FRA) by the Environment Agency.

Canvey Island is located within the study area and is an FRA in its own right. This is due to the nature of flood risk, arising from multiple flooding sources and complex asset maintenance requirements.

There are multiple and interlinked sources of flooding across the three administrative areas, which require a holistic approach to management. Some primary mechanisms of flooding identified, include river valleys (i.e. The River Crouch, Nevendon Brook, North Benfleet Brook, Basildon Brook, Prittle Brook, Rawreth Brook and the River Roach.), low lying areas, railway embankments and cuttings, topographical low points and local drainage network capacity.

35 CDA’s have been identified within the study area and around 6,800 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 could increase to around 12,000 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 South Essex 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%	787	49	3	839
5%	1837	113	10	1960
3.33%	2656	171	12	2839
1.33%	5583	331	19	5933
1%	6803	396	22	7221
0.50%	10194	542	30	10766
1% CCL**	9487	514	29	10030
1% CCU***	12039	628	36	12703

* 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.

Summary of Flood Risk - Basildon District

Table 1

AEP*	Residential	Non-Residential	Critical Service	Total
10%	468	27	2	497
5%	1108	55	3	1166
3.33%	1588	100	3	1691
1.33%	3372	213	6	3591
1%	4115	263	7	4385
0.50%	6121	362	9	6492
1% CCL**	5718	343	9	6070
1% CCU***	7231	421	11	7663

Table 2

			Residential Properties
No.	CDA Ref.	CDA Name.	1% AEP	1% AEP+CCU
1	NBAS_001	Felmore	17	108
2	NBAS_002	Barstable	111	244
3	NBAS_003	Lee Chapel North	17	77
4	NBAS_006	Laindon	39	111
5	NBAS_007	Southfields	28	51
6	NBAS_008	Vange	47	75
7	NBAS_009	Pitsea	0	0
8	NBAS_010	Runwell	83	147
9	NBAS_011	Wickford Centre	169	281
10	NBAS_012	Bromfords	234	454
11	NBAS_013	Cranfield Park	69	330
12	NBAS_014	South Green	4	10
13	NBAS_015	Sunnymede	42	67
14	NBAS_016	Billericay	117	167
15	NBAS_017	Stock Road	71	96
16	NBAS_018	Great Bunstead	11	28
17	NBAS_019	Bowers Gifford	32	33
18	NBAS_020	Kingswood	116	199
19	NBAS_021	Lee Chapel South	27	105

Summary of Flood Risk - Castle Point District

Table 1

AEP*	Residential	Non-Residential	Critical Service	Total
10%	34	7	0	41
5%	92	11	2	105
3.33%	141	13	2	156
1.33%	286	19	2	307
1%	353	21	2	376
0.50%	566	27	2	595
1% CCL**	523	26	2	551
1% CCU***	679	29	2	710

Table 2

			Residential Properties
No.	CDA Ref.	CDA Name.	1% AEP	1% AEP+CCU
1	NCAST_001	South Benfleet	60	91
2	NCAST_002	North Canvey Island	0	0
3	NCAST_003	Leighbeck	0	1
4	NCAST_004	Reeds Hill Farm	3	9
5	NCAST_005	New Thundersley	97	264

Summary of Flood Risk - Rochford District

Table 1

AEP*	Residential	Non-Residential	Critical Service	Total
10%	285	15	1	301
5%	637	47	5	689
3.33%	927	58	7	992
1.33%	1925	99	11	2035
1%	2335	112	13	2460
0.50%	3507	153	19	3679
1% CCL**	3246	145	18	3409
1% CCU***	4129	178	23	4330

Table 2

			Residential Properties
No.	CDA Ref.	CDA Name.	1% AEP	1% AEP+CCU
1	NROCH_001*****	Eastwood	298	509
2	NROCH_002*****	Southend On Sea	604	1352
3	NROCH_003	Rayleigh	27	79
4	NROCH_004	Hockley	127	232
5	NROCH_006	Rayleigh West	54	109
6	NROCH_007	Watery Lane	5	24
7	NROCH_008	Lower Hockley	77	112
8	NROCH_009	Little Wakering	5	32
9	NROCH_010	Garon Park	14	64
10	NROCH_011	Great Stambridge	5	12
11	NROCH_012	Ashingdon/ Rochford	104	163

*****Critical Drainage Area (CDA) extends beyond the Essex County Council administrative boundary into Southend City Council. As a Unitary Authority Southend City Council operate an independent Lead Local Flood Authority (LLFA) function and should be contacted directly about any issues of Surface Water or Groundwater flooding within their area.