Tidal Level Data Request:
Tidal Dee Defended Peak Water level Information
Environment Agency Wales, now Natural Resouces Wales, requested an update to the Tidal
Dee Flood Mapping Report (2007) to incorporate revised extreme sea levels as outlined in the
Coastal flood boundary conditions for UK mainland and islands report (February 2011).
The revised extreme sea levels at the mouth of the Dee Estuary are lower than previous
estimates, as shown in Table 1.
Table 1 Comparison of Extreme Sea Levels at mouth of Dee Estuary
Level (mAOD)
Study
1.33% AEP
1% AEP
0.5% AEP
North Wales Tidal Flood Mapping
6.06
6.17
6.38
Study (Levels to 2007 baseline)a
Coastal Flood Boundary
Conditions Study (Levels to 2008
5.84
5.88
5.97
baseline)b
0.1% AEP
6.70
6.19
The guidance considers these Extreme Sea Levels to be accurate to only one decimal place
and these estimates also now come with associated 95% uncertainty bounds (quoted in Table
2).
Table 2 Tidal Still Water levels (2011) at mouth of Dee Estuary (m AOD) and Confidence
Limits
Extreme Sea Level
Confidence Intervals
5% AEP
5.67
+_0.1
1.33% AEP
5.85
+_0.1
0.5% AEP
5.98
+_0.2
0.1% AEP
6.20
+_0.3
ISIS/TuFLOW hydraulic models of the tidal Dee were updated/developed as part of the Dee
Strategy (2010) using new survey data made available for the strategy.
Tidal Dee Peak levels at each node in the 1D model have been extracted for the defended
model scenarios. The Tidal Dee defended water levels for the node points closest to the site
location are shown in Table 3 for a range of return periods (events). E.g. The 1 in 200 year
return period tide, which is equivalent to the 0.5% AEP (Annual Exceedance Probability).
Table 3- Tidal Dee Defended Peak Water Levels, extracted from the 1D model produced for the Tidal Dee Flood Mapping Update 2011. (mAOD).
The base year used is 2011.
Climate Change Scenarios
Node Point ID Eastings Northings
00010114710
00010114210
00010113710
00010113210u
00010112990
00010112710
00010112210
00010111710
00010111450
00010111210
00010110710
00010110210
00010109710
00010109210
00010108710
00010108210
340258
339782
339680
339762
339581
339413
339090
338769
338602
338367
337869
337413
336984
336557
336129
335701
365532
365578
366030
366511
366629
366420
366037
365653
365454
365402
365347
365514
365773
366035
366296
366557
0.5%
AEP
(2011)
6.31
6.32
6.35
6.42
6.42
6.40
6.43
6.45
6.46
6.46
6.48
6.48
6.49
6.49
6.49
6.49
0.1%
AEP
(2011)
6.47
6.46
6.48
6.57
6.58
6.55
6.57
6.60
6.63
6.63
6.65
6.65
6.65
6.66
6.67
6.67
0.5%
AEP
(2061)
6.56
6.55
6.55
6.66
6.67
6.64
6.68
6.71
6.74
6.73
6.77
6.78
6.79
6.79
6.82
6.83
0.5%
AEP
(2086)
6.72
6.68
6.66
6.84
6.84
6.79
6.86
6.91
6.95
6.94
6.98
6.97
7.01
7.04
7.06
7.05
0.5%
AEP
(2111)
6.99
7.01
6.99
7.11
7.11
7.07
7.11
7.15
7.19
7.17
7.22
7.22
7.25
7.26
7.28
7.28
Sensitivity Analysis
Scenarios
0.1%
AEP
2011
Upper
Band
6.65
6.62
6.62
6.77
6.78
6.74
6.78
6.82
6.86
6.85
6.90
6.90
6.91
6.94
6.97
6.97
0.5% AEP
2111
Upper
Band
7.07
7.10
7.07
7.18
7.19
7.15
7.19
7.21
7.25
7.24
7.29
7.29
7.32
7.33
7.35
7.36
00010107710
00010107210
00010106710
00010106210
00010105710
00010105210
00010104710
00010104210
00010103710
00010103210
00010102710
00010102220
00010101970
00010101720
00010101240
00010100740
00010100240
00010100000
Est_24000
Est_23000
Est_22000
Est_21000
Est_20000
Est_19000
Est_16000
Est_15000
335274
334845
334417
333989
333561
333133
332705
332277
331849
331422
331002
330583
330367
330123
329625
329192
329025
328871
328069
327307
326572
325841
325192
324852
322649
322091
366818
367078
367339
367599
367859
368120
368381
368641
368901
369164
369438
369713
369836
369893
369943
370149
370615
370804
371550
372191
372848
373506
374187
375111
375610
376418
6.49
6.49
6.48
6.47
6.48
6.48
6.48
6.47
6.48
6.48
6.48
6.48
649
6.47
6.49
6.49
6.47
6.47
6.54
6.52
6.52
6.50
6.50
6.49
6.47
6.47
6.69
6.69
6.69
6.69
6.71
6.71
6.70
6.68
6.69
6.70
6.69
6.68
6.70
6.69
6.70
6.71
6.69
6.68
6.75
6.74
6.73
6.71
6.70
6.69
6.69
6.69
6.84
6.84
6.84
6.86
6.88
6.88
6.87
6.86
6.88
6.88
6.87
6.86
6.85
6.85
6.86
6.86
6.83
6.83
6.89
6.88
6.86
6.84
6.84
6.84
6.84
6.84
7.07
7.10
7.12
7.12
7.13
7.15
7.17
7.18
7.18
7.16
7.18
7.19
7.19
7.18
7.15
7.17
7.16
7.15
7.19
7.15
7.13
7.11
7.12
7.13
7.13
7.13
7.28
7.30
7.32
7.33
7.37
7.38
7.40
7.40
7.43
7.44
7.45
7.46
7.47
7.46
7.47
7.47
7.44
7.43
7.51
7.49
7.46
7.45
7.46
7.48
7.48
7.47
6.97
6.98
7.01
7.03
7.04
7.03
7.04
7.06
7.08
7.06
7.04
7.05
7.06
7.05
7.04
7.02
7.02
7.03
7.05
7.03
7.01
6.99
6.99
7.00
7.01
7.01
7.37
7.39
7.40
7.40
7.44
7.45
7.47
7.49
7.53
7.54
7.55
7.58
7.60
7.59
7.62
7.63
7.59
7.58
7.66
7.66
7.64
7.64
7.64
7.65
7.64
7.64
Est_14000
Est_13000
Est_12000
Est_11000
Est_10000
Est_7000
Est_6000
Est_5000
Est_4000
Est_3000
Est_2000
Est_1000
321265
320918
320451
320248
319896
320594
320174
319627
318992
318347
318017
317700
376979
377846
378658
379623
380564
383146
383930
384740
385519
386290
387214
387800
6.45
6.42
6.41
6.36
6.34
6.25
6.21
6.17
6.13
6.08
6.02
5.98
6.67
6.66
6.65
6.62
6.59
6.49
6.45
6.41
6.38
6.32
6.25
6.20
6.82
6.81
6.80
6.78
6.75
6.65
6.60
6.56
6.52
6.46
6.39
6.34
7.13
7.11
7.08
7.08
7.06
6.96
6.92
6.87
6.82
6.74
6.68
6.63
7.44
7.42
7.41
7.39
7.37
7.29
7.25
7.21
7.17
7.09
7.02
6.99
6.99
6.98
6.97
6.95
6.94
6.83
6.78
6.74
6.69
6.61
6.54
6.50
NB/
Please use the relevant ‘Location of Tidal Dee Nodes PDF’ to determine which of the above water levels are closest to your area of interest.
The colour coding above relates to nearest hydrograph label to use. (See diagram below)
7.62
7.60
7.58
7.55
7.53
7.44
7.41
7.37
7.34
7.28
7.21
7.19
Figure 1.1- Tidal Hydrographs in the 0.5% AEP event including the Upper Confidence
Bound in 2111.
Figure 1.2- Applicable Reaches for the Design Tidal Hydrographs
© Crown Copyright. All rights reserved.
1002419, (2012).
Additional Information
For further guidance on the water levels and hydrograph use, please speak to our internal
Development and Flood Risk Team on 01244894582.
References
a.
b.
North Wales Tidal Flood Mapping Phase II Report, Atkins January 2008
Department for Environment, Food and Rural Affairs, 2011. Technical Report Design
sea levels. R&D Report SC060064. Defra/Environment Agency
Notes
The information enclosed all relate to the Tidal Dee Defended scenario.
Undefended scenarios are provided as being a possible worst case scenario in the event of
defence failure. They are used as the basis of the Flood Map.
The scope of the model is the mapping of flood risk, it is not intended for detailed
design. The model should be considered as the starting point for more detailed
modelling, commensurate with the consequences of flooding at the site of interest.
Former EA Wales models are now Natural Resources Wales models, they are available
under licence agreement for the purpose of further development. Contact Natural
Resources Wales External Relations for details of terms, conditions and pricing.
If the data is used in support of an FRA/FCA, please include the reference number.
Please refer to Natural Resources Wales standard terms and conditions