Fao: Loreta Adams / TFS Project Manager
Environment Agency,
Olton Court,
10 Warwick Road,
OLTON
SOLIHULL
West Midlands B92 7HX
03 Jul 04
Dear Loreta,
Re.: MODELLING GUNTHORPE TFS
Your response dated 28 June, posted second class and received after the closing date for
comment to TFS, is noted - I am sorry to say we are going in a circle on this matter. You have
introduced more questions which require answers in some ways.
I am grateful to receive your positive confirmation that the defences for Nottingham (opened
1955) have displaced natural flood plain storage to the detriment of those downstream at
Gunthorpe: this issue will be considered carefully should further proposals be put forward to
add to the defended threshold.
You have introduced a new modelling reference of FR14S (‘spill unit’) which does indeed have
an alignment to reflect the flow (211 cumecs – 100 yr) across the A6097 north of Lowdham
Leisureworld. Unfortunately you do not provide height datum. However I suggest that this is
NOT the reference to identify whether the node against the upstream bridge structure is that
which can be considered as valid: I repeat that 0010 is fully confined by the embanked
topography. In the JBA Tarmac model FR15 and FR16 were positioned to deal with the
question of flow between the main channel and the floodplain. In the JBA and the previous
Newark Model a node ref. 72829U reflected the point B&V have seemingly rescheduled as
0010.
I must have written badly if you feel that I have said that “flow cannot pass to the north of
Gunthorpe”. You will know that we have identified the flows in our detailed observations which
we have submitted and have full working knowledge of where they are positioned. We say that
the embanked access trackways and land restored to higher than original in the area of old
mineral workings (now Lowdham Leisureworld – see LIDAR) means that the main channel
node 0310 is the most appropriate one which does have an open floodplain relationship on the
north bank affecting The Park / Marlock.. I would say that most people referring to the
mapping in the TFS would conclude that the cross sections for 0050 and 0010 are quite
correctly limited in extent. Only 0310 is considered as having full flood plain extent towards
the railway. Both 0010 and 0050 are plotted with the data from LIDAR undoubtedly
indicating an obstruction.
To cross check this situation I suggest that you consider the landform height at the junction of
Main Street and A6097 and the reading by EA for 2000 on the upstream point of the bridge:
this is indicative of my point since the river height 2000 at the point is deemed 17.860 –
17.900mAOD.
I believe you will find the road crown height at the junction to be in the region of
17.600mAOD yet it was covered to a substantial depth – probably 600 – 750mm with water
flowing across very strongly. ( We have often referred to the hydraulic gradient issue from the
junction to Trentside / Unicorn location as being in the order of 500mm – 600mm.).
Due to misunderstanding my point you do not address my statement that the water cannot
pass onto the floodplain at your node ref. 0010. There is no physical continuity. Your own
graphs of the cross sections proves this point. The height data for that node relates only to a
very small cross section (circa 120 metres) – and in no way does it relate to the area of The Park
north of Main Street. Nor does it relate to the flooding in the Trentside location just
downstream of the bridge. On a more basic level my simple mind tells me that if you put a
simple obstruction in a flow of water there is a build-up immediately in front on the obstruction
due to pressure and the capacity which is blocked passes either side if unconfined. Similarly,
we all know that there is a depression on the downstream side for a short distance. I believe
your terminology is “headloss”.
In my letter 15th June I identified a series of node references and the various data: these show
the difference aspect: and it is that difference between the data that is not being answered.
Why does Table 11 show that an apparent increase of 240 cumecs delivers one estimation of rise
of river height at any particular node in the scheduled list I provided and an increase of 181
cumecs delivers a substantially greater rise? That schedule is comparing data for a node and it
becomes irrelevant whether it is the ‘correct’ node.
As you will appreciate unless access is given to other data the reader of TFS is not aware of the
location of FR14S: this is a new element brought in by JBA when they modelled for Tarmac
Central Limited and decided to consider part of the previously annotated GUNTHORPE
Storage Area as a flow route: JBA split the Newark Model node or section references into one
set retaining the Newark Model reference for the Main Channel and a new set providing cross
sections of the north bank floodplain. B&V do have the FR14S flow value in the ISIS dataset but
I do not spot any others from the B&V annotation / mapping.
The issue now appears that B&V and EA choose to ignore the impact of the Report in respect
of how this might reflect on ABI member insurance risk assessment by saying that “this issue is
not part of the remit for this Strategy”: those of us affected find this a remarkable position since
the TFS makes clear that the final mapping will become the replacement Indicative Floodplain
Mapping accessed by third parties in evaluating the flood risk. Surely you must recognise you
have a liability of position in that if you are saying that “X” is the result of your work as the
expert and competent body then that can have consequences which are potentially damaging if
“X” is excessive.
We have all recognised – indeed have demanded from Government - the need for vast
improvements to the management of flood risk and provision of protection. We all recognise
that the Strategy is the first basic step in assessing the general overall picture. I happen to feel
it falls well short of our expectation. A plus 620mm to minus 900mm prediction tolerance is
substantial for a study declared “fit for the purpose” and I know full well that around here
people feel very keenly that local expertise and knowledge dictates that the answers of predicted
height need to be carefully cross-examined. It has been admitted by EA that the reach of river
here is a very challenging sector for modelling in the floodplain. Local people are saying to you
that they have concerns and dispute your theoretical modelling in comparison with their hardbitten years of flooding experience of real events.
Yours sincerely,
Roger Fell