A Basic Appraisal of Flood Risk in Sprowston and the need for Existing Homes to be assured Protection
(By Robert Craggs a member of the Sprowston T.C. Flood Risk Working Party)

Summary & Purpose

The dramatic increase in development in Sprowston has progressively raised concern about the increased propensity for flooding to existing homes and fundamentally because it is in e in a flood plain. New homes and buildings can be sited and constructed to avoid flooding but not existing homes. Hence the focus on preventative action and assurance.

Climate change is blamed for the flooding generally in the UK but in reality it is more attributable to building on flood plains where one can expect the ground to saturated

Introduction:
The purpose of this description is to remind residents of the difficult situation we have been put in by the failure of authorities to ensure proper protection of existing homes, and
worthy though the work now being done by the Greater Norwich Local Plan Team, this should have preceded the approval of the massive developments approved for Sprowston.

It is very apparent now that the initiative taken by Sprowston Parish Council in 2011 in forming their Flood Risk Working Party should have been adopted years ago by both Broadland DC and Norfolk CC because consultation and input of local knowledge is vital to such a strategy

You will see the Interactive Mapping System displayed on the Greater Norwich Local Plan Regulation 18 Draft Plan and it will be very worthwhile to explore this in detail at the forthcoming Roadshow. To make sense of these maps one needs computer facilities to navigate, zoom in and try and understand the interaction of the dynamics in play.

Trying to superimpose massive developments on a map of a flood plain where the presence of groundwater is unknown - in order to understand flood risk - is not easy. Understandably, many will not be up to the task and given the complexity, I tend to put myself in that category. However, the anecdotal evidence of residents is crucial to compiling an authentic map despite the reluctance they may have to disclosing information that might affect the value of their homes.

By way of my own contribution to understanding the propensity of flood risk in this area, I am submitting this basic description of the dynamics of surface water and groundwater in this area, because of the importance but hidden nature of the latter. This description is but of one part of Sprowston but hopefully it may assist residents in identifying key factors contributing to flooding. This description therefore is a microcosm of a wider problem but the principles are the same.

My concerns about flood risk to existing homes spans over two decades where I have been very critical of the failure of Developers, Planning Authorities and the Environment Agency because of their failure to consult on such a critical issue and where due diligence has not been exercised. Consequently, when appeals become complaints and these are still ignored, residents need to exercise their own due diligence to get proper assurances.

Description of drainage systems and propensity of flood risk to some areas of Sprowston.
What follows is a brief description showing how water can travel above and below ground and backing-up to cause flooding.

I do not know when the drainage culverts in Sprowston were created, but it is over thirty years since ‘old timers’ informed me that these had ‘always been there’. It is possible that they preceded the days when clay was extracted for brick-making. Then, drainage channels would have been dug to get access to further deposits but adding to the difficulty now, in understanding where water is coming from and where it is going.

This could explain the dilemma admitted by Peter Brett Associates when they could not understand the flooding dynamics around the Sprowston P&R site when they carried out the FRA in 2012 for the consortium of Developers represented by Beyond Green’s Planning Application 20121516. The old-fashioned drainage pipes I observed appeared to suggest this

The previous FRA carried out before this re-sited P&R was approved, was a disaster when the site was designated as having a 1 in a 100 -year risk of flooding when local residents told them that it was a regular occurrence, just as it was on Home Farm before the area adjacent Wroxham Road was developed.

Water falling on or draining into Sprowston, drains in a northerly direction towards the River Bure, except in the south where it drains into the Wensum and the Yare

Reference to an Ordance Survey map will help to follow this description. GNDP SFRA Index Grid map GN 35, can also be consulted but the area discussed is slightly off this map – in fact this GN35 map fails to show what is described here what in effect is a drainage path:

1. There is a drainage lagoon with boreholes off Roundtree Way which I assume links with:

2. The Drainage Lagoon with 16 boreholes adjacent the UCP/Crown Cork Factory off Salhouse Road. Which has overflowed several times causing flooding

3. This lagoon in turn drains via 3 x 300mm pipes situated under Blue Boar Lane adjacent Wyevale Garden Centre. Also there is another 300mm pipe /drain under the the junction of Blue Boar Lane and Wroxham Road this delivers into the culvert between Wroxham Road and the Tesco Fuel Station

4. These three 300mm pipes deliver into the main drainage culvert on Home Farm that has a 1 in 600 drop running past Tesco Supermarket. When the height of this water increases it obviously starts to back-up and if it meets saturated ground it will back-up much faster which is known to be the case causing the lagoon in 2 above to spill over

5. This main culvert runs past Tesco en-route to the golf course. A water table one metre below ground level was ‘discovered when Tesco re-sited their car park, and where:

6. Frequent overspills have been experienced near Tesco Fuel Station in the vicinity of the bridge over the other drainage culvert that runs parallel with Wroxham Road. Described in 4. above

7. Even before this very large area was asphalted to extend the Tesco Car Park and construct the Fuel Station water drained into this area of Home Farm that left it waterlogged for several months of the year and even evidenced by an abandoned tractor on more than one occasion, besides flooding the sewer pipe

8. This area described in para 7 is now developed with houses that stand on significantly elevated footings to avoid flooding. And under the road system on this development large diameter concrete pipes are installed forming an underground reservoir in conjunction with a large collection chamber on the Blue Boar Lane side of the bridge. This water collection system operates a controlled release into the culvert. This has been overwhelmed in the past

9. This culvert drains into the lagoon created at the junction of Wroxham Road and Marriott Way. This makes three lagoons at this juncture, with the two at the Park & Ride with boreholes that drain into a culvert on that western side of Wroxham Road en-route to the Springs at Rackheath. The other lagoon drains into the series of lagoons off Marriott way

10. Similar drainage facilities on the Sprowston Golf Course will be well known to golfers.

11. There has been a significant increase in the number of drainage lagoons/SuDs systems created in the past few years and it is noticeable how rapidly these fill up as will be observed by drivers along Mallards way.

12. And drainage carries on en-route to Rackheath Industrial Estate that has experienced flooding (as has Rackheath Hall in the past).

13. What is not fully known is the presence and extent of groundwater. It is there under the Sprowston Park & Ride and has even been evident after a drought. Groundwater was not only not plotted or monitored by the Environment Agency, but they never even kept files on what was reported to them about groundwater. Indeed, they did not even monitor flooding unless it occurred near rivers or the sea.

The drainage system or series of systems described above, constitutes but one ‘drainage path’ so to speak, within Sprowston and where flooding has been reported in recent years. To what extent these incidents can be linked to the drainage path described above is a matter of conjecture. For certain, part of this flow of water is linked and most likely this linkage is continuous This can mean that water trying to drain can be impeded and back up, this is not just a possibility but a likelihood, irrespective of the distance involved.

The attenuation of water upstream is a classic means of preventing flooding, but the attenuation of water downstream can do the opposite.

The biggest threat to flooding as we know is saturated ground and this entire area is low lying in a flood plain where groundwater will present a barrier to drainage; while simultaneously surface water run -off, accelerated by ever more hard surfacing, with less land for water to percolate - is a fair description of Sprowston

There are now considerably more drainage lagoons/ SuDs systems between us and the Broads and the sea generally but this does not constitute a safeguard for water backing up, and surface run-off will back up when it meets saturated ground. And it needs to be borne in mind that the Wensum is tidal in Norwich which is an indicator in itself.

Also, water from Old Catton and Spixworth where developments are also planned increase the vulnerability for flooding to existing homes which makes the careful mapping of surface and groundwater behaviour in Sprowston all the more critical.

That the wider area can be designated arid from an agricultural point of view does not detract from the propensity of flooding, on the contrary these environmental conditions are well known bed-fellows.

The Greater Norwich Strategic Flood Risk Assessment is the right approach that we all need to contribute to, but I am dismayed that so little has been achieved in getting to grips with the actual details of drainage within Sprowston and which iI expected to now see mapped, for example on Index Grid GN 35 map having dedicated a meeting in August 2017 discussing this at some length.


What cannot be ignored is the flawed approach to approving Planning Applications.

The Greater Norwich Strategic Flood Risk Assessment acknowledged that previous FRA’s and SFRA’s were flawed and this were critical to planning applications. The GNLP SFRA lists only 5 incidents of flooding in the Sprowston Area but this cannot be a true representation of the situation and facts such as those described above which were well reported but were not analysed to ascertain their potential effect.

Arbitrary but erroneous assessments of ‘once in a hundred-year event’ of risk of flooding occurring have been wrongly stated: For example, the Sprowston P&R site and the Home Farm Development were negligently given such assessments when evidence to the contrary was presented and scrutiny of FRA’s denied despite protest.

This SFRA is assembled by Norfolk County Council as the Lead Local Flood Authority (LLFA), and it is drawn from information from District Councils and the City Council; but Broadland DC Planners stated categorically that they ‘know next to nothing about flood risk’. This may explain why there is an absence of the information about flood risk in Sprowston described above?

The situation was always complex as the river system shows, however, it is now considerably more complicated as a result of very large developments being approved what is disappointing about the JBA Consulting Report for the Greater Norwich Area Strategic Flood Risk Assessment Final Report: Level 1 November 2017 – viz

https://gnlp.oc2.uk/docfiles/46/2017s5962_greater_norwich_area_sfra_final_v2.0.pdf

is that instead of providing actual and progressive analyses of potential flood risk, it largely restates what we called for years ago. Even Planning Policy Statement 25 Development & Flood Risk Dec 2006 served the purpose in stating what should be done before planning applications were approved. This was best done by listening to local anecdotal evidence and scrutinising Developer’s FRA’s and SFRA’s but for reasons yet to be explained this is precisely what was not done.


Statements in this Final report Nov 2017.
Such as, quote: “ ---how interacting sources of water can have a profound effect on the extent of flood risk.” end quote: These were the very grounds of our concerns, especially where there are contiguous developments. Isn’t this precisely what we stressed years ago when the preferred solution was to export water or change the dynamics of drainage.

Major flooding in the Norwich area is a fact of history, and the primary factor in predicting where flooding will occur in the future is where it has occurred in the past. However, minor areas of flooding become much more important where developments are planned and it is imperative to examine these in relation to FRA’s. That only 5 instances of flooding have been reported in the Sprowston area cannot be a true representation.

Site-specific Flood Risk Assessments
Page 11/152 of the above link states that quote: “Developers should, where required, undertake more detailed hydrological and hydraulic assessments of water courses to verify flood extent” end quote. This identifies the biggest single failure because local residents have ‘site-specific’ knowledge, therefore an important source of information and they are best placed to scrutinise FRA’s; but there has been a conspicuous failure here.

Surface water management and SuDS
Page 12/152 of the above link states quote: “Planners should be aware of the conditions and local requirements set by Norfolk County Council, the Lead Local Flood Authority (LLFA), for surface water management for major and minor developments and ensure development proposals and applications are compliant with LLFA’s policy” end quote
Yet the presiding Planning Officer for the Beyond Green Consortium Planning Application 20121516 that includes land owned by Norfolk County Council publicly stated in the Planning Committee Meetings in May 2013 when this application was approved that he ‘knew next to nothing about flood risk’ and did not believe anyone else in Planning did either and stressed this by stating that he did not even know what SuDS were. Despite this creating considerable dismay and complaint, he repeated this virtually verbatim at the Reconsideration Planning Committee Meeting on 11 March 2015. And this despite personal protest about not being allowed to see the Peter Brett Associates FRA before this meeting because I had previously seen a draft that was patently flawed.

Impact of additional development on flood risk. Page 48/152 - also shown as is page 24 of the JBA Consortium of Norfolk Authorities Strategic Flood Risk Assessments) states, quote
“When allocating land for development, consideration must be given to the potential cumulative impact of development on flood risk. The increase in impermeable surfaces and resulting increase in runoff increases the chances of surface water flooding if suitable mitigation measures, such as SuDS, are not put in place. Additionally, the increase in runoff may result in more flow entering watercourses, increasing the risk of fluvial flooding downstream” – end quote. This reinforces the need to have scrutinied the FRS’s and the then respective SFRA’s

Conclusions:
The exhortations in this JBA Consulting Report for this GNLP SFRA Final Reports November 2017 are exactly the same sentiments that turned into warnings years ago. Knowing the impact of development on flood risk, the obvious question is why has Sprowston with its massive planned and approved developments not received priority treatment in mapping and understanding the factors that have dramatically increased the propensity for flood risk?

R Craggs 17 Feb 2020