ROBERTSBRIDGE FLOOD ALLEVIATION SCHEME: THE CHALLENGES OF A FAST-

TRACK APPROACH Nigel Baker BEng CEng MICE *,

John Palmer BSc (Eng) MSc CEng FlCE Fellow* and Garry Elswood. * * *

~ ~ ~~ ~~ ~~ ~~ - ~~~ ~~~~ ~~

ABSTRACT Flooding occurred in many locaHons In the United Klngdom in the aufumn/wlnter of 2 W . One of the worst afected areas was Robertsbrldge, In East Sussex, where, over that wlnter, some properties were flooded up to eight times. Foilowing those events, the Environment Agency targeted defences for this highilsk township as one of /is high priority pro/ects to 'fast-track' to Implementation. WdIes started In January 2001, which recommended a stand-alone scheme that would protect the township against the 1% PrQbabllity flood. Prolect development progressed on a 'fastfrack' basis to allow construction lo stari in September 2002 with completion planned in the summer of 2003. Prolect development and implementatlon is always an obstacle course but the 'fast-track' approach magnifies the obstacles and introduces new ones. This paper describes experience from the Robertsbridge flood a/lev/ation scheme, w h particular reference to some of the problems encountered, both technical and procedural.

Key words: Dedgn and build; 'lasf-tmck'; llood allevlaflon; lkwdgates; and Robertsbd@e.

* Project manager, Environment Agency. ** associate director, Halcrow Group Ltd.

* * * prolect manager, Edmund Nuttail Ltd.

* This paper was originally presented at the Winter Meeting of the Rivers and Coastal Group of ClWEM on 30 January 2004.

INTRODUCTION History Due to its historical location at a crossing point on the River Rother and River Darwell and continued development, Robertsbridge in East Sussex has suffered increased flooding since 1946 Recent flooding has been recorded in December 1993, May 2o00, October and November 2oOo. and February 2001. In October 2000 a flood, estimated to be close to the 1 % event, see Figures 1 and 2, inundated much of the village to depths up to 1.5m and caused substantial damage to over 80 residential and commercial properties.

A study of the Northbridge Street area followed flooding In 1993, but it was the severe problems of 2000. when some properties were flooded eight times, that compounded the need for urgent action. There was considerable support at

local and national level to reduce the flood risk and the scheme's development advanced quickly through studies, design and opprovai. to construction.

A pre-feasibility study was carried out in January/February 2001. which recommended a 'stand-alone' scheme to reduce the risk to the vulnerable parts of the village in parallel with a strategic review of the fluvial reach of the River Eastern Rother. Instructions to proceed through feasibility study, production of a Project Appraisal Report (PAR), and preparation of designs and drawings were given in July 2001, with a timetabie,set for construction to commence in the summer of 2002. This was a challenging programme as the work Included survey and modelling along with a considerable approvals process.

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Fig 1. Ruckley Close, October 2000 Fig 2. High Sheet, October 2000

SCHEME DEVELOPMENT Catchment area The catchment of the River Eastern Rother is shown on Figure 3. The River Rother, which is the major watercourse in the area, rises between Mageld and Heathfield. in East Sussex, and flows eastwards through the High Weaid before skirting the western edge of Romney Marsh and fiowing Into the sea at

Rye. downstream of a tidal sluice at Scot’s Float. About halfway along its course, near Bodiam, the river changes its character from an upland stream to an embanked channel with much of its length below the high tide level. The main upstream tributaries are the Dudwell and the Darwell, which join the Rother at Etchingham and Robertsbridge respectively, and then there are other downstream tributaries, including those draining the Romney Marsh.

lies to the south of the river, except a significant development around Northbridge Street to the north. Since the late 1980s the A21 has bypassed the town to the east (downstream), See Figure 4.

Flg 4. flood envelopes for Robertsbridge

fig 3. River Eostern Rother Catchment

Along much of its length the River Rother has a relatively wide and undeveloped floodplain. which is crossed by several minor and some main roads. In addition, the Hastings to London railway line runs along the valley from Robertsbridge to Stonegate. and crosses the valley upstream of Etchingham. Much of this infrastructure is at risk of flooding, as are parts of Robertsbridge and Etchingham where development encroaches upon the floodplain.

Robertsbridge is a village about 15km north of Hastlngs, at the crossing of the old A21 road and the River Eastern Rother, and where the River Darwell joins the Rother. Most of the town

The Strategic Review and the studies concentrated on the River Eastern Rother from its headwaters down to Udiam gauging station. It was determined that the proposals for Robertsbridge would not affect or be affected by rlver management downstream of Bodiam (near Udiam gauging station), as the river changes character at this point, becoming much flatter and subject to tidal influences (if the Scot‘s Float control structure is not operational).

The catchment area of the Rother down to Udiam is 205km2 with the two main tributaries. the Dudwell and the Darwell, contributing 33km2 and 20km2 respectively, Between Witherenden Mill Weir, near Stonegate. and Udiam. the river falls about 25m over a length of 18km. with an average slope of 1 :720. The flood flow estimates for the Rother at Udiam are in the range of 180m3/s for the five year (20% probability) event to 400m3/s for the 1OUyear (1% probability) event. and 470m3/s for the 200-year (0.5% probability) event.

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Scheme options To determine the best way forward for the provision of flood defence works in Robertsbridge an assessment of generic

options was undertaken: (a) Do nothing - Undertaking no work and allowing

continued (and perhaps more frequent and acute) flooding of the viiiage was deemed to be unacceptable, because it would lead to severe social and environmental disruption and could result in loss of property and livelihood. There are properties, both residential and commercial, which could not be insured for flood risk, or where insurance premiums and/or excess ieveis were not affordable to the owners. There was a consequent risk to the future livelihood and vlbrancy of the communiw.

(b) Do minimum -There are no purpose-built flood defence structures in the viiiage. so simply carrying out ongoing maintenance works on the rivers, clearing out excess debris and build-up of silt would not be sufficient to reduce the risk to local people and their assets.This could have been combined with flood warning as a solution but it had a very low incremental beneflt:cost ratlo.

(c) Improve - This was the preferred approach and a number of options for improving the situation were considered.

The list of possible measures to reduce flood risk at Robertsbridge included: (i) upstream storage (ii) flood diversion (iii) increased conveyance in the channels and over the

floodplain (iv) increased conveyance through the A21 by-pass (v) hard defences (vi) flood prooflng of properties.

These measures were anaiysed and model tested. it was found that defences at the edge of the floodplain provided the best economically justlfled solution that was technically feasible, environmentally acceptable and could be implemented rapidly.

Upstream storage to provide a strategic solution was considered and tested by modelling. but there are no sites that would provide sufficient storage to eliminate the flood risk to downstream properties. The potential for attenuation upstream of Robertsbridge was also tested, but the relative steepness of the vaiiey does not provide for efficient storage over and above that which occurs naturally in the floodplain. A severe restriction on increasing levels upstream of Robertsbridge would be the increased flood risk to the London to Hastings railway line. This option was not considered further.

The issue of the A21 by-pass and its impact on flood risk in Robertsbridge is a sensitive one iocoiiy. The conclusion from the model studies was that there is only a mail head loss as flood flows of the order of those for the 100 year (1%) event pass through the bridges under the A21 by-pass. Removal of the by-pass would reduce the flood level in the Rother by about 0.2m for such an event, but this would be an practical solution and was not pursued.

Fig 5. Location of Works

Scheme description The adopted solution is composed of about 1200m of earth embankment, 800m of floodwaiis. both reinforced concrete and steel sheet piled, and 500m of river realignment protecting the northern, central and southern parts of the town from the 100 year (1 % probability) flood flows in the rivers Rother and Darweii. To secure the defences, four floodgates are necessary to continue the lines of protection across main roads and an access to a factory, and two sections of demountable defences are aiso used. The aim was to continue to maximise the use of the existing natural river floodplain at Robertsbridge without causing increasing flooding locally or to riparian owners downstream.

For this solution the overall scheme can be split into four component parts, as shown on Figure 5 and described below:

(a)The Mill, Rutley Close and Norihbrldge Street - a floodwail, about 1.7m high, to replace the existing

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embankment between the Mill and the River Rother, linking into the road crossing. A floodgate is provided across the road in the vicinity of the bridge linking to a floodwall and an earth embankment, about 1.7m hlgh. to the south of the Mill Stream and through to the A21,

(b) The Clappers - locallsed flood defence of the group of properties, Bridge Bungalow, museum and forge, with the use of an earth embankment approximately 1.5m high. A small wall, about 0.2m high, with a stop-log opening, is provided along the boundary of The Clappers, and there is realignment of the Petty Sewer.

(c) Abbey Mews, High Slreet and Stdon Road (east) - a mix of embankments and floodwalls up to 1.7m hlgh, with a floodgate across the Lower High Street. form the defences from the rear of Abbey Mews and along the right (east) bank of the Darwell to the bridge on Station Road. A floodwall, approximately 1.3m high, continues the defences to the south of the road bridge before tapering into high ground along Piper's Lane.The River Darwell is realigned between Station Road and Lower High Street.

(d) Stdon Road (west) and Village Hall - a series of floodwalls and an earth embankment up to 2.1 m high, including a floodgate and demountable defences around the Gray-Nicolis property, connect to a floodgate across Station Road and an earth embankment, up to 2.3m high, to the south of Station Road and around the Village Hall.

There is appropriate brick or timber cladding to the floodwalls to flt in with the conservation area status of Robertsbridge. The earth embankments are seeded, and there are other areas of landscaping and enhancement.

As Is often the case in village or town environments, the Robertsbridge scheme is compllcated with many complex and varied details, and lime opportunity to standardise units. Poor ground conditions added to the difficulties and over 100 drawings were required to describe the works in detail.

THE FASTRACK APPROACH One of the objectives of the Robertsbrldge scheme was to deliver appropriate works as quickly as possible following the flooding of late 2ooo. indications of a robust stand-alone scheme from the pre-feasibiity study provided the impetus to continue the fast-track approach for scheme development and implementation, and when the feasibility study was started In July 2001, a programme was set for construction to start in July 2002. There were some delays brought about by late delivery of survey data but the contractor mobilised in early September 2002.A~ earthworks form a signiflcant part of the works, there was the realisation that a delay beyond this date would put the programme in jeopardy and result In a

postponement to spring 2003. This was challenging and required collaborative team work

and effective consultation with interested parties to manage the risks associated with such an approach. Factors that contributed to the success were: i. A robust scheme from the pre-feasibility study that allowed studies to advance with confidence

ii. Working with consultees from an early stage, in particular the District Council, Parish Council and local residents

iii. Early involvement of the Environment Agency's senior land's surveyor to prepare the way for land access and compensation agreements

iv. Early information and regular briefings to Defra v. Early development of a suitable procurement strategy, with

appointment and involvement of the cost consultant and preferred contractor from January 2002, ove; three months before the end of the feasibility study

vi. Approval and carrying out of the site investigations in early 2002. before the end of the feasibility study

vii. A public exhibition and consultation before completion of the option appraisal to enable a Planning Applicatlon to be submitted in March 2002, to allow for determination by mid-July 2M)2

viii. Simultaneous review and processing by the Environment Agency's National Review Group (NRG) and Defra from May 2002, concurrent with the determination of the planning application

ix. Advancement of detailed design concurrent with the

approvals p!ocess

Additionally, and most importantly, there has been continuity, integration and close team work. involving staff from the Environment Agency, consultants and contractors. Throughout, a collective commitment to anticipate requirements, to respond to problems and to make the necessary decisions has enabled the fast-track objectives to be realised.

CHALLENGES AND LESSONS LEARNT Throughout development the Robertsbridge flood alleviation scheme has tested the resolve of the team to meet targets and to deliver the required product. Flexibility on the part of the project team has been the key, with open-minded discussions leading to decisions being made promptly and for the good of the project. The experience has. at the same time, been challenging, rewarding and a learning process. and some of the issues are described below.

Programme and concurrent activities The section above on the fast-track approach describes the targets that were set and the factors that contributed to

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meeting those targets. Essential to the achievement were: (i) confidence in the scheme and optimism that C would pass

(ii) a dedicated and committed team prepared to anticipate

(iii) trust within the team that translated into cooperation and

the approvals process

hurdles am to take action to overcome them

support

These and the support from the Environment Agency, Defro and Rother District Council enabled the programme targets to be met. Robertsbridge was not the first fast-track scheme, it will not be the last, but it is another demonstration of what con be achieved when the objective is clear and there is a commitment to it.

Target cost selting and starting with limited works information The involvement of proposed members of the contractor's construction team from an early stage meant that they were familiar with the scheme proposals, which in turn facilitated the estimation of the target cost with only limited works information.The designers and cost consultants were involved in this process, although hindsight suggests that more involvement by the designers and a little more time would have been of benetlt.

In such situations it is inevitable that there are items that are known about but not detailed and specified. The approach taken was to provide provisional sums for those items, such as landscaping. fencing and indeed the floodgates, and then to treat them as compensation events when defined during construction.A better approach would have been to include these items in the risk budget.

Difficulties were encountered in accurately predicting the out-turn cost with this fast-track approach. With limited works information, final construction costs were always going to be uncertain and although elements were included in the risk budget, they subsequently proved to be inadequate by a considerable margin. It is dimcult to predict build costs if details are not known and the risk factors should be comparable to those used on conventional design and build contracts tf future projects follow this example. Flexibility within the project team to balance construction elements with the issue of works information was not reflected within the original target prices and should be recognised during the negotiation process. A tendency towards 'sunny day' estimating of costs and programme should be avoided in such circumstances.

With the situation of limited works information in mind, the risk budget must be set at an appropriate level. What has been learnt on the Robertsbridge scheme is that the risk provision of about 14% ot target cost setting time was inadequate and a figure of double that, and maybe higher,

would have been more realistic. Current guidance on optimism bias would support this, although it must be borne in mind that the process is one of negotiation and there is inevitable pressure from the client to reduce costs.

Design and build Following on from above, the fast-track approach on the Robertsbridge scheme effectively resulted in 'design and build' during construction. This placed addfflonai pressure on both the designer and contractor, and required good co- operation between the parties. A programme w a s agreed at the start of construction to provide the contractor with works information in time to meet his needs. Overall it worked well but flexibility and cooperation was necessary from both sides to adapt to changing circumstances. which again demonstrated the value of integrated team working and trust between its members.

Many factors can affect the programmes of the deslgner or contractor, such as weather, unforeseen conditions, availability of design data, landowner access problems or service diversion delays. Additionaiiy the team has to deal with queries as they arise and this can also disrupt programmes in the short-term as information is adjusted, which points to the need for the project team to have direct control over their design resource in order that the works information can be adapted and issued quickly to mitigate construction delays and costs.

What this has demonstrated is the value of continuity in the design team, the need for sufficient resources to progress designs and drawings and to respond to contractor's queries, and the requirement for flexibility and contingency in the programme to absorb the impacts. As with the risk provision. a float in the programme is recommended on such fast-track projects.

Gates The inclusion of floodgates in a scheme means consequent operation. maintenance and legal implications, and they should be avoided if possible. At Robertsbridge there is the need for the defences to cross public roads at three iocations and sliding floodgates, with heights between 1.0 and 1.4m. were the adopted solution.

The decision process included highway studies, in an attempt to eliminate the need for gutes by raising of road ieveis. but the proximity of junctions, bridges and bends in the roads close to the crossings prevented this. Vertically hinged gates with road narrowing and low road raising were also considered and the traffic calming that w i d have ensued would have been welcomed by the local population. Unfortunately, the traffic calming would have required an independent consultation and decision process, and the

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programme implications of this were unacceptable. Vertically hinged and sliding floodgates plus demountable

defences were considered In the flnal analysls, and the sliding floodgates were selected in consultation with the Environment Agency operations staff. Demountable defences, the likely alternative. would have provided a cheaper solution but the risk of loss of parts whilst in storage, and the time to assemble them, counted against their use. It must be stated, however, that a demountable solution has been used on the scheme to close the defences where they cross a private access track and entrance to the museum.

Programme considerations led to a decision to appoint a sub-contractor with recent experience of manufacture and installation of sliding floodgates of similar dimensions. Subsequent experience does not support that decision and, In retrospect, In-house design and fabrication by a known and reliable sub-contractor would have been better. What happened was further subcontracting of the design and fabrication of the gates to separate companies, but without provision for direct communication between the gate designer, fabricator, civil works designer or the principal contractor. These problems had a detrimental Impact on the overall programme, and small defects proved frustrating to resolve.

Utility companies All utility companies were contacted at an early stage of the studies and information obtained on services known to be In the area.Tria1 pits were also excavated at the locations of the sliding floodgates to determine the depth of services. This provided valuable information and it was apparent that service diversions would present problems in a location such as Robertsbridge with works crosslng roads and in close proximity to existing build1ngs.The reality was much worse than expected, with consequent impacts on programme and costs.

The experience has been that the utility companies remain bureaucratic organisatlons that do not make it easy to have service diversions carried out speedily, their charges for doing work are high, and they take the opportunity to upgrade their equipment. It Is not the place of this paper to single out companies but It is fair to say that some have been worse than others, and there has been the odd case of good cc- operation,

It would have been advantageous to involve the utllltles much earlier In the project in order to foster the aim of getting them to buy into the ethos of the fast-track approach. All efforts In future must be to encourage them to feel that they are part of the project team. In that way they will hopefully take ownership of their crucial role. Nevertheless, it would have helped if the Initial provision of service location

information had been accompanied by details of procedures and who to contact. Thereafter, realistic estimates of costs and dates to do the work would have been an advantage.

Landowners Few schemes are Implemented without some difficulties with landowners. and with schemes such as Robertsbrldge. where the number of landowners affected is relatively high, the diflcuitles can become a problem. The truth Is that out of approximately 25 landowners on whom notice of entry was served, four have proved to be less than co-operative.

The strategy adopted by the team was the early Involvement of the Environment Agency land surveyor to llalse with the landowners to inform them of the proposals and how they would be affected. This resulted In widespread acceptance and the works were allowed to proceed without objection or delay caused by landowners. There has been some accommodation of landowner requirements in the works and there Is much satisfaction with the scheme in the local community, but there have been those who make unreasonable demands.

Those landowners with whom difficult negotiations could be expected were known in advance from previous dealings with the Environment Agency or from informution passed on in discussion with the local community. The options to deal with them are either to accommodate their requirements within reason, or to proceed under the Environment Agency’s powers and accept the decisions of the lands tribunal on compensation. With landowners who are known to be difficult. and when they are advised by land agents, it may have been better to make them offers based on reasonable entitlement. The big risk with this approach would have been delay to the programme if they had decided not to co- operate.

At Robertsbrldge the option of negotiation and accommodation was pursued but the final cost of this course of action is such that It would not necessarily be repeated In similar circumstances. The risk of taking a negotiated approach is that deflning the point at which negotiations should be concluded becomes difficult to assess and if that route is chosen it would be advisable to set a milestone date for resolution with the landowner at the outset. If this date is not met then a more robust approach should be adopted.

DISCUSSION The Robertsbridge flood alleviation scheme is a complex scheme with little opportunity to standardlse component parts and many varied details. Over 100 construction drawings have been required to describe the scheme. approximately 25 landholdings have been accessed during construction, and the utility companies, district and county

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councils and other agencies have been directly involved.The delivery of this complex project within three years of the start of studies is a creditable achievement in which the Environment Agency and the team can take considerable satisfaction. As the title of the paper suggests It has not always been easy, there have been many challenges and lessons have been learnt but with an over-riding commitment to project delivery within the team, the hurdles have been overcome

CONCLUSIONS The conclusions to be drawn from this discussion of the scheme are as follows: @There is a need for decisions on the viability of a

scheme to be taken at an early stage and, if posltlve, the Environment Agency and the team wlli be able to proceed with confidence to impiementatlon. I

ACKNOWLEDOEMENTS The authors wish to acknowledge the Environment Agency, Southern Region for its permission to present and publish this paper. However, the opinions expressed in this paper are those of the authors who are responsible for any errors and omissions.

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