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Type of document: Contract Notice
Country: United Kingdom

HYDRAULIC FLUVIAL MODELLING – SHORT DEADLINE
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Contract type: Service contract
Contracting authority: Costain Skanska JV – HS2 Enabling Works South Delivery. Web: www.costain.com / www.skanska.com, W1K 5JN.
Object of the contract
Delivery point: PROJECT WIDE
HS2 EW South Delivery
At these locations, the Proposed Scheme will run alongside the existing Chiltern Main Line. The existing line is built on an embankment to cross the watercourses and roads.
The embankment will be extended / a new embankment built alongside the existing structure to carry the Proposed Scheme.
There is an existing fluvial hydraulic model for the River Pinn which was used in the prebill stage of development to inform the need and size a potential floodplain compensation scheme. It is the awarding authority’s intention to use this model as a starting point to progress the modelling further.
River Pinn Description
The River Pinn is classified by the EA as a main river. The existing Chiltern Main Line crossing at this point is via an embankment and bridge over the river.
The Proposed Scheme will have an extension to the existing embankment and new bridge over the River Pinn. As this new embankment, will extend into the flood plain to the north of the existing crossing, a floodplain compensation scheme is proposed
upstream of the HS2 crossing.
Ickenham Stream Description
Ickenham Stream is classified by the EA as an ordinary watercourse to the north of the existing railway crossing and a main river to the south of the existing crossing. Its source is Ruislip Lido to the north and it also drains residential areas and the golf course immediately to the north of the existing crossing.
The hydraulic modelling that was undertaken during the pre-bill design (see Figure 1) indicates that there is a build-up of flood water to the south of the existing crossing and this has called into question the flow direction (normally north to south) during certain flood conditions. This shall be addressed in the surveys (Section 4.1) which will determine
invert (bed) levels in the stream.
The Proposed Scheme is that Ickenham Stream shall be blocked at the location of the current railway crossing, and diverted via a channel (which may include culvert sections) which shall run along the north side of the rail embankment and feed into the River Pinn immediately to the north of the HS2 crossing.
Fluvial Hydraulic Models.
The work to determine the impact of the Proposed Scheme and to inform the detailed design should be carried out in a single model as Ickenham Stream will be diverted into River Pinn to the north of the new HS2 crossing.
The initial fluvial hydraulic modelling to determine existing flood characteristics (levels, volumes, risks, etc.) shall also be carried out in a single model for River Pinn and Ickenham Stream. This is required to ensure consistency in approach, model calculations and
results, between the existing and proposed design, even though there may no direct interaction between these watercourses over the relevant reaches.
The hydraulic models will be used to develop and assess the proposed HS2 designs, with the ultimate purpose of informing crossing dimensions for the River Pinn and channel diversions for Ickenham Stream
Applicable Standard
All work is to be carried out in accordance with the HS2 Ltd: “Technical Standard – Fluvial Hydraulic Modelling”, Document no.: HS2-HS2-EV-STD-000-000013, version P07 (17.05.17)
Level of Detail
The hydraulic modelling shall be sufficient and robust enough for providing an understanding of existing flood risk at the site; that arising from the Proposed Scheme; and to inform detailed design such as sizing of crossings, channel diversions, realignments, scour protection and flood risk mitigation measures. The hydraulic model shall be used to determine absolute flood levels and test volumetric changes, to ensure that the Proposed Scheme can operate safely in a range of flood events. It shall further be used to assess any change in flood risk to third parties and key receptors.
Risk Classification
The level of detail used in hydraulic modelling shall account for the sensitivity of the flood risk receptors, such that critical receptors are afforded a higher level of detail in the modelling than those deemed insensitive to flood risk.
Hydrometric Data
For hydrological assessments, the most up to date version of the WINFAP-FEH files shall be downloaded from the National River Flow Archive (NRFA).
Inception Stage
Any existing hydrological or hydraulic models relevant to the study but not specifically produced for HS2 Ltd shall be requested from the Environment Agency, Canal & River Trust, LLFAs, IDBs and others.
The modelling Contractor shall carry out a technical audit of the existing hydraulic model/s produced both for HS2 Ltd and not specially for HS2 Ltd so as to be satisfied with their applicability to deliver the project outputs to the required quality (i.e. where an existing hydraulic model has been prepared with a similar purpose and target accuracy).
For existing hydraulic models not specifically produced for HS2 Ltd. For example existing models produced for Environment Agency Flood Risk Mapping Studies, the template for recording the review of existing hydraulic models shall be completed.
An inception report shall be provided before detailed hydrological and hydraulic modelling commences. This shall consider the available information and level of risk present at each crossing, and make recommendations for the detailed hydraulic modelling.
The inception report shall document: the proposed software for hydraulic modelling and the reasons why; the proposed hydrological approach and required flood events for consideration; and (iii) proposed model conceptualisation and reasoning.
Software Selection
The most up to date version of hydraulic modelling software shall be used. When new guidance on hydraulic modelling is released, updated methods shall be used. No in house, bespoke hydraulic modelling software shall be used The choice of hydraulic modelling software shall be justified in the inception report to be produced on commencement.
The same hydraulic modelling software shall be used for the baseline and the Proposed Scheme conditions at a given site.
Development of Hydrology A hydrological assessment shall be carried out in accordance with the latest version of the Environment Agency’s, “Flood estimation guidelines – Operational Instruction 197_08” (Environment Agency 2015).
A consistent approach to hydrological assessments shall be applied for the River Pinn and Ickenham Stream. This shall include using a consistent method, consistent calibration data and consistent donor sites. Hydraulic models for HS2 design cases shall as a minimum include flow estimates for the 1% AEP (1 in 100 year) + climate change & 0.1% AEP (1 in 1000 year) events ; Climate change allowances for hydrological assessments shall be in accordance with the
approach document HS2-HS2-EV-STR-000-000022. The events to be simulated in hydraulic models shall be justified in the inception report
to be produced on commencement and will depend on the level of flood risk at each site.
Development of Hydraulic Models
The approach to hydraulic modelling should be planned to enable the effective consideration of the Proposed Scheme. This should be achieved by constructing the models to represent the key flood flow routes, flood storage, and structures at the River Pinn and Ickenham Stream locations.
The hydraulic model study area shall include the full reach potentially affected by the Proposed Scheme, including locations away from the Proposed Scheme. The hydraulic model extents shall include appropriate distances upstream and downstream of the Proposed Scheme to ensure no boundary influence at the crossing location. The
hydraulic model extents shall ensure that the site is hydraulically independent from its boundaries.
The Contractor shall take into account the likely impact of the structure or channel
changes associated with the Proposed Scheme when determining hydraulic model boundary locations. It is anticipated that due to the complexity of the existing and proposed structures, including the new embankment, floodplain compensatory storage and diversion of
Ickenham Stream, hydraulic models shall be developed to a high level of complexity using 2D systems.
Surface water flooding due to rainfall is excluded from this requirement
The Ickenham Stream diversions shall be represented in the hydraulic model. Suitable design sections shall be included in the baseline hydraulic model to allow this to be amended in the representation of the revised river design with Proposed Scheme. These sections shall allow incorporation of the revised channel plan, gradient and proposed
cross section dimensions. QMED and 20% AEP (1 in 5 year) events shall be run through the hydraulic model to represent the Ickenham Stream diversion to provide information to inform the design of the diversion.
Calibration and Sensitivity Testing
Wherever practicable, the hydrological assessment and the hydraulic model should be calibrated against recorded flows and/or water levels from observed flood events. If calibration data is available, a hydraulic model shall be calibrated using at least three separate events.
Accuracy: Calibration of hydraulic models shall be within ±250mm of the measured water level, or 10% of the observed flows. If calibration of hydraulic models within ±250mm of the measured water level, or 10% of the observed flows is not possible, the best results achievable shall be justified in the Flood Levels Analysis Report.
Validation: If no data is available to calibrate or verify a hydraulic model, then a degree of confidence checking shall be undertaken. For example checking to ensure the 50% AEP (1 in 2 year) event roughly equates to a bankfull level, the 10% AEP (1 in 10 year) event is the onset of flooding and the 1% AEP (1 in 100 year) event fills the floodplain.
Sensitivity: The range of parameters used in sensitivity tests of hydraulic models shall reflect uncertainties, possible changes due to climate change and variations in hydraulic coefficients (e.g. from seasonal changes or periodic maintenance). Parameters to test the sensitivity of a hydraulic model shall be at the return period critical to the site and
dependent on the design.
Blockage of critical HS2 Ltd or other structures in a hydraulic model shall be tested where the effect could be significant to the Proposed Scheme and offsite receptors. The Environment Agency, IDB or LLFA shall be consulted to identify any structures represented in a hydraulic model known to be prone to blockage problems. This will not
apply to the Ickenham Stream crossing (which is proposed to be closed off); however, it may apply to the River Pinn crossing and the small (vehicle) bridge immediately to the north of the River Pinn crossing.
Results of sensitivity testing of a hydraulic model shall be reported in the Flood Levels Analysis Report relative to the Proposed Scheme and potential receptors (i.e. does the sensitivity test result in the Proposed Scheme being flooded). Commentary shall be given in the Flood Levels Analysis Report to justify the hydraulic model results in the context of the results of sensitivity tests, and advice given to HS2 Ltd on the degree of operational risk likely at each site.
Quality Assurance
Quality assurance requirements are specified in the HS2 “Hydraulic Modelling Quality
Assurance Framework” (HS2-HS2-EV-SPE-000-000028).
A full model audit log shall be kept of model changes implemented as part of the design development assessment process.
Deliverables
The following is a summary of the deliverables that shall be provided
Model Files:
All model logs;
model log and audit sheet. The model log shall clearly show the final files required for
running the baseline, Proposed Scheme, and sensitivity models;
calibration and validation data;
Hydraulic model results files, including flood extents, flood levels and results grids
shall be provided.
Model files to be delivered shall include: all input model, run control, schematic and
output results files for all final runs required, including: baseline (all AEPs), calibration
runs; sensitivity, design runs, etc., but shall not include any interim/development models
generated as part of the model build
Reports:
Inception Report;
Flood Levels Analysis Report
Flood Mapping:
GIS shapefile of flood extents for all modelled return periods;
Cross section lines for 1D model reach results;
Maximum flood depth grids;
Maximum velocity data;
Hazard mapping
Flood Levels Analysis Report
The Flood Levels Analysis Report shall cover both the hydrological assessment and the hydraulic model build, as well as the analyses and sensitivity tests completed. It shall describe the topographic survey work undertaken (in brief), the modelling method adopted and assumptions included in the model.
In particular, the hydrology section of a Flood Levels Analysis Report shall contain information on flood estimation and a discussion of the results and amendments made to inflows following integration into the hydraulic model.
The modelling approach and software used, shall be justified and the report shall provide details of model parameters, and a discussion of the uncertainty associated with those parameters.
Flood Mapping
Flood mapping shall be undertaken for the following:
The design runs following completion of calibration, sensitivity testing and review.
All the design runs for the baseline scenario before testing the impacts or design of the Proposed Scheme.
All the design runs incorporating the Proposed Scheme.
Flood extent maps shall be produced in a format compatible with Arc GIS and shall show the extents of flooding for design return periods, and include the following:
Tables of peak flood flows for all modelled design flood event probabilities. The flows presented shall be the total flows in the full valley section at every model node, rather than just those that are in-channel or attached to an individual model node;
Tables of peak flood levels for all modelled design flood event probabilities at all nodes along the center line of the main channels and other flow paths; and Cross section lines with attributed water levels at each File Formats and Data Transfer.
All reports and deliverables, both draft and final, shall be supplied in editable digital format compatible with the following software versions: Microsoft Office 2007 suite,
ArcGIS 10.1, or AutoCAD 2014 as appropriate (alongside the hydraulic modelling software used), and also in Adobe Acrobat ‘pdf’ format.
Maps shall be provided as layers, tables, meta-data and / or files (as appropriate) in a GIS format compatible for direct import into ArcGIS.
CPV: 90733700, 24951300, 90730000, 71350000
Administrative Information
Supply chain ID: 11854-HS2 EW South Delivery
CompeteFor response deadline 18.8.2017 (12:00:00)
Note: This is a CompeteFor opportunity. Opportunities may be with both public and private sector businesses. To apply, please click the following link to register on the CompeteFor portal Web:
Other Information
Opportunity Method: Contract Opportunity
Opportunity Status: Open
Opportunity Type: Public Sector
Notice Type: Notice
About the buyer’s selection process:
In review & selection of potential bidders to receive an Invitation to Tender for the works package, the awarding authority will base the decision on a range of factors – Previous relevant experience, Health & Safety, Quality, Environment, EDI, Ethical Sourcing, Company financial standing, Registration on Achilles Building Confidence.
If shortlisted, a further PQQ will be sent which contains project specific questions & evidence to be provided. This will assess capacity, capability, sustainability, equality, diversity & inclusion and environment and legacy requirements. Suppliers will also have to sign and return the Clients’ Non Disclosure Agreement as part of the PQQ process.
Following PQQ process selected suppliers will be invited to Tender. Please note that the assessment of tenders will be based on a balanced set of evaluation criteria. The awarding authority is not bound to accept the lowest price in selecting the successful tender for award.
About the buyer:
The Awarding Authority is a planned high-speed railway in the United Kingdom linking London, Birmingham, the East Midlands, Leeds and Manchester. The project will link eight of our major cities and serve millions of people. Travelling for work or pleasure will become much easier – crucially between the cities of the Midlands and the North.
The Enabling Works Contracts which have been awarded cover the whole of Phase One, from London to Birmingham.
For the Enabling Works phase, 3 joint ventures have been appointed of which the Awarding Authority has been awarded Area South, which covers the length of the planned route from London Euston out to the M25.
Under the contract the Awarding Authority will deliver a range of activities within this geographical area including utility diversions, ecology surveys, demolition, ground remediation, watercourse activities, highways realignments, monitoring and instrumentation, structural reinforcements archaeology, site clearance as well as establishing site compounds.
Estimated tender close date: 09/09/2017
Estimated contract award date: 16/10/2017
Estimated contract start date: 17/10/2017
Additional information for bidders Include any special notes for bidders: If you are successful in this package, any sub-subcontracted work should be advertised on CompeteFor using our supply chain id 11854-HS2 EW South Delivery
TKR-2017811-EX-536323