Construction work

Description

Scottish Borders Council (the Council) intends to take forward a series of flood protection measures in Hawick town centre which will protect over 900 business and residential properties against the effects of the 1 in 75-year flood event in the River Teviot. The works will comprise around 6 km of flood defences walls and embankments, new culverts, surface water pumping stations, Hawick waste water treatment works pumping station, replacement of 3 footbridges and the provision of new landscaping and reinstatement of the riparian corridor. Further details of the proposals, including a list of organisations who have registered an interest in becoming part of the multi layered supply chain that will deliver this project can be found at www.hawickfloodscheme.com. The Hawick Flood Protection Scheme (HFPS) will provide a significant benefit to the residents and businesses of Hawick by virtue of alleviating the effects of a major flood event in the River Teviot. The town has suffered from flooding in the recent past, including large numbers of properties inundated in 2005 and 2015, causing significant economic and human adverse effects. The HFPS will comprise the construction of nearly 6 km of entirely new flood defences, the great majority of which are flood defence walls. The walls will generally be sheet pile cored to a depth of between 4 and 12 m below ground level, with reinforced concrete pile cap and stem. Exposed concrete will either be clad in natural stone or finished with a formlined pattern. Around 60 glass panels, each 2.5 m wide and up to 1.4 m deep are to be set into the floodwalls. Approximately 1.8 km of the defences will require to be constructed directly within the watercourse. A short section of embankment will comprise a sheet pile core with locally won granular shoulders. Eight entirely new automatic surface water pumping stations will provide further protection, comprising wet wells up to 6 m deep and 5 m diameter, valve chambers up to 4 m deep and 6 m diameter and GRP kiosks to house the power and control units. The MEICA design for the surface water pumping stations will be the main contractor design element. The discharge capacity of the submersible pumps will vary within each pumping station, with the largest requiring to deliver up to 450 l/s. A ninth pumping station will be required within the Hawick waste water treatment works to assist the works during high flows and flood events, with submersible pumps capable of delivering up to 1100 l/s of storm water. Approximately 275 m and 185 m of new culvert will be required to discharge the Stirches and Boosie Burns respectively into the River Teviot. Requirement to install 9 new single leaf lift hinge floodgates within the flood defences to maintain pedestrian and vehicle access and 2 sets of stop log type demountable barriers are also required. The existing Lawson, Victoria and Mansfield steel truss footbridges will, as a minimum, require to be raised by 1.0 m, 1.0 m and 0.4 m respectively at their current location, comprising new abutments and extension legs welded to the deck supports at midspan. The current preferred option which is currently subject to Sustrans funding confirmation, is to remove the existing bridges from their supports and replace with entirely new steel truss structures at new locations, with deck widths up to 4.0m wide. If Sustrans funding is confirmed, the new bridges will be part of a new 7.0 km combined pedestrian and cycle route throughout Hawick, which will be delivered by this procurement excercise. The replacement bridge option will be the scenario which is to be priced as part of this procurement exercise. Further details of the work description are appended to the ESPD. Construction of the HFPS will be subject to a number of environmental and pedestrian / traffic management constraints, including restrictions on the time of year when works can be carried out within or adjacent to the river channel in order to reduce the impacts on salmon migration, and restrictions on which roads and footpaths can be closed simultaneously. The Council are currently carrying out an advance works contract which comprises the diversion of a large number of existing public utilities and the felling of the majority of trees which may be impacted by construction of the project. This procurement exercise will still require the protection and small scale diversion of some public utilities and a small amount of tree felling. The Council intend to appoint a main contractor to carry out the construction of this project under the terms and conditions of NEC3 (Engineering and Construction Contract) Option A contract.