Description of the contract
The project involved the implementation of measures in the Afon Bach to provide flood alleviation and protect banks from erosion in the centre of the village of Llansannan.
The project begins before you enter the village from the south where an existing 1200 diameter culvert passes under the A544. This culvert was replaced with an 1800mm dia culvert. Other works included but not limited to, construction of a new upstream headwall, installation of a precast downstream headwall including wing walls and stone scour protection to the river bed. The existing screen was to be removed and river bed to be re-graded.
Moving downstream the river passes through the private garden of Dalar Bach. From where it emerges from the Maes Aled culvert to an existing footbridge in the garden, the banks and bed are to be improved and strengthened. Here the river bed was to receive a rock amour placed on a bed of smaller rocks on a non-woven geotextile membrane. The bed was to be stepped to take out the abruptness of the existing weir. The banks were to be reformed and strengthened with a “Rootlok Wall” as specified by Geogrow. There were also some removal of existing walls as necessary. And a number of existing trees were to be removed with compensatory planting outside of the proposed earthworks.
Next the river passes a private car park and in front of a terrace of houses at Llain Hiraethog before entering into the 900mm diameter culvert that passes under the junction between the A544 and Ffordd Gogor. Adjacent to the car park a new reinforced concrete wall, clad with Penrhyn slate, was to be constructed to provide protection from flooding to the car park. The existing timber fence was to be removed and a new fence installed alongside the new flood wall. The access bridge to the car park is to be removed and the new access to be formed using a 2.1m wide 1.0m high precast box culvert. In front of Llain Hiraethog the existing south bank was to be retained. The northern bank was to be removed and the channel made wider and then replaced with a “Rootlok” retaining wall by Geogrow. The existing concrete river bed in this location was to be replaced with a new reinforced concrete bed. 100mm high alternating baffles at 3m centres assist fish travelling upstream by providing resting points. The existing pedestrian bridge was to be replaced with a 2.1m by 1m by 6m long precast box culvert which also provided a new communal area.
Finally just before the junction with Ffordd Gogor the river goes into an existing 900 diameter pipe which goes across Ffordd Gogor and outfalls back into the river to the east. This was being replaced, and partly on a new line, by a new 2.1m x 0.8m box culvert. Where it ties back into the river at the downstream end of the scheme there was to be a new reinforced concrete outlet structure with masonry cladding.
The Contractor was to provide a suitable traffic and pedestrian management system that maintains public access to adjacent properties/businesses and their Clients at all times unless prior arrangement has been made and agreed with the Client.
The contractor was responsible for organizing and arranging and carrying out all necessary temporary and permanent utility diversions necessary for the scheme, and coordinating the works by others
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