Lizard Lane is a busy link road connecting the Whitburn and Marsden areas of South Tyneside. Frequent heavy rain and clay soil led to the carriageway remaining flooded for long periods, even after the rain had stopped.
This posed a danger to pedestrians, drivers and other road users and was especially disruptive on a stretch of the highway passing the local golf club and riding school. Surface water would run off the golf course and adjoining horse paddocks and onto the sloping road, overwhelming the inadequate drainage.
The lack of space in the verge and complications from other services underground required flexibility in the design as well as a more effective drainage system.
The verges and footpath alongside the road are not very wide and there are several other services, both underground and above ground, that any excavation and drainage installation had to safely work around. Ground penetrating radar studies also showed an uneven bedrock requiring changes of level in the installation.
In addition, the drainage scheme had to integrate with improved traffic calming measures on a busy link road with frequent incidents between speeding vehicles and pedestrians or horse riders.
Super gullies – large capacity concrete kerbside collection chambers – were installed to rapidly clear the surface water from the road and direct it to the Hydrorock modules for buffering and infiltration. Four such modules were arrayed along the length of the project site underneath the roadside footpath and verge.
To provide a Sustainable Drainage System (SuDS) solution that harvests and buffers the rainwater and runoff, before infiltrating within the confines of the site, our Hydrorock natural aquifer block water infiltration System was installed.
Each block is lifted into place and connected to the block behind with a simple push-fit connector. Once a whole width of blocks has been installed, back-filling can begin immediately – in this case with a gravel mesh and shingle – for extra load bearing – prior to the topsoil.
The ends of each module were then connected to the kerbside gullies with the middle block of three being connected to a breather vent. As the Hydrorock module fills with water, the air is expelled through these breather pipes and as the water is released into the soil, air is drawn back in.
The two site plan drawings below (© Lynas Engineers Limited) show the road in the middle with the other services in different colours already in the verge. At the bottom of each drawing is the underlying bedrock profile and slope. The placement of the Hydrorock modules A-D are shown in dark blue. As can be seen, module B had to be split and connected around a power-line pole.
Click to enlarge.