Tuesday, 28 February 2017

The ebb and flow of SUDS and Planning. A project in drainage - by Haroon Lulat

This is a story of successive problem solving
combining technical knowledge with innovative design and planning.

Part of a massive urbanisation project outside Hinckley in the Midlands, JMS were appointed to introduce a flow control system at the point of exit to main Water Authority drainage for 6 industrial units at Nutts Lane.  The drawings being submitted were necessary for Planning Permission.

This sensitive area comprises a site of six new industrial units with HGV hard standing off a lane bordered by the Ashby de la Zouch Canal.

Two major problems were evident from the outset – firstly that the drop to the main pipes was too shallow for the smaller pipes to achieve effective flow; and there is no natural infiltration on site as the ground has no permeability. 

And this was for just three of the six units.

Instead of a Planning Officer, JMS needed to secure the approval of the Drainage Officer at Hinckley Burrough Council, who required considerably more efficient water treatment plans to deliver SUDS requirements and secure planning.

Water leaving the site would pass through a bypass oil interceptor for treatment before reaching the main drainage (right). 

However the system being designed for a 1 in 100 +40% storm / heavy weather at greenfield rate of 5 litre per second outflow would exceed the flow controller’s capacity, backing up into the site.  

We had to slow the flow down and introduce effective permeability to clean the water further before infiltration. 
The text book first step was to introduce catch pits (left) to filter out sediment contamination. 

The next text book solution was permeable paving whose porosity would filter the water into the manufactured and natural sub-structure. But – this wouldn’t support the weight of standing HGVs.

To get round this, hard standing and areas of permeable paving were alternated across the overall standing area in front of the units.

Channel drains were added to the end of each hard standing enabling excess water to flow back into the sub-base, supporting attenuation and, in turn, now making the hard standing an integral part of the whole drainage system.

To aid attenuation further, the pipes being employed were specified to be porous – but (yes, another one) to protect them from HGV movement they would have to be concreted in:

 ... bang goes porosity, bang goes infiltration, bang goes planning. Surely.

Thanks here to Topmix Permeable concrete from Tarmac (view here). 

The pipes can now be concreted in and well protected . The permeability of the combined solutions finally prevail. Hooray ... surely!!

With planning permission being dangled before our very eyes, the plans now highlighted the remaining three units. Their drainage had nowhere to go but into the drainage system so expertly crafted for the first three units. 

There was no room for permeable paving, channel drains, catch pits etc. This water would flow, petrol, oils, silt, debris and it would all come at once.

There was however room for just one thing – bring on the Downstream Defender (right). 

This, the latest of the X-Men, cleans and filtrates the drainage to such a high standard, that the water leaving it to flow into the lower drainage system actually now helps the cleaning process. 

It has become a further integral part of the overall site drainage solution.

The result – Planning Permission approved ... just another day in the mud !

Thank you Haroon. 

Haroon is part of the team at JMS Midlands, based in Nuneaton. 
For JMS Midlands, please call 02476 350 505.

We add value to every project we have been,
are, and will be equally proud to support.