Surface Water

By Edward Vine

About Me

I have lived in Harlow since 1983. I am a retired iSTEMplus physics teacher, served as a school governor at 2 Harlow Schools. I am a charity worker at Church Langley Association and South East Harlow Sports and Youth Association. Whilst working a teacher I received a National Teaching Award. I have also received a Nesta Foundation National Award for innovation in Education.

How the Stort Crossing will affect surface water

Surface water, rainfall has always been managed, traditionally by ditches, ponds and streams. When there were plenty of trees, wetlands and flood plain flooding was not such a problem. Only idiots who built  on the flood plain really got flooded.

Harlow has suffered relatively little problem with flooding over the 74 years because it’s a town designed using these traditional ideas and when there was too much rainfall in too short a time the surface water runs into the sewer system. 

As more building development happened flooding began to be an occasional problem. 

Recently when rainfall has been more intense more often we have seen homes built near the river or on the flood plain, flooded, 

The sewage system has been overwhelmed and untreated sewage flushed into the natural and built environment. 

Unfortunately, the practice of not separating surface water from industrial sites and busy roads from cleaner run off has led to rivers being polluted. Unfortunately the run off from agricultural land is often polluted with fertilisers and pharmaceutical products used to treat animals, (powerful hormones of different kinds being present in even low quantities are a particular problem)

The  Harlow systems are old and beginning to show warning signs. Last Summer saw homes flooded, the discharge of untreated sewage, pollution in Canon’s Brook from the Pinnacles industrial area and foaming detergent pollution in the River Stort. The main trunk sewer has particularly deep manholes and it has been thought that this would not be overwhelmed by flash flooding but it has. 

This summer The  Climate Change Committee report exposed the fact that previous practices and assumptions about flooding have not been adequate.

Rainfall intensity and  volume are going up, what falls in 3 hours will fall in 2 hours with more rainfall.  A 30 % increase in load. 

Gilston is being built with a sustainable surface water system: basically less concrete, more sand under surfaces like block paving and surface water drains kept separate from the sewage system, more ponds and swails. It’s called attenuation, The water from storms is held up, slowed to help prevent flash flooding. Great! 

But all of this surface water and sewage is being run down into the Valley towards Harlow adding to the volume from the already over stretched Harlow systems. 

This is likely to make flooding worse and because the sewage is entering the same main trunk sewer, the discharge of untreated sewage into the fragile ecology system in the Valley more likely. 

Add to this load, the water from the other new housing developments around Harlow and the new development proposed at Hatfield and multiply that by the effects of increased rainfall from Climate Change.  Increased rainfall over prolonged periods saturates the ground and fills the ponds and so any additional and intense rainfall immediately will cause flash flooding. The Eastern Crossing design will make matters worse by dividing the flood plain making upstream wetter and downstream drier and changes due to both crossings will decrease the area of effective flood plain needed. There are obvious alternative optional routes that would mean that the Eastern Crossing is eliminated and other transport strategies that would eliminate the expansion of the central crossing. 

With 10000 homes over an extensive area of land the flood plain that’s already inadequate needs to be increased at least in proportion to the area of the development.

We basically need lots more flood plain! 

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