Tag Archives: Defra

New London Partnership Project to tackle Urban Pollution

We have teamed up with Thames 21 on a new project to tackle urban pollution across London’s rivers.

Many improvements in the quality of urban rivers have been made in recent years, but lots of serious water quality issues remain. One of the biggest issues is ‘urban runoff’, where a toxic mixture of contaminants derived from urban areas drain straight into rivers.

With surface water drains often running straight into rivers, these contaminants are washed directly and unfiltered into urban rivers when it rains. During these ‘first flush’ events, river water often changes from being clear and colourless to being an opaque grey-black colour, and water analysis shows that a complex mixture of hydrocarbons, fine particles, nutrients, microorganisms and heavy metals are the cause.

First Flush samples from the River Wandle

First Flush samples from the River Wandle

In urban areas the contaminants causing rivers to run grey-black in colour may have a greater impact, but the locations at which they enter a river are often unknown, and they are relatively costly to survey, with samples needing to be processed by a lab.

Our project with Thames 21 is testing a low-cost sampling method that can be used by volunteers to identify complex urban contamination. In particular, it aims to investigate Surface Water Outfalls (SWOs) which discharge contaminated urban runoff into London’s tributaries of the River Thames.

The method being developed is based on evidence from data collected on the River Wandle, and urban sites in Wigan in NW England, which show that Total Suspended Solids (TSS) are strongly correlated with several important heavy metals and E. coli (a bacterium which can indicate faecal matter) and can therefore be used as a low-cost proxy to identify problematic concentrations of these contaminants.

The next step in this project is for us and Thames 21 to create Pollutant Profiles for our rivers to see if they match this correlation. You can follow progress on the project on our Twitter feed @SE_Rivers_Trust with #TSS!

Action on the River Teise!

We’ve started our project on the River Teise to make a weir passable for fish migration.

Weirs were introduced years ago to help control the flow of water, allowing our ancestors to operate mills. Nowadays many remain in rivers despite no longer being required.

Weirs are a barrier to fish passage and leave the habitat fragmented with fish populations isolated. In the event of pollution or other presures like climate change, these isolated populations are at greater risk with nowhere to escape to.

Although being a barrier to fish migration is a significant problem, weirs also interrupt the natural flow of rivers, resulting in a degradation of habitat. Upstream of weirs, water is slowed down which causes silt to drop out and accumulate in the channel.

This image from the Wild Trout Trust explains the effects of weirs on fish habitat:

WTT Weir

Funded through Defra’s Catchment Partnership Action Fund, we’ve started works on a weir on the River Teise – where Olly and Rosie carefully removed a number of boards from the top of the weir.

Weir Board Removal

After removing the boards, the impounded water levels upstream dropped noticeably, revealing many natural features of the river which had been drowned out when the weir was put in place.

Before

Before

AfterAfter

New Habitats

Some of the diverse new habitat revealed by lower water levels above the weir

The next phase of the project is to remove the impoundment and enable full fish passage and habitat restoration, so watch this space!