Love the Lea – Community Modelling

Rivers are the lifeline of our communities, but can easily become neglected. They face many pressures from the towns and cities that surround them, which the people in those urbanised areas have a duty to address. Yet those communities need to work not in isolation, but adopting a catchment-wide approach so that a solution in one part of a river does not adversely affect the waterway up or down stream as a consequence. 

Communities can shape water quality solutions

Poor water quality is one of the main themes across London’s rivers. The water faces challenges from pollution including oils and metals from road run-off to oil spillages and plastic pollution. Community modelling aims to tackle poor water quality by teaching communities to use water quality modelling software to choose solutions which best suit an area.

The software allows them to test solutions and present decision makers with them.

Over the first nine months of the project, Thames21 has worked with communities groups in three urban catchments in North London, the Pymmes Brook, Salmons Brook and Ching Brook, developing bespoke solutions.

What are the issues?

North London suffers from poor water quality which can be caused by:

  • Misconnections: some areas of London have separate sewers where foul water and rain water go into different pipes. If the pipes are incorrectly connected, foul water from bathrooms can enter a river.
  • Surface run off: this can be caused by agricultural or urban sources where sediment and oils run directly into a river.
  • High nutrient concentrations:  Nutrients such as phosphate and nitrate are much-needed in our rivers to keep them healthy, but when fertiliser run-off and combined sewer outflows release untreated sewage into a river, this can upset the natural balance of nutrients that allows nature to thrive.

Long term effects

A reduction in the amount of oxygen available in a river is a result of an increase in suspended sediment and nutrient concentration. Increases in suspended sediment, algae and nutrients reduce the amount of oxygen available for fish and invertebrates, limits habitat for fish spawning and prevents daylight reaching the riverbed.

What are we doing about it?

We are giving people the tools to shape solutions. We helped establish three groups, one for each catchment and empowered them with the skills and tools to address the issue of poor water quality in North London.

To understand the constraints and topography of the catchments, we undertook walks from source to mouth.

Improving water quality and alleviating flooding

North London contains a variety of sustainable drainage solutions such as wetlands – including Firs Farm Wetlands – swales and rainscapes. These can alleviate flooding and improve water quality. 

The community groups assessed the feasibility of the sites using a combination of mapping software QGIS, investigations and site visits. INCA, which simulates water quality in a catchment, was used to quantify the reductions in nitrate, phosphate and ammonium at a local and catchment scale.  Meanwhile, data was used to identify and map the potential sites highlighted by the community groups.

Water quality improvements

An initial identification of 50 sites was proposed, which has since been refined to 18 on the Pymmes Brook, 12 on the Ching Brook and 4 on the Salmons Brook. Both Pymmes Brook and Ching Brook scenarios created a status change with water framework directive status improving from poor to moderate or moderate to good for water quality. The model was run before scenario testing at low flows, providing a base line data for which comparisons can be analysed.

All models are calibrated with spot samples over a 17-year period from 2000 to 2017 taken by the Environment Agency. Additional monitoring of Firs Farm Wetlands, Enfield over a six-month period between October and March 2017-18 was inputted into the model to provide observed data of the constructed wetlands. Comparison of the observed and simulated data demonstrate the model is under predicting the benefits of constructed wetlands.

A cleaner waterway – wetlands or rivers – will provide a better habitat for wildlife and attract a wider diversity of species.

What next?

Thames21’s community modelling project will investigate the potential flood risk benefits of these constructed wetlands and share the knowledge and evidence created during this project.

Thames21 and the community groups are looking for people to volunteer to learn how to use INCA and help to inspire a sustainable future for London’s rivers. No prior experience is necessary – just a willingness to  help improve London’s rivers.