Essex Rivers Hub

This catchment consists of the River Colne, Stambourne Brook, Toppesfield Brook, Pebmarsh Brook and Salary Brook. The Colne has been split into 3 sections and covers a total length of 50km. Stambourne (6km in length) and Toppesfield Brook (6km in length) flow into the middle section of the Colne (identified as Great Yeldham to Doe’s Corner), Pebmarsh (5km in length) and Salary Brook (15km in length) flow into the downstream section (identified as downstream of Doe’s Corner). Bourne Brook also flows into the River Colne.

The River Colne has a Water Framework Directive (WFD) classification of moderate in the upstream section but this falls to poor in the middle and downstream sections. All three sections are failing for flow and phosphates, the phosphate fluctuate slightly through the Colne starting as bad in the upstream section (the worst classification possible), which improves to moderate in the middle section but then drops to poor in the downstream section. Morphology is a failing element in the middle and downstream section so more diversity within the channel in needed in these areas. Fish (poor) and dissolved oxygen (bad) are failures within the middle section and these elements maybe linked, poor oxygen levels are impacting on fish populations. In the downstream section plants are being impacted and both diatoms (plants not visible to the naked eye) and macrophytes (plants visible to the naked eye) are failing elements, suggesting high levels of nutrients maybe an issue here so levels of phosphate need to be addressed. This section is also failing for annex 8 chemicals. On the positive side dissolved oxygen levels are good in the upstream and downstream sections and ammonia levels are very low throughout. There are also good aquatic invertebrate populations in the middle and downstream sections as well as very good fish populations downstream.

Stambourne and Toppesfield Brook both have a WFD status of moderate and both flow through rural areas, mainly agricultural land. They are both failing for phosphates and dissolved oxygen. The phosphate results for Toppesfield Brook are slightly better at moderate compared to poor in Stambourne Brook whereas the dissolved oxygen levels are worse and classified as bad compared to poor in Stambourne Brook. Diatoms (plants not visible to the naked eye) are also a failing factor in Stambourne Brook and fish are a failing factor in Toppesfield Brook. Both Brooks have very low ammonia levels and good flows; Toppesfield Brook also has good Aquatic Invertebrate levels so this is not the reason for the reduced fish populations.

Pebmarsh Brook has a WFD status of good meaning it has very good fish populations and very low phosphate and ammonia levels and very high dissolved oxygen levels. It also has good in channel habitat variation (morphology) and good flows.

Salary Brook has a WFD status of moderate and is failing for fish, phosphates and flows. Some positives for this brook are the high levels of dissolved oxygen and low levels of ammonia.

Phosphates are a catchment wide issue and depending on where the river flows will depend on the source. In rural areas the most likely cause is agricultural land management and in urban areas it will be misconnections from housing. Sewage treatment works and other sewage discharges are also having a major impact. In most areas more investigation is needed into the exact location of diffuse pollution sources and the impact of drainage from agricultural areas. Therefore more surveys are needed and water quality testing throughout the year and in all weather conditions. In areas where sewage treatment works are found to be the cause then phosphate stripping should be considered. If agricultural practices are found to be having an impact then farm visits should be conducted so that land managers can be advised on how they can reduce their impact.

Fish populations were found to be affected in the middle section of the Colne, Toppesfield Brook and Salary Brook. In the Colne limited habitat within the river, low dissolved oxygen, and low flows and barriers were found to be the cause. Low flows and dissolved oxygen was also found to be the cause in Toppesfield Brook and sediment and barriers were the causes in Salary Brook. Low flows in the two brooks are resulting in reduced dilution of effluent discharges which is also found to have an impact. In order to improve populations in these areas then mitigation measures need to be actioned that deal with removal or modification of any barriers, also sediment and low flows need to be addressed. Low flows will also be impacting on the low dissolved oxygen levels.

Dissolved oxygen is having the most impact in the middle section of the Colne, Toppesfield Brook and Sandon Brook. The upstream section is not failing for low dissolved oxygen but there is a concern that in the summer falling levels could impact on fish. Dissolved oxygen failures are linked to natural factors and seasonal changes in summer months when flows are at their lowest and temperatures are at their highest, which are both factors that impact on dissolved oxygen. Also lower flows means that there is less dilution of effluent in the water. This situation needs further investigation so invertebrate surveys should continue and the impact on fish populations assessed.

Flow was found to be an issue throughout the Colne and also in Salary Brook. The reasons for this are not clear and in some situations this is not having an impact on the ecology of the habitat, however continued monitoring is needed to ensure this remains the case and any possible improvements to flow should be made.

Morphology was only found to be an issue in the middle section of the Colne. The reason for this should be determine and ways to rectify this should be determined.

Diatoms are a failing factor in the downstream section of the Colne and Sandon Brook. The reasons for the failures are not clear so more investigation is needed to determine the cause.

Macrophytes and Annex 8 chemicals were failing elements within the downstream section of the Colne. The macrophyte failure is linked to excessive nutrients in the water however the reason for the chemical failure is unclear and needs further investigation

Some mitigation measures have not been carried out so these need to be assessed to determine if they are still necessary and if so they should be actioned as soon as possible. The following mitigation measures are outstanding for the middle section of the Colne:

  • Increase in channel morphology, remove obsolete structures and improve other structures so they are passible for fish.

Outstanding for the downstream section of the Colne:

  • Remove obsolete structures
  • Increase in channel morphological diversity
  • Modify structures so they are passible.

Outstanding for Toppesfield Brook:

  • Improve morphology in channel
  • Manage flows so they are not impacting on ecology.

 

 

 

 

 

 

 

 

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