Essex Rivers Hub

This catchment consists of the Upper River Stour, which is split into 2 parts (Upper Stour and Upper Stour upstream of Lamarsh), Chad Brook, Lower Glem, Upper Glem, Chilton Brook, Belchamp Brook, Stour Brook and Bumpstead Brook. Upper Stour and Upper Stour upstream of Lamarsh are the main water bodies within the catchment and the others are tributaries that flow into the Upper Stour a part from the upper Glem which flows into the Lower Glem.

Overall the catchment has a Water Framework Directive (WFD) classification of moderate however there are a few sections that are classified as poor; Chad Brook, Upper River Stour and Belchamp Brook. The biggest failures within the catchment are phosphate, dissolved oxygen and morphology (river structure) and a part from a few exceptions the catchment has low ammonia levels and good fish populations.

Phosphate is a failing element for most of the water bodies a part from Belchamp Brook where the WFD classification is good. The whole of the Upper Stour is classified as moderate as is upper Glem, however the Lower Glem has the worse classification of poor. Chad Brook, Bumpstead Brook and Stour Brook also have a classification of poor, while Chilton Brook has the worst classification possible of bad. In most cases the source of the pollution is not known so more investigation is needed throughout the catchment. Within Stour Brook it is possible that the input from the Ely Ouse water transfer scheme (this is where water is fed into the brook from these rivers to increase water availability within this catchment) could be increasing phosphate levels, however there has been no indication of ecological impact so this needs further investigation also. Failures in Bumpstead Brook has been linked to sewage treatment works discharges and agricultural runoff. In this case more should be done to work with water companies and land managers to help them reduce their impact.

Dissolved oxygen is a failing factor for 5 out of the 9 water bodies in this catchment. Those failing are Upper and Lower Glem, Chilton Brook, Chad Brook and Belchamp Brook. All are classified as moderate except Chilton Brook which is classified as poor. The whole of the Stour, Stour Brook and Bumpstead Brook all have good levels of dissolved oxygen. Of those water bodies that are failing due to low levels of dissolved oxygen, the exact cause is unknown and more investigation is needed, however in Chilton Brook the low levels have been linked to seasonal variation which means levels are lowest in summer and autumn when flows are low and temperatures are high. In most cases the dissolve oxygen levels do not seem to be having an impact on the ecology of the water bodies so no urgent action is needed at this time except to continue to monitor to ensure that this does not change.

Aquatic invertebrates are found to be low in Chad Brook, Bumpstead Brook and Stour Brook but Lower Glem, and the whole of the Stour have good populations. Within the Upper Stour the levels fluctuate so the classification may change in the next round of testing. The low populations are linked to the presence of the non-native invasive Signal Crayfish in Chad Brook and Bumpstead Brook and this maybe impacting on the Upper Stour also. Low flows and dissolve oxygen may also be a contributing factor in Chad Brook. Other factors affecting invertebrates in Bumpstead Brook is agricultural runoff and reduced flows, however the data for this brook maybe unsafe and different sampling points for invertebrate surveys need to be used that are characteristic of the whole water body. The reason for the failure in Stour Brook is currently unknown so more investigation is needed.

Diatoms (plants not visible to the naked eye) are a reason for failure for Chad Brook, the whole of the Upper Stour and Bumpstead Brook. All have a WFD classification of poor a part from Upper Stour upstream of Lamarsh, which has a slightly improved classification of moderate. In most cases, the reason for failure is not known and more investigation is needed, however the failure in Bumpstead Brook has been linked to the high phosphate levels so this may be the case in all water bodies.

Morphology, or river structure, is an issue in many of the water bodies in this catchment. The only water bodies that have a classification of good for this category are Upper Glem, Lower Glem and Belchamp Brook, the rest have a classification of moderate. There is no information about the exact reasons for failure but mitigation measures may address many of the problems

Hydrology, or flow, is an issue in 4 of the water bodies within this catchment; Upper Stour, Stour Brook, Bumpstead Brook and Belchamp Brook and are all classified as moderate. Upper Glem and Chad Brook have good flows. In Stour Brook, Belchamp Brook and Bumpstead Brook the exact cause of the failure is not clear so more investigation is needed to determine the reasons for low flows. Upper Stour has been designated as heavily modified and this could be the cause of low flows here, mitigation measures may address some issues around flow. Another action is to continue to monitor fish and aquatic invertebrate populations to ensure flow is not impacting on these.

Ammonia is a failing element for Chilton Brook only and this water body has a WFD classification of poor for this element. The reason for the failure here is not clear and more investigation is needed. All other water bodies have low levels of ammonia which is a positive result for this catchment. One possible problem that may occur is that the levels for Bumpstead Brook do fluctuate and could result in a failure if acceptable levels are not agreed with the sewage treatment works on this water body.

Fish populations are only failing in Belchamp Brook, the rest of the water bodies have good populations. The reason for the failure in Belchamp Brook has been linked to a barrier and problems with water quality. Therefore fish passage and water quality issues needed to be addressed in this water body.

No water bodies in this catchment have failed due to annex 8 chemicals.

The following mitigation measures are outstanding in this catchment:

  • Appropriate channel maintenance strategies and techniques- minimise disturbance to channel bed and margins.
  • Remove obsolete structure
  • Increase in channel morphological diversity
  • Structures or other mechanisms in place and managed to enable fish to access waters upstream and downstream of the impounding works.

There are no mitigation measures for Upper Stour upstream of Lamarsh.

 

 

 

 

 

 

 

 

Website key stakeholders:

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Design by LTD Design Consultants and build by Garganey Consulting based on an original concept by Herts and Middlesex Wildlife Trust