Avon waterbody update for AEF:  Comments by Roger Furniss shown in blue

 

From the desk study, it can be seen that the failures on the Avon are for low pH in the headwaters and for fish. 

 

Our interpretation of the data is that the low pH is a natural effect from the river draining Dartmoor, a granite moorland system.  However, the Dart Fisheries Association along with WRT are pulling together a literature review to gather evidence on their hypothesis that acid rain has exacerbated the acidic nature of the water coming off Dartmoor, specifically impacting the R. Dart salmon populations.  We will consider the findings of this document in due course. DFA has visited the upper Towy/Llyn Brianne catchment in West Wales where catchment treatment with lime has reversed the trend to lethally low pH events

 

The fish failures are driven primarily by two Poor survey points just downstream of the reservoir and upstream of Lydia Gorge.  This could be access over the falls but is more likely to be habitat driven – the river runs largely over bedrock with very limited spawning gravels as a result of the dam cutting off the natural downstream flow of gravels from the upper reaches. How is the Avon performing against its Salmon Conservation Target?

 

We have also identified 3 barriers lower down the Avon:  a tidal flap on a 'drain' below Aveton Gifford; a sluice for a water wheel on an offtake from the main Avon & a large tidal weir on the main Avon which is a complete barrier to eels and elver.  Complete barrirs to eels and elvers are very unusual given their ability to travel over wet surfaces. Is the weir also a barrier to salmon and sea trout?

 

The tidal weir on the main Avon could be impacting the results upstream as a number of the failures are being driven by low eel numbers.

 

The Avon waterbody is very large and the current status is Moderate.  This is driven predominantly by the impacts from the low pH and the possible impact of the reservoir and natural gorge.  The reality is more complicated. The Avon catchment consists of ? waterbodies summarised as follows:

 

  1. R113 – main Avon from Avon Dam to the junction with the Torr Brook, designated Moderate because of pH and fish, with fish targetted to be Good by 2015 but no specific actions to achieve it. pH is regarded as ‘Disproportionately expensive’ to achieve Good by 2015. Quantity and Dynamics of Flow, and Morphology are classified as ‘Supports Good’. This appears wrong given the impact of the reservoir on flows and gravel starvation in the river from Avon Dam to the Glazebrook confluence (see L6 below)
  2. R76 - lower Avon from Torr confluence to the tidal limit, designated Moderate because of phytobenthos regarded as ‘Technically infeasible’ to achieve Good by 2015. Designated under the Freshwater Fish Directive but no fish classification.
  3. R77 – Torr Brook currently classified as Good but no biological data to support this, including fish – designated under Freshwater Fish Directive.
  4. R75 – unnamed lower tributary current status Moderate based on expert judgement with no data. Technicall infeasible and disproportionately expensic=ve to achieve Good by 2015. Clearly needs monitoring
  5. R56 tidal Avon currently Moderate because of Fish (Moderate, uncertain) and technically infeasible to achieve Good by 2015
  6. L6 – Avon Dam – designated HMWB, classified as Moderate with Mitigation Measures regarded as Technically Infeasible. They include providing a flow to move sediment downstream; ensuring an appropriate baseline flow downstream(ie compensation flow); and maintaining a sediment management regime to avoid degradation of the natural habitat downstream (ie reverse the effect of gravel starvation which effectively prevents any fish spawning above the Glazebrook confluence

 

 

One option, was to designate the whole waterbody as Heavily Modified (for water storage/regulation) which would mean that it would have to reach Good Ecological Potential, rather than Good Ecological Status, and we would set some mitigation measures which would have to be met.  However, we felt that this was not a true reflection of the state of the Avon and therefore, I have made the following suggestion. In the current consultation on redesignation of some HMWB’s this is confirmed, ie no redesignatiion

 

We split the waterbody into 2 waterbodies – a smaller waterbody that includes the Avon reservoir, which we then designate Heavily Modified and develop appropriate mitigation measures for the reservoir. Avon Dam is already a separate Waterbody (L6) designated as Heavily Modified (perhaps it should be designated as an Artificial Waterbody) and it is not WFD practice to combine waterbodies designated as lakes with sections of river – the ecological requirements are entirely different. If part of the river is to be separated off into a separately designated waterbody where would the boundary be? The Minister has agreed that the approach in the River Basin Plans which separated catchments into a number of small waterbodies did not make sense and that a catchment –wide approach is the way forward  The rest of the Avon would then be a separate waterbody which would then be likely to achieve Good status although we still need to look at the sites where fish are not as good as we’d like them to be.  Is this likely to be proposed? If so then it should have been included  the consultation on A/HMWB’s which closes on 18 November

 

Actions currently programmed in:

 

 

Can they help?

 

-       do they think that the suggested way forward with splitting the waterbody is a pragmatic way forward? No, unless it is limited to redesignation of the upper river (Avon Dam to the Glazebrook confluence as a HMWB

-       do they know of any issues at Avonwick/Cocks Brook?  We should be surveying these sites this summer which will provide more up to date evidence. 

-       Can they identify the owners of the 3 obstructions on the Avon so that we can contact them?

-        Volunteer work on walkover surveys, monitoring, habitat improvements, assessment of weirs (cf Dart, Teign, Exe and Taw)

-       Involvement of Westcountry Rivers Trust

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750 Tidal Flap AvonIn order:

 

                                                         

782 Avon

751 Avon