Avon Reservoir Trial Fisheries Releases – 2015/16
Information to External Stakeholders
1.
Background
1.1
As part of the SHRImp project, managed by West Country Rivers Trust, trial fisheries
bank releases were made during 2014/15.
1.2
Although the above project has now finished, the EA and SWW have agreed to
continue with the trials to develop further understanding of the best potential use of
the “freshet releases” for fisheries as mentioned in the Avon abstraction licence.
2.
EA and SWW Documentation
2.1
Any release is triggered by the Environment Agency, who send a form to SWW with
details of the requested trial release.
2.2
A sample template is shown in the attached appendix.
2.3
As can be seen, the agreed trial releases are set out as a series of options
depending on the time of year. These are based on trials as developed in
conjunction with West Country Rivers Trust.
2.4
During these periods, SWW will send to the EA a daily update of Avon storage and
the total flow downstream of the Dam.
3.
Looking ahead
3.1
It is currently anticipated that similar trials will continue in 2016/17 to give
experience during different hydrological situations.
SWW
April 2015
Appendix
Avon Reservoir Fisheries Water Bank Trial Releases – 2015/16
Example of documentation between SWW and EA
FROM :
.................................................. (EA)
TO:
Glenis Pewsey (SWW)
Email addresses:
wtrstrat@southwestwater.co.uk;
gpewsey@southwestwater.co.uk
Phone
1.
01392443514
DETAILS OF THE TRIAL RELEASE REQUESTED BY THE ENVIRONMENT
AGENCY
Requested date of trial release
..................................
Ideal approximate requested time of start of releases........................... (24 hr clock)*
Details:Q
D
Steady state total maximum release rate (equivalent Ml/d
rate)
(includes the compensation flow of 0.068 m3/s (5.875
Ml/d))
Approximate duration of steady state maximum release
rate (as part days if necessary)
Ml/d
Hrs
V1
Approximate total volume of specific releases including
compensation flow
Ml
V2
Approximate total volume of specific releases excluding
compensation flow
Ml
* It is recognised the start time might change for SWW operational reasons
Signed ..............................………….for Environment Agency
Print Name ...........................……… Date ...............................
2.
AGREED TRIALS
2.1
The agreed trial releases are set out below which detail different possible options
depending on the time of year.
2.2
During these periods, SWW will send to the EA a daily update of Avon storage and
the total flow downstream of the Dam.
Option 1. Smolt migration period (approx 1 April to 31 May)

Maximum duration: around 2 days

Maximum rate of release: 65 Ml/d including the compensation release from the reservoir.

Trigger for release: when the flow below the reservoir has not exceeded the
compensation flow for a period of the order of 4 days*

Request for each release: Environment Agency to email South West Water by 12.00am
on the day before the release is to take place

The release will ‘turn on’ at the end of the day and ‘turn off’ at the beginning of the day **.
This will ensure targeted use of water resources to night time periods when smolts are
known to migrate

Request for a release may be repeated after reservoir storage recovers to 95%***
*
This is a working guide - the EA will assess the prevailing hydrological conditions before formally requesting a
release from SWW. ‘In the order of…’ wording was agreed to allow flexible working around weekends etc.
**
These are taken as 15:00 hrs and 09:00 hrs respectively to fit in with SWW operational requirements.
** * The 95% was the storage agreed for the 2014 trials. In the longer term it may be more appropriate to use a virtual
storage type of calculation with 100% full to take into account hydro-electric releases
Option 2. Low flow period (approx 1 June to 30 September)

Maximum duration: 24 days*

Rate of release: 0.095 cumecs (1.8 mgd or 8.2 Ml/d). This figure includes the
compensation release of 0.068 cumecs

Trigger for release: when the flow below the reservoir has not exceeded the
compensation flow for a period of the order of 4 days**

If a release under option 1 has been made, reservoir storage must have recovered to
95% before an option 2 release can be requested***

Request for a release may be repeated after reservoir storage recovers to 95%***

Request for each release: Environment Agency to email South West Water by 12.00am
on the day before the release is to take place
*
This duration is for trial period only and is based on the total volume of storage used being of the same sort of order
as the size of a fisheries bank in other abstraction licences
**
This is a working guide - the EA will assess the prevailing hydrological conditions before formally requesting a
release from SWW.
** * The 95% was the storage agreed for the 2014 trials. In the longer term it may be more appropriate to use a virtual
storage type of calculation with 100% full to take into account hydro-electric releases.
Option 3. Adult migration and spawning period (approx 1 Oct to 31 January)

If a release under option 2 has been requested and the reservoir storage has not
recovered to 95% *, then the total requested release from option 2 and 3 must not
exceed a total of 60 Ml (excluding compensation flow)**

If reservoir storage has recovered to 95%* since an option 2 release, then a
maximum volume of 200 Ml can be requested (excluding compensation flow).

The rate of release will be requested by the EA, taking into account: the minimum release for HEP is around 45 Ml/d ie about 39 Ml/d above the
compensation flow and
 the maximum release for HEP is around 65 Ml/d ie about 59 Ml/d above the
compensation flow(1)

Trigger for release: when the flow below the reservoir has not exceeded the
compensation flow for a period of the order of 4 days***

Request for each release: Environment Agency to email South West Water by
12.00am on the day before the release is to take place

The release will ‘turn on’ at the end of the day and ‘turn off’ at the beginning of the
day ****. This will ensure targeted use of water resources to night time periods.

Request for a release may be repeated after reservoir storage recovers to 95%****.
*
The 95% was the storage agreed for the 2014 trials. In the longer term it may be more appropriate to use a virtual
storage type of calculation with 100% full to take into account hydro-electric releases.
**
This total is for trial period only and is based on the total volume of storage used being of the same sort of order as
the size of a fisheries bank in other abstraction licences
***
This is a working guide - the EA will assess the prevailing hydrological conditions before formally requesting a
release from SWW. ‘In the order of…’ wording was agreed to allow flexible working around weekends etc.
**** These are taken as 15:00 hrs and 09:00 hrs respectively to fit in with SWW operational requirements.