Our Reference: EIR/546/2020

Dear Sirs,

Request for information

We refer to your request for information, which was received on 1^st July
2020 for the following:

Information on the duration and time of any  emergency water discharges
from all reservoirs into the Taff river for the period from the 10th
February 2020 and 20th February 2020.

We are dealing with your request as one made under the Environmental
Information Regulations 2004 (“the Regulations”).

In accordance with the Regulations, we will respond to your request within
20 working days of the date of receipt.

We have assigned reference EIR/546/2020 to your request. Please kindly
note this in all correspondence with us regarding this matter.

In the meantime, if you have any queries, you can contact us at
[1][email address].   

Yours faithfully

G Andrews​
Dŵr Cymru Welsh Water

_______________________________________________________ Dwr Cymru Welsh
Water is firmly committed to water conservation and promoting water
efficiency. Please log on to our website www.dwrcymru.com/waterefficiency
to find out how you can become water wise. Mae Dwr Cymru Welsh Water wedi
ymrwymo i warchod adnoddau dwr a hyrwyddo defnydd dwr effeithiol. Mae
cyngor i' ch helpu i ddefnyddio dwr yn ddoeth yn
www.dwrcymru.com/waterefficiency

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Our Reference: EIR/546/2020

Dear Mr Evans,

Request for Information

We write further to your request for information dated 1 July 2020, which
we have been considering under
the Environmental Information Regulations 2004.

In relation to our assets at Llwynon and Pontstic, we can confirm, both
reservoirs were on spill during the Storm Dennis period of the 14th and
17th of February 2020, no valves were operated to release any additional
water.

Please note, our assets performed as designed and DCWW did nothing
manually to increase the flows into the river.

Llwynon

o Flow on 16^th February 2020 was 511 Ml/d.
o Flows peaked at 700mm over the dam crest.

Pontstic

o Maximum recorded flow on 16^th February 2020 was 2000 Mld. The missing
data on the 16^th (orange graph) is due to high flows in excess of
2000Mld - we can only measure up to 2000Mld.
o Flows peaked at 890mm over the dam crest.

In the data sets above, when the “spill level” is above 0 then the
reservoir is in spill.  Once in spill, we have no control over the volume
of water entering the rivers.  This is because the dams are designed to
spill when they are full. This is a safety mechanism which is built into
all dams in order to protect the structural integrity of the dam itself. 
Excess water in the reservoirs travels down the spillway rather than
overtopping the dam and eroding the structure.

Welsh Water's company policy/procedure on when a Dam should be opened to
release water into the surrounding system.

For information, our company policy is to meet all legal requirements and
agreements for the controlled release of water from reservoirs into a
downstream water course. These are governed through licences and consents
issued by Natural Resources Wales (NRW). The exception to this is when
there is a risk to the integrity of a reservoir/dam which might need a
quick response to reservoir lowering which is undertaken through
consultation with an appointed ‘Panel’ Engineer.  Reservoir discharge
consents are issued and monitored by NRW to ensure that discharges do not
have a significant adverse impact on the rivers downstream of reservoirs.

These discharges fall into 4 categories:

o Compensation releases legally controlled through abstraction licences
issued by Natural Resources Wales (NRW). These specify the discharges
that must be made.
o River regulation releases which are again specified through
abstraction licences and govern how and when releases must and can be
made.
o Ongoing consents to discharge water for short durations in order to
test the ability of a reservoir to be drawdown when necessary.
o One off consent to discharge water, in order to manage water levels so
that reservoirs can be maintained. These specify the volumes that can
be discharged and duration.

We have processes in place to ensure that reservoir releases are managed
in line with the legal provisions above. These releases are controlled by
our Dam Safety Engineers and technicians. There is also a legal
requirement, under the Reservoir Act 1975, to exercise all the scour
valves that are critical to the safe operation of a reservoir/dam through
their complete range at least twice a year.

We hope this information is helpful, should you require anything further,
you can contact us at [1][email address].  

If you are dissatisfied with the handling of your request, you have the
right to ask for an internal review. Internal review requests should be
submitted within 40 working days of the date of receipt of this response
and should be addressed to Company Secretary, Pentwyn Road, Nelson,
Treharris, Mid Glamorgan, CF46 6LY.

If you are not content with the outcome of the internal review, you have
the right to apply directly to the Information Commissioner for a
decision.

Yours sincerely,

G Andrews
Dŵr Cymru Customer Services

_______________________________________________________ Dwr Cymru Welsh
Water is firmly committed to water conservation and promoting water
efficiency. Please log on to our website www.dwrcymru.com/waterefficiency
to find out how you can become water wise. Mae Dwr Cymru Welsh Water wedi
ymrwymo i warchod adnoddau dwr a hyrwyddo defnydd dwr effeithiol. Mae
cyngor i' ch helpu i ddefnyddio dwr yn ddoeth yn
www.dwrcymru.com/waterefficiency

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