Dŵr Cymru Welsh Water Environmental Assessment of Cefni Reservoir Drought Permit (8001-5) Final March 2019 Client: Dŵr Cymru Welsh Water Title: Environmental Assessment of Cefni Reservoir Drought Permit (8001-5) Project No: ED10929 Date of Issue: March 2019 Status: Final Version No: 1.1 Produced By Authorised for Release By ……………………………….. …………………………………… Dr Anne Fairhead John Sanders Principal Environmental Scientist Technical Director This report is the Copyright of Welsh Water and has been prepared under contract to provide consultancy support on drought planning by both Cascade Consulting (Environment & Planning) Ltd and by Ricardo Energy & Environment.* The contents of this report may not be reproduced, in whole or in part, nor passed to any organisation or person without the specific prior written permission of Welsh Water. Cascade Consulting (Environment & Planning) Ltd and Ricardo Energy & Environment accept no liability whatsoever to any third party for any loss or damage arising from any interpretation or use of the information contained in this report, or reliance on any views expressed therein, other than the liability that is agreed in the said contracts. *As part of a share purchase agreement in August 2015, Cascade Consulting (Environment & Planning) Ltd transferred its business to Ricardo plc. All employees transferred to Ricardo Energy & Environment, a trading name of Ricardo-AEA Ltd which is a wholly owned subsidiary of Ricardo plc. The work described in this report spanned the pre-acquisition and post-acquisition period and throughout this time the consultants involved maintained a continuity of service both as employees of Cascade Consulting and then subsequently as employees of Ricardo Energy & Environment. CONTACT DETAILS: Ricardo Energy & Environment Bright Building, First Floor Manchester Science Park Pencroft Way Manchester M15 6SGZ Tel: +44 (0)1235 753000 Dŵr Cymru Welsh Water Environmental Assessment of Cefni Reservoir Drought Permit (8001-5) Final NON-TECHNICAL SUMMARY INTRODUCTION AND PURPOSE OF THIS REPORT Welsh Water’s Drought Plan provides a comprehensive statement of the actions Welsh Water will consider implementing during drought conditions to safeguard essential water supplies to customers and minimise environmental impact. It encompasses a number of drought management options that will only be implemented if and when required and includes drought permit / order options. A drought permit or order is a management action that, if granted, can allow more flexibility to manage water resources and the effects of drought on public water supply and the environment. The objective of this report is to provide an independent and robust assessment of the potential environmental effects of implementing a drought permit at Cefni Reservoir, over and above those arising due to natural effects of drought and those which would occur under "normal" abstraction licence conditions. Cefni Reservoir is located in Welsh Water’s North Eryri Ynys Môn Water Resource Zone (WRZ) – this area includes the mainland adjacent to the Menai Straits (North Eryri) and Ynys Môn (Anglesey). Water is supplied from five impounding reservoirs; on the mainland Ffynnon Llugwy, Llyn Cwellyn and Llyn Marchlyn Bach and on Ynys Mon, Llyn Alaw and Llyn Cefni. The resources are operated conjunctively with the ability to feed water from the mainland to parts of the island from the gravity resources of Llyn Cwellyn, Ffynnon Llugwy and Llyn Marchlyn Bach when storage allows. As storage declines, the area of Ynys Môn supported from the mainland is reduced and the area supported by Llyn Alaw and Llyn Cefni increases. The Afon Cefni is a component of the Malltraeth Marsh / Cors Ddyga Sites of Special Scientific Interest (SSSI) therefore consideration has been given to the potential impacts of drought permit implementation on the features and species of these designated sites. The assessment also considers how the proposed drought permit may affect the environment in combination with the effects of other existing abstraction licences, environmental permits and other drought management plans. This report is a ‘shelf-copy’ report which would be updated to support an application to Natural Resource Wales (NRW) for a drought permit at Cefni, which may be required by Welsh Water in the future. PROPOSED DROUGHT PERMIT DETAILS In order to protect public water supplies within Welsh Water’s North Eryri Ynys Môn WRZ in the event of a future severe drought, Welsh Water would make an application Ricardo Energy & Environment Dŵr Cymru Welsh Water Environmental Assessment of Cefni Reservoir Drought Permit (8001-5) Final to NRW for a drought permit to vary the conditions of abstraction from Cefni reservoir. If granted, the drought permit involves a proposed reduction in the statutory compensation release from Cefni Reservoir to the Afon Cefni of 0.9Ml/d, from 1.8Ml/d to 0.9Ml/d. The drought permit is most likely to occur during the summer and autumn months period, to conserve the longevity of reservoir storage for use in direct supply during a drought. This is based on modelling of Cefni Reservoir’s performance under normal operating conditions in dry summers. The drought permit scheme will influence the downstream Afon Cefni from the outflow at Cefni Reservoir to the tidal limit. The drought permit is most likely to occur during the summer to winter period, and is considered not to extend outside the period July to December. This has been confirmed by Welsh Water’s water resources modelling. The revised abstraction arrangements would legally be authorised for 6 months but would be removed sooner if water resources have returned to adequate levels to safeguard future water supplies, as agreed with NRW. NEED FOR THE DROUGHT PERMIT Application for a drought permit is a precautionary approach. Due to the time needed to determine a drought permit application, Welsh Water will potentially apply for a drought permit more frequently than it will be used. The justification for the drought permit sought will be set out in a “Needs Statement”. This will be produced by Welsh Water at the time of a potential future application, and will form part of the full drought permit application. ALTERNATIVE SOURCES CONSIDERED Details of alternative sources considered by Welsh Water will be completed at the time of application for the drought permit at Cefni. This will demonstrate justification for the proposed drought option details applied for. POTENTIAL IMPACTS OF DROUGHT PERMIT IMPLEMENTATION The scope of the assessment has been defined by a screening and scoping exercise. Ricardo Energy & Environment Dŵr Cymru Welsh Water Environmental Assessment of Cefni Reservoir Drought Permit (8001-5) Final Summary of the Hydrological Assessment The assessment has concluded that there is a major impact on flows in the Afon Cefni as a result of implementing the drought permit. These hydrological impacts are assessed as leading to moderate impacts on the physical environment of the river, including minor beneficial impact on water quality. Summary of the Environmental Features Screening Environmental assessment is required and included for features where screening has identified a major or moderate impact. Screening identified WFD status and Community Assessment / Habitats Directive designated habitats and species, SSSI designated features and Environment (Wales) Act Section 7 species, invasive species and recreation as environmental features for which an environmental assessment was required. The assessment has concluded that during periods when release from Cefni Reservoir is restricted to compensation flow only there are major impacts on fish, and moderate impacts on macroinvertebrates and macrophytes and minor impacts on phytobenthos. The impacts on Malltraeth Marsh / Cors Ddyga SSSI are assessed as minor and as major on the Dingle / Nant y Pandy Local Nature Reserve. Cumulative Impacts No cumulative effects of implementing the drought permit with existing licences, consents and plans are currently anticipated. However, this should be reviewed at the time of any future application for a drought permit at Cefni Reservoir. MITIGATION AND MONITORING The environmental assessment has identified significant impacts of implementation of a drought permit at Cefni Reservoir. Consequently, in line with the DPG, an Environmental Monitoring Plan has been proposed. Potential mitigation measures have also been proposed and further discussion with NRW is required in order to develop suitable mitigation measures. CONCLUSIONS In summary, it has been concluded that the environmental effects on river flows, water quality and ecology of implementing a drought permit at Cefni Reservoir during July to December inclusive, over and above those conditions that already exist under "normal", i.e. licensed, baseline conditions, with the onset of a natural drought, would be major. Ricardo Energy & Environment Dŵr Cymru Welsh Water Environmental Assessment of Cefni Reservoir Drought Permit (8001-5) Final Contents 1 Introduction ............................................................................................. 1 1.1 Purpose of the Environmental Assessment ............................................................. 1 1.2 Supporting Studies...................................................................................................2 1.3 Consultation .............................................................................................................3 1.4 Structure and Content of the Report