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Project title

Low-Flow statistics for Assimilative Capacity Assessments

Primary Funding Agency

Environmental Protection Agency (EPA)

Co-Funding Organisation(s)

Met Eireann

Lead Organisation

University of Galway

Lead Applicant

Edelle Doherty

Project Abstract

Climate change is significantly altering Ireland’s hydrological patterns, with projections and recent observations indicating a clear trend toward wetter winters and drier summers. This shift is disrupting historical assumptions about river flow conditions that underpin environmental regulations, particularly those related to the setting of emission limit values (ELVs) for treated wastewater discharges based on assimilative capacity assessments. Current methodologies typically apply a single, annual low-flow value (e.g., Q95), derived from long-term historical data, across the entire year. While such an approach may protect vulnerable aquatic ecosystems during prolonged summer low flows, it also potentially underutilizes available dilution capacity during higher winter flows. The WACFlows project proposes a novel, climate-resilient approach to address this regulatory gap. The project aims to develop a scientifically robust methodology for generating seasonally differentiated low-flow river statistics that reflect observed and projected seasonal variability in river flows. In doing so, it seeks to improve the accuracy, adaptability, and environmental effectiveness of assimilative capacity assessments used in water quality regulation. Key objectives include: (1) a critical review of national and international low-flow assessment methodologies, with an emphasis on climate adaptation; (2) an analysis of long-term flow records from selected EPA hydrometric stations, evaluating the suitability of traditional Q95 values versus other low-flow assessment metrics identified in the literature; (3) a sensitivity analysis using state-of-the-art Irish climate projections (e.g., TRANSLATE) to examine the regulatory implications of seasonal low-flow trends; and (4) the development of practical guidance for the EPA to incorporate seasonally differentiated low-flow statistics or other techniques into regulatory frameworks, including case studies and implementation tools. The project will build on findings from recent EPA-funded initiatives such as HydroPredict and the Irish Hydrometric Reference Network (IHRN) update, and will consult best practices from Water Framework Directive (WFD) Member States like the UK, France, and Spain. Stakeholder engagement with the EPA, OPW, and Uisce Éireann is central to the project’s design, ensuring that recommendations are operationally relevant and aligned with national policy needs. By moving beyond static flow metrics and embedding seasonal and climate considerations into regulatory practice, the WACFlows project will help future-proof water quality regulation in Ireland. The outcomes will contribute to more sustainable wastewater management, greater protection of aquatic ecosystems during low-flow periods, and more efficient use of assimilative capacity when flows are higher. Importantly, this work will support national climate adaptation strategies and Ireland’s ongoing obligations under the Water Framework Directive. Deliverables include an EPA guidance document, a seasonal low-flow dataset, and an educational training module aimed at building capacity among early-career wastewater professionals. In addressing both the scientific and operational dimensions of low-flow assessments, WACFlows offers a timely and actionable contribution to the evolving challenge of regulating water quality under changing climate conditions.

Grant Approved

€158,840.33

Research Hub

Protecting and Restoring Our Natural Environment

Research Theme

n/a

Start Date

31/03/2026

Initial Projected Completion Date

30/09/2027