Source water vulnerability and protection in complex catchments

Abstract

This research investigated catchment scale approaches for assessing and protecting surface source waters prior to treatment for distribution. The cross-border River Derg catchment (384 km2), in the northwest of Ireland, was used as a case study. Recognised water quality pressures in this region are associated with agricultural and forestry practices. Three experimental investigations were undertaken.

First, the dominant hydrological pathways of the acid herbicide MCPA were assessed. Pathways were determined using enhanced resolution temporal sampling and discharge datasets, coupled with flow and load separation techniques. Over a seven-month period, 85kg (0.22kg km-2) of MCPA was exported from the catchment, with up to 72% lost in quickflow pathways and 12% in more persistent baseflows.

Second, an incentivised agri-environmental scheme (AES) was evaluated as a pre-water treatment step to lower turbidity and colour burdens prior to abstraction and treatment. Using high resolution water quality and discharge datasets and incorporating a BACI design, modest monthly reductions were observed in turbidity during average conditions (50th Percentile, 2.7%) while colour concentrations remained unchanged.

Finally, two phases of afforested peatland management were assessed. For in-stream measures to lower sediment flux following clear, reductions of up to 69% were observed using a range of mitigation methods. A novel, forest to bog cell bunding restoration technique was also monitored for 1 year following peatland disturbance. However, the cell bunding technique exhibited the greatest variation in shallow groundwater and colour concentrations when compared to other restoration techniques.

This research highlights the value of catchment-based approaches for assessing and addressing risks in source water catchments with dominant surface water pathways. It also demonstrates the intricacies linked to source water protection practices, particularly where land use and water quality threats are complex and varied. These findings have wider implications for water utility providers, associated treatment processes and integrated catchment management initiatives.

Date of Award	Sept 2023
Original language	English
Supervisor	Paul Mc Kenzie (Supervisor), Sally Cook (Supervisor), Phil Jordan (Supervisor) & Rachel Cassidy (Supervisor)