Assessing the impact of diffuse and wastewater point source discharges on bathing waters

Northumbrian Water - Bathing Water Studies

Northumbrian Water is dedicated to protecting the bathing water quality along the coast and has a goal to have the best rivers and beaches in the country. To aid in this mission, they reached out to us to deliver a programme of comprehensive desk and modelling investigations to better understand bacterial water quality at several bathing water sites on the North East Coast, and to understand reasons for both deterioration and improvement in water quality.

As part of our Investigations, we analysed the apportionment between the individual pollution sources and identified solutions to help improve water quality. We simulated the flow and pollutant transport along the coast under various meteorological and tidal conditions. We collected 10-year flow and concentration time-series data for all continuous, intermittent, and third-party wastewater discharges. We then fed these results into our inhouse SWIM (storm water impact model) software, which we calibrated by varying diffuse contributions and bacterial decay rates to match observed sample data. We also conducted site investigations that helped reinforce the conclusions of the modelling, giving the regulator both the confirmation and confidence to sign off the compliance assessments for Northumbrian Water.

For both Northumbrian Water and the regulator, the overall water quality and apportionment data and evidence can help inform their future investments.