Created by potrace 1.16, written by Peter Selinger 2001-2019

CSO Standards for Inland Bathing Waters

WRc consulted the Environment Agency regarding Combined Storm Overflow (CSO) impacts on inland compared to coastal bathing waters.

How WRc model catchment water quality

Conducted

dedicated investigations involving tailored simulation of the client's case using expert modelling software

Provided

the client with the required answers, along with detailed explanations of the observed consequences

Ensured

legislative decisions regarding human health were thoroughly investigated and not based on assumptions

Ensuring bathing water safety

There is increased interest in designating more riverine waters as safe to bathe in under the legislative framework that ensures bacterial monitoring and classification of both inland and coastal bathing waters. Bathing Water status is undertaken during the May to September bathing season by comparing the weekly monitoring data to 95%ile (90%ile for Sufficient) standards for intestinal enterococci and E. coli. These bacteria are introduced to rivers from point and diffuse sources, including: continuous sewage discharges, intermittent overflows (such as Combined Sewer Overflows (CSOs)), agricultural runoff, and wildlife.

Not one size fits all

Loads introduced to rivers vary considerably. In extreme wet weather, contributions from intermittent and rainfall-generated runoff can increase relative to continuous discharges operating in both dry and normal wet weather conditions. In recognition of this, spill frequency standards have been developed to protect the status of estuarine and coastal designated bathing waters; an average of either 2 or 3 spills per bathing season is permitted for either Excellent or Sufficient/ Good waters.

The primary question to be addressed for the EA was whether the 3 (or 2) spill frequency design standard applied to estuarine and coastal bathing waters is also appropriate to riverine bathing waters, given the different factors that arise relating to intermittent discharges.

Advising on a key environmental safety standard

A SIMPOL modelling exercise was undertaken on an idealised river catchment that simulated representative inputs of E. coli from point and diffuse sources to a river comprising a bathing water. 

The investigation concluded that it was likely that background concentrations of E.coli would cause failure of the Sufficient bathing water classification standard; adopting the same approach as used in the coastal situation is not appropriate for the following reasons:

    Bacteriological load in an upstream catchment can, by itself in dry weather, result in a bathing water classification of Poor (i.e., below the Sufficient) standard.

    The impact duration of spill is likely to be less than 24 hours but will vary according to riverine bathing water characteristics, and is a factor that needs to be addressed further.

    The actions of wind, wave, tide and UV accelerate the dispersion and breakdown of bacteria in the coastal environment, but these processes are not applicable to an inland river.

    Market-leading environmental modelling expertise

    Trusted industry-wide to deliver strategic, authoritative advice

    Assessment based on critical environmental evidence

    Related items

    Created by potrace 1.16, written by Peter Selinger 2001-2019

    Start a conversation

    Full name
    Email address
    Company name
    How can we help?

    Can we stay in touch?

    Your details will be stored within our CRM to allow us to handle your enquiry. We'd love to keep in touch and send you our newsletters and other notifications we think may be of interest to you. Please let us know if we have your permission for this.

    Full name
    Company name
    Email address
    Phone number

    Can we stay in touch?

    Your details will be stored within our CRM to allow us to handle your enquiry. We'd love to keep in touch and send you our newsletters and other notifications we think may be of interest to you. Please let us know if we have your permission for this.