The detrimental influence of storm sewer overflows on urban river quality has been widely recognised for many years. One objective of the WRc River Basin Management programme is the development of a river impact model capable of predicting the transient quality changes in receiving waters due to intermittent storm sewage discharges. The production of SPRAT (Spill Pollution Response Assessment Technique) is the first step in the development of such a model.
SPRAT incorporates a number of significant simplifications, most notably plug flow and instantaneous mixing, and does not implicitly take into account the effects of dispersion. These simplifications reflect the large errors associated with the model inputs. These errors severely limit the potential accuracy of any river impact model.
The model has been applied to the Bolton river system in North West England. The development and application of SPRAT has enabled the requirements for a more sophisticated river quality impact model to be clearly defined, in addition to highlighting the problems associated with gathering suitable data with which to build and calibrate such a model.
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