Author(s): Virginia Stovin; Ian Guymer; Paul Gaskell; Lorraine Maltby
Linked Author(s): Ian Guymer
Keywords: Highway; Model; Pollutant; Rainfall; Runoff; Sediment; Turbidity
Abstract: The ability to predict temporal variations in concentrations and loads from highway runoff, including potential first flush effects, may inform the design of interception/treatment devices and the impact on receiving water ecology. A recent UK study included the collection of rainfall, highway runoff rates and sediment load and quality data from six different sites where motorway runoff drained directly into a receiving watercourse. This data set is used to critically evaluate a previously-published model (Kim et al, 2005) aimed at predicting temporal variations in quantity and quality in response to specific rainfall inputs. The comparisons consider total suspended sediment (TSS) concentrations only. However, given that a high proportion of significant highway-derived contaminants are known to be associated with sediments, this represents a useful generic starting point for a more comprehensive pollution load prediction model. At each site rainfall inputs were monitored using a tipping bucket rain gauge, whilst water depth and velocity were monitored in the highway drain just upstream from its outfall. Flow depth within the drainage pipe was used to calculate flow rates, based on a calibrated weir head/discharge relationship. Discrete samples were collected during the storm event. A representative subset of the sampled storms has been used to evaluate the usefulness and accuracy of the model presented by Kim et al. (2005). This model, developed from data collected by the California Department of Transportation, relies on calibrated regression relationships to define four parameters, which enable the prediction of temporal concentration profiles for 8 water quality parameters, including TSS. The model uses four parameters (derived from storm runoff characteristics) to predict TSS as a function of the cumulative proportion of total runoff. This general approach appears to be valid and useful in the present context. However, the model shows some questionable behaviour, including the possibility of negative TSS values and/or an initial drop in concentration values. Preliminary comparisons with the observed UK data suggest that the calibrated model does not fit well, and a simplification of the model, based on just two parameters, is proposed.