Commonality of rainfall variables influencing suspended solids concentrations in storm runoff from three different urban impervious surfaces

Finding a common set of rainfall variables to explain the concentration of suspended solids in runoff from typical urban impervious surfaces has many applications in stormwater planning. This paper describes a statistical process to identify key explanatory variables to non-coarse particle (suspended solids < 500 μm size) event mean concentrations measured from road, carpark and roof surfaces located in Toowoomba, Australia. The dominant variables for all surfaces were rainfall depth and peak 6-min rainfall intensity. Storm duration, defined as the time period when rainfall intensity exceeds 0.25 mm/h and antecedent storm rainfall were also important predictors, but was less dominant. The regression model fitted to non-coarse particle concentration across all surfaces was proportional to rainfall depth raised to a negative power and peak 6-min rainfall intensity raised to a positive power; the proportionality constant varies by surface type. The form of this common model has a physical basis and is analogous to the modified universal soil loss equation widely used for soil loss estimation for non-urban areas.