A long-term suspended solids runoff simulation in a highway drainage system.

A long-term monitoring investigation was carried out in a highway drainage system in Winterthur, Switzerland. Several runoff quality and quantity simulations were carried out using the distributed model 'InfoWorks-CS'. Serial rainfall monitoring data was used for investigation of SS runoff behavior from the highway. Under continuous rainfall conditions, the quantity simulation showed a good agreement with the measured hydrograph. However, in some cases where rainfall was not continuous, overestimation of the peak height was found at the later stage after the end of the rainfall. It was believed that the initial/depression loss on the road surface was recovered during the halting period of rainfall. The consideration of regenerated depression loss significantly improved runoff simulation results in the on-and-off type rainfall events. A single event quality simulation underestimated the SS load in light rainfall events. One of the reasons was possibly inadequate consideration of pipe sediment conditions. A long term simulation was carried out to establish the initial condition of surface and pipe sediment for the target event. The newly simulated pollutograph gave a good agreement with the measured one. It revealed that it was essential to consider appropriateness of the initial condition of pipe sediment as well as surface sediment.