Effects of rainfall patterns on highway runoff pollution and its control

The magnitude of pollution from highway runoff is highly dependent on rainfall patterns. To demonstrate the effects of rainfall on the characteristics of highway pollution and its control, runoff from two sections of a major highway in Taiwan was monitored, representing respectively the uncontrolled runoff and the runoff treated using a swale system. Event mean concentrations (EMCs) of suspended solids, chemical oxygen demand, total nitrogen, total phosphates, iron, copper and zinc were calculated from monitored data. Annuals loads were also obtained from long-term simulations using the US Environmental Protection Agency Stormwater Management Model. Results indicated that, despite high traffic volumes, both EMCs and annual loads from the studied highway were low compared with those found in literatures. The lower potentials of runoff pollution were attributed to a pattern of infrequent but intense rainfalls of the study area. The specific rainfall pattern also caused the swale system to be less effective in controlling nitrogen and phosphorus because of significant erosion.