Wednesday, January 7, 2015

What is an outfall?

A stormwater outfall is defined as any “point at which storm water is discharged to waters of the state or to a storm sewer” (NR Code 216). Outfalls are further categorized by 2 types – major and minor. A major outfall is essentially one that is large in size and drains a large area of land. Minor outfalls are the remaining outfalls of various sizes and drainage areas.

Superior has over 100 stormwater outfalls (19 of them are major). Outfalls get screened every year during dry weather (at least 2 days after rainfall) to detect Illicit Discharge. Read more about Illicit Discharge from a previous blog post. Half of major outfalls get screened every year (2-year rotation) and 1/5 of minor outfalls are every year (5-year rotation). The trickiest part of outfall screening is FINDING the outfall. All outfalls have been mapped many years ago, but the terrain has changed since then . . . especially after the 2012 flood. Minor outfalls can be small (6” in diameter) and can be buried underground. Outfalls should be dry during periods of no rain so any flow from an outfall could potentially be an illicit discharge. In this past 2014 field season we did observe flow from outfalls, but they were all likely due to infiltration from natural water source or tap irrigation. Fortunately we didn’t notice any odd discharge. 

So if you noticed two strange people parked along the side of the road, looking in the nearby fields or staring at the storm drain off the road during the summer . . . they may be trying to find the outfall in the field or off the road.

No comments:

Post a Comment