Most cities that have combined storm and sanitary sewer
systems have either had problems with combined sewer overflows in the past or
have looked ahead uneasily to the possibility.
Until now, most of the capacity
problems were caused by cities simply outgrowing their sewer systems. More users
create greater demand on the existing pipes, and a larger amount of impervious
surface sends runoff into those pipes during a storm.
Recently, some stormwater managers
have become concerned about another stressor on the system: climate change.
Increasingly severe storms and unpredictable weather patterns could exacerbate
an already serious problem. (See how Montreal
is dealing with its water problems, for example.)
There are many ways to deal with
the problem, all of them expensive. Increasing the size or the number of water
treatment plants is one. Separating the sewer systems—or at least portions of
them—so that stormwater doesn’t get treated along with the sanitary sewage is
another. Incorporating more low-impact development techniques to increase
infiltration of stormwater runoff—and therefore take some of the pressure off
the existing infrastructure—is a third and increasingly popular one.
If your city has a combined sewer,
what do you think is putting the greatest stress on the system: Ongoing
development? Climate change? Something else entirely? And what do you see as the
most viable solution?