The catch basin (storm sewer) openings we see on our streets don't lead to a treatment facility, they
empty into our streams and lakes.
Local contractors are helping us to remember this by stamping newly poured concrete with the phrase "No Dumping, Leads to Lake".
Older catch basins can also be marked. See our Volunteer Storm Drain Marking page to learn more!
View "Liquid Assets Minnesota" a 56-minute documentary exploring concerns anout the state's aging water infrastructure produced by tpt's MN Channel and Central States Environmental Assoc.
Moving water around Duluth
A Simple Look at Duluth Hydrology
What is hydrology?
Hydrology is the study of water's properties, distribution and circulation on Earth.
Take a moment to think about how we use and move water
through the city of Duluth. Water is pumped from Lake Superior
to the Lakewood Water Treatment Plant. It is cleaned and
sent through the drinking water system to homes, businesses
or storage tanks in Duluth. Depending on how we’ve
used the water, it gets carried away by either the sanitary
sewer system or the stormwater sewer system.
Sanitary Sewer System: Dirty water that goes down our drains
and toilets is called wastewater. Wastewater travels to
the Western Lake Superior Sanitary District (WLSSD) through
the sanitary sewer system. The wastewater treatment plant
at WLSSD cleans the water before it is discharged back
into the St. Louis River. Water released into the river
must first meet strict regulatory standards for pollutants.
Take a tour
of the City's network of underground and overland water conveyance system - some of
which demonstrates the remarkable craft of the era which could be quite beautiful.
Stormwater Sewer System: The stormwater sewer system is
designed to collect rainwater and snowmelt. This system
is operated and maintained by the City of Duluth. Most
of the open grates you see on the streets lead to the stormwater
sewer. It also collects water and pollutants that run off
of sidewalks, driveways, and lawns. Stormwater pipes drain
directly into one of the city’s 43 named streams (all of
which drain into Lake Superior). This water does not get
treated, so all pollutants in the water are carried directly
to steams and lakes.
Between the sanitary and stormwater sewer systems, there
is a lot happening below the streets of Duluth. The City
of Duluth maintains more than 431 miles of underground
storm sewer lines, 100 miles of roadway ditches and culverts,
two lift stations, 13 sediment boxes, and 5,600 manholes.
WLSSD has nearly 75 miles of sanitary sewer pipes, 16 pump
stations and receives an average of 40 million gallons
of wastewater per day.
How is URBAN Hydrology different than natural hydrology?
Development on the land changes how water naturally
travels through the watershed. As mentioned above, with a natural
ground cover about 50% of rainfall infiltrates into
the ground, 40% evaporates or is transpired through
plants (these together are called evapotranspiration), and only about 10% actually
runs off the surface. As we develop the land, we add structures
onto the surface, such as roads, houses, parkinglots,
sidewalks, and driveways. All of these are impervious
surfaces: water cannot pass through them as it can through soil, and
so instead of the water infiltrating, it is forced to
either evaporate or run off.
Considering that much of the evapotranspiration is due
to plants, and the impervious surfaces we construct
are not plant-friendly, this option is largely removed, and runoff increases.
The amount of impervious surface within a watershed
determines how great the change in runoff will be. At 10 to 20%
impervious (similar to medium-density residential areas),
runoff is doubled, and the amount of water infiltrating is reduced. At
30 to 50% impervious (such as in high-density residential
developments), runoff is tripled, and at 75 to 100% impervious (as
is common in commercial areas), the majority of rainfall
becomes runoff, and infiltration is less than 1/3 of what it was prior
The results of increased runoff and reduced groundwater
are two-fold. First, the large amount of extra runoff
causes the streams to have much higher flows than natural, and
the flow rate increases much more rapidly and drops off more rapidly
after the storm. Second, due to the reduced infiltration
volumes, there is less water available to be released
slowly into the stream over time, resulting in lower water levels between
rainfall events. In effect, much of the water that under
natural conditions infiltrated into the ground and slowly made
its way into nearby creeks now enters the stream all at once.