6th Grade Urban Hydrology

The STORM DRAIN SYSTEM

Students consider the storm drain system, and how any water that flows into the storm drain will enter the Huron River or one of its tributaries (creeks). This water is not filtered or cleaned in any way, so whatever is carried into the drain by rainwater and snow melt will eventually reach the Huron. Check out the City of Ann Arbor's Stormwater Webpage for more information. Teachers, the short video on this page could be a wonderful way for students to preview trip content!

Students conduct monitoring of the Huron River main stem and near the mouth of Allen Creek, checking for turbidity and conductivity as indicators of possible pollutants.

IMPERVIOUS SURFACES

Side walks, roof tops, driveways, streets - any surface that is hard and cannot absorb water is "impervious" and allows water to run off into the storm drains. Pervious surfaces - vegetation, forests, fields - allow water to filter slowly down into the aquifer. Plants clean and cool the water as it "percolates" through the soils. Students should understand and be able to recognize "impervious" and "pervious" surfaces prior to the field trip.

NON POINT SOURCE POLLUTION

Pollutants entering from a known source (e.g. a factory), are POINT SOURCE pollutants. Pollutants entering from a variety of vague, undefinable sources are NONPOINT SOURCE pollutants. Fertilizers, pesticides, herbicides, dog poop, salt, dirt, leaves, trash and motor oil are types of nonpoint source pollutants. Go to HRWC.org to learn more.

FERTILIZER and ALGAL BLOOMS

Nitrates and phosphorus make the grass grow and, unfortunately, these fertilizers also make the algae in waterways "bloom" and grow out of control. In 2015, Lake Erie, which is the source of drinking water for 11 million people, had the worst algal blooms on record (below). Of particular concern is the growth of a blue/green algae that produces a toxin called microcystin; in high enough concentrations, the water becomes too toxic for consumption. In 2014, concentrations of microcystin in the water supply for Toledo lead to a sustained drinking water ban.

Locally, Ford Lake is a case study for the damage caused by algal blooms. Dr. John Lehman's study examines inputs from upstream and the effects of phosphorus trapped in the sediments at the bottom of the lake.

The Huron River was once too polluted to swim in, but today - thanks to the efforts of many communities - the Huron is approved for "full body contact." Below are some of the efforts that helped improve and restore the Huron River.

IMPROVEMENTS to PROTECT WATER RESOURCES

KEEP OUT SEDIMENTS

Is dirt really a pollutant? Oddly enough, it is considered a pollutant. The sediment flowing off streets and construction sites causes creeks and habitat to infill, plus it increases the turbidity (cloudiness) of the water. Contractors use a mesh material to keep dirt out of the storm drains. This same materials is used as silt fencing around construction sites.

SLOW the WATER DOWN and CLEAN IT

Pervious concrete allows water to filter through the road bed. Rock "braces" are used to slow water runoff and reduce erosion. Vegetative "swales" are used to filter the water, slow it down, and cool it before it enters the aquifer or the surface water. Examples of swales can be found throughout the area.

USE ROOF TOPS to REDUCE RUNOFF

Green roof technologies turn an impervious surface in to a pervious one. Mallets Creek Library (pictured), City Hall, and AC3 Collaborative Architecture are examples. Click HERE for a local article and HERE to learn about the benefits of building with a green roof.

PAY ATTENTION to the GROUND WATER/SURFACE WATER CYCLE

In 4th grade, students should have learned about groundwater recharge cycles, surface water, and drinking water supplies. Urban hydrology should reinforce that pollutants we put into the system are difficult to remove. Students should understand that the water cycle is CLOSED and there is no "new" water being "made" on earth. Today's water supplies must be kept clean and safe for future generations.

Chemical threats to water quality in the Huron River watershed

*To learn more about PFAS in and around Ann Arbor, click HERE.