Our www.lakesuperiorstreams.org network of stream sensors and a bank restoration project in the Upper Amity Creek watershed survived some really big storms in the past, including a monster event in August 2011. It’s true that our June 2012 storm was bigger, but it also happened after many weeks of wet weather, including another big storm May 23-24 that left the soil saturated with water. This meant that more water entered the streams faster, and so peak flows generated more water than the stream channels and our urban and rural stormwater systems could handle. Enormous amounts of water and mud were powerful enough to move boulders weighing as much as your car and uproot mature shoreline trees that were there for many decades. The trees provided shade that kept the water cooler, stabilized the banks, and the occasional limbs that fell ("large woody debris") created diverse fish and bug habitat. Too much tree and shrub fall from the June 19 storm exacerbated flood damage to culverts and bridges and led to unexpected flooding problems.
Now think about what it would be like to be a trout in Amity, Tischer, Chester, Miller, or Kingsbury Creek. The momentum of the water alone is probably going to push you out of your daily routine and into Lake Superior if you can’t find cover to survive the pounding. Those of us who have been sandblasted in a desert windstorm have some sense of the abrasion a fish or aquatic insect’s sensitive gills experienced. I’ve heard fisheries biologists speculate that the youngest year classes of steelhead trout in the streams probably suffered massive mortality but that older fish likely had already moved into Lake Superior ― timing is everything. The fate of other species may take a while to become evident from future DNR surveys. The loss of clarity is also a problem for the many types of fish and bugs that are visual predators. Even though the water cleared up substantially within a week, this is an unusually long time period for smaller critters.
After the creeks returned to their base flows last week and the water was clear I picked up cobbles in Tischer and Amity that would normally feel somewhat slimy with a layer of the algae (some green and some brown) and bacteria that form the base of the food web for bugs to eat. They felt like they’d been cleaned with a scrub brush, with far fewer caddis flies, mayflies and other critters stuck on the bottoms of the larger rocks than usual. I noticed the same thing yesterday (7/2/12) in the Gooseberry River. They’ll come back, but it may take a few years. The thing is, we had a scour event last August that also had a big effect on the bugs. How "normal" is it to have this happen 2 years in a row? What’s the effect going to be on different fish species and different age fish? Tough to know when a few sites on Amity where we have summer bug data for only one survey in about 5 or 6 different years out of the last 8, is the most comprehensive data set available for the region. Other riffle areas that are prime habitat for coldwater animals were smothered with sand and silt from upstream banks and channel erosion. How long before it gets washed clean again? Are birds and bats that feed heavily on emerging aquatic insects in summer going to have problems finding enough food to survive next winter?
How about Lake Superior? Even though it’s one of the largest volumes of liquid freshwater on the planet and all that muddy water eventually gets diluted, "eventually" can take a long time. Meanwhile, the silt laden water has persisted in the much shallower and biologically productive nearshore waters for nearly two weeks now. Scientists at UMD’s Large Lakes Observatory sampled the western arm of the lake last week and found that the muddiness was also present throughout the water column to as much as 100 feet. The lake’s response is unclear until more data is collected but we do know that the loss of clarity (sunlight penetration) acts to reduce algal photosynthesis while the enormous amounts of phosphorus, and other nutrients, contributed to the lake by the St. Louis and Nemadji Rivers, as well as smaller Minnesota and Wisconsin streams, should stimulate algal growth. In the near term we might expect a negative effect on zooplankton, the small crustaceans that eat algae and are in turn eaten by virtually all fish species at some point in their life cycle, because the soil particles are not very nutritious and can clog their food filtering apparatus. In the nearshore zone it’s also unclear what the overall effects will be. Lots of fish spawning habitat has been buried under fine silt that settles out as water velocity slows. These fine particles also carry other pollutants deposited on the soil from the atmosphere, such as mercury and PCBs, some of which ends up in fish. And of course despite all of Duluth’s, Superior’s, and WLSSD’s efforts to eliminate sewage overflows from inflow and infiltration, their systems could not cope with the storm. These discharges released lots more nutrients to Lake Superior and also increased human health risks from disease causing microbes. This shows the need for continued efforts to seal our sanitary sewer systems in addition to reducing stormwater runoff.
It is also interesting to speculate on how wetland frogs and other amphibians have fared this year. Several months ago there was concern that they would be hammered by the lack of water because we had so little snowmelt runoff, an early thaw, and a very warm March. Then it cooled and rained, and rained, and rained, and ponds were flushed so thoroughly that I’ve seen tadpoles in the new batch of road potholes. The long-term effect will take time and continued monitoring to become apparent. Scientifically, these really dramatic but infrequent weather events provide important "markers" that can lead to a better understanding of how things work and what we need to do to better manage them and conserve them.
It’s hard to get people to understand that their single lot home, their yard, their driveway, contributed to the high levels of stormwater runoff that caused so much damage. But multiply each property by the tens of thousands over the Duluth landscape and in the roads and parking lots and that’s a lot of water that can’t soak into the ground. While the City of Duluth has made great progress in addressing its stormwater management issues ― including the enormous sanitary overflow tanks that prevented tens of millions of gallons of sewage from running into Lake Superior ― the recent flood was exceptional. But the overall footprint of Duluth is large and increasingly sprawling. When you replace vegetation and soil with asphalt and concrete and roofs, there is an awful lot of rainwater no longer soaking into the soil. It usually is directed off the property, into the street, and then right into the streams. The curbs and gutters are basically trout stream shoreline and Lake Superior shoreline and need to be managed as such.
Hopefully, we won’t have that much rainfall in that short period of time for a long time. But unfortunately, the trends in our weather over the past 20 years or so, and the predictions for the future, indicate otherwise. If we want to learn something from the June 2012 Flood, it might be the value of continuing to take stormwater management very seriously and that long-term protection is far less expensive than re-construction and restoration.