If It Ever Stops Raining, Can We Go To The Beach? Exploring Precipitation, Beach Closures and the Summer of 2018.

Photo by Jeff Miller / UW-Madison

by Adam Rexroade

For Madison residents, the summer of 2018 was a summer of heavy rain, ongoing flooding and inaccessible lakes. Pictures of kayakers floating down flooded streets and sandbags holding back floodwaters littered newspapers all summer long. These dramatic photos earned those front cover pages—Madison received almost 20 inches of rain from June through August. Much of that rain came during individual storms that delivered multiple inches of rain over the course of a couple of days. 

As a result of the rain, Lake Mendota’s water level rose to just over 852 feet above sea level, the highest ever recorded. Entire docks sank below the surface and a county-wide slow-no-wake restriction was enacted to prevent shoreline damage and erosion. Of the 26 beaches the City of Madison monitors for E. coli bacteria and cyanobacteria, 19 of them were closed for at least one day due to unsafe bacteria levels. 2018 saw 170 days of beach closures (1 beach closed for 1 day = 1 closed beach day ). The combination of the slow-no-wake ordinance and the closed beaches quickly turned Madison’s lakes from recreation hotspots to beautiful but unusable landscapes.

Total summer (June 1 – August 31) precipitation from UW-Madison arboretum. Source: NOAA

2018 is likely to be remembered the excessive precipitation, shocking photos of high water, and dozens of front cover stories on the topic, but was 2018 really that unusual? From a precipitation standpoint, yes. For the year, Madison received more precipitation than any year since the 1880s. But did all of that extreme weather cause Madison’s beaches to close more often than previous years? I decided to look into this as an independent project with professor Hilary Dugan at the Center for Limnology.  

What we found was that, while 2018 was an abnormally wet summer (26 inches of rain at the UW arboretum, versus an annual average since 2000 of only 13 inches), there are warmer summers on record (2016, 2012, 2009 to name a few), and years with more beach closures (2009 with just under 200 days and 2007 with just over 200 days)(Figure 1). In 2018, more than half of all beach closures were a result of high cyanobacteria levels. At over 100 days, this was double the average number of closed beach days due to cyanobacteria over the last five years. The number of beach closures in 2018 caused by E. coli was similar to recent trends. In fact, 2018 actually had the fewest closures because of E. coli since 2011. However there did not seem to be a clear trend of increasing or decreasing amounts of beach closures in the past decade (Figure 2).

Total days of beach closures for Madison area beaches 2004-2018. Reasons for closures include high toxin levels from cyanobacteria blooms (BGA) and high concentrations of E. coli. Data source: Public Health Madison and Dane County

We hypothesized that weather conditions would be linked to individual beach closures, as E. coli levels can spike from agricultural or urban runoff during large rain events, and cyanobacterial blooms are often associated with calm, hot weather. However, efforts to model beach closures based on weather proved nearly impossible. There was very little correlation between precipitation, maximum temperature, minimum temperature, wind, precipitation over the previous week, maximum temperature from the previous week, etc. These climate metrics accounted for a very small percentage of the variance in the likelihood that a beach would need to be closed due to excessive levels of cyanobacteria or E. coli.

Part of our inability to predict weather-driven beach closures is due to human-engineered solutions that allow beaches to remain open. Beaches are a major recreation draw in the summer and, to maximize beach days, Dane County has installed filtration systems at certain popular beaches. Lake Mendota County Park, Goodland County Park and Warner Beach have seen the installation of what officials refer to as “Clean Beach Corridors” – areas of clean, filtered water that are curtained off from the rest of the lake.

Photo: M.P. King, Wisconsin State Journal

When these corridors were first developed in 2010, they consisted only of a floating boom with an attached curtain that hung one foot below the surface (Lathrop et al., 2013). These booms were found to be effective at preventing algal build-up but did not address issues related to E. coli. So in 2011, filtration systems were added. Water Exclosure-Treatment System (WETS) is a filtration system that combines large strainers, sand filters and UV lights to kill E. coli bacteria. In addition to adding WETS to these beach enclosures, the curtains were also modified to extend from the surface of the water to the bottom of the lake. Each system costs just under $600 per summer to operate and costs approximately $25,000 to build (Reimer el al., 2017).

According to pilot studies on the effectiveness of the curtains and WETS, as well as beach closure data from Public Health Madison and Dane County, the corridors have been effective at drastically reducing the number of days a beach is closed due to cyanobacteria or E. coli. Brittingham beach has closed less than half a dozen times since 2011, when a curtain and WETS was installed, as opposed to anywhere from 4 to almost 40 times in a single summer before the corridor was installed. Other beaches have seen similar success.

Swimming is a risky business during a cyanobacteria bloom.

Despite the success of these systems, these are cosmetic solutions that only impact small areas of specific beaches and do not address some of the other issues associated with harmful algal blooms and E. coli. While beach closures as a result of cyanobacteria and E. coli aren’t increasing or decreasing over the last 15 years, closures may be increasing or decreasing as part of a larger trend taking place over the course of multiple decades and not yet observable to us.

Further monitoring and research is required before accurate conclusions can be made about the severity of these threats and before long-term solutions can be developed, effectively implemented and the results observed. While it would be beneficial to understand how to use weather to predict when a beach may be unsafe for swimming, the truth is that we can’t.At least, not yet.

While it was a little underwhelming to reach this conclusion, it wasn’t too surprising. Ecology is complex and there are always so many variables at play. While bacteria growth may be influenced in part by precipitation and temperature, it can also be influenced by nutrient cycling in the lakes and random events like where geese choose to poop along the shore or where a storm triggers a sewage overflow. This complexity only reinforces the importance of continuing to monitor and study Madison’s Lakes, especially since we’re likely going to see more and more seasons like the summer of 2018