Summer 2019: A Tale of Two (Storm) Sewers

A while back (ok, quite awhile back), in my “My Research” post, I talked about how a part of my research involves monitoring stormwater. Well, that part is front and center this summer and is all about the FIELD WORK!

It’s one thing to say Best Management Practices (BMPs) work in reducing the impact of stormwater on urban streams, but we need proof! Having real, quantitative data is important to the scientific process (to confirm hypotheses and observe phenomena), but it is also vitally important in helping urban residents to understand why they should care. Knowledge is power and we can’t ask that urban residents trust the science if we don’t have the actual proof to back it up. Cue my work this summer (and next summer as well!).

I am conducting a pseudo paired-watershed study monitoring stormwater runoff from residential areas. My main study goal is to quantify the effects of urban residential stormwater best management practices by examining how much stormwater flows off of residential neighborhoods, and analyzing water samples for pollutants and excess nutrients.

We want to know how much stormwater is being generated from these neighborhoods, and what kinds of pollutants and nutrients are found in that stormwater. Remember, here in Iowa (and in much of the country), stormwater is NOT treated at any water treatment facility before it dumps into our local streams and lakes. That means that everything that ends up on the ground, ends up in our waterways. All those grass clippings, full of lawn fertilizer, that dog waste that didn’t get picked up, those cigarette butts that are thrown out car windows, the oil that leaks from our engines, even the brake dust that grinds off of our car brakes, all gets picked up by stormwater the next time it rains and washes directly into our streams.

When it comes to stormwater, if it’s on the ground, it’s in our water.

Back to my actual study. I am monitoring the stormwater that is generated by two small watersheds of around 50 homes each. Over the course of my project, we will work closely with neighborhood residents, local stakeholders, and project partners to encourage residents of one of the two neighborhoods, called the Treatment watershed, to install and adopt small scale residential stormwater BMPs (things like installing rain gardens or rain barrels, or picking up all pet waste or using phosphorus free lawn fertilizer). We will then monitor how these practices effect the stormwater generated in that watershed, and compare the results to the other paired watershed, the Control. I say this is a pseudo paired-watershed study because a true paired-watershed study requires a 2-3 year calibration period before any practices are installed or adopted. This would be followed by a period of installation and adoption, followed once more by 2-3 years of monitoring.

Unfortunately, as is typical in research and graduate degrees, we neither have the funding or the time for a study of that scope. My study will have to accelerate the calibration and installation periods into 1 year and then follow up with 1-2 years of monitoring. This will affect how and what we can conclude from the data, but we can still get a meaningful set of data that will be able to demonstrate how the cumulative effects of numerous small practices can have a meaningful, positive outcome on a larger scale.

To identify two small watersheds, in an urban area, that were of similar size, and had similar characteristics proved to be rather difficult. City stormwater sewer systems are complex and often incompletely digitized as many of the records originally existed only on paper. The first big step is delineating the watershed, which means simply identifying the boundaries of the watershed. Once you know where the watershed boundaries are, you know that any rain that falls inside those boundaries will drain to one point, a storm sewer outfall. Any rain that falls outside those boundaries will drain somewhere else.

I used GIS, or Geographic Information Systems software to delineate the watersheds in my study. The process is complicated in natural systems where many different factors such as elevation, aspect, and slope affect watershed boundaries, but in urban areas the process is complicated even more by roads and underground sewer networks..

The whole process took many iterations, site visits to confirm, questions and meetings with city engineers, and weeks of work, but eventually I identified two watersheds that were perfect (or more realistically, as perfect as we could get). The watersheds needed to be similar in: size (and small, around 50 homes), total and connected impervious surface area, age of development, and socio-economic factors. We weren’t able to identify sites that meet all of these criteria perfectly, but the most important characteristics, the size and hydrological constraints, were met.

And with that, I had field sites! This is my first summer actually out in the field and it’s been a whirlwind of excitement, nervousness, errors and mistakes, and accomplishments. Tune in for more posts about all my summer adventures!

Oh how glamorous my field sites are!

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