By Dan Kirk
Many of us in California get excited for the first rain of the season, even if you’re not one of us at The Watershed Project who literally waits outside for the “first flush” (first hefty rain of the season) with rain gear on and a bunch of stormwater monitoring equipment and data sheets. What are we up to with our gear? Yes, you guessed it, we monitor water, specifically we test the stormwater for pollutants.
On November 1, Satoko Mills, our water quality monitoring leader, brought stormwater monitoring gear to Booker T. Anderson Community center parking lot, where in between Baxter Creek and the parking lot lies a bioswale that The Watershed Project built. Part of the maintenance is keeping the bioswale plants alive and thriving, which often means weeding, pruning and trash removal. Somewhat equivalent to the “routine check-up” you might do to a piece of equipment or machinery to see if it’s functioning efficiently, our “first flush” routine is a way for us to see how effective the bioswale is through sampling the inflow and outflow of stormwater coming into and out of the bioswale. The bioswale helps prevent flooding and reduces the amount and potency of runoff that enters the creek behind it, so if it’s functioning efficiently, we should be able to prove this through our monitoring efforts.
Depending on how hard it’s raining, the first step we do is gather an “inflow” sample, which is the water that runs off the parking lot that is captured right before it enters the bioswale at the curb cuts. Once we have a large enough sample, about 2L, we send this to a lab and that tests for heavy metals and diesel/ motor oil. We at the same time, or shortly after, set up our “outflow” sample gathering stations, which is inside the storm drain (the storm drain is located in the center of the swale). We remove the storm drain lid and place a container underneath the outflow pipe – this requires a somewhat heavy and steady rainfall because after a long dry season, the soil and plants absorb much of the water that enters the bioswale, potential causing quite a time gap from the time of capturing the inflow to capturing the outflow (it takes a while for the landscape to get saturated). Once we get a large enough outflow sample, we send the sample to the lab as well.
In addition to testing what is in the water before and after runoff enters the bioswale, we measure the time difference between when the water first enters the bioswale and when it leaves the outflow pipe. This helps us collect data that shows how effective bioswales are in slowing down water that would otherwise pool quickly and flood. We are proud of the work we do and the fact that many of our projects are holistic: we don’t just stop after we build something, we continue to monitor its effectiveness and use sites as an educational learning tool for community members and students.