Flattening the (Diurnal) Curve during COVID

If there’s anything the COVID pandemic taught us, its that our lives and normal daily habits had to be adjusted for reasons outside our control. A recent sewer basin study revealed much more than was anticipated during the pandemic. York County, South Carolina, a rural suburb just south of Charlotte, North Carolina, has seen steady growth in development as the Charlotte metropolitan area has grown. STV performed a sewer basin study to assess current and future sewer capacities for the basin. The hydraulic modeling study and field visits revealed how COVID changed the diurnal curve in this basin compared to what was expected or considered “normal.” The study also caused us to stop and consider exactly why this occurred. The results of this study revealed that a flatter diurnal curve with a greater afternoon peak (mirrored curve) was observed compared to a typical curve. This can be attributed to less commercial flow (or zero) and residential habits of getting up later, being home and using water throughout the day, and a consistent evening usage time (dinner, washing, etc.). This paper will compare diurnal curves from other basins of similar and differing taxonomy in the region, discuss how daily habits due to COVID changed the diurnal curve in an aged but actively developing sewer basin, and summarize the findings and recommendations of the study. How people used water throughout the day during COVID versus a pre-COVID normal daily life was an interesting finding. The paper will conclude with the engineer’s recommendations and options for the basin’s future build-out, which included a pump station force main, parallel relief sewer, or dig/replace the existing sewer (upsizing). This study allowed York County to better understand the existing flows and capacity limitations and project forward the ultimate capacity at basin build-out conditions.