As the population of a collection system increases, what happens to the ratio of peak flow to average daily flow?

When the population of a collection system increases, the ratio of peak flow to average daily flow tends to decrease. This is due to the nature of wastewater generation. As more people are added to a system, wastewater generation becomes more consistent over the day, which can result in a smoothing effect on the peaks and valleys of flow.

In larger populations, the daily activities of a community – such as bathing, cooking, and using sanitation facilities – become more distributed throughout the day and night. This can lead to a reduction in extreme high flows (peak flow) since the increased average daily flow represents a larger number of constant, steady contributions rather than sporadic bursts of usage. Consequently, while absolute flows may increase as population grows, the ratio of peak flow to average daily flow decreases because the average flow increases at a rate that outstrips the peak flow fluctuations.

Therefore, understanding the dynamics of population impact on wastewater generation is crucial for effective management and planning in wastewater systems.