Statistical analyses of flow rates of stormwater treatment bioretention media

The design and performance of stormwater controls is affected by the treatment flow rates of bioretention media. This article presents the results of a large number of laboratory column tests conducted to examine the treatment flow rates for various mixtures of stormwater bioretention media. Statistical analyses were conducted to identify the treatment media having targeted treatment flow rates. It was found that the bioretention media treatment flow rates were most affected by the median particle size (D₅₀) and uniformity coefficient (C_u) of the media, and the amount of organic matter. Statistical models were developed to evaluate and compare the treatment flow rates for various bioretention media mixtures. The findings of previous research (Sileshi, 2013) using two level, four factors (2⁴, with varying texture [T], uniformity [U], organic content [OC], and compaction [C]) full-factorial experiment study indicated that T and U of the media mixture have the greatest effect on the measured final infiltration rates of the media, followed by interactions of T and U; C; interactions of T and OC of the material; and interactions of U and OC of the material. As expected, media containing primarily larger particles (higher sand percentage) and, that is, uniformly graded (small uniformity coefficients) had the largest treatment flow rates. Compaction had minor effects if the organic matter content was low, but had significant effects on the flow rates for high organic matter content. Practitioner points: Bioretention media treatment flow rates were most affected by the median particle size and uniformity coefficient of the media, and the amount of organic matter. Statistical models were developed to evaluate and compare the treatment flow rates for various bioretention media mixtures. The media containing primarily larger particles and, that is, uniformly graded (small uniformity coefficients) had the largest treatment flow rate.