Defining predevelopment hydrology to mimic predevelopment water quality in stormwater control measures (SCMs)

As part of Low Impact Development, stormwater control measures (SCMs) are expected to mimic pre-development hydrology. This generally results in a comparison between outflow volumes discharged from SCMs and a target condition annual runoff. Such a simplistic evaluation overlooks multiple pathways of water present in target watersheds and SCMs, namely shallow interflow and groundwater surge. This discussion suggests a more refined means of evaluating cognate conditions for SCMs in terms of hydrology and effluent water quality by discretizing SCM discharge into three pathways: runoff, shallow interflow, and groundwater surge. Preliminary evidence using deuterium isotopes from bioretention outflow supports this concept, and future research routes are suggested.