In October 2015, the stormwater management utility in Northern Kentucky (SD1) began to require new developments to comply with a stormwater requirement aimed at limiting excess stream erosion downstream of new developments. The so called “Qcritical criteria” limited the discharge of the 2-year design storm to not exceed the regional critical discharge for streambed erosion. Qcritical was observed at an array of regional monitoring sites to be both geomorphically and biologically relevant – flows that mobilized the streambed not only contributed to chronic channel downcutting, degradation, and enlargement, but also created an unnatural disturbance frequency for benthic macroinvertebrates.
Since its adoption in 2015, over 500 new development sites have been permitted with stormwater control measure designs that incorporate the Qcritical criteria, in addition to complying with the regional flood control and water quality criteria. During this time SD1 has continued its rotational sampling of macroinvertebrates across its 3-county service area, creating a dataset with nearly 20 years of macroinvertebrate data in the region. Prior to the implementation of the Qcritical criteria, the coefficient of the linear regression between the index of macroinvertebrate biological integrity (MBI) and the relative cover of total impervious area in the sampling site’s watershed (%Imp) had a strong negative relationship. Since the adoption of the Qcritical criteria, the coefficient between MBI and %Imp has become sequentially less negative compared to prior years.
This presentation will attempt to unpack whether the positive trend in macroinvertebrates can be reasonably attributable, in part, to the Qcritical criteria.