Can Hydrologically Relevant Stormwater Management Regulations Improve In-stream Biological Conditions? A 20-Year Case Study from Northern Kentucky
Bob Hawley, PhD, PE
Nora Korth, PE
Katie MacMannis, PE
Sustainable Streams, LLC
Louisville, KY
Authors: Hawley, R. PhD, PE, Wooten, M., Korth, N., P.E., MacMannis, K., P.E., Fet, E.
In 2006, the stormwater management utility in Northern Kentucky (NKY), Sanitation District No. 1 (SD1), initiated a comprehensive stream monitoring program that included biological, habitat, water quality, and geomorphological components with goals of better understanding baseline stream conditions and how streams might respond to better management decisions regarding stormwater runoff. The first decade of monitoring identified several key NKY stream characteristics, such as degraded biology, habitat loss, and accelerated erosion rates, and how they responded to development and the associated hydrologic changes. This led SD1, in October 2015, to require new developments to comply with a stormwater discharge rate aimed at limiting excess downstream impacts. Based on trends observed at an array of regional monitoring sites, this discharge rate is 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. The new “Qcritical criteria” limited the discharge of the 2-year design storm to not exceed the regional critical discharge for streambed erosion. Since the adoption of Qcritical criteria in 2015, several hundred new development sites have been permitted to incorporate stormwater control designs with the updated criteria. During this time SD1 has continued its monitoring across its 3-county service area, creating a dataset with nearly 20 years of macroinvertebrate data. Prior to the implementation of the Qcritical criteria, the Kentucky Macroinvertebrate Bioassessment Index (MBI) and 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, at least in part, to the Qcritical criteria.
About Bob Hawley, PhD, PE
Robert J. Hawley is a licensed Professional Engineer in five states and the Principal Scientist at Sustainable Streams in Louisville, KY, a company dedicated to stream and watershed science, service, and solutions. Dr. Hawley uses his professional and research projects to make stream restoration and stormwater management more ecologically and socioeconomically sustainable. He has more than 120 miles of stream restoration experience and stormwater management experience in watersheds that collectively drain over 70,000 square miles, with more than $100M in constructed projects. Dr. Hawley has authored more than 30 peer-reviewed publications with over 1,000 citations and tens of thousands reads/downloads.
About Nora Korth, PE
Nora Korth is a Project Manager at Sustainable Streams. She has 15 years of experience and is a Professional Engineer in Kentucky and Ohio. She leads hydrologic modeling and design of stormwater controls at Sustainable Streams, with nearly 100 retrofits to stormwater BMPs developed to reduce channel erosion. Her experience also includes stream and wetland restoration projects from conceptual planning through construction.
About Katie MacMannis, PE
Katie MacMannis is a Project Manager at Sustainable Streams with 16 years of experience in the fields of stormwater management, watershed planning, stream channel stability, and water quality. Katie has written several watershed plans throughout Kentucky and Ohio and has been a key developer of assessment tools for stream stability. Her knowledge of stream restoration permitting continually results in successful approvals.