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Illinois River watershed briefing warns of rising streambank erosion and gaps in post‑construction stormwater oversight
Summary
Illinois River Watershed Partnership reported widespread streambank erosion in NW Arkansas—assessing 983 banks (249 miles) with an average modeled retreat of ~5.2 ft/yr and estimated phosphorus loading ~56,000 lb/yr—while DEQ staff told legislators that long‑term stormwater detention responsibility typically rests with local municipalities after construction permits end.
Nicole Hardiman, executive director of the Illinois River Watershed Partnership, told the Agriculture Committee that rapid urbanization in Northwest Arkansas and land‑use change have increased high‑flow events and streambank erosion across the Illinois River watershed.
Hardiman summarized a 2017 stream‑bank erosion assessment covering 983 banks (about 249 miles) and reported a model estimate of average erosion at roughly 5.2 feet per year in the study area. She said the study‑area sediment loading was just over 37,000 tons per year and estimated phosphorus loading at about 56,000 pounds per year. Hardiman compared that to average municipal wastewater contributions and said streambank erosion in the study area produced more phosphorus than a single wastewater treatment facility.
She described consequences including loss of productive land (the study area is losing roughly 40 acres per year to erosion), safety hazards from bank collapse, and risks to bridges and drinking‑water infrastructure. Hardiman warned that targeted, well‑designed restoration is expensive—up to about $250 per linear foot in some cases—but that prioritizing locations could improve cost effectiveness.
Committee members raised questions about the role of development and detention/retention pond design. DEQ representatives explained that state permitting follows federal NPDES rules and that DEQ’s construction‑stormwater authority covers controls during the active construction period (including requirements for sediment ponds sized to handle a 10‑year, 24‑hour storm). DEQ said its authority generally ends after a site is stabilized and that long‑term maintenance and post‑construction stormwater management are typically subject to local municipal ordinances or developer responsibility.
Committee members asked the agencies to provide further coordination and to update rules or guidance where necessary, noting the Illinois River’s interstate implications and prior legal and study efforts with Oklahoma. DEQ staff described an interstate steering committee and a technical study recommending a phosphorus standard (0.037 mg/L under specified flow conditions) and said Oklahoma is moving toward promulgating related standards.
