Has anyone designed stormwater basins to support native amphibians while still meeting detention and water-quality targets? I’m leading a species protection program for chorus frogs in the Upper Midwest, piloting a 2-acre basin with 4:1 shelves and native sedges, and I’m looking for maintenance tips and design tweaks that keep ecological balance without blowing O&M budgets.
For chorus frogs, use a seasonal drawdown gate; keep ‘4:1 shelves’ drying midsummer. https://stormwater.pca.state.mn.us/ Agree?
I’ve had good luck keeping basins “fish-free” by routing the inlet to a shallow forebay and spilling over a low broad‑crested weir into the main cell, with a removable 6 mm mesh rack on the forebay outlet — O&M has just been a quick spring debris rake and it made chorus frog recruitment jump. @zhenya56, do you flag micro‑pools (10–15 cm hollows) so crews don’t grade them out during sediment cleanouts?
On a chorus‑frog basin in Ramsey County, the one tweak that paid off was adding a cluster of clay‑lined micro‑pools (15–20 cm) on the 4:1 shelf and calling them out on the O&M sheets so cleanout crews don’t grade them flat; they held spring water but dried by early July, so detention calcs stayed intact. @zhenya56, do you stake those in the field to keep contractors from filling them during cleanouts?
Consider a winter salt bypass — split snowmelt flows offline before the amphibian cell; for your ‘2-acre basin’, is deicing upstream heavy?
If you’re keeping predators out like @benson44 noted, add an adjustable stop-log on the low-flow outlet and run a simple “hold-and-release” schedule: keep about 30–45 cm through May, then drop to dry the shallow zone in June. It’s a dimmer switch for hydroperiod — do you have someone who can pull one plate once a year?
Cheap win: stake a south‑facing 10–20 cm “no‑mow/no‑cut” egg bench on the shelf and put it in the maintenance plan so shallow cover and depth targets aren’t erased during cleanouts. If there’s any chance of fish washing in, add a 6–10 mm inlet screen or a shallow rock riffle as a barrier and schedule a quick spring clog check. Curious whether upstream fish or cattail pressure is on your radar.
One tweak that’s saved our chorus frog cells: add a removable mid‑level ‘tadpole‑safe’ shroud over the low‑flow orifice (March–June) so you draw from mid‑column and cut entrainment, then pull it for summer cleanouts; it’s cheap, but plan a quick monthly clog check. Do you have room in the O&M plan for a 5‑minute sleeve swap each spring?
And hard lesson in the Upper Midwest: give that 2‑acre basin a seasonal snowmelt bypass to let the “first‑flush” chloride skip the chorus frog cell; reopen once spring rains dilute it. Pair it with a small armored notch on one 4:1 shelf so you hold shallow water without letting fish ride in during storms. Do you have any grab samples for chloride/EC yet to time the reopening?
One thing that’s helped our amphibian basins: add a seasonal fish‑exclusion screen at the main inlet — angled about 45° with 6–10 mm mesh — and pair it with a small forebay so predators don’t colonize while detention still works; it’s a bouncer for minnows. @mia_jones57, have you seen issues with this around prairie sedge shelves? Making the screen removable keeps spring debris maintenance to a quick brush‑off.
Building on @benson44, we’ve had good luck with a seasonal stop‑log at the outlet to hold a “wet spring, dry late summer” hydroperiod so chorus frogs finish, then draw down to reset and keep fish out; costs are minimal if the structure can take boards. Small caveat: late drawdown can slough those 4:1 shelves, so we stabilize a 2–3 ft fringe with rush plugs before the first season. Would your outlet accommodate a simple board slot?