I run an open-source groundwater forecasting site (GrounwaterCast) and recently extended it to river low-flow. Before publishing any river forecast, every gauge has to pass its own leakage-safe hindcast gate: 14-day forecasts at Jun–Oct origins across multiple years, judged on (1) skill against a naive fixed-rate recession baseline, (2) P10–P90 coverage after honest band-widening, and (3) band sharpness — each gauge scored twice, once with observed rainfall through the window (the ceiling) and once with day-of-year climatological rain (the memory-only floor). Tier 1 = still beats-or-matches recession with sharp bands even when the rain information is worthless.
The result is the map: 97 of 1,087 gauges pass tier 1, and plotted together they trace the chalk and limestone country — Wessex chalk, the Ebble/Wylye/Allen valleys, the Test and Itchen, Cotswold oolite, the Yorkshire Wolds — despite the gate having no geology input whatsoever. Baseflow memory is the physics; the statistics found it. (however, a handful of tier-1 gauges sit on unlikely geology — west-country outliers that pass on pure statistics, likely regulated or spring-fed, which is rather the point of judging each gauge individually. And 582 more gauges show real skill only when the rain forecast is good — a different kind of forecast, published with wider bands and a caveat.)
The model is standard Pastas with two stresses on log-flow — log Q = d + (FlexModel recharge ⊛ Γ_slow) + (rain ⊛ Γ_fast) + AR(1) — the fast pathway is what fixes the winter rising limb. 50 gauges are live as a pilot ("RiverCast") with daily ENS-driven fans and P(Q < Q95 within 14 d) as the headline; methods and caveats at groundwatercast.com/methods, code at github.com/dominicm2023/groundwatercast-uk. Forecasts are labelled indicative — a verification archive is accruing before any skill claims :)
Does anyone know of other operational per-gauge low-flow forecast products (any country)? UKCEH's Hydrological Outlook is monthly/catchment-scale and eFLaG is projections — I've found nothing daily and per-gauge, which seems like a gap someone must have filled somewhere.