Takeaway: HydroForecast predicted flows that remained within a band of roughly 0 - 10 cfs for multiple months accurately, with predictions that assimilated evenly with the gauge data as it became available over the period.
Event description: While flows on the James River can reach over 2,000 CFS during large events, they are often extremely low. Between September 2020 and April 2021, for instance, flows never rose above 10 CFS. In fact, the most recent significant peak before this period was in April 2020. While the spring freshet historically arrives in early April, often pushing flows up close to 150 CFS, the observed flows during April 2021 remained below 10 CFS (historical daily median flows are plotted as gray dots in the figures below). At such low and stagnant flows, small errors in streamflow predictions can be significant relative to the observed flow. Even under these circumstances, HydroForecast was able to accurately forecast the low flows at this location throughout the duration of the competition.
It should be noted that observations at the location are seasonal due to ice affecting the gauges in the winter time. This creates a period of uncertainty in the fall and spring when freeze and thaw can be problematic for reliable data. In this instance, it is likely that the streamflow forecasts are a more reliable indicator of actual flow than the gauge data.