How often do the levels update?
It depends on the source of the gauge. Most river levels update every hour; although some only update every 4 hours. A few river levels only update daily.
How is the trend (rising, falling, or flat) determined?
For gauges that have hourly data, the trend is based on the level change for the most recent 2 hours of data. For gauges that only update daily, the trend is the 24-hour change.