The water surface elevation data shown above is based on direct staff gauge readings (Actual), electronic gage readings (Gauge) and precipitation records (Precip) from the Hayward airport recording station.
The left axis (elevation) is mean sea level (NAVD 88). Note that 0.1 feet equals 1.2 inches. The right axis (precipitation) is in inches.
The actual readings are taken periodically at the staff gauge on the County Highway B bridge. RLPOA used a surveyor to establish the benchmark elevation for this staff gauge.
The gauge readings are take every 5 minutes, 24 hours a day, 7 days a week, excepting any downtime from technical/mechanical failures. The gauge is a pressure transducer that measures the “weight” of the water column above the sensor. More weight means higher water level; less weight means lower water level. The daily reading is obtained by average the 2 hours of readings between 11:00 a.m. and 1:00 p.m. We used the actual readings and gauge readings to develop a calibration curve using linear regression—this lets us convert the gauge reading into an estimated true lake level. We are continuing to work with the vendor to better calibrate this gauge.
The precipitation data comes from NOAA records for the Hayward airport.