Data Sources & Methodology

Understanding where our data comes from and how we process it.

Primary Data Sources

🇺🇸 USGS National Water Information System (NWIS)

The primary source for real-time streamflow, lake elevation, and water quality data. USGS operates over 8,000 active stream gauging stations nationwide. Reservoir elevation data is typically collected via pressure transducers or staff gauges and transmitted in near real-time. Update frequency: every 15 minutes to hourly, summarized to daily for our platform.

🏗️ Bureau of Reclamation (USBR) — LC DataWeb

For major Western federal reservoirs including Lake Mead, Lake Powell, Hoover Dam, and Glen Canyon. The Bureau of Reclamation manages 476 dams and 338 reservoirs, providing storage and elevation data through its public data systems. Update frequency: daily.

🌦️ NOAA & US Drought Monitor

Drought classification data (D0–D4) by state is sourced from the US Drought Monitor, a joint product of the National Drought Mitigation Center (NDMC), USDA, and NOAA. Drought data is updated weekly every Thursday.

🌡️ Open-Meteo Weather API

Localized weather conditions (temperature, precipitation, humidity) are retrieved from Open-Meteo's free weather API using each reservoir's geographic coordinates. Weather data is cached for 6 hours to ensure site performance.

Fill Percentage Calculation

Because US reservoir data is reported in surface elevation (feet above sea level) rather than volume percentage, we calculate an approximate fill percentage using the formula:

        Fill % = (Current Elevation − Historical Low) ÷ (Full Pool − Historical Low) × 100
      

This provides a normalized operational fill percentage that accounts for the actual usable range of each reservoir. Note that this is an approximation — actual storage volume in acre-feet depends on hypsometric (elevation-area-volume) relationships that vary non-linearly by reservoir.

Data Accuracy & Limitations

All data is sourced from publicly available government systems and presented in good faith. Equipment malfunctions at gauge stations, transmission delays, and maintenance periods can occasionally produce anomalous readings. We recommend cross-referencing critical data with official agency sources for operational or legal decision-making.