Study case of using radar and pressure sensor methods for direct streamflow measurement and prediction in forested watersheds from Brașov

Abstract

Accurate measurement of streamflow in small mountain basins is critical for flood forecasting and water resource management, yet it remains challenging due to harsh conditions and lack of infrastructure. This study evaluates two modern direct discharge monitoring methods, a non-contact radar sensor and a submersible pressure transducer in forested headwater catchments of the Carpathian Mountains in Romania. The radar device (Sommer RQ-30) and pressure sensor (METER Hydros 21) were installed in comparable small basins to continuously record water level and discharge. We describe the measurement principles, field installations, and operational advantages and limitations of each system. Two representative flood events were analyzed: a summer flash flood (peak discharge ~4.6 m³/s) monitored by the radar in a 14 km² basin, and a spring snowmelt-driven flood (peak ~1.4 m³/s) captured by the pressure sensor in a 0.87 km² basin. The radar sensor provided real-time hydrographs with clearly defined peaks and minimal signal noise, while the pressure sensor (paired with a V-notch weir) yielded accurate discharge estimates but required data filtering and maintenance. Overall, the radar method better performed in capturing rapid flood dynamics and operational reliability in remote sites, whereas the pressure sensor method offered cost-effective accuracy for moderate flows and baseflow calibration. Key findings highlight the complementarity of these techniques for small mountain basins: the radar ensures safety and continuity under extreme events, and the pressure sensor remains valuable for detailed low-flow measurements. The paper discusses the comparative performance under field conditions and provides recommendations for integrating both technologies in monitoring networks.