Background Water and soil loss has been a major environmental issue, and people's demands on environment quality are raised constantly in China. In this context, a nationwide water and soil loss monitoring network was set up, the count of water and soil loss monitoring stations increased to 738 recently. Although network built quickly, but the dedicated devices used in water and soil loss monitoring still fall behind very much. For example, manual throughfall collecting tank was invented centuries ago, but it's still used widely now in China. Therefore, developing and testing automated dedicated devices used in water and soil loss monitoring is an urgent and long-term task, which can enhance people's ability of monitoring and controlling water and soil loss. Automatic hillslope runoff measuring device is a gauge that can be used in a scale of runoff plot to replace human beings to measure, which can enhance the monitoring efficiency greatly.

Methods This paper took the measurement accuracy of a Runoff & Sediment Real-time Measuring Device as research object, the relative errors between theoretical value and measurement value were calculated based on the artificial runoff-producing simulation. Analysis of partial correlation was used to uncover the cause of error. With regression analysis, a fitted relationship between the runoff true value and the measured value was established.

Results The results showed that the range of the relative error of runoff was -4.33%-24.01%, and the range of the stabilization time was 55-130 s. Based on the analysis of partial correlation, the stabilization time for measured values had a significantly positive correlation with sediment concentration, and had a significant inverse correlation with design flow (P < 0.05). The accuracy of measurement had a significantly positive correlation with sediment concentration and design flow, but both sediment concentration and design flow presented limited influences on accuracy of measurement(α=0.05). Regress equation between the measurement of runoff and revised values was found by using the regression analysis. It was proved that accuracy of the measurement and the stabilization time for runoff measurements was significantly improved. Furthermore, the research also demonstrates that increasing waves cutting device and enlarging the size of waves filter can be conducive to improve accuracy of the measurement.

Conclusions These results were beneficial to understand the measuring performance of device in this study. With the rainfall intensity range 3.60 mm/h -66.96 mm/h, runoff can be measured accurately by the device, the range of rainfall intensity mentioned above can represent different rain types, such as moderate rain, heavy rain and rainstorm in northern China. For improving measurement accuracy in the future, the impact of silt content and mechanical composition should be considered and explored.