The Assessment of Stream Discharge Models for an Environmental Monitoring Site on the Virginia Tech Campus

In the Spring of 2012, hydraulic data was collected to calibrate three types of discharge models: stage-discharge, single-regression and multi-regression index velocity models. Unsteady flow conditions were observed at the site (â H/â t = 0.75 cm/min), but the data did not indicate hysteresis nor variable backwater effects on the stage-discharge relation. Furthermore, when corrected with a datum offset (α) value of -0.455, the stage-discharge relation r2 was equal to 0.98. While the multiple regression index velocity models also showed high correlation (r2 = 0.98) values, high noise levels of the parameter index velocity (Vi) complicated their use for the determination of discharge. Because of its reliability, low variance and accessibility to students, the stage-discharge model [Q = 5.459(H-0.455)^2.487] was selected as the model to determine discharge in real-time for LEWAS. Caution should be used, however, when applying the equation to stages above 1.0m. The selected discharge model was applied to ADCP stage (H) data collected during three runoff events in July 2012. Other LEWAS models showed similar discharge values (coefficient of variation = 0.14) while the on-site weir also produced similar discharge values. Precipitation estimates for July 19 and 24 rain events over the Webb Branch watershed were derived from IDW interpolated rain data and rainfall-runoff analyses from this data yielded an average ratio of 0.23, low for the urbanized watershed. However, since the three LEWAS models were very similar, and the on-site weir showed a lower value to LEWAS, it was concluded that any error in the ratio would be attributed to the precipitation estimate, and not the discharge models developed in this study.