Reply on RC1

Abstract

Advances in geodetic altimetry instruments are providing more accurate measurements, enabling satellite missions to hand over useful data in narrow rivers and streams. Altimetry missions produce spatially dense land and water surface elevation measurements in remote areas where in-situ data is scarce, that can be combined with hydraulic/hydrodynamic models to simulate water surface elevation and estimate discharge. In this study, we combine ICESat-2 land and water surface elevation measurements with a low-parametrized hydraulic calibration to simulate water surface elevation and discharge without the need for a rainfall-runoff model. ICESat-2 provides an opportunity to map river cross-section geometry very accurately with an along-track resolution of 0.7 m using the ATL03 product. These measurements are combined with the inland water product ATL13 to calibrate a steady-state hydraulic model to retrieve unobserved hydraulic parameters, such as river depth or roughness coefficient. The low-parametrized model together with the assumption of steady-state hydraulics enables the application of a global search algorithm for parameter calibration at a manageable computational cost. The model performance is similar to that reported for highly parametrized models, with a root mean square error of around 0.41 m. With the calibrated model, we can calculate water surface elevation time series at any chainage point at any time of an available satellite pass within the river reach, and estimate discharge from water surface elevation. The discharge estimates are validated with in-situ measurements at two available gauging stations. In addition, we use the calibrated parameters in a full hydrodynamic model simulation resulting in a RMSE of 0.59 m for the entire observation period.