Establishing Synthetic Rating Curves by Integrating the Height Above the Nearest Drainage with Hydrodynamic Computation

This study introduces a novel workflow, HAND-RAS, designed for the generation of synthetic rating curves (SRCs) utilizing the Height-Above-the-Nearest-Drainage (HAND) method. The HAND-RAS workflow proposed in this study advances tra- ditional methods for generating SRCs by incorporating the application of the sophisticated hydrodynamic computation from the HEC-RAS model to capture detailed hydraulic fea- tures, thereby enhancing the accuracy of the stage-discharge relationship. The performance of the HAND-RAS workflow is tested in a regional-scale river basin located in central Tai- wan. The analysis results indicate that the generated HAND- based SRCs exhibit strong agreement with gauge observa- tions, with r 2 > 0 . 8 5 and RMSE<0.509m. The performance of HAND-RAS is also validated with the physically simulated H-Q ratings from field topographic surveys. The comparison between HAND-SRCs generated using both conventional meth- ods (Manning's equation) and the proposed HAND-RAS work- flow is also conducted in this study. The comparison results show that HAND-RAS can produce comparable results in steep channels dominated by gravitational force and demonstrates better capability in capturing hydraulic behaviors in chan- nels characterized by milder slopes, where pressure gradi- ent plays a significant role. The workflow proposed in this study offers a modified method for generating reach-scale representative synthetic rating curves with hydraulic prop- erties derived from the HAND method, thereby enhancing accuracy and avoiding erroneous calibration processes.