**5. Conclusions**

This technical note provides a practical set-up to derive both time-varying and period-averaged vegetation drag coefficients (*CD*) following the direct measuring method [36–38]. Different from previous studies, standard force sensors are applied to compose four synchronized force–velocity measuring systems in the current experiment. These standard force sensors are robust and suitable for flume applications. The composed force–velocity measuring systems can provide synchronized force–velocity measurement. Although one of the ADV instruments failed, the other three ADVs functioned well during the experiment. Importantly, an automatic algorithm was developed to realign the obtained force and velocity signals for direct *CD* deviation. This algorithm is expected to be able to accommodate a variety of velocity measuring techniques, providing possibilities to extend current application range. The developed force–velocity measuring systems and the automatic realignment algorithm may assist future experiments on vegetation–wave interactions for better understanding and prediction of vegetation-induced wave dissipation.

**Author Contributions:** P.Y., Z.H., B.H. and Q.Y. conceived and designed the methodology and experiments. P.Y., H.C., C.T. and L.R. performed the experiments. P.Y., L.R. and B.H. analyzed the data. All the authors contributed to the writing and editing of the manuscript.

**Funding:** The authors gratefully acknowledge financial support of the National Key R&D Program of China (No. 2016YFC0402607), the National Natural Science Foundation of China (No. 51609269, 51709288), the Joint Research Projects NSFC (No. 51761135022)—NWO (No. ALWSD.2016.026)—EPSRC (No. EP/R024537/1): Sustainable Deltas, and the Open Foundation of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering (Grant No. 2016491711), and the 2017 Guangdong Oceanic and Fishery Department scientific research and technological development program.

**Acknowledgments:** We thank the three anonymous reviewers for their comments and suggestions.

**Conflicts of Interest:** The authors declare no conflict of interest.
