Understanding river discharge

Understanding river discharge is essential to estimating landscape responses to rainfall and other climatic driving forces, planning infrastructure, predicting floods and droughts, and assessing ecosystem conditions. Discharge measurements in Africa are scarce. Yet, there are several highly affordable and locally viable innovative techniques to measure discharge. On Friday 1 November, as part of the annual SADC_WaterNet symposium, Micha Werner, Mark Graham, Leisa Mokuoane, Dr. Hubert Samboko, Nicholas B. Pattinson, PhD, Camila Justine Jacinta Haux and Hessel Winsemius organized a fieldwork experience to demonstrate these methods. This was a collaborative effort between Rainbow Sensing, GroundTruth, OpenDroneMap, University of Zambia, Lesotho Department of Water Affairs, UNICEF and IHE Delft Institute for Water Education. The event was supported by the EU HORIZON project TEMBO Africa, UNICEF, and GroundTruth in partnership with the International Water Management Institute (IWMI) within the CGIAR Initiative on Digital Innovation.

Nicholas and Mark demonstrated the hashtag#Velocity hashtag#Plank, a transparent measurement rod. The Plank only costs about 55 USD and allows citizen scientists to measure river cross-section depths and in-stream velocities, ultimately allowing citizen scientists to estimate river discharge. Micha showed the sudden gulp salt dilution gauging method. By injection of a known amount of dissolved ordinary kitchen salt in the stream, and through measuring the change in concentration with an Electrical Conductivity (EC)-meter, river discharge can be calculated. Hubert showed very accurate bathymetry measurements with a fishfinder, very low-cost Global Navigation Satellite System (GNSS) devices and a simple PVC-built floater. Leisa, representing the WaterNet 2024 host nation Lesotho,demonstrated both a propeller and electromagnetic approach to measure water velocities. Finally, Hessel demonstrated how smartphone videos can be turned into accurate surface velocity and discharge estimates through the open-source software platform hashtag#LiveOpenRiverCam, providing a method to measure discharge very frequently and at many sites.

During the demonstration to over 40 participants from the WaterNet symposium, all methods gave similar discharge results. This demonstrates that there are viable, accurate, and precise measurement methods that are also affordable, repeatable, and accessible via hashtag#citizenscience methods, using devices that can be locally acquired. The primary feedback from the demonstrations was “we had too little time to fully appreciate everything”. Next year’s WaterNet conference will be held in Chongwe - Zambia. Would you like us to do more next year and perhaps even extend the activities to a full day? We are considering a full fieldwork day with more citizen science related methods. Please like or respond below if you are keen!