The authors propose methods for estimation of the potential of riverflows for electricity production at hydrokinetic power plants. The methods can be applied to any river or its span where it is possible to move using a floating means. The methodical part includes validation of the flow velocity and bed depth measurement data using the available statistics as well as a case study. Analysis of the in-river measurement results for the selected spans of river Daugava shows that the flow rate variations exert only a minor influence on the flow velocity at particular sites. This testifies the hydrokinetic power plants as stable and predictable sources of electrical energy, both in a long term and, especially, in a short one. The proposed estimation methods could be useful in explorations of rivers, making them simpler and cheaper.