We show how a distributed borehole flowmeter can be created from armored Fiber Optic
cables with the Active-Distributed Temperature Sensing (A-DTS) method. The principle is that in a flowing
fluid, the difference in temperature between a heated and unheated cable is a function of the fluid velocity.
We outline the physical basis of the methodology and report on the deployment of a prototype A-DTS
flowmeter in a fractured rock aquifer. With this design, an increase in flow velocity from 0.01 to 0.3 m s⁻¹
elicited a 2.5°C cooling effect. It is envisaged that with further development this method will have
applications where point measurements of borehole vertical flow do not fully capture combined
spatiotemporal dynamics.Keywords: Fiber optics, A-DTS, Flowmeter, Heated, Borehol
