Flume studies often seek to measure and record the interstitial flow within plane‐bed sediment bodies and within sediment beds with wavy surfaces, such as those typified by salmonid fish spawning nests and river‐dunes. A simple, inexpensive method is described to record and map, at discrete points, the spatial variation in interstitial flow speeds in experimental fine gravel beds. The procedure uses activated carbon granules to capture a tracer: Rhodamine WT dye. Calibration of the uptake of dye by the carbon for known interstitial flow speeds allows mapping of point flow speed data initially in the nominal x‐dimension. Using interpolation procedures available in a range of commercial ‘mapping’ software packages, the point data can be used to produce quasi two‐dimensional ‘slices’ along sampling planes within the three‐dimensional gravel bed. Similarly, three‐dimensional representations can be produced within which lines of equal current speed (‘isovels’) are interpolated such that the flow vectors (in x, y and z coordinates) may be inferred.