Intricate networks of tidal channels such as are found in fjordic, barrier island and branching estuarine systems are often at risk from contaminant inputs and can be important as spawning grounds or migration pathways for marine organisms. These intricate systems are rarely spatially resolved in regional-scale numerical tidal models, and the setting up of a specific detailed numerical model for the purpose of rapidly assessing the likely tidal behavior of such geometrically complex systems carries a high overhead. As a first step we describe a simple, not published before, algorithm, which permits rapid assessment of the linear tidal dynamics in a single tidal channel. The method will be extended to channel networks in a companion article. The method needs only a minimum of input data, namely, (1) the forcing tidal elevation amplitude and phase at the entrances of the channel directly exposed to the open sea and (2) the length and depth of the channel. The performance of the method is tested against observations in the Menai Straits, UK, by applying the case of a single channel forced at either end with friction.