Description:
<jats:title>Abstract</jats:title><jats:p>Most river cross‐sections display some degree of asymmetry for which there is no adequate quantitative definition. Indices of asymmetry are derived using two principles based on areal differences and maximum depth displacement relative to the channel centreline. The indices are assessed firstly by comparing values for a set of constructed channel shapes which are ranked in order of increasing visual asymmetry, and secondly by analysing a series of 50 cross‐sections from a small mountain stream. Two indices, <jats:italic>A</jats:italic>* and <jats:italic>A</jats:italic><jats:sub>2</jats:sub>, are probably the most valuable, and could be used to test and generate hypotheses regarding the related changes to cross‐sectional and planimetric form which occur during the transition from a straight to a meandering channel, particularly if parallel measures of flow asymmetry are defined.</jats:p><jats:p>Part II of this paper, concerned with ‘Mode of Development and Local Variation’ will be published in a subsequent issue of this journal.</jats:p>