John T. Hack 1973 <p>The generally regular three-dimensional geometry of drainage&nbsp;networks is the basis for a simple method of terrain analysis&nbsp;providing clues to bedrock conditions and other factors that determine&nbsp;topographic forms. On a reach of any stream, a gradient-index value can&nbsp;be obtained which allows meaningful comparisons of channel slope on&nbsp;streams of different sizes. The index is believed to reflect stream power&nbsp;or competence and is simply the product of the channel slope at a point&nbsp;and channel length measured along the longest stream above the point<br />where the calculation is made. In an adjusted topography, changes in&nbsp;gradient-index values along a stream generally correspond to differences&nbsp;in bedrock or introduced load. In any landscape the gradient index of a&nbsp;stream is related to total relief and stream regimen. Thus, climate,&nbsp;tectonic events, and geomorphic history must be considered in using&nbsp;the gradient index. Gradient-index values can be obtained quickly by&nbsp;simple measurements on topographic maps, or they can be obtained by&nbsp;more sophisticated photogrammetric measurements that involve simple&nbsp;computer calculations from x, y, z coordinates.</p> application/pdf en U.S. Geological Survey Stream-profile analysis and stream-gradient index article