Quantitative analysis of watershed geomorphology

TLDR

Recent quantitative geomorphic methods enable measurement of drainage basin size and form, relying on geometrical similarity where corresponding length dimensions are in fixed ratios and dimensionless numbers are identical across basins of different scales. The study employs two classes of descriptive numbers—linear scale measurements such as stream length and drainage density, and dimensionless ratios and angles—to quantify basin geometry and link these metrics to hydrologic and sediment‑yield data independent of basin area.

Abstract

Quantitative geomorphic methods developed within the past few years provide means of measuring size and form properties of drainage basins. Two general classes of descriptive numbers are (1) linear scale measurements, whereby geometrically analogous units of topography can be compared as to size; and (2) dimensionless numbers, usually angles or ratios of length measures, whereby the shapes of analogous units can be compared irrespective of scale. Linear scale measurements include length of stream channels of given order, drainage density, constant of channel maintenance, basin perimeter, and relief. Surface and crosssectional areas of basins are length products. If two drainage basins are geometrically similar, all corresponding length dimensions will be in a fixed ratio. Dimensionless properties include stream order numbers, stream length and bifurcation ratios, junction angles, maximum valley-side slopes, mean slopes of watershed surfaces, channel gradients, relief ratios, and hypsometric curve properties and integrals. If geometrical similarity exists in two drainage basins, all corresponding dimensionless numbers will be identical, even though a vast size difference may exist. Dimensionless properties can be correlated with hydrologic and sediment-yield data stated as mass or volume rates of flow per unit area, independent of total area of watershed.