Hydro-geo-morphological characteristics of rivers

The hydro-geomorphological characteristics of a river describe its flow regime and the form of its channel and valley, which result from the interaction of flow, sediment and geology.

1. Longitudinal profile (course of the river)

 elev.
  |\ upper course (steep)
  | \
  |  \__ middle course
  |      \____
  |           \______ lower course (flat)
  +------------------------- distance

• Upper (youth) stage: steep slope, V-shaped valley, rapids and waterfalls, high velocity, vertical erosion, coarse bed material.
• Middle (mature) stage: moderate slope, valley widens, lateral erosion, meanders begin; transport of sediment is the main process.
• Lower (old) stage: very flat, wide floodplain, meanders and oxbow lakes, deposition of fine sediment, delta at the mouth.

2. Channel pattern

 Straight        Meandering        Braided
 ========        ~~~~~~~~~~        =\\/=\\/=
                                    /\\ /\\

• Straight: rare and short; low sinuosity (< 1.1).
• Meandering: sinuosity > 1.5; erosion on the outer bank, deposition on the inner bank (point bars); forms cut-offs and oxbow lakes.
• Braided: many channels separated by bars, with steep slope, coarse and abundant sediment and wide fluctuating flow; typical of Himalayan rivers in the Terai (Koshi, Narayani).
• Anastomosing: several stable channels with vegetated islands.

3. Cross-section

 floodplain   bank          bank    floodplain
 ____       __/              \__       ____
     \_____/   \____channel___/   \_____/

Parts: main channel (bank-full discharge), floodplain, levees and terraces. The width-depth ratio is large in braided rivers and small in meandering rivers.

4. Other characteristics

• Stream order and drainage pattern (dendritic, trellis, radial).
• Slope and sinuosity: $S = \Delta h/L$; sinuosity = channel length / valley length.
• Bed material and sediment load: bed load (boulders, gravel), suspended load (silt, clay) and dissolved load.
• Flow regime: perennial snow- and glacier-fed rivers (e.g. Koshi, Gandaki, Karnali); rain- and spring-fed Mahabharat rivers with low dry-season flow; and flashy Siwalik (Churia) rivers with high floods in the monsoon and very low or no flow in the dry season.
• Dynamic equilibrium: rivers adjust width, depth, slope and pattern to the discharge and sediment supplied. Changes in these (e.g. by dams or land-use change) cause aggradation or degradation.