Anastomosis and the continuum of channel pattern

TLDR

Anastomosing rivers feature multiple channels separated by islands cut from the floodplain. The study assesses anastomosing rivers’ status within the channel‑pattern continuum defined by flow strength, bank erodibility, and sediment supply. Using an ordinal L–M–H scale of flow strength, bank erodibility, and sediment supply, the authors classify channel forms and argue that limited sediment data and aggradation imply a moderately high supply, while high supply in low‑flow, resistant‑bank channels can trigger shoaling, lateral constriction, and anabranch formation, and that concentrated large floods in low erodibility settings foster new channel development. Anastomosing rivers average (L,L,M/H) on the continuum, indicating a less definitive pattern than others, yet they can act as transitional forms and persist long‑term in some systems.

Abstract

Abstract Anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain. Their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables—flow strength, bank erodibility and relative sediment supply. Using an ordinal scaling (L(ow)–M(oderate)–H(igh)), the traditional forms of straight, meandering and braided have respective representations of (L,L,L), (M,L/M,L/M) and (H,H,M/H) in terms of those variables. The anastomosing pattern is on average represented by (L,L,M/H) but not so definitively as other forms. Specification of the third element (sediment supply) is particularly hampered by the paucity of data but aggradation, a characteristic of many anastomosing rivers, can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport. A sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and/or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches. A flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity. Anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems.