A genetic classification of floodplains

TLDR: In this paper, the relation between a stream's ability to entrain and transport sediment and the erosional resistance of floodplain alluvium that forms the channel boundary provides the basis for a genetic classification of floodplains.

About: This article is published in Geomorphology.The article was published on 1992-04-01 and is currently open access. It has received 952 citations till now. The article focuses on the topics: Floodplain & Stream power.

Figures

Table 2. Floodplain transformations

Fig. 2. Medium-energy, non-cohesive floodplains. (i) Braided river floodplain showing gravel bars and fine overbank deposition on the floodplain. (ii) Lateral-migration scrolled floodplain (after Nanson, 1980). (iii) Lateralmigration/backswamp floodplain (after Blake and Ollier, 1971 and Kesel et al. 1974). Lateral migration results in a central deposit of laterally accreted alluvium flanked by organic and fine-grained clastic overbank accretion. (iv) Lateral-migration counterpoint floodplain (after Nanson and Page, 1983). The counterpoint floodplain is forming against the concave bank of the nearest bend at a slightly lower elevation with its surface deposits finer grained and higher in organics than those on the rest of the floodplain. Flow is towards the observer.

Fig. 3. Low-energy, cohesive floodplains. (i) Anastomosing river, organic-rich floodplains (after Smith and Smith, 1980). Vertical accretion is laying down overbank muds and lacustrine deposits around near-vertical stringers of sand or gravel beneath each channel. Swamps and lakes can result in widespread paludization. (ii) Anastomosing river, inorganic floodplains (after Nanson et al., 1986, 1988 and Rust and Nanson, 1986). To the right of the diagram, anastomosing channels are incised into cohesive floodplain mud with coexistent shallow braid-channels over the floodplain surface. To the left of the diagram, a waterhole has scoured beneath the mud into a sand sheet deposited during an earlier flow regime (Nanson et al., 1988).

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "A genetic classification of floodplains" ?

The relation between a stream 's ability to entrain and transport sediment and the erosional resistance of floodplain alluvium that forms the channel boundary provides the basis for a genetic classification of floodplains. 

Q2. Why is the erosive power concept used in the classification of floodplains?

Because stream power is diagnostic of flow and sediment properties, the erosive power/resistance concept is employed here as the primary basis for organising river floodplains into classes. 

Q3. What is the effect of the scroll bars on the river?

During formation, they appear to generate a convergent flow pattern of secondary currents that moves sediment from the swales towards the ridge crests, thereby maintaining the scroll pattern even in the presence of abundant overbank deposition (Nanson, 1980). 

Q4. What is the basis for a genetic classification of floodplains?

The relation between a stream's ability to entrain and transport sediment and the erosional resistance of floodplain alluvium that forms the channel boundary provides the basis for a genetic classification of floodplains. 

Q5. What is the main limitation in using any measure of channel hydraulics?

An important limitation in using any measure of channel hydraulics is that it relates to within-channel processes in a classification that should also emphasise on-the-floodplain processes. 

Q6. What is the importance of sediment load in determining floodplain geomorphology?

the amount and texture of the sediment load is seen to be very important in determining channel and floodplain geomorphology (Schumm and Khan, 1972; Carson, 1984) for both are closely related to stream power (Bagnold, 1966). 

Q7. What is the effect of a floodplain that is slowly building?

It is either gradually building by vertical accretion and, therefore, deepening its channel while slowly increasing specific stream-power, or it is severely eroding and thereby rapidly decreasing its specific power across a wider channel cross-section.