tipos de ríos Chang

River classifications
Rivers may be classified according to channel pattern or channel type. An index used to describe the channel planform is the sinuosity, defined as the ratio of the valley slope to the channel slope, or the ratio of channel lenght to valley lenght.
Channel patterns
The three major channel patterns classified by Leopold and Wolman (1957) are straight (or sinuous), meandering,and braided.
Truly straight rivers are rare in nature. A straight river in this classification refers to one that does not have a distinct meandering pattern; that is, its sinuosity is less than about 1,5. Although a river may have a relatively straight alignment, its thalweg, or the flow path , usually wanders back and forth from one bank to the other.
A meandering river has a sinuosity greaterthan 1,5, and it consist of alternating bends and a distinct sinuous planform. Although the sinuosity varies among meandering rivers, there exists a marked similarity in the ratio of radius of curvature to channel width, common to bends in rivers of different sizes and in different physical province.
In a sample of 50 different rivers, Leopold et al. (1964) found that two-thirds of the ratioswere in the range 1,5 - 4,3., with a median value of 2,7. This geometry similarity often makes it difficult to tell one meandering river from another, as viewed from a plane or observed on an aerial photograph.
In view of this striking regularity of winding rivers, Leopold and Langbein (1966) suggest that meanders are no accident and that they appear to be in the form in which a river does theleast work in turning.
This nearly constant ratio of kak will be analytically established as the maximum curvature for which a river does the least work in turning.
The maximum curvature certainly limits the sinuosity of regular meanders.
However, the river usually also meanders partly because of topographical effects.
The total sinuosity (TS) is the channel length divided by air distance, and thevalley sinuosity (VS) is valley length divided by air distance. Two indices defining the components of sinuosity in porcentage were suggest by Mueller (1968):
In a survey of 10 point-bar complexes on the Beattom River in British Columbia, Canada, Nanson and Hickin (1983) found (1) that the rate of meander bend migration reached a miximum value when the value of kak approximated 3 and (2) that itrapidly declines for bends with kak values greater or less than 3, as shown in fig 1. The migration rate is given in meters per year. The mean radius of the circle passing through x1y1, x3y3 and x5y5; and the digitizing interval, dx, for the five sets or coordinates is equal to the mean channel width in the straight reach.
A braided river is usually on a steep slope, characterized by a wide andshallow course that is subdivided into several branches around interlaced islands, as illustrated in fig 2,9. The river a whole has a straight planform, although the anabranches are usually sinuous. Despite the poorly defined and unstable banks, braided channels can be considered in quasi-equilibrium if there is no aggradation.
Lane (1957) concluded that the primary causes that may be responsible forthe braided condition are: (1) overloading, that is, the stream may be supplied with more sediment than it can carry, resulting in aggradation, and (2) steep slopes.
The braided condition of streams in quasi-equilibrium is associated with steep slopes. Analyses of braiding are given in Chapters 11 and 14.











Clasificaciones de los ríos
Los ríos pueden ser clasificados de acuerdo a la formadel canal o al tipo de canal. Un índice usado para describir la forma en planta de un canal es la sinuosidad, definida como la relación entre la pendiente del valle con la pendiente del canal, o la relación entre la longitud de canal con la longitud del valle.
Formas de canales
Las tres principales formas de canal clasificados por Leopold y Wolman (1957) son rectos (o sinuosos), meándricos, y...