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<br />22
<br />
<br />RIVER MEANDERING
<br />
<br />V AUEY SLOPE
<br />100
<br />
<br />
<br />100
<br />HYDROLOGY
<br />
<br />(flood charactar'
<br />
<br />100
<br />SEDIMEN. LOAD
<br />(amount. type'
<br />
<br />I'ig. 3.
<br />
<br />Triangular diagrlll!l ahawing _les of primary influence
<br />100' of va)ley slope, hydrology (flooclll109nitude and
<br />discharge/variability) and sediment load (size and type of
<br />load) on river patterns (meandering or braided). Ni.mt>ers
<br />refer to dvers as followa: 1) Braided reach of lower
<br />ChiW""a R., Wisconsin, gradient steepened by avulsion and
<br />channel straightening (23), 2) Meandering reaches of Jordon
<br />R., Israel, and IlississiWi R., IUssissiWi, on steep valley
<br />resches (20, 27), 3) Meandering channel reaches in
<br />Louisiana and KississiWi, valley slope steepened by active
<br />tectOnics (4), 4) Meandering reaches of Arkansas R.,
<br />COlorado, and Sm:llcy Hill R., Kansas, a result of high
<br />suspended sed1nent loads introduced fran tributaries
<br />(16,22), 5) Braided, Yuba R. and Bear R., California,
<br />due to sggradation IU), 6) lIeanderlng lIurroroidgee R.,
<br />Australia, a result of change of sediment load fran bedload
<br />to mixed load (22), 7) Braided Niobrsra R.. Nebraska, a
<br />result of high aand load with a very steady discharge;
<br />8) Braided Yal1ahs R. I Jmnaica (9) end Tonero R. I Venezuela
<br />(2~) the result of flashy seasonal discharge; 9) Meandering
<br />Buff Bay R.. J8IIl8ica (9) ond Guanipa R., Venezuela (29), the
<br />result of steady discharge. Sllsded zone is where IlOst
<br />rivers will plot.
<br />
<br />~
<br />
<br />RIVER MORPHOLOGY AND BEHAVIOR
<br />
<br />23
<br />
<br />gullying in anoth~r and a limited response elsewhere. The change
<br />depends on the nature of the landscape, climatic conditions and geology.
<br />An incr~ase of energy due to increased discharge or perhaps neotectonic
<br />steepening of a valley floor (4) may cause very different river pattern
<br />response, for example, a straight stream may begin to develop a sinuous
<br />pattern, a low sinuosity meandering stream may become more sinuous. a
<br />highly sinuous stream may braid, or a braided stream may remain braided
<br />(Fig. 4).
<br />
<br />. The great range of channel patterns and types are all a result of
<br />a single process, flow in an open channel. Clearly, similar processes
<br />and causes can produce very different landforms and effects; therefore,
<br />any na.tu~al system must be thoroughly understood before extrapolation
<br />can be acceptable.
<br />
<br />Singularity:
<br />
<br />Just as all people ~re the same but each has singular character-
<br />istics, rivers and river reaches have sufficient differences so that
<br />they can be considered to be singular. Hence. each should respond to
<br />change in slightly or significantly different ways and at different
<br />rate~, This really is the k~y to the difficulty of short-term pre-
<br />dictlon, General relatlonshlps Oaws) w111" be of little specific
<br />assistance, For example. when a channel variable Is plotted against
<br />dfscharge. the data will usually scatter over half B 109 eye1e and
<br />perhaps over a full log cycle. This is a poor basis from which to
<br />predict individual response,
<br />
<br />An example of singularity in time is the downstream shift of a
<br />meander. If a bridge is present downstream the high~ay englneeT ~\11
<br />be concerned about the rate of movement of the meander toward the
<br />structure and the need to provide protection against it (Fig. 1). A
<br />study of the morphology of the meander and a study of old maps and
<br />aerial photographs may indicate that during the past one hundred years
<br />the meander has shifted downstream at a rate of a meter per year. If
<br />the n~ander is a kilometer above the bridge, presumably the stte will
<br />be safe for one thousand years, If the rate of movement appears to be
<br />on the order of two hundred meters per year there will be problems in
<br />five years. However, during the next year, that meander may encounter
<br />very resistant alluvium in the flood plain or a buried bedrock control
<br />that causes it to cease its downstream movement. On the other hand a
<br />series of major floods may cause great acceleration of meander shift,
<br />or it may cut off, removing the problem. Thus, there is need to
<br />specify that any prediction is a "normic statement".based upon average
<br />circumstances. Any variation of the control11~g variables will cause
<br />a ch~nge in r~te of change and perhaps even tn the morph01og1c
<br />characteristics of the feature being investigated.
<br />
<br />Uncertainty of prediction pertains to all sciences. but accurate
<br />prediction in ptlysics and chemistry are based upon large "clean-
<br />samples, whereas in the earth sciences samples are very small, with
<br />respect to population size and because of the different characteristics
<br />of each component of the sample, each may be consfdered singular if not
<br />unique (17). Exact reprOdUCibility of a geomorphic situation cannot be
<br />expectedJ There is, therefore, singularity of form and process in space
<br />
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