16
2.3.3 Quantitative Fluvial Geomorphology
An tmde;rstanding of the quantitative aspec,:ts of fluvial geomorphology developed simultaneously with
the work carried out on descriptive fluvial geomor�
phology that was discussed in. the previous section.
The reason fOr separating these two aspects of the
work is that they have received very different degrees
of attention by clastic sedim�ntologists. Those
studying ancient fluvial sediments have generally
made some attempts, with varying degr�es of sophisH
tication, to r�late the features of their deposits to the
morphology and behavior of modern rivers, but
qu�ntifi catio:p of these relationships has Peep atH
tempted only recently.
In this section, the development of some of the
principal ideas concerning quantitative aspects of
river behavior will be described briefl y, �mphasizing
those aspects most used by geologists.
Early attempts to relate velocity and discharge to
chann�J morphology were carried 01.1-t by engin�ers
for the purpose of designing irrigation canals in
India, Egypt, and arid parts of the United States.
Kennedy (1895) published the first i!nportant worl<
in this fi eld, relating velocity to flow depth and width
in a series of empirical graphs derived from work in
India. Contribution.$ by many later wor:k;ers were
summarized by Lane (1935), who showed that empirical equations were not necessarily of universal
applicability, depending on a variety of factors that
earlier workers, working within the confines of a
limited geographic area, had not previously recognized. Lane listed the following factors that may
enter into a determination of channel shapes: (a)
hydraulic factors (slope, roughness, hydraulic radius
or depth, rne&n velocity, velodty distrib-ution, aiJ.d
temperature); (h) channel shape (width, depth, and
side slopes); (c) nature of material transported (size,
shape, specific gravity, dispersion, quantity, and
bank and suhgrade materials); and (d) miscellaneous (alignment, uniformity of flow, and aging).
"A grad�d stream respopds to fl. change in conditions tn
accordance with Le Chatelier's general law: - 'if a stress is
brought to bear on a system in equilibrium, a reaction
occurs, displacing the equilibrium in a direction that tends
to absorb the effect of the stress"'.
This is the primary conclusion of Mackin (1948)
in an important geomorphologi<:al paper on the concept of the graded stream - the first to deal with this
subject in depth since Gilbert's (1880) pic;meer wor\<.
Mackin discussed the effects on a river of changes in
discharge, load, slope, base level, and other parameters. His discussion is qualitative, but in setting
Historical Background
out the logical cause� and-effect nature of river behavior he provided an essential rationale for the
detailed empirical work which was in progress at
that time on rivers in the United States.
Mackin provided a warning to those engaged in
the study of fluvial sediments to the effect:
"{1) that deposits fo rmed by or associated with a g grading
streams differ markedly from the loads carried by them;
(2) that distinguishing between channel and overbank de�
posits is the first essential step in interpreting mod�rn
valley fi lls or ancient fluviatile s�diments; and (3) that even
after this distinctjon i. s made it is virtually impossible to
work dire�tly from the grade sizes represented in the
�hannel deposits to the characteristics of the depositing
streams because there is no simple relationship between
the deposits of an aggrading stream and such partly inde�
pendent factors as slope, dLschar g e, channel characteris�
tics, velocity, "and load. We cannot proceed directly from
laboratory�determihed laws relating to str�am trapsporta�
tion processes to interpretations of ancient stream d�pow
sit$. An alternative and prornisjng route of attack on the
problem is via study Qf d�posits n.ow being fo rmed by
natural streams of many types to determine whether the
sum tot;tl of all <;haracteristics of given deposits is uniquely
related t() the particular modern streams by which they are
being formed, and to proceed thence to an understanding
of ancient streams by comparison of their deposits with
deposits of modern streams of known characteL"
In this statement, Mackin succinctly outlined
the problems we are still tackling in the area of
paleohydraulics, and fo reshadowed what was to become the most powerful tool in the hands of sedimentologists: fades analysis of modern and an<;:ient
sediments.
Lane's work was continued by Leopold and
Maddock (1953), who drew on "the mass of data on
streamflow collected ov�r a period of �eventy years
rep_resent�ng rivers <,t].l over the United States". This
included concurrent measurements of mean velocity, width, shape an4 area of cross section, dis.,
charge) and suspended-&ediment c.oncentrations.
They provided a series of graphs showing the relationships between these parameter() for specific ri.,.
vers, and arrived at some general relationships that
theoretically could he applied to a variety of settings
by adjusting the values of various exponents and
coefficients. This work was continued by the same
group of workers for some years (Leopold and
Wolman 1957; Leopold et al. 1964), and additional
data on the suspended-sediment load, the relationship of meander wavelength to channel width and
radius of c\],rvature, flood mag.nit11de and recurrence
interval, and the relationship between discharge and
drainage area were published. A. later paper
(Langbein and Leopold )966) showed that:
2.3.3 Quantitative Fluvial Geomorphology
An tmde;rstanding of the quantitative aspec,:ts of fluvial geomorphology developed simultaneously with
the work carried out on descriptive fluvial geomor�
phology that was discussed in. the previous section.
The reason fOr separating these two aspects of the
work is that they have received very different degrees
of attention by clastic sedim�ntologists. Those
studying ancient fluvial sediments have generally
made some attempts, with varying degr�es of sophisH
tication, to r�late the features of their deposits to the
morphology and behavior of modern rivers, but
qu�ntifi catio:p of these relationships has Peep atH
tempted only recently.
In this section, the development of some of the
principal ideas concerning quantitative aspects of
river behavior will be described briefl y, �mphasizing
those aspects most used by geologists.
Early attempts to relate velocity and discharge to
chann�J morphology were carried 01.1-t by engin�ers
for the purpose of designing irrigation canals in
India, Egypt, and arid parts of the United States.
Kennedy (1895) published the first i!nportant worl<
in this fi eld, relating velocity to flow depth and width
in a series of empirical graphs derived from work in
India. Contribution.$ by many later wor:k;ers were
summarized by Lane (1935), who showed that empirical equations were not necessarily of universal
applicability, depending on a variety of factors that
earlier workers, working within the confines of a
limited geographic area, had not previously recognized. Lane listed the following factors that may
enter into a determination of channel shapes: (a)
hydraulic factors (slope, roughness, hydraulic radius
or depth, rne&n velocity, velodty distrib-ution, aiJ.d
temperature); (h) channel shape (width, depth, and
side slopes); (c) nature of material transported (size,
shape, specific gravity, dispersion, quantity, and
bank and suhgrade materials); and (d) miscellaneous (alignment, uniformity of flow, and aging).
"A grad�d stream respopds to fl. change in conditions tn
accordance with Le Chatelier's general law: - 'if a stress is
brought to bear on a system in equilibrium, a reaction
occurs, displacing the equilibrium in a direction that tends
to absorb the effect of the stress"'.
This is the primary conclusion of Mackin (1948)
in an important geomorphologi<:al paper on the concept of the graded stream - the first to deal with this
subject in depth since Gilbert's (1880) pic;meer wor\<.
Mackin discussed the effects on a river of changes in
discharge, load, slope, base level, and other parameters. His discussion is qualitative, but in setting
Historical Background
out the logical cause� and-effect nature of river behavior he provided an essential rationale for the
detailed empirical work which was in progress at
that time on rivers in the United States.
Mackin provided a warning to those engaged in
the study of fluvial sediments to the effect:
"{1) that deposits fo rmed by or associated with a g grading
streams differ markedly from the loads carried by them;
(2) that distinguishing between channel and overbank de�
posits is the first essential step in interpreting mod�rn
valley fi lls or ancient fluviatile s�diments; and (3) that even
after this distinctjon i. s made it is virtually impossible to
work dire�tly from the grade sizes represented in the
�hannel deposits to the characteristics of the depositing
streams because there is no simple relationship between
the deposits of an aggrading stream and such partly inde�
pendent factors as slope, dLschar g e, channel characteris�
tics, velocity, "and load. We cannot proceed directly from
laboratory�determihed laws relating to str�am trapsporta�
tion processes to interpretations of ancient stream d�pow
sit$. An alternative and prornisjng route of attack on the
problem is via study Qf d�posits n.ow being fo rmed by
natural streams of many types to determine whether the
sum tot;tl of all <;haracteristics of given deposits is uniquely
related t() the particular modern streams by which they are
being formed, and to proceed thence to an understanding
of ancient streams by comparison of their deposits with
deposits of modern streams of known characteL"
In this statement, Mackin succinctly outlined
the problems we are still tackling in the area of
paleohydraulics, and fo reshadowed what was to become the most powerful tool in the hands of sedimentologists: fades analysis of modern and an<;:ient
sediments.
Lane's work was continued by Leopold and
Maddock (1953), who drew on "the mass of data on
streamflow collected ov�r a period of �eventy years
rep_resent�ng rivers <,t].l over the United States". This
included concurrent measurements of mean velocity, width, shape an4 area of cross section, dis.,
charge) and suspended-&ediment c.oncentrations.
They provided a series of graphs showing the relationships between these parameter() for specific ri.,.
vers, and arrived at some general relationships that
theoretically could he applied to a variety of settings
by adjusting the values of various exponents and
coefficients. This work was continued by the same
group of workers for some years (Leopold and
Wolman 1957; Leopold et al. 1964), and additional
data on the suspended-sediment load, the relationship of meander wavelength to channel width and
radius of c\],rvature, flood mag.nit11de and recurrence
interval, and the relationship between discharge and
drainage area were published. A. later paper
(Langbein and Leopold )966) showed that: