United States. Inland Waterways Commission.

Preliminary report of the Inland Waterways Commission. Message from the President transmitting a preliminary report online

. (page 60 of 83)
Online LibraryUnited States. Inland Waterways CommissionPreliminary report of the Inland Waterways Commission. Message from the President transmitting a preliminary report → online text (page 60 of 83)
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No. of
floods.


No. of
days of
flood.


1838-1847 . . ...


34
50
55


102


1888-1897


147


1898-1907


220







On the Cumberland River at Burnside, Ky., there has been a
similar increase in the number of floods above the stage of 40 feet.
No figures are available for the period before 1891.

^ f No. of
Period. ZVl daysof

flood.




1891-1895 3 3

1896-1900 8 19

1901-1905 13 13

The Alabama River at Selma shows a like increase for the period
for which figures are available. The floods are above a stage of 35
feet.



Period.


No. of
floods.


No. of
days of
flood.


1891-1895


6
5
11


62


1896-1900 -. .


41


1901-1905 -■


86







The Savannah River at Augusta, the Santee, and many other south-
eastern streams show similar increase. The losses from floods on
southern Appalachian streams during the past ten years aggregate
more than $35,000,000, more, probably, than those of all the rest of
the United States.

« Figures are not available for the period between 1848-1887.



SPECIAL. RELATIONS OF FORESTS TO RIVERS 523

In addition to the interference which periods of high and low water
cause to navigation, there is, during freshets, a deposit of sand and
silt bars in eddies, which lessen the channel depths and require fre-
quent dredging to maintain open waterways. The source or this de-
posited material is in part the forest soil, where it is inadequately
protected by humus, ^\4lich has been destroyed by fire or reduced by
grazing, or by both; but to a larger extent its source is farming land
which has been either injudiciously tilled or which is too steep for
tillage without erosion. While turbidity of southern streams is no
recent phenomenon, the present turbidity is excessive. When it is
the fault of the manner or tillage, more rational cultural methods can
eliminate or reduce it. "\Mien it is from the erosion of steep land and
cannot be prevented by better methods of culture, and it is evident
that the amount and rapidity of the erosion are such as to jeopardize
the future earning power of the land, this land and other areas of the
same kind should be regarded as forest land and nonagricultural.
Such land should be withdrawn from a use which means its ultimate
loss of earning power as w^ell as continuous injury to the rivers, to be
preserved by applying it to a different use as an active factor in the
nation's future wealth.

The Alabama River \\ath a drainage area of only 15,000 square
miles bears off annually 3,038,900 tons of soil, " chiefly the scourings
of the fertile farming soils of northwestern Georgia and northeastern
Alabama.

The Savannah River yearly carries 1,000,000 tons removed from
the area above Augusta.

The Roanoke River deposits more than 3,000,000 tons in its own
channel and in Albemarle Sound.

The Tennessee River, with a basin of 35,000 square miles, washes
nearly 11,000,000 tons a year from the farming and forest soils on its
basin.

Erosion increases at an accelerated rate with the height of the
floods, on account of the greater eroding power of water, which in-
creases six times whenever its velocity is doubled. More numerous
and higher floods are insured by further clearing of very steep land
which must eventually be abandoned; and by further depletion of the
humus in the forest. These will be accompanied by more frequent
changes in navigable channels due to larger, more rapidly forming,
and more quickly changing sand bars, the more extensive under-
mining of stream banks, and the obstruction of channels by trees and
drift, A very great portion of the appropriation for the improve-
ment of these rivers is expended for dredging, and the necessary ex-
penditure for this purpose will in the future increase in direct propor-
tion to the increased silt burden of the streams. In event of exten-
sive canalization the silt and sand continue a menace to channel
depth, since slowly moving canal water affords suitable conditions for
settling of the heavier material; and should the adjustment of stream
flow by storage reservoirs be undertaken, the high silt burden would,
unless eliminated by protecting the soil from erosion, yearly reduce
the capacity and value of the reservoirs and eventually entirely de-
stroy their usefulness. This extensive erosion is in like manner

a Soil burden of these streams based ou data furnished by Herman Stabler of the
U. S. Geological Survey.



524 REPORT OF THE INLAND WATERWAYS COMMISSION

detrimental to water power utilization, reducing after each flood the
impounding capacity of the reservoirs. It is stated by Mr. W. S.
Lee" that the capacity of the reservoirs of the Southern Power Com-
pany, on the Catawba and Broad rivers, is being so reduced by silting
up that in a few years only the flow of the streams will be available
for power.

The natural means for attaining greater regularity of stream flow,
for reducing the height and number of freshets, and for shortening the
dry season low flow, is the same as that for lessening erosion, the pro-
motion of soil absorption of storm water, and the reduction in the
amount of surface run-off. While a perfect regimen can not be fully
realized, it is possible by proper means to greatly improve the present
conditions:

(1) By thereestablishment of proper humus conditions in the forests
of both the mountains and the Piedmont Plateau. (2) By the refor-
esting of steep lands in the mountains which have been in cultivation
and which have become so exhausted that they no longer will retain
a grass sod. When this condition obtains, rapid erosion takes place.
(3) By the reforesting of all steep land in the Piedmont Plateau which
can not be cultivated without erosion, since it is impossible to maintain
a grass sod on steep land in this section on account of the low humidity
and long, hot growing season. (4) By improvement in the method
of tillage on such soils as are deemed agricultural, in order to prevent
erosion from them and promote absorption of heavy rainfall by them.
This can be done by terracing, by deeper plowing, by an increase in
the amount of humus, and by rotation of crops. The effects will be
beneficial not only upon stream flow and in lessening erosion, but in
improving the value and increasing the yield of farming lands. (5)
By plantmg trees along the banks of brooks and small streams
which are bein^ badly washed, and by reforesting or maintaining in
forest alluvial lands which are subject to flooding and which erode
when cleared.

RIVERS OF THE EASTERN SLOPES OF THE ROCKY MOUNTAINS

This group of rivers embraces many streams of great length flowing
east and south tlirough the j)lains or from the eastern and southern
sldpes of the Rocky Mountains, The most important are the Mis-
souri, Piatt, Arkansas, Kansas, Red, Trinity, Brazos, Sabine, Colo-
rado (of Texas), Rio Grande, and Colorado rivers. Only a few of
these streams are navigable, on account of their erratic flow, a period
of high water in the late spring or early summer being follo^yed by a
long period of extremely low water, with very high freshets at irregular
intervals. Many of them, however, can be canalized, and they are
valuable as sources of power and for irrigation. The silt burden is so
excessive that many or the rivers have meandering channels from the
deposit of the sedirnent. Thirteen rivers heading in the Rocky Moun-
tains or in the Great Plains, including the Red, Sabine, and the
rivers of Texas, have total navigable water of 2,869 miles, averaging
220.5 miles for each river. The period of navigation is very short,
however, on account of the prolonged low water,

o Before the Committee of Agricultxire, House of Representatives, January 30, 1908.



SPECIAL RELATIONS OF FORESTS TO RIVERS 525

The basins of most of these streams are naked except at headwaters,
the forested area being small compared with the extensive unforested
portion. Stream flow is chiefly maintained by the melting of the
mountain snow and the subterranean drainage which also comes
largely from the snow. The rainfall on the plains, 10 to 30 inches,
consists chiefly of summer precipitation, which augments the flow from
the mountain sources for a short time, but in autumn becomes insigni-
ficant. In addition to the violent fluctuations between the maximum
flow and minimum dry-season flow, the constant washing of banks
and formation of silt bars in the shifting channels are serious prob-
lems. The material of these silt bars is largely deposited during the
spring freshets, being carried in part from the banks of the main
river and in part from the banks of the smaller tributaries of the
plains, from the unconsolidated sands and silts which constitute the
prevailing soils of the plains; and to a less extent it is material brought
down in flood by the mountain streams. This silt burden is the
highest of all streams m the United States, The Missouri above
Ruegg, with a drainage area of 528,700 square miles, has a yearh^ silt
burden of more than 176,000,000 tons. The Arkansas above Little
Rock, with a basin of 148,000 square miles, discharges more than
40,000,000 tons of earth. The Brazos above Waco, with a drainage
area of 30,000 sqiiare miles, bears more than 3,200,000 tons.

The Missouri River is the most important river flowing eastward
from the Rocky Mountains. While it is navigable to Fort Benton
and has been navigated above there, it offers only a precarious chan-
nel with a depth on the upper reaches of only 2 to 2^ feet. The very
high waters of the spring and summer floods are followed by extremely
low water, while constant shifting of the channel and many changing
silt bars make navigation uncertain.

The sources of the Missouri are partly in the Yellowstone, Big-
horn, and Rocky Mountains of Montana and Wyoming. The
mountain streams are mostly of low turbidity, being fed by springs
and the melting of snow on north slopes and on the liigher peaks.
The snow melts earlier and more quickly than in the Columbia basin,
and the snow waters are reenforced by the midsummer rains of the
plains, which are the heaviest in June. With the passing of the
floods, the autumn stages of the river are low, while the dry winds and
high temperature of the plains make a high evaporation factor, which
reduces still lower the flow of the streams of the plains.

So erratic is the flow of these streams that the Smoky Hill River,
one of the chief tributaries of the Kansas, wath a drainage area of
8,000 square miles, has a minimum discharge during the low-flow
season of only 10 cubic feet per second. A comparison of this with
a typical eastern stream — the Potomac River at Point of Rocks, Md.,
wdiere the basin has a drainage area of 9,000 square miles — shows that
the minimum flow of the Potomac, wliich for a twelve-year record is
990 cubic feet per second, is 99 times as great as that of the headwaters
of the Smoky Hill River.

The headwaters of the Arkansas, which rise in the mountains of
Colorado, in comparison with the Kansas show a much more steady
flow. At Canyon, Colo., the Arkansas drains a basin of 3,000
square miles and has a minimum flow of 108 cubic feet per second, or
a flow thirty times as great as that of the Kansas River. The same



526 REPORT OF THE INLAND WATERWAYS COMMISSION

conditions exist on the mountain tributaries of the Missouri as on the
head of the Arkansas River.

The flow of the main river during the dry season is maintained almost
entirely by the mountain tributaries. Since this flow largely comes
from the melting snow and subsoil percolation of snow water, the
development of the protective forest mantle to its widest limit is
necessary to retard melting of snow and to promote absorption and
storage of snow water. Of the entire forest area of the basin, only
14,921,600 acres are situated in the national forests, and more than
two-thirds of tliis has within the past fifteen years been badly burned,
and the humus, through which absorption is largely promoted, has been
partly or entirely destroyed. And this condition is applicable to all
of the rivers of the plains which have their sources in the mountains.
The mountains are the origin of the water of their dry-season flow.
The streams which lie entirely in the plains either go dry or nearly so
during periods of drought.

Notwithstanding its large drainage basin, the flow of the Platte is
erratic, being especially characterized by the low dry-season flow.
The rainfall of the basin is too limited in quantity, averaging less
than 25 inches, and too irregularly distributed, being marked by a
high midsummer maximum and a low winter precipitation, to main-
tain a steady stream flow. Moreover, there is a marked deficiency of
snowfall on the mountainous portions of the basin. A very small
proportion of the basin is forest covered. Of the forested area,
2,609,576 acres are situated in national forests.

The excessive silt burden of the Platte is largely derived from the
treeless areas below the mountains. Many .of its most important tribu-
taries normally pass from the mountains as clear streams, their tur-
bidity being acquired from tributaries which enter below the moun-
tains and which are not navigable. Its surcharge of silt adds to the
excessive turbidity of the Missouri, with its marked infiuence on the
deposits of the lower Mississippi. The limited silt burden of the per-
ennial head streams is undoubtedly greatly influenced by the forests
which protect them.

The rainfall on the Platte rapidly decreases immediately below the
mountains to 10 inches or less, but again increases eastward until it
amounts to 35 inches at its mouth. The banks of most of the tribu-
taries on the plains are unprotected by trees, and are subject to exces-
sive corrasioh, and at the same time most of the soil moisture is sub-
jected to an evaporation by drv winds, and this evaporation amounts
to several times the annual ramfall.

All the streams rising in the eastern or southern slope of the Rocky
Mountains, or in the plains to the east of the Rocky Mountains, have
characteristics similar to those of the Alissouri or Platte — an ex-
tremely low minimum run-off for the size of the drainage basin, a
heavy silt burden, and so great a deposit of sand and silt as to cause
meandering.

The Kansas, which heads in the plains, is not navigable.

The Arkansas, which exhibits the same influences, has its head-
waters fed by the snow fields of the high mountains of central Colo-
rado, especially of the Continental Divide, and its lower course re-
ceives many steady tributaries from the Ozark region, a section of
broken topography and heavy precipitation. Its headwaters are
protected oy 1,861,426 acres of national forest, including 431,360



SPECIAL RELATIONS OF FORESTS TO RIVERS 527

acres of the Arkansas national forest. The banks of the streams of
the plains require protection, and the tributaries from the deeply
dissected Ozark region, which can become, wdth the development of
agriculture, the seat of extensive erosion, demand a permanent forest
cover.

The Red, Trinity, Brazos, Sabine, and Colorado (of Texas) rivers
exhibit many of the salient characteristics of the Missouri and
Kansas. The lower stretches of the Red River lie in the level por-
tion of the JVIississippi River Valley, where it is a deep-channeled
meandering stream, navigable for many miles. Its lower tributaries
are all well within the heavy precipitation zone of the Gulf, amount-
ing to from 50 to 55 inches. While its turbidity is high, it does not
reach the maximum of the streams of the plains. Between Fulton,
Ark., and Denison, Tex., it winds in a shifting channel, between
banks frequently several hundred yards apart, and with a low-water
depth of from 1.5 to 4 feet, but is navigable during high stages.

The Trinity, Brazos, and Sabine also lie in part within the region
of heavy Gulf precipitation and in a partly forested region. They
drain rolling to nearly level basins, but bear liigh silt burdens. They
are navigable during a portion of the year, but are subject to high
freshets and extreme low water.

The Rio Grande duplicates the conditions of the Arkansas. Its
headwaters are fed from the high mountains of New Mexico and
Colorado, being protected by 6,885,053 acres of national forest. In
Colorado the snowy peaks of the San Juan and the Cochetopa ranges
are the source of its most constant tributaries, but its volume shrinks
from seepage in the great stretch of plains and desert through which
it passes, and the high evaporation and seepage factors reduce its
maximum flow to a very low point, while heavy rains in the summer
on the lower parts of its basin produce disastrous freshets.

The Trinity, Brazos, and Colorado (of Texas) rivers rapidly deposit
silt bars in the harbors at their mouths.

The headwaters of many of these rivers, rising in the mountains,
are already protected by means of the national forests. By far the
larger portion of the protective forests of the central and southern
Rocky Mountain region he on the watershed of the western Colo-
rado, a nonnavigable stream, but. one subject to violent fluctuations.
These forests have at different times been extensively damaged by
fire, the entire forest cover being destroyed, as well as the shallow
humus, which in places formed almost the only soil on the naked rocks.
The reestablishment of the forests and the development of normal
humus conditions will be beneficial, while the extension of the forest
area over lower slopes which are at present treeless will cause greater
stability of the stream flow and lessen the erosion from this type of
land.

These two conditions are potent:

1 . The dry season flow of the rivers is maintained by the discharge
of the mountain streams, which are fed by the snow which accumu-
lates in the forest. In Montana the forest prevents the snow from
being too rapidly melted by the Chinook wind , and protects it from
insolation. Farther south it protects it from evaporation by the
hot winds of spring and summer, as well as from melting by the sun.



528 REPORT OF THE INLAND WATERWAYS COMMISSION

The climate of the southern part of the Rocky Mountains is very
different from that of the northern portion. Not only is the snow-
fall lighter, but the summer temperatures are higher, the humidity
lower, and winds higher, developing general conditions which accel-
erate the destructive oxidation of humus, and at the same time
retard its development by determining a more xerophytic forest type
than that which characterizes the region north of Yellowstone Park.
The natural factors which effect the destruction of humus act more
rapidly and the means for its replacement operate more slowly. For
these reasons it is more necessary to nurture in the south the sources
of its accumulation, and to take every precaution to lessen its
destruction. This condition, which is the same as that which exists
in the Appalachians, increases just as it does in the Appalachians
toward the south, so that it becomes in the southern portion of the
Rocky Mountains more difficult to maintain a humus covering and a
freely permeable soil.

2. The silt burden is largely derived from the imconsolidated soils
which form the banks of the streams of the plains. This silt when
once washed into the main channel is either borne in suspension, as
is the case with the light silt, or rolled alon^ on the bottom, as is the
sand. The mountain streams bear a small proportion of this silt.
Agricultural lands contribute a relatively insignificant part of this.
Protection of the banks of large navigable streams can be effected
only by engineering means, though in some places it is possible that
shrubs might be planted along them. Trees on stream banks are
dangerous to navigation, but on the smaller streams the banks can
be protected by shrubs, and by trees whenever there is no danger of
their being washed up and carried into navigable channels.

STREAMS OF THE SACRAMENTO BASIN

The Sacramento, San Joaquin, and Feather rivers are the chief
waterways of California, the navigable portions of the two former
being largely limited to the tidal estuary channels. Low-water
stages, therefore, do not seriously affect them, but their value for
navigation has been menaced by silting. In addition, meandering
of the streams has in cases taken place, threatening the destruction
of riparian property, as well as interfering with navigation.

Three navigable streams heading in the western slope of the Sierra
Mountains have 492 miles of navigable water, or an average of 164
miles for each river. These streams differ from those of the south-
easterly and eastern slope of the Rocky Mountains in possessing navi-
gable estuar}'' channels, while the precipitation on their basins is
largely during the winter months, when it is often concentrated in
heavy showers. The streams are subject to violent bsltIj spring
freshets, originating in the heavy rains m the mountains, while their
high silt burden has damaged the navigable estuary channels. The
greater portion of the silt of these streams was formerly the product
of hydraulic mining, but the necessary means have been taken to
control this through settling beds. In spite of this the Sacramento
River yet bears annually more than 2,250,000 tons of solid burden.
Much of this is acquired in the foothills and plains, though much
erosion takes place from forest land on account of the insufficient
humus. Corrasion is active on the Tuolumne, Stanislaus, and other



SPECIAL RELATIONS OF FORESTS TO RIVERS 529

streams of the Sierras which debouch into the Sacramento or San
Joaquin rivers. This corrasive action is more or less constant, being
a characteristic of streams coursing through unconsoUdated soils or
those deficient in cohesion, as are many of those of the California
basin. This action might be lessened on the smallest tributaries by
protective planting. Violent irregularities in the character of the
precipitation add to the streams' degrading influence, and make the
lessening of erosion an important consideration. While the general
rainfall of California is light, 12 to 35 inches, one-half of it falls during
the three months of December, January, and February, and in years
of maximum precipitation the rainfall during this three months'
period will often equal or exceed that which would fall in the south-
east Atlantic States during the same time. The rainfall of lower
altitudes is frequently concentrated, a character especially favorable
for erosion. Only at the higher elevations is a large part of it
snow, and its melting is often forced by a warm rain. Perpetual
snow fields are found only at the highest altitudes, as on Mount
Shasta and Mount Whitney, and they do much toward sustaining
stream flow during the dry season.

An additional factor favoring erosion is the thinness of the cover of
protective vegetation. This is due to the irregularity of the rainfall
as much as to its scantiness, while the high transpiration factor,
which in the southern part of the State is probably the highest in
the United States, hkewise reduces the available soil moisture.

As the arid foothills are entered there is a wide belt with steep
slopes and loose soils, which on account of the irregular concentrated
rainfall is subject at times to excessive washing. This is below the
natural forest limit. If no arborescent species can be maintained
upon this zone, deeply rooted chaparral should be favored to lessen
erosion so far as possible.

The snow fields of Mounts Shasta and Whitney, wliich yield per-
ennial streams, do much to maintain equable stream flow. The
protection of the snow by the forests of the high Sierras and the
maintenance of good humus conditions is essential to safeguard

freater extremes of flow, accompanied by further corrasion of stream
anks and additional meandering and silting of lower level reaches.
The necessity under these conditions for the fullest development of
the protective forest cover and its accompanying humus are evident,
while the difficulty of maintaining it, as has been pointed out, is pro-
portionately great, on account of the restrictive influence of irregular
precipitation and a high evaporation factor, due to an arid cHmate,
and desiccating wind.

The area of national forests protecting the Sacramento River
watersheds amounts to 5,567,094 acres, and that protecting the
Sacramento River basin to 5,023,014 acres. A very large portion,

Erobably 50 per cent, of this forest, as well as of other forests on their
eadwaters, has been opened by repeated fires, and the naturally poor
humus has been destroyed or further depleted. The accumulation



Online LibraryUnited States. Inland Waterways CommissionPreliminary report of the Inland Waterways Commission. Message from the President transmitting a preliminary report → online text (page 60 of 83)