[From the American Journal of Science, Vol. II, July, 1896.] 
THE HYDROLOGY OF THE MISSISSIPPI. 
James L. Greenleaf, C. E. JAMES L. GREENLEAF, C. E. 
Consulting Engineer, 
No. 1 Broadway. 
NEW YORK, Art. V.-The Hydrology of the Mississippi ; by James L. 
Greenleaf, C.E. 
A river of the size of the Mississippi necessarily has many 
and important tributaries, with their individual peculiarities of 
watershed, channel, and variation in flow. Each of these trib- 
utaries exerts its proportionate influence upon the stream which 
is the resultant, and a knowledge of them is therefore essential 
to a study of the hydrology of the main river. For this reason, 
sixteen of the branches especially influential in forming the 
character of the Mississippi, have been selected for a brief dis- 
cussion. 
As a preliminary, it will be well to consider for a moment 
the point of view from which the engineering profession ex- 
amines the hydrology of a watershed. Whatever the purpose 
that the engineer has in working upon a river, be it water 
power, water supply of towns, irrigation, the training of the 
current to prevent devastating overflows or to maintain a 
depth for navigation; in each and all of these problems two 
fundamental considerations force themselves upon his attention. 
They are the degree of regularity, and the amount of the 
volume of flow from the tributary country. Thus, in the south, 
the Mississippi River Commission and the Levee Boards find 
the flow volume a vital feature in their efforts to confine the 
stream in a definite channel. At the north, the Engineer Corps 
of the United States Army are constructing a system of reser- 
voirs for holding back the freshets and aiding navigation upon 
the upper river during the season of low flow. 30 
J. L. Greenleaf-The Hydrology of the Mississippi. 
Another item of interest, if not of importance, is the amount 
of the annual rainfall and its distribution. Although the flow 
of the streams, or " run off " as it is sometimes called, depends 
upon the rainfall, yet it bears by no means a direct and simple 
relation to the latter. The percentage varies with the nature 
of the country, the climate, and the season of heaviest rainfall, 
from eighty or ninety down to less than five per cent. Merely 
Fig. 1. 
to suggest some of the causes of its variation, the following 
may be mentioned. A steep and rocky region will rapidly 
pour most of its rainfall into the stream. A level country, 
over which the water settles and flows off slowly, may expend 
nearly all in evaporation. A sandy soil absorbs the rain like a 
sponge as fast as it falls, to feed the never failing springs, and 
consequently gives a high ratio of flow; or, on the contrary, 
the water may sink too deep for that, and possibly make its 
first appearance in some far distant valley belonging to another 
watershed. A winter rain storm will perhaps all find its way J. L. Greenleaf-The Hydrology of the Mississippi. 
31 
over the frozen ground to the water channels, and a summer 
shower may be entirely absorbed by the thirsty land and grow- 
ing vegetation. In fact, the ratio of " run off " to rainfall is 
so uncertain, that engineers consider volumes of flow deduced 
merely from records of rainfall of small importance, as com- 
pared with a long series of actual gaugings of the stream. But 
gaugings are seldom available, and hence the percentage that 
the flow bears to the rainfall is of more than mere scientific 
interest. 
From the foregoing it may be concluded that, in studying 
the hydrology of a watershed, the engineer considers the area 
of drainage, the rainfall and its distribution through the sea- 
sons, the temperature, the character of the region as influenc- 
ing the percentage and regularity of flow, and, most valuable 
of all, actual gaugings of the streams-if he can obtain them. 
The basis of this discussion of the Mississippi is a report by 
the writer upon certain water-powers for the Tenth Census of 
the United States. The data there given have been amplified 
to cover the flood and low water as well as the average dis- 
charge of the Mississippi and its tributaries, and have been 
brought up to date by study of the subsequent gaugings con- 
ducted by the Corps of Engineers of the United States Army. 
Acknowledgment is due to this source of information, without 
which any study of the river would be impossible, and also to 
the many individual members of the Corps from whom cour- 
teous replies have been received to letters of inquiry concern- 
ing details. It is believed that the conclusions here offered 
are an essentially correct statement of the conditions of flow 
pertaining to the Mississippi watershed. The yearly reports of 
the United States Corps of Engineers, wdiich are awaited with 
interest, will either substantiate still further the diagrams here 
offered, or furnish data for their alteration. 
Figure 2 illustrates some of the principal features of the 
branches selected as especially influencing the Mississippi. 
The shaded rectangles represent the watersheds in the order 
of their occurrence from the source to the mouth, and the 
unshaded rectangles the intermediate areas tributary directly 
to the main river. The horizontal widths of the rectangles are 
proportional to the respective drainage areas, and their heights 
show the yearly average flow in terms of cubic feet per square 
mile per second. The areas of the rectangles may therefore be 
said to give a measure of the relative influence of the tribu- 
taries upon the average discharge of the main stream. 
The diagram exhibits the peculiarities of the tributaries, but 
fails to furnish an explanation, and that information we must 
seek for. It will be noticed on the diagram, that the rainfalls, 
shown by the horizontal lines, increase from the north toward 32 
J. L. Greenleaf-The Hydrology of the Mississippi. 
40 in. 
05 cu.ft 
3 0 in. 
2 sin. 
a2scu.fi 
zo in. 
-i3irt. 
> of flout 
SCALE OF FLOW PER SQUARE MILE PER SECOND, 
cl nd of KAIN FALL 
2.7S cujt - 
2.a cu.fi. 
2CU.fi. ■ 
t. 3 cu.fi. ■ 
SSiitr.f 
yom 
I cu.ft. 
45 in. 
| ajscu.fi. 
1 35 in. 
3thn.iS/Z 
5i.«in. 70% 
12774 tn. 
2 «in. I b'/o 
isjooo 
(including White Riic) 
4 Mm. 70%- 
77*7't-'k 
Fig. 2.-Hydrology of the Tributaries of the Mississippi River. 
Average Discharges. 
The shaded rectangles represent the principal tributaries, the unshaded rectangles 
the groups of smaller streams located between the mouths of the larger rivers. 
Vertical heights represent the yearly average flow from the watersheds in cubic 
feet per square mile per second. 
The horizontal widths of the rectangles are proportional to the respective drain- 
age areas. 
The positions of the heavy check lines indicate in inches the average yearly rain- 
falls on the watersheds. 
<?3 in. 30% 
zihooo sq.m. 
inches rainfall ii%flouj 
sziioo square miles 
37 tn. 24% 
2 you <7. rn. 
3«*in. 20% 
Hbqo «o. fn« 
31 in. 24% 
HH6b 
jj.sin. 347. 
10113 m 
35 in. 36% 
i.iiso $<j. «». 
3H in. 37% 
9'7' '1- m' 
10 in. »7% 
7476 
2» in. 23% 
Tn. 
23 in 32% 
30*5 s<|. m. 
27 0 in.37% 
3560 acj.m. 
27 in 37 % 
f3S4 *<|.Tn. 
the south, attaining one maximum on the Iowa basin. Also, the 
main stream down to Rice River, the Crow Wing, Saint Croix, 
Chippewa, Wisconsin, and Rock, may be termed high flow 
streams. Their percentages of flow to rainfall are from thirty- J. L. Greenleaf-The Hydrology of the Mississippi. 
33 
five to thirty-seven, and in this respect they are only equalled 
by some of the tributaries in the far south. The actual volume 
of flow, however, is not as great as the figures might lead one 
to infer, for the annual rainfall is slight, being over a portion 
of the tributary region only twenty-seven inches in depth. In 
consequence these streams yield a yearly flow of 0'625 cubic 
feet per square mile per second, rising to 0'928 cubic feet in 
the case of the Wisconsin, while the Ohio, for example, 
although only a thirty per cent stream, gives 0'953 cubic feet 
of average flow, because of its greater rainfall. 
Why is it that the percentage of flow to rainfall for the 
rivers mentioned, is sufficiently large to raise them into the list 
of high flow streams in spite of their light rainfall? It may 
be due, in part, to the spring rainfall being slightly greater 
relatively to the summer rainfall for the first five hundred 
miles or so of the Mississippi than for the second, and to the 
later advance of warm weather at the upper waters causing a 
delay in evaporation, and in the demands of vegetation. But 
the principal reason must be sought in the character of the 
country drained. A sandy soil that absorbs the rain and yields 
it to the streams wuth comparatively little loss from evapora- 
tion is a feature of a large part of this region. Pine forests 
that check the dry winds and moisture-searching sun of sum- 
mer also abound at the sources of the Mississippi, Saint Croix, 
Chippewa, and Wisconsin. 
In contrast to the high flow tributaries is the Minnesota. 
This river has nearly the drainage area of the Mississippi above 
where the Minnesota enters it, but in the volume of flow does 
not approach to the importance of the latter. It is a true 
" prairie stream," running high at one season, and then dwind- 
ling with dry weather, or a cold winter, to almost nothing. Its 
percentage of average flow to rainfall is only twenty-three, and 
its average discharge is 0'474 cubic feet per square mile per 
second. The Iowa and Des Moines likewise flow from an open 
prairie country and are no better in ratios of flow, yielding only 
twenty-four and twenty per cent respectively, but in them the 
increased rainfall shows its effect. Upon these watersheds 
there is a rainfall of thirty-eight inches annually as against 
twenty-eight for the Minnesota, and the ten extra inches raise 
the rectangles considerably above that for the latter river. 
The Illinois drains 29,000 square miles to the east of the 
Mississippi, and is the most important tributary met with thus 
far in passing down the river. Its rainfall, percentage of flow, 
and discharge per square mile happen to be almost precisely 
the same as for the Iowa. The drainage basin also is similar 
in many respects. The land is level, or gently undulating, but 
not quite so pronounced a prairie region as the country lying 
Am. Jour. Sol-Fourth Series, Vol. II, No. 1.-July, 1896. 34 
J. L. Greenleaf-The Hydrology of the Mississippi. 
west of the Mississippi. An extensive swamp drains into its 
head waters from Indiana. 
Jost below the Illinois is the mouth of the Missouri. Its 
drainage area is three times as great as that of the entire Mis- 
sissippi above the junction. It rises in the heart of the Rocky 
Mountains and flows for nearly three thousand miles through 
mountain land and prairie. Greatly varying conditions of 
hydrology prevail within the limits of the watershed, but one 
fact stands pre-eminent: of all the branches of the Mississippi 
it makes the poorest record for the area it drains. If its flow 
was proportionately as great as from the Ohio, its discharge 
alone would equal the entire volume that passes New Orleans 
each year. The diagram illustrates the peculiar weakness of 
the Missouri, due primarily to its low average rainfall, and to 
the extremely small percentage of flow. Twelve per cent of 
less than twenty inches rainfall give only 0T78 cubic feet per 
square mile per second for the average discharge. It is well 
to remember, however, that these are averages, and that in 
flood the Missouri is a mighty torrent of muddy water. 
A short distance below the mouth -of the Missouri, the 
Ohio enters, with less than half the drainage area of the former, 
and more than the total yearly discharge. It reaches so far 
eastward that dwellers on the Atlantic coast look upon its 
upper waters as neighboring streams. Mountains and wood- 
land cover a large portion of its basin. The rich, undulating 
farm lands of Ohio, Indiana and Illinois are tributary to it. 
The large average discharge is not due- especially to the per- 
centage of flow, for its thirty per cent is a moderate 
amount, but to the forty-three inches of annual rainfall. The 
warm moist air currents which flow from the Gulf region up 
the Mississippi valley have a decided tendency to the north 
and east rather than westerly, and this is chiefly the cause of 
the preponderance of the Ohio over the Missouri. The area 
of its rectangle in the diagram equals seven-ninths of the com- 
bined areas of all the rectangles preceding it, including the 
Missouri. 
The Arkansas is another large river entering from the west, 
draining 189,000 square miles, and is in many respects a small 
imitation of the Missouri. Its average ratio of flow to rainfall 
is only sixteen per cent, and all that tends to raise its standing 
is the larger average rainfall of twenty-eight inches.* 
The Red River is the last important tributary of the Missis- 
* The White River, draining 28,000 square miles, has been included with the 
Arkansas in Figure 2. It is true that they enter the Mississippi together, but 
strictly speaking they are distinct rivers. It will be noticed that where it is 
more necessary, as in Figure 4, the Arkansas and White are given separate treat- 
ment. J. L. G-reenleaf- The Hydrology of the Mississippi. 
35 
sippi. It flows from the west, bringing the drainage of 
97,000 square miles. It maintains not only a slightly better 
ratio of flow than the Arkansas, but is subject to a decidedly 
higher rainfall. The former is eighteen per cent, and the latter 
averages over thirty-eight inches annually. As a result, the 
Red River yields an average discharge of 0'515 cubic feet per 
square mile per second. The mouth of the Mississippi is, in 
a hydrological sense, situated where the Red River enters 
it, for at this point the Atchafalaya Bayou taps the river and 
draws off a considerable share of its waters. 
It will be noticed that two rivers of marked peculiarities are 
represented in the diagram. The Saint Francis and the Yazoo 
are the largest of several streams entering in the vicinity of the 
Arkansas and the Red, which are comparatively small and do 
not extend far to the west or east. They are consequently 
directly in the track of the heavy rainclouds from the Gulf. 
The rainfall upon their watersheds either sinks rapidly into the 
sandy soil and thus escapes evaporation, as is the case on a 
large part of the Yazoo watershed, or else flows quickly into the 
swamp reservoirs that characterize both the Yazoo and the 
Saint Francis. Hence the ratio of flow is as high as seventy 
per cent of the rainfall, and the yearly average flow amounts to 
2'130 cubic feet per square mile per second, for the Saint 
Francis, and to 2'749 cubic feet for the Yazoo. 
The second diagram, giving the average flow and rainfall 
lines of the Mississippi River, follows directly from the dia- 
gram of the tributaries. Its special interest lies in the infor- 
mation it affords as to the resultant effect which the branches 
have upon the main river. The line of flow, " CCC," gives 
in cubic feet per second the yearly average of total flow at 
each point from source to mouth. This line will be seen to 
corroborate a previous statement concerning the large discharge 
of the Ohio River. 
The line " BBB " gives in inches, at any point selected, the 
yearly precipitation in rain and melted snow, averaged for the 
entire area tributary to the Mississippi above the point in 
question. If the point selected is at the mouth of some inflow- 
ing river, the line shows the average rainfall above its tribu- 
tary watershed, and also the effect of including this watershed 
in the general average. 
The line " AAA" is by far the most significant of the three 
in the study of the hydrology of the Mississippi. It represents 
for each point from source to mouth the yearly mean flow in 
cubic feet per square mile per second, averaged for the entire 
area tributary to the Mississippi above the point in question. 
If the point selected is at the mouth of some inflowing river, 36 
J. L. Greenleaf-The Hydrology of the Mississippi. 
the line shows the average flow from the area above its tribu- 
tary watershed, and also the effect of including this watershed 
Hydrology Lines of the Mississippi River. 
Fig. 3-The line AAA represents, for any point from source to mouth, the yearly mean flow in cubic feet per square mile per 
second, averaged for the entire area tributary to the Mississippi above the point in question. 
The line BBB gives in inches, at any point selected, they early rainfall averaged for the entire area tributary to the Mississippi 
above the point in question. 
The line CCC gives in cubic feet per second the yearly average of total flow at each point from source to mouth. J. L. Greenleaf-The Hydrology of the Mississippi. 
37 
in the general average. The line " AAA " is not a simple 
exponent of totals, as is the line " CCC " of total flow. It is a 
function of the varying average of rainfall, the varying tribu- 
tary area as the branch streams are passed, each with its large 
or small watershed, and the varying percentage of flow to rain- 
fall in force upon these side basins. In the use of this line 
area enters as a factor of equal importance with volume in the 
study of the hydrology of the river. 
It will be noticed that the effect of any one tributary area 
upon the line " AAA " is much less marked toward the mouth 
of the Mississippi than would be the case if its watershed were 
located at the upper waters. The obvious reason is that it has 
the weight of all the large areas tributary above it to work 
against before it can influence the general average. If, for 
example, the Yazoo and Wisconsin, which have nearly equal 
drainage areas, were to change places, the latter would cause 
but slight alteration in the lower end of the line, while the 
Yazoo, in its new position, would raise the line to a flow of over 
one cubic foot per second. 
It remains to see what general deductions the diagram 
affords. In the first place, it shows that there is abundant 
reason for the popular division of the river into the upper and 
lower Mississippi. The line " CCC " gives the upper river a 
gradual increase of volume to where it joins the Missouri. At 
that point begins the lower Mississippi, and the great accretions 
from the Missouri, and especially the Ohio River, immediately 
force the line to a higher level. Then the Arkansas and Red 
Rivers make the rate of increase much greater than for the 
upper Mississippi. But the line "AAA" exhibits in a decided 
manner a difference still more fundamental between the upper 
and the lower divisions of the river. A glance along this line 
from source to mouth will make apparent the great depression 
that it undergoes from the Missouri south. The upper river 
is a high flow stream throughout its length. The lower river 
belongs just as decidedly with the low flow class. 
The depressing effect that the prairie streams have on the 
Mississippi is marked. Wherever a drop occurs in line "AAA" 
it is caused by a river upon which prairie influences prevail. 
The Crow Wing, Crow, Minnesota, Iowa, Des Moines and 
Illinois exert such effect. The Arkansas causes a decided drop 
in spite of the large area above that its watershed is averaged 
with. The Red River alone, of all its class, does not lower the 
line. This is due in part to its large rainfall, and partly to the 
line being already well pulled down by the Arkansas to meet 
it. As for the effect of the Missouri, it is deserving of special 
notice. A profound drop in line "AAA" occurs at its mouth. 
If it were not for this, the main river would continue a high 38 
J. L. Greenleaf-The Hydrology of the Mississippi. 
flow stream to the Gulf. The extremely small rainfall and 
percentage of flow, of the Missouri, coupled with its half million 
square miles of drainage area, determine the main river to its 
mouth. The pronounced high flow character of the Ohio 
results in the lifting of the line "AAA" at once through forty 
per cent of the drop occasioned by the Missouri, but even the 
Ohio, magnificent as it is in drainage area, and with a high 
rank among the tributaries for its volume of flow, cannot 
redeem the character of the Mississippi after its debasing union 
with the Missouri River. 
It is interesting to notice that the dual action of the Missouri 
and Ohio has its imitation toward the north. The low flow 
Minnesota causes, on a small scale, a drop in the line "AAA" 
similar to that produced by the Missouri, and below it the 
Saint Croix and Chippewa are the first of a series of branches 
culminating in the Rock River, which more than make good 
the depression. 
The influence of the heavy rainfall and large percentage of 
flow in the south is shown by the gradual rising of the line 
"AAA." The Saint Francis and Yazoo and lesser streams, 
draining all together only 43,000 square miles, make a percept- 
ible headway in the averages, even against the inertia of all 
the vast drainage area lying to the north, east and west of 
them. If their condition of rainfall and flow prevailed over 
the entire 1,259,000 square miles forming the Mississippi water- 
shed, the average discharge would be fully three million cubic 
feet per second ; more than forty times its actual volume. These 
figures indicate what the Mississippi, grand river that it is, 
might be if the trade winds and moist air currents from the 
Gulf of Mexico did but sweep the semi-arid regions to the 
northwest, and pour a plenteous rainfall over their vast 
extent. 
Thus far the discussion has been confined to a study of aver- 
age flow, and is therefore open to the criticism that all averages 
are liable to, for it states nothing concerning the variations of 
flow characteristic of the rivers. Indeed, the average flow may 
even be looked upon as a theoretical quantity, inasmuch as it 
has no real and tangible existence, except for a few brief periods 
during the year. No apology need be offered for its presenta- 
tion, however, for a study of averages is an important aid to the 
understanding of the actual relation of flow which the rivers 
bear to one another. Attention will now be given to the vari- 
ations in the volume of flow of the tributaries of the Missis- 
sippi, and the relations which these variations bear to the 
climatic and topographical features of the watersheds. Figure 
4 and the subsequent notes present particulars concerning rain- J. L. Greenleaf--The Hydrology of the Mississippi. 
39 
fall, minimum and maximum flows, and the time variations in 
the amount of flow for each of the principal tributaries.* 
A glance over the diagram makes wide differences apparent. 
The Ohio, Yazoo, Saint Francis and White have comparatively 
large flood flows per square mile per second. The Arkansas, 
Red, Missouri and Minnesota have especially small flows per 
square mile per second. The determinating causes for these 
and other differences are the amounts of rainfall on the water- 
sheds, the distribution of these amounts through the seasons, 
the degree of storage of winter precipitation to be liberated in 
the melting of the snow and ice at spring time, the nature of 
the country and vegetation, and the amount of natural storage 
in the form of lakes and swamps. It should be borne in mind 
that the southern rivers of limited drainage area have a heavy 
rainfall, and a large amount of this occurs in the winter and 
spring, when evaporation and the demands of vegetation are 
slight. The same is true of the Ohio watershed, because of 
the marked tendency for the moisture laden air-currents to 
flow over it to the northeast in the early- months of the year. 
For these reasons one would expect the southern rivers to 
carry high rates of flood-volume as compared with streams dif- 
ferently conditioned. The tributaries farther north, on the 
contrary, and particularly the Arkansas and Missouri, which 
extend their lines of drainage far westward, have average 
amounts of annual rainfall greatly below that of the Ohio, for 
example, and of this the greatest activity occurs in summer, 
when the tendencies are strongest to absorb and evaporate it 
* Adverse criticism is almost inevitable when one puts in concrete form con- 
clusions from a series of data which are so liable to various interpretations as are 
gaugings of the flow of rivers. It is very largely a matter of judgment as to 
what shall be taken for the characteristic minimum flow or maximum flow, and 
one's impression of the time of occurrence of the annual greatest flood, or of low 
water, is apt to be influenced by some special case which has fixed itself on the 
mind, rather than by impartial averages. It is the latter that I have tried to fol- 
low. I hope to disarm adverse criticism by frankly holding myself open to con- 
viction regarding the conclusions offered, and by stating that they are the result 
of a somewhat extensive study of all the available gaugings by the United States 
Engineer Corps, checked and compared with the opinions so kindly given by a 
number of the officers stationed along the rivers. The aim has been to give the 
discharges at decidedly low and high water, but at the same time to avoid using 
any special and extreme case as a criterion. It is proper to state that discharge 
data concerning the Yazoo and, above all, the Saint Francis, are especially meagre 
and more or less uncertain. Capt. Willard's gaugings upon the Yazoo are about 
the only reliable figures to start with. The Saint Francis is so liable to overflow 
from the main river as to make gaugings of it well nigh impossible of interpreta- 
tion. Fortunately the climatic conditions are quite uniform over the region of 
country concerned, giving some authority to a comparison between neighboring 
watersheds of limited extent. Therefore, by comparing first the Yazoo and 
White, giving due value to the proportions of upland and bottom land, and then 
applying the results to the Saint Francis, and checking by a proper balance be- 
tween the three rivers, results have been obtained which I believe to fairly repre- 
sent the truth. J. L. Greenleaf-The Hydrology of the Mississippi. 
40 
Fig. 4.-Hydrology of the Tributaries of the Mississippi River, High, 
Average, and Low Discharges, and Rainfall. 
General Explanation of 
Diagram. 
All rectangles are meas- 
ured from the common 
base line BB. 
Lengths of rectangles re- 
present the flow in cubic 
feet per square mile per 
second. 
Widths of rectangles are proportional to the 
areas of the watersheds (in square miles). 
H denotes high water, A denotes average flow, 
L denotes low water. 
The average rainfalls for each of the four 
seasons and for the year, reduced to cubic 
feet per square mile of watershed per second, 
are shown by the broken lines. 
Notes on the Times of High and Low Wateb. 
Mississippi above the Minnesota. High.-Rise begins in early April, due to 
Spring rains and melting snow-reaches a max. in end of April to May, and 
often is the max. of the year. Effect of melting ceases, but rains maintain a 
fair stage. Decided rise in June to July, due to rains-sometimes the highest 
of the year. Generally a brief Fall freshet. J. L. Greenleaf-The Hydrology of the Mississippi. 
41 
Low.-The low water of Fall occurs in August to Nov.-usually lowest in end 
of Sept, to mid. Oct. Lowest water of year in end of Nov. to end of Dec., 
due largely to freezing of the ground. 
Minnesota.-Practically the same in period of rise and fall as the Mississippi 
above it, but much more fluctuating in amount, because of the comparatively 
few lakes and swamps, and more open prairie on its watershed. 
Upper Mississippi (down to Missonri River). High.-Rise begins in Feb., due to 
rains and melting snow. A good stage maintained well into July. Usually 
two occasions of especially high water. The smaller may occur any time 
from latter part of Feb. to end of March, due to rains and melting snow. 
The greater may occur any time from April to July, due to rains and some- 
what to melting snow. There is often a brief Fall freshet. 
Low.-The lowest water of the Fall occurs in Aug. to Oct., generally in Oct. 
The lowest of the year is in Dec, due largely to freezing of the ground. 
Missouri. High.-The volume of flow increases from early in Feb. on, reaching a 
max. in April, due to rains and melting snow. Owing to the large differ- 
ences of elevation on the watershed, melting snow influences the stage of the 
river until Aug. A fall occurs in May, as the bulk of the snow disappears. 
Then there is a rise in June to the max. for the year, falling in July and Aug. 
Low.-The river runs low in Sept., Oct. and Nov., and in the latter part of Nov. 
into Dec. occurs a sudden drop to the lowest stage of the year, due to freez- 
ing of the ground. 
Ohio. High.-The river usually begins to rise in the latter part of January and 
is liable to maintain a fair stage until into July. In latter part of Feb. on, 
into the latter part of March, occurs the max. rise of the year, due to winter 
and spring rains and melting snow. Again, in April to middle of May is the 
height of a secondary rise, due to rains solely. The Fall rains cause an occa- 
sional rise in Nov. 
Low.-The low water is in August through to Jan., and the lowest is any time 
from the first of Oct. to the middle of Nov. 
Saint Francis. High -The river rises to a good stage in the middle to end of 
Jan., diminishing through May. The highest stage usually occurs in the 
latter part of March. 
Low.-Low water runs through Sept, to Dec., usually reaching the lowest point 
in the end of Oct. to the end of Nov. 
White. High.-There is usually a good stage from Jan. to June, a fall sometimes 
intervening. The highest water may occur any time between those limits, 
with the chances in favor of its coming in May. 
Loro.-Low water occurs from July into Dec., and the lowest stage of the year 
from Sept, to Nov., especially in Nov. 
Arkansas. High.-A good stage of water is liable from Jan. to June. A max. 
occurs in Feb., and again in April or May, and the chances are about even 
in the long run for either of these being the max. for the year. There is 
often a brief freshet in the Fall. 
Low.-The river falls in July, and, except for Fall freshet, runs low into Dec. 
Lowest stage of the year is liable from end of Sept, to middle of Nov. 
Yazoo. High.-There is a good stage of water from Jan. to June or July, cul- 
minating usually in April. An irregular and occasional rise occurs any time 
from Aug. to Dec. 
Low.-The river runs low as a rule from July through Dec., reaching a mini- 
mum in the latter part of Oct. to the end of Nov. 
Red. High.-The river rises in Jan. and holds a fair stage until into June. The 
highest water of the year may occur any time from Feb. to May, and probably 
in April to May. There is an occasional short rise in late Summer or Fall. 
Low.-The river falls in July and runs low as a rule until in Dec. The lowest 
water for the year may occur in Sept, Oct. or Nov. 
The Main River. High.-The river begins to rise early in January, and attains a 
max. stage usually in latter part of April or May, falling in June, July and 
August. 
Low-The low water occurs from Sept, on to the end of the year, reaching the 
lowest point, as a rule, in Nov. 42 
J. L. Greenleaf-The Hydrology of the Mississippi. 
Watershed. 
Rainfall. 
Flow per Second. 
Annual. 
Spring. 
Summer. 
Autumn. 
Winter. 
Minimum. 
Average. 
Maximum. 
Inches. 
Depth. 
Cu. ft. 
per sec. 
per sq. 
mile. 
Inches. 
Depth. 
Cu. ft. 
per sec. 
per sq. 
mile. 
Inches. 
Depth. 
Cu. ft. 
per sec, 
per sq. 
mile. 
Inches. 
Depth. 
Cu. ft. 
per sec. 
per sq. 
mile. 
Inches. 
Depth. 
Cu. ft. 
per sec. 
per sq. 
mile. 
Total In 
1000's of 
cu. ft. 
Cu. ft. 
per sec. 
per sq. 
mile. 
Total in 
1000's of 
cu. ft. 
Cu. ft. 
per sec 
per sq. 
mile. 
Total in 
1000'b of 
cu. ft. 
Cu. ft. 
per sq. 
mile. 
Mississippi 
above mouth of Minnesota 
Riv. (19,500 sq. miles) 
27'2 
2-000 
7-1 
2-158 
10-7 
3-296 
6-8 
1-994 
2-7 
0-780 
3 
0-154 
13 
0-674 
50 
2-56 
Minnesota 
(16,000 sq. miles) 
280 
2 061 
7-0 
2-070 
11'8 
3-476 
6-6 
1-944 
2'6 
0-772 
0-5 
0'031 
7-6 
0-474 
x60 
3 75 
Upper Mississippi 
above mouth of Missouri 
Riv. (173,000 sq. miles) 
34'7 
2'555 
9-0 
2-650 
12-8 
3-769 
8-2 
2-415 
4-6 
1-355 
25 
0-144 
118 
0-688 
550 
3-17 
Missouri 
(528,000 sq. miles) 
19*6 
1-443 
6-1 
1-796 
6'4 
1-885 
4-4 
1-296 
2-7 
0-795 
25 
0-047 
94 
0'178 
600 
1-14 
Ohio 
(214,000 sq. miles) 
43-1 
3-173 
11'9 
3-504 
11-8 
3-925 
8-5 
2-503 
10-9 
3-210 
35 
0-163 
204 
0-953 
1200 
5 61 
St. Francis 
(80.000 sq. miles) 
41'3 
3 041 
12 4 
3-652 
10'2 
3-004 
8-6 
2-533 
10-3 
3-033 
23-5 
0-438 
17 
2-130 
436 
4-50 
While 
(28,000 sq. miles) 
420 
3 092 
13-0 
3-828 
11-0 
3-239 
10 0 
2-945 
8-0 
2 356 
4-5 
0-161 
20 
0-750 
120 
4-29 
Arkansas 
(161,000 sq. miles). 
4 
0-024 
48 
0-300 
28-3 
2-082 
8-6 
2-518 
9-3 
2-748 
6-3 
1-864 
4-1 
1-207 
250 
1-55 
Yazoo 
(13,000 sq. miles) 
53'3 
3-924 
17-8 
5-239 
10-9 
3'222 
89 
2-621 
15-7 
4-615 
'5 
0-384 
35 
2-749 
480 
615 
Red 
(97,000 sq. miles) 
38'3 
2-798 
11-5 
3-386 
10-2 
3-019 
8-4 
2485 
8-2 
2-400 
3-5 
0-036 
50 
0-515 
180 
1-86 
Mississippi 
above its mouth_(l,259,000 
sq. miles) . 
175 
0-139 
664 
0-528 
1800 
1-43 
Table of Rainfall and Discharge Data for the Principal Watersheds of the Mississippi System. 
1 Probably much exceeded at times. 2 Obtained from a comparison of the Yazoo and White. 
3 Derived chiefly from gaugings by Captain Willard; checked by comparison with the White. 
4 Result chiefly of a comparison with the White, allowing for differences of rainfall and topography.-Somewhat uncertain. J. L. Greenleaf-The TLydrologxj of the Mississippi. 
43 
before it reaches the streams. Again, heavy rainfalls are liable 
to be somewhat local in their extent, when the entire drainage 
basin of a large river is considered. In the case of the Mis- 
souri, for instance, while the early spring rains are falling upon 
the regions near its mouth, the upper and elevated watershed 
is supplying comparatively nothing to the flow. The natural 
tendency of such a condition as this is to pull down the average 
rate of the high flow per square mile for an extensive drainage 
area. On account of the above reasons it is not surprising that 
the northern and large western tributaries of the Mississippi 
should carry comparatively small rates of maximum flood 
volume per square mile. To be sure, they have an advantage 
over the strictly southern rivers in drawing upon large quanti- 
ties of melting ice and snow which may concentrate the winter 
precipitation in a brief period of melting. The winter pre- 
cipitation upon their basins, however, is far lower in rate than 
for the other three seasons of the year, and the melting occurs 
chiefly before the heaviest rainfalls, which tend toward the late 
spring or summer. There result from this simply two freshets, 
the first due to melting aided by rains, and the second due 
principally, if not entirely, to rains alone. Between these two 
freshets occurs a more or less pronounced tendency to a merely 
fair or average stage of water. 
Upon turning to consider the rates of low flow and their 
causes one is confronted at once with the much smaller annual 
rainfall upon the entire northern and western portion of the 
Mississippi watershed. Behind this prominent fact are a num- 
ber of minor considerations. Thus, the proportionate, and 
probably the absolute loss from evaporation and absorption by 
vegetation is greater for regions with a light, than for those 
with a large rainfall. The proportion of natural storage per 
square mile in the form of lakes and swamps is smaller for 
large than for small watersheds. Finally, the climatic condi- 
tions are such over the major part of the Mississippi watershed, 
that the period of light rainfall in the autumn dominates a 
wide extent of country. So, while it is true that all portions 
of any one of the large watersheds will not at any one time be 
giving their maximum flood volume for the year, the converse 
is not true, for they may uniformly concur in yielding their 
minimum flows. The entire watershed of the longest tributary 
of the Mississippi, for instance, may at one and the same time 
be suffering from a greatly diminished rainfall, and one part 
of the area cannot be counted upon to maintain the flow while 
another part is subject to drouth. The above causes readily 
account for the exceedingly low flow per square mile of 0'047 
cubic feet per second from the Missouri, and 0'024 cubic feet 
from the Arkansas, and for the uniformly low rate of minimum 44 
J. L. Greenleaf-The Hydrology of the Mississippi. 
flow from all the smaller streams in the northwestern part of 
the Mississippi watershed. 
Passing now to the extreme upper waters of the river, the 
upper Mississippi above the mouth of the Minnesota, and the 
Minnesota itself show certain interesting and instructive dif- 
ferences. The total amount and the distribution of the rain- 
fall is nearly the same for both, the Minnesota having a slightly 
more pronounced concentration of rainfall in the summer 
months. The Minnesota is preeminently a prairie stream, 
whereas the main river is characterized, to an unusual degree, 
by lakes and swamps. It is not strange, therefore, that the 
flood-flow per square mile is nearly fifty per cent larger from 
the Minnesota than from the main stream. Neither is it to be 
wondered at that the Minnesota dwindles away to 0'031 cubic 
feet per square mile per second in low water, exhibiting the 
true character of a prairie stream, while the natural lakes and 
swamps of the main river hold it, in spite of the low rainfall, 
up to 0T54- cubic feet per square mile per second. 
The upper Mississippi, at the point where it unites with the 
Missouri to form the lower river, takes high rank in the matter 
of rates of flow, in spite of its average climatic conditions 
being essentially those already described as pertaining to the 
northern and western tributaries. Its high rate of low flow is 
largely the result of the natural storage in the immense num- 
ber of lakes and swamps in the States of Minnesota and Wis- 
consin. This storage affects to a marked degree the main 
river above St. Paul, the Saint Croix, Chippewa. Wisconsin, 
and other tributary streams. As a result, these rivers with- 
stand very successfully the depressing effect of the prairie 
streams like the Minnesota, which enter from the west, and 
they maintain the low flow at 0T44 cubic feet per second per 
square mile.* But not alone in its low flow as compared with 
the climatic conditions, is the upper Mississippi noticeable. 
Although its average annual rainfall is slight, yet it has heavy 
summer rains widely enough distributed over its 173,000 
square miles of watershed to hold it well up toward the ranks 
of the high flood-flow tributaries. Also, its spring melting is 
sufficiently concentrated in point of time to have a very 
important influence npon the records of flood volume. 
The Ohio demands special mention because of pronounced 
activity among its fellow tributaries. In a hydrological sense 
* Attention is here called to the fact that this paper is written throughout with 
reference to the natural conditions of the Mississippi drainage; the conditions 
which would pertain if the artificial storage works installed by the United States 
Government at the sources of the river were not existing. These works, uncom- 
pleted as they are, have resulted in maintaining a stage at St. Paul during the low 
season considerably more than a foot above the natural conditions of the river. J. L. Greenleaf-The Hydrology of the Mississippi. 
45 
it is the ruling tributary of the Mississippi system. Although 
it has less than half as large a drainage area as the Missouri, 
yet its low, high, and average flows all exceed in total amounts 
the like volumes from the Missouri. In rates per square mile, 
these flows are only exceeded in the cases of certain southern 
rivers. In fact, the Ohio is rightly classed with the southern 
rivers, even granting that the annual melting of snow and ice is 
a prominent feature upon its basin. It has been pointed out 
that upon most extended drainage areas, the rate of high flow 
is pulled down by the averaging of districts where the rains 
may be falling, with regions that happen at that time to be 
comparatively dry. Not so for the Ohio. There is a strong- 
tendency for moisture-laden air to be whirled in broad sheets 
over the watershed dear to the Alleghanies, and deposit heavy 
rainfalls during the same month over nearly the entire length of 
the basin. When this is taken into account with the relatively 
large average rainfall of 43 inches, and with the fact that the 
winter rains are only slightly less in amount than those of 
spring, the greatest of the year, and occur at the time when 
the snow and ice are going out, it is easy to understand why 
the Ohio should tower far above the other large tributaries of 
the Mississippi in its rate of high flow. That the Ohio is 
above even the upper Mississippi in its rate of low flow, is due 
primarily to its higher annual rainfall, and also to its important 
southern branches extending into a region of considerable 
autumn rainfall. 
The lower Mississippi, the main channel into which all the 
tributaries flow, claims final attention. It is the resultant of 
these tributaries, but a resultant in which the element of time 
is a potent factor. If all the tributaries were high and low 
together, it would be easy to compute the high flow or low flow 
of the main stream by a simple process of summation. Owing, 
however, to a lack of unanimity among the streams in this 
respect, it is an exceedingly complicated and, in fact, impossible 
task to reason out conclusions concerning the flow of the main 
river simply from the general data for the tributaries. The 
tributaries do conspire to a considerable degree in producing the 
low stages of the main river, for the area of light rains in the 
fall is very widely extended over the Mississippi watershed. All 
the rivers are not at their lowest during the same time, however, 
for if they were the aggregate flow would be only 110,000 
cubic feet per second, whereas the low water discharge of the 
Mississippi may be taken at 175,000 cubic feet per second, 
although lower gaugings have been recorded. 
Fortunately for the well-being of the dwellers within the 
Mississippi valley, the tributary streams differ very widely in 
their times of flood. A simple calculation shows that if high 46 
J. L. Greenleaf-The Hydrology of the Mississippi. 
water occurred simultaneously with them all, the main river 
would have to carry over three millions cubic feet of water per 
second to the Gulf. As a matter of fact, it is an extremely 
rare coincidence for more than two of the large tributaries to 
be at their highest yearly stages at the same time. The 
greatest annual flood upon the Ohio, for example, has disap- 
peared before that from the Missouri reaches the Mississippi. 
Thus the aggregate in the main river is kept down, so that 
1,800,000 cubic feet per second may be considered a large flood 
discharge from the Mississippi. The combination of condi- 
tions is such that the lower river usually reaches its maximum 
volume for the year in April or May, and its lowest stage in 
October or November. The diagram shows, by a convenient 
comparison of rates of flow per square mile per second, the 
resultant effect of all the tributaries upon the main river. The 
rate of low flow, 0T39 cubic feet per square mile per second, 
is fairly well up, in spite of the downward pull given by 
the Missouri and Arkansas. The rate of high flow is kept 
down to 1'43 cubic feet per square mile per second,-which is 
only surpassed in smallness in the case of the Missouri,-by the 
above mentioned lack of coincidence in the times of flood from 
the various tributaries.