The Influence of Drainage and Cultivation on Subsidence of
Organic Soils under Conditions of Everglades Reclamation. (1)
R. V. Allison (2)
Agriculturists working highly organic soils such as we have to
deal with over vast expanses of the Florida Everglades have been conscious
for a long time that you can not drain and cultivate these soils in any
normal manner and keep them. In other words, they are something like the
cake which we can not eat and keep at the same time.
Thus in the early development of some of the Fenlands of England
we are told that the early drainage lines were dug entirely in the deep,
fibrous peat that completely covered the marl beneath. In due course the
marl seems to have appeared at the bottom of the canals, as they were deep-
ened, in consequence of the steady subsidence of the land's surface. Finally,
it is said, the deep blanket of organic soil disappeared entirely and farming
in those areas, for many years now, has been largely in the marl which former-
ly underlaid the peat and in which the drainage lines now are wholly cut.
In contrast to such a situation as the British Fenlands, which
originally had marl under them, the greater part of the organic soils of
the Everglades are underlain by lime rock that is hard and uncompromising.
Around the margin of this great area the organic formation is underlain,
locally, by sand or marl or the two interstratified. This, of course, con-
stitutes quite a different situation.
The facts of these subsidence trends in our Everglades soils have
been pointed out many times and in many different ways in the past, as for
instance in a paper presented by the writer before the Florida State Horti-
cultural Society in 1947 (Proceedings Volume 59: pp. 8-16). In that paper
the subsidence curve showm in Figure 1, and repeated herewith, under the
(1) Paper presented before the Organic Soils Sub-Section, Soil Science
Society of America, November, 1952.
(2) Fiber Technologist, Everglades Experiment Station, Univ. of Fla.,
same number, illustrated-the situation only too well, as does also Figure
2 of that same paper. In the latter it is shown that during the period 1914-
1943 a loss of as much as six feet of soil was experienced from various
causes including compaction from drainage and cultivation, natural oxidation
and by open fires.
According to the surface subsidence trend shown in Figure 1 it is
only too obvious that the time must come when the depth of the peat over the
rock will be too shallow for most cultivated crops. The most critical tim
will come, of course, when the depth to free soil water that must be main-
tained for any particular operation is such that the water table must take
a position in the rock itself and the direct contact between it and the re-
maining muck is lost. At such time as this situation develops other uses
obviously will have to be found for this land and this area. Naturally the
more diligently the planning for this eventuality is done in advance, and
the more carefully it is thought out, the better the resulting land use
schedule will fit the situation when it arrives.
This irresistable trend in the subsidence of the land surface
under drainage and use in the "Upper Glades" area in the general vicinity
of Okeelanta is clearly set forth by the bench mark shown in Figure 3 that
has been used as a reference point for a subsidence line in the izediate
area for a number of years. This level was established by the Drainage Div-
ision of the Bureau of Public Roads in 1916 at which time only about 18
inches of the pipe was showing above the land surface. The photo at the
left in Figure 3 was taken in 1932. The latest photo of this installation,
on the right in Fig. 3, was taken in March of 1943 by which tim more than
18 additional inches of the pipe were exposed to view above the surface of
the soil over and above that exposed by 1932. This bench mark was destroyed
by field operations shortly after the photograph was taken in 1943.
LUme Rock Base
eat mck sinie 191h at a location about h miler suth of South
?i&re 1. raph shoring rate of surface subsidence on Okeechobee
peaty mrck since 1911 at a location about h miles scnzth of South
aavy. The rather pharp, downward trend during the last few vears
of record shown thereon is presumably due to increased cultivation
as well as the occasional fires that swept the area during the in-
terval of those measurements.
Cf EL iJ14-jb
.s. ., .--^ y f *..- -,
Figure 2. Temporary benchmark set up about 2 miles south
of South Ray at the time of the inspection trip through the
heart of the Everglades which was arranged to follow the
Interim Meeting of the Soil Science Society of Florida held
in Belle nlade on March 17, 1943 for a discussion of Ever-
glades problems. This shows that the ground elevation at
this point in 191h, according to the best engineering data
available, was nearly six feet higher than at the time the
picture was taken in 1943.
Figure 3. Benchmark originally located in the vicinity of
Okeelanta on Okeelanta peaty muck which short : the subhidenc
of the land since 1916 to the date of the photogrenh, left,
July, 1932 and, right, March 1913.
Without doubt the most impressive evidences of subsidence in our
organic soils are those that develop in association with buildings of one kind
or another. This is probably due to the fact that we see them more often and
sueh tendencies become more real in that relationship than in any other. At
least under such conditions the obviousness of the trend can scarcely be missed
or ignored. A couple of landmarks of this nature are shown in Figures 4 and
5 with which the legends are sufficiently complete to tell the story. Both
photos were taken on the grounds of the Everglades Experiment Station.
Volume Weight and Shrinkage Studies
-In the course of early volume weight and shrinkage studies on these
soils, several profiles were excavated and samples were taken, in some cases all
the way from the surface to the underlying rock or sand. Particular mention will
be made of only two of these and of some of the values that were developed around
them at that time and in the course of more recent samplings that have been made.
Profile No. 195 was first taken in April of 1929 from a typical area of
Everglades Peat on the grounds of the Everglades Station. At that time it showed
a depth of 78 inches to lime rock. Profile No. 197 was first taken from an area
of Okeechobee muck in April of 1929. This, of course, was in a position much
nearer Lake Okeechobee than the Everglades peat. At the time of the first exca-
vation of this latter profile the muck showed a depth of 105 inches from the
surface to the rock.
The nature of the Excavated profiles, and the manner in which they were
taken, is well shown in Figure 6 where Nos. 195 and 197 are both shown in their
desiccated form in the 6" x 9" x ~8" heavy, galvanized pans in which they were
taken. The excavation of such profiles was accomplished by pressing the heavy
pan into the side of a vertical cut at the position desired in relation to the
profile of the soil as examined in the exposed cut. It was then dug out with
a considerable over-burden at the back. The pan was then played down flat and
the overburden carefully cut away level with the exposed edges of the pan.
Figure L. A concrete floor slab that was poured direqty
on the ground surface for a small building that was bUt
at the Everglades Station in 1925. At that time the top
of the slab was formed at approximately the level of the
soft top soil of the adjacent area. The present photo,
taken in 1952, shows a surface subsidence of about 3A feet
in 27 years. This slab is at the rear of the main build-
ing at the Everglades Station which is shown in the back-
Figure 5. Line of labor cottages (above) shown shortly following
their construction during the period 1924-26 and one of the last
of'them (below) in 1950 at about the time it was removed. There
had been no change in the foundation in the meantime. They were
simply constructed on piling driven to the rock. As in the photo-
graph of Figure 4 and many others that could be shown, the subsi-
dence of the land surface becomes exceedingly obvious under such
The nature of the opening of the soil to rock at the time of the
later (1952) sampling of the Everglades peat at the Experiment Station, Profile
No. 195, is well shown in Figure 7 where the surface of the soil oame considerably
below the level of the workman's shoulder as he stands directly on the rook on
which the soil mantle rests.
The comparative volume weight values taken at the time of the earlier
samplings and others taken from November samplings of the present year from the
same locations that were represented by both profiles are shown in a somewhat
graphic manner in Figures 8 and 9 where the detailed legends bring out the main
points of interest in both of them.
If the weight and other values are fully substantiated by further
samplings it would appear that the Everglades peat profile has been somewhat
more compressed by drainage and cultivation thru the years since the gain in
volume weight within the profile is considerably greater than it is in that of
the Okeechobee much. To be sure the weight measurements in this profile study
extend much closer to the rock than the earlier ones and at that level have en-
countered heavier than the average of materials found in the upper part of the profile.
It will be of considerable interest to follow up the above relationships
in the evaluation of the comparative effect on subsidence of pasture cover and
grazing and that of cultivated crops. As a result of some preliminary observations
made quite recently along this line there seems to be good reason for believing
that pasture covers cause a somewhat slower subsidence of the land surface than
cultivated crops. This is doubtless due to the action of one or more factors
that may be active under such conditions such as: a) reduced surface temperature
of the soil by the continuous shading it receives: b) exclusion of air by the
firm packing it receives from tramping by animals; c) tolerance of most pasture
crops of a higher average water table than cultivated crops: and d) the compara-
tively heavy accretion of roots and other organic residues of pasture plants
through the years.
Figure 6. Completely shrunken profiles of
No. 195, Everglades peat (left) and No. 197,
Okeechobee muck (right), after drying for
several months in the greenhouse.
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Figure 7. The excavation shown in this photo is the
1952 examination of the Everglades peat profile, No.
195. The worker is standing fully on the rock at the
bottom of the pit while the bottom edge of the cross-
bar is exactly at land level. The average depth of
the peat at this point was found to be 54 inches
whereas in 1929 it was 78 inches and in 1912 it was
approximately 156 inches or 13 feet.
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ORIGINAL LAND SURFACE
574 19 --26b
400 26"-30 0"-6"
702 30"-40 6"-
540 40"-50 18"-24"
Lbs 50 -74 36-42'
42"-54" 15.08 06-4-5
"74"-78" 56.95 Total Lb.
Figure 8. Comparative depth and volume weight values
of the Everglades peat profile (No. 195) as studied in
April of 1929 and later in November, 1952.* Note that
the approximate depth of the peat in the general area
of this profile in 1912 was 13 feet; in 1929 it was 6j
feet and in 1952 it was 54 inches. On the other hand,
according to the volume weight values taken at the diff-
erent times of examination the top 50 inches of soil on
a cubic foot basis weighed 38.01 pounds in 1929 and 56.95
pounds in 1952 in the lower and apparently much more com-
oressed position that it occupied by that time.
*The writer wishes to acknowledge the good assistance
of M'r. Alan L. Craig, Soil Conservation Service, (USDA),
stationed at the Everglades Experiment Station, in con-
nection with the sampling and taking of the consequent
records of the 1952 excavation of profiles No. 195 and
ORIGINAL LAND SURFACE
Vol. Wt 0"-9"
5.47 26-33" '
26.71 33"-58r 12"- 18
8.56 516-7 2"
I LZ-2.87 -72"-77"-
Total Total 77"-94" 48-62"
103.06 Total Lba
Figure 9. Comparative depth and volume weight values
of an Okeechobee muck profile (No. 197) as studied in
April of 1929 and later in November of 1952. Note that
the approximate depth of the muck in this area in 1912
was 13 feet; in 1929 it was 8 feet and 8 inches while
in 1952 it was 75 inches. Note also that a 62" sec-
tion of both profiles, as measured from the 12 and 13
inch depth on the Okeechobee muck profiles, for 1929
and 1952, respectively, show very little difference in
total weight when calculated as that cubic depth based
on a square foot of surface. This is in striking con-
trast to the Everglades peat profile shown in Figure 7
under the same general conditions of examination.
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Shrinkage studies also have shown surprising results not only in
relation to the amazing amount of "collapse" these soils experience upon drying
but also the limited amount of reversability that takes pa ce upon rewetting.
Thus, in Profile No. 195 (Everglades peat) shown in Figure 6, the total profile
that had been excavated (48 inches in depth) shrunk from an original volume of
2592 cubic inches to 925 cubic inches or 2.8 volumes into 1. In the instance
of the Okeechobee muck profile (No. 197) it was found that the same original
volume of the profile as above shrunk to 882 cubic inches or 2.94 volumes into
1. Some of the strata in profiles of this nature shrank as much as 5 volumes
Upon rewetting (flooding) dried soils of this nature the swelling of
the material back towards its original volume scarcely ever was found to exceed
a twenty percent recovery of the volume lost upon drying. This was true even
after it had been soaked for as long as two months. As already noted, these
profiles had only been air dried in the greenhouse but thru a period of several
Outlook for the Future
In view of the great water conservation and control program that is
in process of development by the Corps of Engineers, U. S. Army, cooperatively
with the newly created Central and Southern Florida Flood Control District the
question of organic soils conservation is one of paramount importance. It was
with this thought in mind that Mr. J. C. Stephens of the Soil Conservation Service,
U.S.D.A., and Mr. Lamar Johnson, Assistant Engineer, Central and Southern Florida
Flood Control District, reviewed all available engineering and research data on
the question of organic soil subsidence under Everglades conditions and prepared
a highly comprehensive report on the subject.* In this report it was concluded
that there was grave likelihood that subsidence losses approximating one inch per
* This report served as the basis and background for a panel discussion on the
general subject of Everglades Conservation, Water and Soil, that was held under
the auspices of the Soil Science Society of Florida as a part of the program of
its annual meeting in West Palm Beach in October 1951. The discussion is reported
in full in Proceedings Volume XI of the Society, in which the Stephens-Johnson
report also is published in full in the appendix*
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year would continue though they pointed out in a cautious way that the use of
the land for pasture and grazing might cause quite appreciably less subsidence
than when cultivated crops are grown continuously on the same and. It is this
factor of soil conservation that could be developed through the flooding of the
land that would be required for this crop that has helped to stimulate interest
in rice production in the Everglades. Of this, Dr. Green will speak to you a
little later in this program.
On the basis of land levels in the Everglades known from the early
records and the average annual rate of subsidence since cultivation began,
Messrs. Stephens and Johnson went much further than most reports in the past
on this subject by preparing soil depth lines over the agricultural section
of the Everglades in what really amounted to soil depth contours and projecting
these forward at ten year intervals to the year 2000. According to their cal-
culations and tentative conclusions there will be only limited areas of organic
soils in the Everglades area deep enough at that time to permit of any type
of general farming. This manner of evaluation is well shown by the numerous
graphs that appear in the original report at the intervals indicated, the
last showing approximately the conditions as to remaining soil depths that
are expected to prevail by the year 2000.
What of the Future the Everglades As An Extensive Wild Life Area
As the use of Everglades lands for agricultural purposes approaches
the sunset of their experience in this field of production there is little
doubt that transition into a wildlife area of ultimate world fame will follow,
perhaps in an easy and natural manner, especially if there be a reasonable
amount of preparatory planning to that end in the meantime. The most important
part of that planning will be, of course, an ever enlarging program of study
on the mineral soils to the east, the north and the west of the Everglades
area since it is out onto these lands that the agriculture of the Glades must
move as it becomes necessary to leave the great swampland area. It is fortunate,
therefore, that a good start in the above referred to studies already has
been made by the Everglades Experiment Station on the study areas that are
being developed on these lands, one near Fort Pierce, the Indian River Field
laboratory, and the other near Ft. Lauderdale, the Plantation Field Laboratory.
There can be no doubt that by the end of the present century the
population of the coastal areas to the east and west will be getting very heavy
indeed and that the "Playground" outlook for these sections could be immeasurably
benefitted by having such a huntsman and fisherman's paradise spreading out in
vast proportions within the main body of the Florida peninsula at this latitude.
The use of these lands for this purpose will be enormously abetted, of course,
by the great amounts of residual fertilizer materials that will have accumulated
in them as a result of several decades of intensive agricultural use to which
they shall have been subjected by that time.
This residual fertility that will have accumulated in the soil of
cultivated areas by the time the area is ready to return to swampland conditions
should also do great things for the restoration and growth of the native sawgrass
cover, a probability that should provide pleasant contemplation for those hardy
pioneers in the pulp and paper industry who feel so strongly that this plant is
certain to prove a saving source of raw material for this purpose in the future.
The importance of an extensive wild life area in this section of the
State in the future is also emphasized by the rapidity with which what used to
be considered readily available hunting areas in other sections of Florida are
being fenced and developed for pasture and other purposes. Naturally such a
rewatering of this great area should also very appreciably affect the winter
temperatures of this section over and beyond what mipht be expected of the huge
water conservation areas that are being set up at the present time to the east
and southeast of the agricultural area.
It is also quite certain that demands for water will increase several
times over during the next few decades in South Florida if development of popula-
tion, industry and agriculture takes its natural course and is not hampered by
such a controlling influence as lack of adequate water supply. Naturally, as
the Everglades returns to an essentially wild life area in the years'to ome,
its capacity for receiving and holding water, when assisted by the water control
facilities now in process of installation, would be tremendous. Such a visuali-
zation for the area in the future then, becomes simply a gradual change of duty
for this great peat and muck land area that will enable it to deliver a diversity
of services and values which, while substantially different from the agricultural
types of the present and of the immediate future, may prove to be of equal or even
greater importance to the economy of the State at that not too distant time.