July 24, 1972
REs MEAN ANNUAL FLOOD
Is the mean annual flood part of the stream?
For the purpose of determining ownership, there is no basis
in law, at this time, to support the proposition that the stream
and therefore the stream bed, is defined by the mean annual flood.
By the authority of g253.12(1), Florida Statutes, the state
is vested with title to the land underlying all navigable streams,
lakes and rivers. This land is deemed to be public property,
and although rights therein may be given, title cannot be granted
away. Holland v. Ft. Pierce Financing & Construction Co., 157
Fla. 649, 27 So. 2d 26 (1946).
To determine the nature and extent of ownership and to resolve
the questionepresented it is necessary first, to determine the
limits of a stream, and second, to determine the extent to which
the term "mean annual flood" comports with those limits.
I Florida case law states that the bed of the stream is
that "land below the ordinary high water mark." United States
v. Ray 423 F 2d 17 (C.A. Fla. 1970) at 20. ThAs, the limits
of a stream may be found by locating the high water mark.
The definition of "high water mark" was first articulated
by the Supreme Court of Florida in Tilden v. Smith. 94 Fla. 402,
113 So. 708 (1927). The Court adopted the Minnesota definition
stating at 712#
'" (the) high water mark..., a line between
a riparian owner and the public, is to be de-
termined by examining beds and banks, and
ascertaining where the presence and action of
the water are so comaon and usual, and so long
continued in all ordinary years, as to mark
upon the soil of the bed a character distinct
from that of the banks, irjweepeet to vegetation,
as well as respects the nature of the soil itself.."
The Court also noted a New Hampshire case, Dow, v.
Electric Co. 69 N. H. 498, 45A. 350, which stated:
'"The high-water mark on fresh water rivers
is not the highest point to which the stream
rises in times of freshets, but is the 'line
which the river impressed upon the soil by
covering it for sufficient periods to deprive it
of vegetation and to destroy its value for
From these descriptions it can be seen that the high water
mark is the product of a constant, sustained flow. It results
from the regular and continuous action of the stream; it is not
the line reached by the water at flood stages, nor is it the line
ordinarily reached by annual swellings of the stream possible
caused by a wet season. (See also, Maloney, Water Law and
Administration, University of Florida Press, 1968, pp 68-72)
Thus, the boundaries of a stream, marking the extent of
state ownership, should be clear upon inspection.
II Before diving into the mean annual flood, it is well
to keep in mind the common definition of "flood," or "flood
waters." This term is defined as "waters above the highest line
of the ordinary flow of the stream." Fla. Jor, Waters and
The "mean annual flood" is defined as "the flood having
a recurrence interval of 2.33 years." U. S .geological Survey Water
Supply Paper 1543-A at 5. The recurrence interval is equal to
the "average interval of time within which a flood of a given
magnitude will be equaled or exceeded once." Id. at 5. Briefly,
the mean annual flood is found by measuring and recording the
annual floods of a particular watercourse over a given interval
of time. This data is then weighed against known topographic
features and a curve is constructed.
One study has indicated that twelve years of record are
required to define the mean annual flood within 25 per cent.
Geological Survey Water Supply Paper 1543-A at 24.
The mean annual flood point is measured in cubic feet
per second. Thus, with this known volume it is not difficult to
determine the corresponding points on each side of the stream.
It should be noted that these points will be outside
the points designating the high water mark. Thus, at present,
there is no basis in law for holding that the state owns out to
the mean annual flood point, or stated another way, that the mean
annual flood is part of the stream.
It is not probable that mean annual flood will become a
standard in this regard in the near future. In many cases, topo-
graphic maps are not available for computing necessary topographic
characteristics for many parts of Florida. geological Survey
Supply paper 1543-A, at 30.
As an aside, the significance of the mean annual flood
is found in flood frequency analysis, a procedure useful in flood
plane zoning. using these techniques accurate estimates can be
obtained describing the extend of flooding of a particular water-
course over a number of years.