UNITED STATES DEPARTMENT OF THE INTERIOR
MAP SERIES NO. 81
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY
I I I I I I I I I
HYDROLOGIC UNIT CODE
-RUNOFF FROM HYDROLOGIC UNITS
G. H. Hughes
U.S. GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF WATER RESOURCES MANAGEMENT
FLORIDA DEPARTMENT OF ENVIRONMENTAL REGULATION [1
The accompanying map is one of a series of map Because of va
reports designed to furnish generalized hydrologic infor- of runoff from dif
mation and to provide a general description of various for the same time
aspects of the hydrologic cycle as it applies to Florida. The data for 1951-74
map shows the average annual runoff from hydrologic those drainage bi
units in Florida. A hydrologic unit is a geographic area Subregion 09, w
designated as a basis for cataloging and processing hydro- results of various
logic data and other information compiled in the National were helpful in es
Water Data network. Florida is within the South Atlantic- some hydrologic u
Gulf Region (Region 03) and encompasses part or all of 8 Runoff from
(Subregions 07-14) of the 18 Subregions included in that not measured be
Region. The hydrologic units in Florida, previously com- Runoff from such
piled by Conover and Leach (1975), are listed in the accom- the gaged runoff
paying table, units. Some hy
Runoff, that part of precipitation that appears in sur- 140102, 100206,.
face streams (Langbein and Iseri, 1960), includes water along the coast;
that flows directly into gullies, creeks, and rivers, and also computation of r
includes water that infiltrates to ground-water bodies and accompanying ma
subsequently emerges in surface streams within the area land area consists
under consideration. The quantity of runoff from an area is islands-such as
commonly expressed in terms of inches of water uniformly not exist. Because
distributed over the area that contributes the water. In in these units
other words, an inch of runoff represents a 1-inch layer of infiltrating the gi
water covering the drainage basin that contributed the emerging in surf
water, areas was assum
FACTORS AFFECTING RUNOFF represents the su
Long-term streamflow records show that the annual particular unit. T
runoff from Florida averages about 14 inches statewide, through two unit
but locally it averages from less than 5 inches to more than determined as t
30 inches, and, of course, it also varies greatly from year to upstream unit an
year. Areal variations in runoff are caused by several In some parts of 1
factors. Regional differences in rainfall are an important hydrologic unit n
factor. For example, in northwest Florida the average aquifer to emerge
annual rainfall is several inches greater than the state- subsurface-flow
wide average of about 53 inches, as is apparent from the outflow from the
rainfall map just to the right. Hence, all other things being from that unit.
equal, the annual runoff in northwest Florida ought to be downgradient un
greaterthan the statewide average, amount of the gr
greater unit. For most hyi
The annual runoff from an area is also influenced by inflow probably i
the evaporation potential of the atmosphere and the extent runoff to -crioius
to which water remains on or near the land surface to known exception
sustain evaporation from land and water surfaces and Gulfof Mexico fr
transpiration by plants. In short, any part of the rainfall Florida which is
that is taken up by evapotranspiration cannot produce from hydrologic
runoff from the area. (Cherry and othe
The evaporation potential of the atmosphere, repre-
sented by the map of average annual lake evaporation in SE
figure 2 (Visher and Hughes, 1969), is several inches
greater in southern Florida than in northern Florida. Thus, Cherry, R. N., St
on the basis of evaporation potential of the atmosphere, the 1970 General
annual runoff should be considerably greater in northern Florida:
Florida than in southern Florida. ology Re
For water to be evaporated or transpired it must remain Clark, W. E.,
on the land surface or in the soil within the reach of plant Cagle, J. W., Jr.
roots. The extent to which this occurs is determined by the 1964 Water R
topographic and geologic characteristics of the area. For Union (
example, steep land slopes and relatively impermeable soils Conserv
promote rapid runoff from the area, thereby reducing the Conover, C. S. an
opportunity for water to be evaporated or transpired. Flat 1975 River ba
land slopes and surface depressions promote the ponding of Florida
water which in turn promotes evapotranspiration. Per- Ser. 72,
meable soils and substrata promote the rapid infiltration of Crain, L. J., Hug
water which greatly reduces the opportunity for water to be 1975 Water r
evaporated or transpired, especially if the water table is Dept. N
several feet below land surface. Of course, any water that 75 p.
enters the subsurface flow system may eventually emerge Florida Departm,
in surface streams where it again becomes available for 1974 Florida
evapotranspiration, but the wetted area in this instance is Kissimr
usually much smaller than the upland area where water Kenner, W. E.
first infiltrated the soil. 1966 Runoff
Man's activities also can affect runoff. The diversion of Geology
water from one basin to another reduces the natural runoff Kohler, M. A., Ni
from the losing basin and increases the apparent runoff 1959 Evapora
from the gaining basin. The storing of water in artificial WeatheT
surface reservoirs, or the spreading of water over the land Langbein, W. B.,
surface-as in the irrigation of crops--increases evapo- 1960 General
transpiration and thereby decreases runoff. Drainage U.S. Ge
canals tend to lower water levels in general and to remove 29 p.
water from an area more rapidly than would have occurred Musgrove, R. H.,
naturally, thereby reducing evapotranspiration and in- 1965a Water r
creasing runoff from the area. Urbanization also affects in nort
runoff. The creation of impervious areas tends to increase Consery
the overland flow from the urbanized area and decrease the Musgrove, R. H.,
recharge to the subsurface-flow system of the area. The 1965b Water
more rapid removal of a greater part of the available water Countie
tends to decrease evapotranspiration and increase runoff Div. Ge
from the area. The effects of man's activities are sometimes U.S. Dept. Comm
partly compensating. For example, areas that are drained 1972 Climate
by canals often are irrigated. Urbanization usually entails the Un:
an increase in the consumptive use of water. Atmosp
Runoff varies greatly with time as well as with location. 31 p.
The annual runoff from a stream basin can vary several fold Visher, F. N. and
between extremely wet and dry years. For example, as 1969 The dif
shown in figure 3, runoff from the Santa Fe River basin in evapora
northeast Florida (Hydrologic Unit 110206) during the 44 sources,
years when data were available ranged from about 39
inches in 1948 to about 9 inches in 1956. Within each year
the runoff rate varies widely, of course, because of the
seasonal variation in rainfall.
HYDROLOGIC i'\ *ii -I..i..iiiT N ,r ... .. i .N.. ,F. ... .... l..
Sub- Account- Cat, .
region ing unit ing .
variations in the yearly runoff, comparisons
ferent areas are more meaningful if made
e span. For the accompanying map, runoff
were used for all parts of the state except
asins that lie south of Lake Okeechobee in
'here data for 1965-74 were used. The
water-resources investigations in Florida
estimating the average annual runoff from
the low coastal areas of Florida is usually
cause the streams are affected by tides.
areas is herein assumed to be the same as
from inland areas of the same hydrologic
drologic units-such as units 140101,
and others-include areas of saline water
these areas were not included in the
runoff values used in preparation of the
ap. For those hydrologic units in which the
s almost entirely of offshore sand bars and
units 130014 and 090203-runoff data do
e the surficial materials of the land areas
are relatively permeable, rainfall, after
round, could move to the shoreline without
ace streams. Hence, the runoff from these
ed to be minimal.
each of the hydrologic units supposedly
rface outflow produced by rainfall on that
'hus, in places where surface streams pass
ts, the runoff of the downstream unit was
he difference between runoff from the
nd the combined runoff from the two units.
Florida, water derived from rainfall on one
moves underground through an artesian
ge in another unit downgradient in the
system. In such instances, the surface
upgradient unit represents the true runoff
However, the surface outflow from the
lit is greater than the true runoff by the
round-water inflow from the up-gradient
drologic units in Florida, the ground-water
s not large enough in relation to the true
ly distort the areal runoff pattern. One
to this is the apparent high runoff to the
om hydrologic unit 100207 in west-central
caused by substantial ground-water inflow
unit 100208 immediately to the east
rs, 1970, p. 62-76).
ewart, J. W., and Mann, J. A.
hydrology of the middle gulf area,
Florida Dept. Nat. Resources, Bur. Ge-
ept. Inv. 56, 96 p.
Musgrove, R. H., Menke, C. G., and
Resources of Alachua, Bradford, Clay, and
Counties, Florida: Florida State Board of
v., Div. Geology, Rept. Inv. 35, 170 p.
.d Leach, S. D.
asin and Hydrologic Unit map of Florida:
Dept. Nat. Resources, Bur. Geology, Map
hes, G. H., and Snell, L. J.
sources of Indian River County: Florida
at. Resources, Bur. Geology Rept. Inv. 80,
ent of Natural Resources
water and related land resources,
nee-Everglades area, 180 p.
in Florida: Florida Board Conserv., Div.
Map Ser. 22, 1 sheet.
ordenson, T. J., and Baker, D. R.
ition maps for the United States: U.S.
r Bureau Tech. Paper 37, 13 p., 5 pl.
and Iseri, K. T.
introduction and hydrologic definitions:
*ol. Survey Water Supply Paper 1541-A,
Foster, J. B., and Toler, L. G.
sources of the Econfina Creek basin area
western Florida: Florida State Board
v., Div. Geology Rept. Inv. 41, 51 p.
Barraclough, J. T., and Grantham, R. G.
resources of Escambia and Santa Rosa
es, Florida: Florida State Board Conserv.,
ology Rept. Inv. 40, 102 p.
e of the states, Florida: Climatography of
ited States No. 60-8, Natl. Oceanic and
heric Adm. Environmental Data Service,
I Hughes, G. H.
ference between rainfall and potential
tion in Florida: Florida Dept. Nat. Re-
Bur. Geol. Map Ser. 32, 1 sheet.
'For units which extend in-
T i &..NR I
DEPARTMENT OF NATURAL RESOU1
BUREAU OF GEOLOGY
This public document was promulgated at a
cost of $764.00 or a per copy cost of $.38 f
purpose of disseminating hydrologic data.
Figure 2.-Average annual lake evaporation in Florida.
(From Kohler and others, 1959.)
0 10 20 30
Figure 3.-Annual runoff of Santa Fe River near Fort
White (in Hydrologic Unit 110206).
FL..ORIDAl GE( O IC SLOC MP
r-- Accounting Unit
S11 03 07020 Subregun Caaloing Unit
1.13o IERA.GE ANNLI AL RL'NOFF IN INCHES
L 110205 1 2
,Fig.urer ,---J- e l r f i---I 5
.. .. 1-,--
LA"OCE A ""-
._.: ._" I .
t A AN.. .
L 0 102 0 20 0 03_ _
foR 0ttath C 1 7. '/.L IL---- ---.....L.L LU__ IE. o o. -
L-n .. 1 rainfall,- mann0
20 -- ---
' L I
C-i 3 9 3
I I I