FROM THE DESK OF THE CHIEF HYDROLOGIST f
Last month I told you that, despite the widely-believed notion of many people,
we do not have unlimited quantities of water in Florida for our use. True, at
times of flood we have too much water; then a great hue and cry is raised to
get rid of the water. But, where can we put it? Currently about all we can do
is drain it off, as waste water, to the Gulf of Mexico where it becomes mixed
with salt water. In the Southwest Florida Water Manarement District there
are no deep river valleys in which to store the flood waters behind big dams.
-Thus, we can't hold much of such flood water -- even behind low retention
dams --while we slowly recharge it to the aquifers or save it for direct later
withdrawal and use.
Most of the rain that falls either evaporates and transpires back into the air
or it runs off to the r-f. In either c' oc it i'.cst for our use. To gain an
understanding of our water situation, let's work out a simplified water-budget
accounting of a typical year's water supply for our District and see how much
water we have to work with.
But first, let us think of the comparison between a budget of our water supply
and a family's financial budget. In both cases we have income, outgo and
(hopefully) some savings. For example, suppose that your income is S10, 00
a year, that your outgo expensess for food, clothing, shelter, insurance, auto-
mobile costs, doctor's and dentist's bills, music lessons for the kids, taxes,
etc.) amounts to $9, 000. That leaves you $1, 000 that you can use for pleasures,
buying a new car, taking a vacation trip, or laying a nest egg aside as savings.
You can think of water resources in much the same way.
Income is rain plus ground and surface water inflow into the area.
Outgo is the water lost by evaporation and transpiration back into the air from
open bodies of water and from the breathing of plants and animals plus runoff
of water in streams and ground water seepage to the Gulf or as spring discharge
into salty water.
Savings is the balance left after taking the outgo from the income. This can be
either in the surface water (streams, lakes, etc.), ground water (aquifers), or
in soil moisture.
However, when we are concerned with a hydrologic unit the size of our fifteen-
county District with drainage boundaries that do not encourage inflow, then
income becomes just rain.
Le.t us consider a simple system:
where P signifies rain (Income)
Et is evaporation transpiration (Outgo)
R is runoff (Outgo)
With this equation we can develop an easily understandable accounting of what
happens to our water and the quantities we mnay have to work with. We can do
some calcuiating as to how much w;atcr we have to support our. growing popu-
lation and how long our supplies will last \without having to borrow.from the
bank (our savings -- represented by storage in aquifers, streams, lakes and
in the soil).