Impact of anthropogenic development on coastal ground-water hydrology in southeastern Florida, 1900-2000

Southeastern Florida is an area that has been subject to widely conflicting
anthropogenic stress to the Everglades and coastal ecosystems. This stress is a direct
consequence of the 20th century economic competition for limited land and water
resources needed to satisfy agricultural development and its expansion, its displacement
by burgeoning urban development, and the accompanying growth of the limestone
mining industry. The development of a highly controlled water-management
system designed to reclaim land for urban and agricultural development has severely
impacted the extent, character, and vitality of the historic Everglades and coastal
ecosystems. An extensive conveyance system of canals, levees, impoundments, surface-
water control structures, and numerous municipal well fields are used to sustain
the present-day Everglades hydrologic system, prevent overland flow from moving
eastward and flooding urban and agricultural areas, maintain water levels to prevent
saltwater intrusion, and provide an adequate water supply. Extractive mining activities
expanded considerably in the latter part of the 20th century, largely in response to
urban construction needs.
Much of the present-day urban-agricultural corridor of southeastern Florida lies
within an area that is no more than 15 feet above NGVD 1929 and formerly characterized
by freshwater marsh, upland, and saline coastal wetland ecosystems. Miami-
Dade, Broward, and Palm Beach Counties have experienced explosive population
growth, increasing from less than 4,000 inhabitants in 1900 to more than 5 million
in 2000. Ground-water use, the principal source of municipal supply, has increased
from about 65 Mgal/d (million gallons per day) obtained from 3 well fields in 1930
to more than 770 Mgal/d obtained from 65 well fields in 1995. Water use for
agricultural supply increased from 505 Mgal/d in 1953 to nearly 1,150 Mgal/d in
1988, but has since declined to 764 Mgal/d in 1995, partly as a result of displacement
of the agricultural industry by urban growth. Present-day agricultural supplies are
obtained largely from surface-water sources in Palm Beach County and ground-water
sources in Miami-Dade County, whereas Broward County agricultural growers have
been largely displaced.
The construction of a complex canal drainage system and large well fields has
substantially altered the surface- and ground-water hydrologic systems. The drainage
system constructed between 1910 and 1928 mostly failed to transport flood
flows, however, and exacerbated periods of low rainfall and drought by overdraining
the surficial aquifer system. Following completion of the 1930s Hoover Dike
levee system that was designed to reduce Lake Okeechobee flood flows, the Central
and Southern Florida Flood Control Project initiated the restructure of the existing
conveyance system in 1948 through canal expansion, construction of protective
levees and control structures, and greater management of ground-water levels in the
surficial aquifer system.
Gated canal control structures discharge excess surface water during the wet
season and remain closed during the dry season to induce recharge by canal seepage
and well withdrawals. Management of surface water through canal systems has successfully
maintained lower ground-water levels inland to curb urban and agricultural
flooding, and has been used to increase ground-water levels near the coast to impede
saltwater intrusion. Coastal discharge, however, appears to have declined, due in part
to water being rerouted to secondary canals, and to induced recharge to the surficial
aquifer system by large municipal withdrawals. Southeastern Florida is underlain by Holocene- to Tertiary-age karstic limestone
deposits that form (in descending order): a highly prolific surficial aquifer system, a
poorly permeable intermediate confining system, and a permeable Floridan aquifer
system. Prior to construction of a complex drainage netwo