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3: Freshwater Quality and Availability

Eduardo Figueroa-Gibson, U.S. Geological Survey, Florida Integrated Science Center, Ft. Lauderdale, Florida

The USGS has been interested in acoustic technology to measure water velocity and stream flow since the late 1960s. Beginning in the early 1980s, the USGS has worked cooperatively with manufacturers to develop and enhance the application of acoustic Doppler instruments to improve the accuracy and efficiency of stream flow measurements. Acoustic Doppler Current Profilers (ADCP), the processing software, and techniques have greatly improved to measure a wide range of water velocities and stream discharges with good accuracy.

The best deployment platform to make stream flow measurements with an ADCP is dependent upon site characteristics. Each site will differ from other sites in characteristics such as water velocity, channel width, depth, and access considerations, such as the presence of boat ramps, bridges, or cableways. Three common types of deployment platforms for the ADCP are manned boats, tethered boats, and remote-control boats. A manned boat deployment requires at least two personnel with one operator trained in boat safety, and access to a boat ramp. The tethered boat deployment generally requires a bridge or access to both sides of the stream. To deploy a remote control-boat, the operator only needs access to the stream.

The advantage of a remote-control boat is that the ADCP can be deployed in situations where a manned or tethered boat may not be feasible or ideal. The remote-control boat eliminates the safety risks associated with a manned boat. The hydrographer remotely maneuvers the boat across the river or lake, allowing the technician to collect data by radio communications.

South Florida has many streams and deep canals with low velocities where remote-control deployments are ideal. In these types of streams, a remote-control boat can be deployed quicker than a manned boat which increases the number of measurements a team can collect.

Commercially available models of remote-control boats, however, are costly, large, and heavy. The Ft. Lauderdale office designed and built a remote-control boat that operates well in the low velocity streams of South Florida. Smaller and lighter than commercially available remote-control boats, the Ft Lauderdale boat is easier to handle. The cost is significantly less than commercially available models.

Contact Information: Eduardo Figueroa-Gibson, U.S. Geological Survey, Florida Integrated Science Center, 3110 SW 9th Avenue, Ft. Lauderdale, FL 33315; phone: 954-377-5933; email: efig@usgs.gov

David L. Fulcher and Richard L. Kane

U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida

Hurricanes destroyed or damaged several USGS hydrological monitoring stations along the entire Gulf of Mexico coast within the last five years. In response to the damage produced by Hurricanes Katrina and Rita, the USGS received a supplemental appropriation to assist in the rebuilding of gages destroyed by the storms and to harden stream gages against future hurricane activity. Flood hardening was carried out on National Streamflow Information Program (NSIP) gages and on select tidal gages with an emphasis on those gages used by the National Weather Service for flood forecasting. During 2007 and 2008, 134 gages were flood hardened along the Gulf of Mexico coast including 44 in Florida. The primary objectives of this project were to flood harden continuous stream gages, relocate or replace and upgrade equipment in select continuous record streamgages, and flood harden select open-water tidal/water quality stations.

During 2007, stage for the 200-year flood recurrence interval was chosen as the primary criteria for the flood hardening for the NSIP flood forecast stations. The stage for the 200-year flood recurrence interval was determined for each NSIP gage using the existing stage-discharge rating where available, or if the rating was not high enough to cover this recurrence interval, by extending the existing ratings.

Several methods were used to strengthen stream gages to withstand the water level and stream velocity of the 200-year flood discharge. These methods included strengthening existing structures, raising existing stilling wells to an elevation exceeding the 200-year flood stage, and establishing auxiliary instrumentation to provide backup data if the primary gage failed as a result of flooding.

Contact Information: David L. Fulcher, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 35512; phone: 813-975-8620; email: dfulcher@usgs.gov

Mark C. Kasmarek and Natalie A. Houston

U.S. Geological Survey, Texas Water Science Center, Woodlands, Texas

The Chicot aquifer (in Holocene- and Pleistocene-age sediments), Evangeline aquifer (in Pliocene- and Miocene-age sediments), and Jasper aquifer (in Miocene- and Oligocene-age sediments) are the three primary aquifers in the Gulf Coast aquifer system in Texas. The hydrogeologic units are laterally discontinuous, fluvial-deltaic lenticular deposits of gravel, sand, silt, and clay that dip and thicken from northwest to southeast. The units thus crop out in bands inland from and approximately parallel to the coast, becoming progressively more deeply buried and confined toward the coast. The Chicot aquifer outcrop, which comprises the youngest sediments, is the closest of the aquifer outcrops to the coast, followed farther inland by the Evangeline aquifer outcrop and then farthest inland by the Jasper aquifer outcrop.

The USGS, in cooperation with the Harris-Galveston Subsidence District, the City of Houston, the Fort Bend Subsidence District, and the Lone Star Groundwater Conservation District, publishes an annual report on the water-level altitudes and water-level changes for the Chicot, Evangeline, and Jasper aquifers and compaction of subsurface sediments in the Chicot and Evangeline aquifers in the Houston-Galveston region. The 2008 report (Scientific Investigations Map 3031) shows potentiometric surfaces as low as 200 feet below sea level for the Chicot aquifer in central Harris County; 300 feet below sea level for the Evangeline aquifer in northern Harris County, and 150 feet below sea level for the Jasper aquifer in southern Montgomery County. Additionally, for the period 1977–2008, the report shows water-level rises of as much as 200 and 260 feet in the Chicot and Evangeline aquifers, respectively, in southeast Harris County.

The Houston-Galveston region is the largest urban area in the U.S. affected by land-surface subsidence caused by ground-water withdrawals. Sustained withdrawals cause water levels in the aquifers to decline, which in turn causes depressurization and dewatering of the clay lenses. Subsequently, the individual grains of the clay lenses begin to realign and compress. Measured subsidence data using spirit-leveling and GPS techniques indicate that as much as 10 feet of subsidence has occurred in areas of southeastern Harris County. For the same area, data derived from subtraction of a 1915–17 DEM from a 2001 DEM show that land-surface elevation has declined as much as 13 feet. Land-surface subsidence is especially problematic for coastal areas having low topographic relief. Impervious land-surface cover, surficial clay in the Chicot aquifer, and Gulf of Mexico low-pressure systems with storm surge and high rainfall, combine to make areas affected by subsidence more flood prone.

Contact Information: Mark C. Kasmarek, U.S. Geological Survey, 19241 David Memorial Drive, Suite 180, Conroe, TX 77385; phone: 936-271-5318; email: mckasmar@usgs.gov

Melinda A. Lohmann, Eric D. Swain, and Jeremy Decker

U.S. Geological Survey, Florida Integrated Science Center, Fort Lauderdale, Florida

As proposed Everglades restoration scenario(s) are implemented, the hydrology and ecology of ENP and BNP may be affected substantially. To protect sensitive ecosystems, model-predicted hydrologic conditions that result from restoration need to be evaluated prior to implementing substantial changes in water delivery. The development of a numerical model that can simulate salinity and surface- and ground-water flow patterns under different hydrologic conditions is fundamental to this effort.

Two local USGS hydrologic models have been linked to create a larger, sub-regional model of southern Florida that includes Everglades National Park (ENP) and Biscayne Bay National Park (BNP). Because surface-water flows in the study area have been compartmentalized extensively by levees and canals, scientists are able evaluate surface-water restoration effects on these parks individually. In contrast, ground-water flow within the Biscayne aquifer, present beneath both parks, is continuous and not constrained by man-made boundaries. This interconnected system complicates the evaluation of restoration effects, because modifications in one park can affect conditions in the other. The USGS sub-regional model is designed to address this issue by providing a comprehensive assessment of the effects of changes to ground-water flow and surface water conveyance on both National Parks.

The USGS model consists of the Tides and Inflows in the Mangroves of the Everglades (TIME) model and the Biscayne Bay model. The TIME model was developed to simulate the potential effects of various restoration scenarios on the southern Everglades, and the Biscayne Bay model was developed to identify causative factors for Biscayne Bay hypersalinity. The combined model domain encompasses all of ENP and Miami-Dade County, and is solved using the Flow and Transport in a Linked Overland/Aquifer Density Dependent System (FTLOADDS) modeling code. The FTLOADDS code has been updated to simulate heat transport in wetlands and offshore areas. When complete, the sub-regional model will provide deterministic estimates of freshwater flow to the bays, bay salinity, water levels, surface- and ground-water leakage, ground-water flow paths, and temperature. The combined model will also be able to provide predictive hydrologic data to ecological models in the study area. The heat transport component will provide water temperature and salinity predictions that can be used to assess habitat suitability for different aquatic species, such as the West Indian manatee. The sub-regional model will be linked with the South Florida Water Management Model (SFWMM) in order to simulate selected restoration scenarios, and with the Natural Systems Model (NSM) to hindcast pre-development hydrologic system conditions.

Contact Information: Melinda A. Lohmann, U.S. Geological Survey, 3110 SW 9th Ave., Fort Lauderdale, FL 33315, phone: 954-377-5955; email: mlohmann@usgs.gov

Richard L. Marella, U.S. Geological Survey, Florida Integrated Science Center, Tallahassee Florida

The estimated amount of water withdrawn in Florida in 2005 was 18,354 million gallons per day (Mgal/d), of which 63 percent was saline and 37 percent was fresh. Ground water accounted for 62 percent of freshwater withdrawals and surface water accounted for the remaining 38 percent. Palm Beach County withdrew the largest amount of freshwater, Pasco County withdrew the largest amount of saline water in 2005.

Overall, agricultural irrigation accounted for 40 percent of the total freshwater (ground and surface) withdrawn in 2005, followed by public supply with 37 percent. Total ground-water withdrawals during 2005 were made for public supply (52 percent), followed by agricultural self-supplied (31 percent), commercial-industrial-mining self-supplied (8.5 percent), recreational irrigation and domestic self-supplied (4 percent each), and power generation (0.5 percent). Agricultural self-supplied accounted for 56 percent of fresh surface water withdrawn in 2005, followed by power generation (20.5 percent), public supply (13 percent), recreational irrigation (6 percent), and commercial-industrial-mining self-supplied (4.5 percent). Saline water withdrawals (99.9 percent) were from surface water for power generation and were used for once-through cooling.

In Florida during 2005, ninety percent (16.15 million) of the 17.9 million population relied on ground water for their drinking water needs. About 60 percent of the total ground water withdrawn in 2005 was obtained from the Floridan aquifer system; 19 percent was from the Biscayne aquifer. The remainder was withdrawn from the surficial aquifer systems (12 percent), the intermediate aquifer (6 percent), and the sand-and-gravel aquifer (3 percent). Most of the surface water withdrawn in Florida was from managed and maintained canal systems or large water bodies. More than 40 percent of the fresh surface water withdrawn was in southern Florida and is associated with irrigated sugarcane and vegetables acreage in the Lake Okeechobee and the Everglades Agricultural Area of Glades, Hendry, and Palm Beach Counties. Miami-Dade County withdrew the largest amount of fresh ground water, Palm Beach County withdrew the largest amount of fresh surface water in 2005.

Total water (fresh and saline) withdrawn in Florida increased 15,700 Mgal/d (600 percent) between 1950 and 2005, while the population of Florida increased by 15.15 million (550 percent). Between 1990 and 2005, total withdrawals increased 400 Mgal/d (2 percent) while the population increased 4.98 million (38 percent). Ground water withdrawn in 1950 was 614 Mgal/d, compared to 4,242 Mgal/d in 2005. Ground water was the primary source of freshwater in Florida between 1980 and 2005, supplying about 60 percent of the total freshwater withdrawn. Surface water withdrawn in 1950 was 840 Mgal/d, compared to 2,626 Mgal/d in 2005. Between 1950 and 1980, surface water was the primary source of freshwater in Florida, supplying more than one-half of the total freshwater withdrawn.

Contact Information: Richard Marella, U.S. Geological Survey, 2010 Levy Avenue, Tallahassee, FL 32310; phone: 850-942-9500 x3004; email: rmarella@usgs.gov

W. Scott McBride and Jason C. Bellino

U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida

Lake Panasoffkee is the largest body of water in the Withlacoochee River basin and is a major source of water to the Withlacoochee River. Diffuse ground-water seepage and spring flow have been estimated to account for roughly 40% and 35%, respectively, of total inflow. A cooperative study between the United States Geological Survey (USGS) and the Southwest Florida Water Management District (SWFWMD) is currently being conducted to assess and quantify the hydraulic connection between Lake Panasoffkee and the underlying Upper Floridan aquifer. The study will also refine an existing water budget by incorporating on-site estimates of evaporation and ground-water seepage.

The Ocala Platform is a major structural feature in the study area and has many associated faults and fractures that trend from northwest to southeast. It is thought that the location of Lake Panasoffkee is related to the preferential dissolution of limestone along these fractures. A seismic survey of the lake bottom was completed, but the results did not reveal any clear structural or karst features.

The two major surface water inflows to Lake Panasoffkee are Little Jones Creek and Shady Brook. Multiple springs of second- and third-order magnitude constitute the headwaters of both of these streams. The sole surface-water outflow from the lake is Outlet Canal, which drains from the western lake shore to the Withlacoochee River. Streamflow gaging stations have been established on these water bodies to measure daily discharge. An effort also has been made to measure ungaged over-land flow through swamplands adjacent to the lake.

A climatologic data collection raft was deployed over open water in the middle of Lake Panasoffkee to record wind speed and direction, relative humidity, lake temperature, and net solar radiation. These data will be used to quantify outflow from the lake through evaporation. A network of meteorological stations in the State provides data for estimating recharge to the lake through rainfall.

Surface- and ground-water quality are being characterized through analysis of major ions, selected nutrients and trace elements, stable isotopes of oxygen (18O/16O) and hydrogen (2H/1H), and strontium (87Sr/86Sr). The radiogenic Sr isotope ratio should provide some insight into the relative depths from which ground-water discharge is originating. Shallow ground water should have a significantly different signal than deeper ground water from the Tertiary carbonate Upper Floridan aquifer. The oxygen and hydrogen isotope analysis will help to determine the degree of ground-water and surface-water mixing.

Detailed maps of the potentiometric surface of the Floridan aquifer in the study area have been constructed during dry season (May) and wet season (September) conditions. Piezometers located around the lake measure the head gradient between the lake and the shallow ground-water system. Head gradients between the Floridan and surficial aquifer provide information on the potential for upward ground-water flow.

Contact Information: W. Scott McBride, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 33612; phone: 813-975-8620; email: wmcbride@usgs.gov

Scott Prinos, U.S. Geological Survey, Florida Integrated Science Center, Ft. Lauderdale, Florida

In southern Florida, the problem of aquifer contamination from encroaching seawater was caused by the construction of an extensive series of canals during the first quarter of the 20th century as well as groundwater withdrawals. The drainage through the canals was uncontrolled and resulted in water-level declines in local aquifers. Groundwater supply withdrawals near the coast exacerbated this situation by further reducing water levels in the aquifers. The reduced water levels in the aquifers allowed seawater to: (1) encroach along the bases of the aquifers, and (2) migrate inland long distances within unregulated canals and seep into the adjoining aquifers during periods of low rainfall and canal stage and flow.

As a result of unregulated drainage canals, aquifer withdrawals, and droughts, some public water supply well fields were contaminated by seawater and had to be either temporarily shut down or permanently abandoned. For example, the first public water supply well field of the City of Miami was contaminated by seawater in 1925 and was abandoned, and seawater from the Miami Canal contaminated some of the wells in the newly installed Hialeah-Miami Springs Well Field in 1939.

In 1939 the U.S. Geological Survey (USGS), began a cooperative effort with local government to evaluate saltwater intrusion that has aided water-management efforts to reduce and, in some areas, reverse seawater encroachment. In many locations, however, seawater continues to encroach inland or leak from canal systems into aquifers. This continued threat to water supply well fields will become even more serious if sea levels continue to rise. Cooperative network budgetary cuts, however, have reduced the number of monitoring sites by approximately one half within the last 13 years and more reductions are expected.

About two-thirds of the remaining 117 seawater-encroachment monitoring wells are located in Broward and Miami-Dade counties. Encroachment in other south Florida counties is not monitored sufficiently to provide adequate warning. The USGS is working with its cooperative partners in an effort to improve monitoring in areas where insufficient information exists for water-management decisions.

The USGS is mapping seawater encroachment using water quality sampling, electromagnetic induction profiling, ground and airborne Time Domain Electromagnetic Depth soundings, and continuous conductivity logging. Trends are being evaluated using various graphical and statistical approaches. Current studies also use borehole image processing, flow logging, and sequence stratigraphy.

Contact Information: Scott Prinos, U.S. Geological Survey, Florida Integrated Science Center, 3110 SW 9th Avenue, Ft. Lauderdale, FL 33315; phone: 954-377-5944; email: stprinos@usgs.gov

Nicasio Sepúlveda1 and Kevin Rohrer2

1 U.S. Geological Survey, Florida Integrated Science Center, Orlando, Florida
2 South Florida Water Management District, West Palm Beach, Florida

The permeability of the semiconfining layers of the highly productive Floridan Aquifer System may be large enough to invalidate the assumptions of the leaky aquifer theory. These layers are the intermediate confining and the middle semiconfining units. The analysis of aquifer-test data with analytical solutions of the ground-water flow equation developed with the approximation of a low hydraulic conductivity ratio between the semiconfining layer and the aquifer may lead to inaccurate hydraulic parameters. An analytical solution is presented here for the flow generated by a partially penetrating well in a leaky two-aquifer system. Flows in the confined leaky aquifer, the overlying storative semiconfining layer, and the unconfined aquifer are derived. Horizontal and vertical flow components are assumed in the semiconfining layer. The boundary-value problem describing is solved analytically to provide a method to accurately determine the hydraulic parameters in the confined aquifer, semiconfining layer, and unconfined aquifer from aquifer-test data. Analysis of the drawdown data from an aquifer test performed in central Florida showed that the flow solution presented here for the semiconfining layer provides a better match and a more unique identification of the hydraulic parameters than an analytical solution that considers only vertical flow in the semiconfining layer.

Contact Information: Nicasio Sepúlveda, U.S. Geological Survey, Florida Integrated Science Center, 12703 Research Parkway, Orlando, FL 32826; phone: 407-803-5528; email: nsepul@usgs.gov

Amy Swancar1 and David M. Sumner2

1 U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, Orlando, Florida

Evapotranspiration (ET) is a large, yet poorly quantified, part of the hydrologic cycle. The U. S. Geological Survey operates sites across Florida that measure ET over a variety of landscapes as part of a statewide ET network. Two of these sites, Ferris Farms in Floral City and Starkey Addition near Odessa, are in Bahia grass (Papsalum notatum Flugge) pastures. These two sites vary in depth to the water table. The water table at the Ferris Farms site is typically greater than 5 m deep and the water table at the Starkey site is typically less than 1 m deep. Because Bahia grass has roots only within about the top 0.5 m of soil, the location of the water table affects the ability of the grass to transpire. In addition, when the water table is at the surface, as sometimes occurs at the Starkey site, direct evaporation can occur. Bahia grass will go dormant during extended dry periods and during the winter months.

The combined effects of growth cycle, moisture availability, and energy input to the near-surface system control ET rates from pastures. Monthly rates between May 2003 and February 2005 ranged from 23 mm (Jan 2004) to 122 mm (June 2004) at the Starkey site, and from 19 to 97 mm at the Ferris Farms site for those same months. Monthly ET rates were consistently higher at the Starkey site except for July 2004, when ET at Ferris Farms was slightly higher (114 compared to 110 mm). Depending on water availability and the onset of the summer rainy season, peak ET occurs in June, if rains come early or if the water table is already elevated, or in July. Maximum incoming solar radiation, which ultimately drives ET, occurs in May. If water is not available, however, some energy is converted to sensible heat rather than latent heat (the energy equivalent of ET). In other words, energy goes into heating up the air rather than converting water from liquid to gas phase.

Annual ET rates at pastures in west-central Florida range from about 660 to 900 mm. As a percentage of annual rainfall, ET ranges from 46 to 88 percent, with the lower percentages corresponding to wetter years (rainfall exceeding 1600 mm). During droughts (annual rainfall less than 900 mm), annual ET from pastures in this area can be between 80 and 90 percent of rainfall, leaving little water to recharge surface- or ground-water systems.

Contact Information: Amy Swancar, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 33612; phone: 813-975-8620; email: aswancar@usgs.gov

Michael Wacker, U.S. Geological Survey, Florida Integrated Science Center, Fort Lauderdale, Florida

The borehole geophysical logging program at the U.S. Geological Survey-Florida Integrated Science Center (USGS-FISC) provides data to scientists and managers needed to resolve geologic, hydrologic, and environmental issues in Florida. The program includes the acquisition, processing, display, interpretation, and archiving of borehole geophysical data. Additionally, USGS-FISC can address a wide range of water issues in Florida using other USGS borehole, and land- and water-based near-surface geophysical tools available through the USGS Branch of Geophysics.

Although most borehole geophysical log acquisition is performed from a vehicle, equipment portability also provides for easy transport to remote well sites, such as those located in offshore marine or wetland environments. Well depths up to 3,280 ft and well diameters greater than 2 inches can be accommodated, providing access to all major aquifers in Florida, including much of the Floridan aquifer system.

In addition to acquiring standard borehole log data such as caliper, gamma, spontaneous potential, and electromagnetic induction, USGS-FISC utilizes new technologies and procedures to generate non-standard logs. An OBI-40 Mark IVTM optical televiewer is equipped with a high-resolution digital camera that creates a detailed 360-degree image of the borehole wall. The OBI-40TM digital borehole image can be used for: (1) accurate placement of well completion intervals, (2) positioning recovered core to its exact depth, (3) acquisition of a high-resolution borehole image that serves as a surrogate over those intervals having no core recovery, and (4) characterizing the pore system of aquifers. Fracture and bedding plane orientations can also be determined, as borehole images are oriented to the magnetic north pole. In combination with our new MATRIXTM log acquisition system, a digital borehole image can be acquired at relatively high logging speeds (about 3 to 15 ft/min, depending on desired pixel density).

Log presentation software (WellCADTM) is routinely used by USGS-FISC personnel to create 36-in wide, multilog, paper displays, that also can be viewed on a computer monitor using non-proprietary software readers (for example, Adobe AcrobatTM or WellCADTM Reader). The USGS-FISC also provides assistance with importing borehole images and logs into reports. Other log processing and display software, such as ViewlogTM and LogCruncherTM are also available.

In addition to logging, USGS-FISC provides interpretive reports for recovered cores as well as construction of conceptual hydrostratigraphic frameworks. Planning, management, and analysis of tracer, aquifer performance, and other hydrologic tests are also available. Further assistance is available from USGS assets nationwide to assist in solution of any hydrologic problem.

Contact Information: Michael Wacker, U.S. Geological Survey, Florida Integrated Science Center, 3110 SW 9th Avenue, Ft. Lauderdale, FL 33315; phone: 954-377-5949; email: mwacker@usgs.gov