Geology topics

D. K. Yobbi

Publications and source records attributed to D. K. Yobbi.

16 recordsLinked to original sources

USGS2009

Surface-Water and Groundwater Interactions along the Withlacoochee River, West-Central Florida

A study of the Withlacoochee River watershed in west-central Florida was conducted from October 2003 to March 2007 to gain a better understanding of the hydrology and surface-water and groundwater interactions along the river. The Withlacoochee River originates in the Green Swamp area in north-central Polk County and flows northerly through seven counties, emptying into the Gulf of Mexico. This study includes only the part of the watershed located between the headwaters in the Green Swamp and the U.S. Geological Survey gaging station near Holder, Florida. The Withlacoochee River within the study area is about 108 miles long and drains about 1,820 square miles. The Withlacoochee River watershed is underlain by thick sequences of carbonate rock that are covered by thin surficial deposits of unconsolidated sand and sandy clay. The clay layer is breached in many places because of the karst nature of the underlying limestone, and the degree of confinement between the Upper Florida aquifer and the surficial aquifer is highly variable throughout the watershed. The potential for movement of water from the surface or shallow deposits to deeper deposits, or from deeper deposits to the shallow deposits, exists throughout the Withlacoochee River watershed. Water levels were higher in deeper Upper Floridan aquifer wells than in shallow Upper Floridan aquifer wells or surficial aquifer wells at 11 of 19 paired or nested well sites, indicating potential for discharge to the surface-water system. Water levels were higher in shallow Upper Floridan aquifer or surficial aquifer wells than in deeper Upper Floridan aquifer wells at five other sites, indicating potential for recharge to the deeper Upper Floridan aquifer. Water levels in the surficial aquifer and Upper Floridan aquifer wells at the remaining three sites were virtually the same, indicating little or no confinement at the sites. Potentiometric-surface maps of the Upper Floridan aquifer indicate the pattern of groundwater flow in the aquifer did not vary greatly from season to season during the study. Potentiometric contours indicate groundwater discharge to the river in the vicinity of Dade City and Lake Panasoffkee. During dry periods, groundwater from the underlying Upper Floridan aquifer contributed to the flow in the river. During wet periods, streamflow had additional contributions from runoff and input from tributaries. Groundwater has a greater effect on streamflow downstream from the Dade City station than upstream from the Dade City station because confinement between surficial deposits and the Upper Floridan aquifer is greater in the Green Swamp area than in downstream areas. Estimates of streamflow gains and losses were made along the Withlacoochee River during base-flow conditions in May 2004, April 2005, and April 2006. Base flow was higher in April 2005 than in May 2004 and April 2006. Consistent net seepage gains were identified in 16 of 20 subreaches analyzed during all seepage runs. The direction of exchange was variable in the remaining four subreaches. Low specific conductance, pH, and calcium concentrations in water from the Withlacoochee River near the headwater area indicated a surface-water system not directly connected to the Upper Floridan aquifer. Downstream from the Dade City station, higher specific conductance, pH, and calcium concentrations in the river water indicated an increasing influence of groundwater, and were similar to groundwater during low-flow conditions. Strontium isotope ratios indicate groundwater originates from shallow parts of the Upper Floridan aquifer in the upper reaches of the river, and from increasingly deeper parts of the aquifer in the downstream direction. Mean annual base-flow estimates also indicate increasing groundwater discharge to the river in the downstream direction. Mean annual base flow estimated using standard hydrograph separation method assumptions ranged from about 4.7 to 5.1 inches per year

Scientific Investigations Report↗

USGS2001

Hydrogeologic framework and geochemistry of the intermediate aquifer system in parts of Charlotte, De Soto, and Sarasota counties, Florida

The hydrogeologic framework underlying the 600-square-mile study area in Charlotte, De Soto, and Sarasota Counties, Florida, consists of the surficial aquifer system, the intermediate aquifer system, and the Upper Floridan aquifer. The hydrogeologic framework and the geochemical processes controlling ground-water composition were evaluated for the study area. Particular emphasis was given to the analysis of hydrogeologic and geochemical data for the intermediate aquifer system. Flow regimes are not well understood in the intermediate aquifer system; therefore, hydrogeologic and geochemical information were used to evaluate connections between permeable zones within the intermediate aquifer system and between overlying and underlying aquifer systems. Knowledge of these connections will ultimately help to protect ground-water quality in the intermediate aquifer system. The hydrogeology was interpreted from lithologic and geophysical logs, water levels, hydraulic properties, and water quality from six separate well sites. Water-quality samples were collected from wells located along six ground-water flow paths and finished at different depth intervals. The selection of flow paths was based on current potentiometric-surface maps. Ground-water samples were analyzed for major ions; field parameters (temperature, pH, specific conductance, and alkalinity); stable isotopes (deuterium, oxygen-18, and carbon-13); and radioactive isotopes (tritium and carbon-14). The surficial aquifer system is the uppermost aquifer, is unconfined, relatively thin, and consists of unconsolidated sand, shell, and limestone. The intermediate aquifer system underlies the surficial aquifer system and is composed of clastic sediments interbedded with carbonate rocks. The intermediate aquifer system is divided into three permeable zones, the Tamiami/Peace River zone (PZ1), the Upper Arcadia zone (PZ2), and the Lower Arcadia zone (PZ3). The Tamiami/Peace River zone (PZ1) is the uppermost zone and is the thinnest and generally, the least productive zone in the intermediate aquifer system. The Upper Arcadia zone (PZ2) is the middle zone and productivity is generally higher than the overlying permeable zone. The Lower Arcadia zone (PZ3) is the lowermost permeable zone and is the most productive zone in the intermediate aquifer system. The intermediate aquifer system is underlain by the Upper Floridan aquifer, which consists of a thick, stratified sequence of limestone and dolomite. The Upper Floridan aquifer is the most productive aquifer in the study area; however, its use is generally restricted because of poor water quality. Interbedded clays and fine-grained clastics separate the aquifer systems and permeable zones. The hydraulic properties of the three aquifer systems are spatially variable. Estimated trans-missivity and horizontal hydraulic conductivity varies from 752 to 32,900 feet squared per day and from 33 to 1,490 feet per day, respectively, for the surficial aquifer system; from 47 to 5,420 feet squared per day and from 2 to 102 feet per day, respectively, for the Tamiami/Peace River zone (PZ1); from 258 to 24,633 feet squared per day and from 2 to 14 feet per day, respectively, for the Upper Arcadia zone (PZ2); from 766 to 44,900 feet squared per day and from 10 to 201 feet per day, respectively, for the Lower Arcadia zone (PZ3); and from 2,350 to 7,640 feet squared per day and from 10 to 41 feet per day, respectively, for the Upper Floridan aquifer. Confining units separating the aquifer systems have leakance coefficients estimated to range from 2.3 x 10-5 to 5.6 x 10-3 feet per day per foot. Strata composing the confining unit separating the Upper Floridan aquifer from the intermediate aquifer system are substantially more permeable than confining units separating the permeable zones in the intermediate aquifer system or separating the surficial aquifer and intermediate aquifer systems. In Charlotte, Sarasota, and western De Soto Counties, hydraulic

Water-Resources Investigations Report↗

USGS2000

Application of nonlinear least-squares regression to ground-water flow modeling, west-central Florida

A nonlinear least-squares regression technique for estimation of ground-water flow model parameters was applied to an existing model of the regional aquifer system underlying west-central Florida. The regression technique minimizes the differences between measured and simulated water levels. Regression statistics, including parameter sensitivities and correlations, were calculated for reported parameter values in the existing model. Optimal parameter values for selected hydrologic variables of interest are estimated by nonlinear regression. Optimal estimates of parameter values are about 140 times greater than and about 0.01 times less than reported values. Independently estimating all parameters by nonlinear regression was impossible, given the existing zonation structure and number of observations, because of parameter insensitivity and correlation. Although the model yields parameter values similar to those estimated by other methods and reproduces the measured water levels reasonably accurately, a simpler parameter structure should be considered. Some possible ways of improving model calibration are to: (1) modify the defined parameter-zonation structure by omitting and/or combining parameters to be estimated; (2) carefully eliminate observation data based on evidence that they are likely to be biased; (3) collect additional water-level data; (4) assign values to insensitive parameters, and (5) estimate the most sensitive parameters first, then, using the optimized values for these parameters, estimate the entire data set.

Water-Resources Investigations Report↗

USGS1997

Simulation of subsurface storage and recovery of effluent using multiple wells, St Petersburg, Florida

The potential for subsurface storage and recovery, otherwise called aquifer storage and recovery, of effluent in the uppermost producing zone of the Upper Floridan aquifer in St. Petersburg, Florida, was studied by the U.S. Geological Survey, in cooperation with the city of St. Petersburg and the Southwest Florida Water Management District. The success of subsurface storage and recovery depends on the recovery efficiency, or the quantity of water, relative to the quantity injected, that can be recovered before the water that is withdrawn fails to meet salinity limits. The viability of this practice will depend upon the ability of the injected zone to receive, store, and discharge the injected fluid. A three-dimensional numerical model of ground-water flow and solute transport, incorporating available data on aquifer properties and water quality, was developed to evaluate the effects of changing various operational factors on recovery efficiency. The reference case for testing was a base model considered representative of the aquifer system underlying the Southwest St. Petersburg Water Treatment Facility. The base simulation used as a standard for comparison consisted of a single cycle of 90 days of simultaneous injection of effluent in three wells at a rate of 4.0 million gallons per day and then equal rate withdrawal of 4.0 million gallons per day until the pumped water in each well reached a dissolvedsolids concentration of 1,500 milligrams per liter. A recovery efficiency of 14.8 percent was estimated for the base simulation. Ten successive injection and recovery cycles increased recovery efficiency to about 56 percent. Based on model simulations for hypothetical conditions, recovery efficiency (1) increased with successive injection and recovery cycles; (2) increased when the volume of injectant increased; (3) decreased when storage time increased; (4) did not change significantly when the injection rate or recovery rate increased, or when the ratio of recovery rate to injection rate increased, and (5) was not significantly affected by any particular geometric arrangement of wells or by the number of wells when the volume of water injected remained constant. Recovery efficiency from multiple wells was nearly the same as from a single well. Recovery efficiency ranged from about 7 to 56 percent, in several tests. Sensitivity of recovery efficiency to variations in selected parameters such as dissolved-solids concentration of the injection zone, permeability, vertical anisotropy, longitudinal and transverse dispersivities, and effective porosity was tested. Changes in the dissolved-solids concentration of the injection zone produced the greatest change in recovery efficiency. Uniform changes in dispersivity values produced the second greatest change in recovery efficiency. Generally, recovery efficiency increased when the above parameter values were decreased and recovery efficiency decreased when these parameter values were increased. Density difference between native and injected waters was the most important factor affecting recovery efficiency in this study. For the base simulation, sensitivity tests indicated that recovery efficiency increased from about 15 to 78 percent when the dissolved-solids concentration of the native water decreased from about 7,800 to 500 milligrams per liter. Dispersivity is another important factor affecting recovery efficiency. For the base simulation, sensitivity tests indicated that recovery efficiencies from about 9 to 24 percent can be obtained for different dispersivity values. A field determination of dispersivity was not made as part of this study, and values used may not be representative of the actual dispersive characteristics of the aquifer system at the study site. However, dispersivity values tested are within the range of values used in previous studies.

Water-Resources Investigations Report↗

USGS1996

A guide to safe field operations

Most functions of the U.S. Geological Survey (USGS), Water Resources Division (WRD) require employees to participate in numerous field activities ranging from routine meetings with cooperators, other federal and public officials, and private citizens to potentially hazardous assignments, such as making flood measurements and scuba diving to service underwater instruments. It is paramount that each employee be aware of safety procedures and operational policies of the WRD to ensure that (1) their activities avoid or minimize personal injury to the employee, coworkers, or anyone in the vicinity of the field activity, and (2) their conduct does not infringe on the personal or property rights of any individual or organization. The purpose of the guide is to familiarize employees with the operational and safety procedures expected to be followed by each employee as a representative of the WRD. It is also intended as a training tool for all new employees and a document to be reviewed by each employee before undertaking a field assignment. It includes general procedures that are standard and applicable to all field operations, such as communication, vehicle operation, and adequate preparation for anticipated weather conditions. It also includes a discussion of specific procedures and safety considerations for most of the routine field assignments undertaken by hydrologists and hydrologic technicians of the WRD. The guide is not intended to be a technical handbook outlining step-by-step procedures for performing specific tasks or a comprehensive discussion of every possible activity that may be undertaken by a USGS employee. Employees are referred to the Techniques for Water-Resources Investigations (TWRI) series for specific technical procedures and to the U.S. Geological Survey Safety and Environmental Health Handbook 445-1-H (USGS, August 1989), USGS Occupational Hazards and Safety Procedures Handbook 445-2-H (December 1993), the WRD notebook on Safety Policy and Guidance Memoranda, and other references for procedures and safety issues related to nonroutine activities, such as operations on large vessels and aircraft.

Open-File Report↗

USGS1996

Simulation of subsurface storage and recovery of treated effluent injected in a saline aquifer, St. Petersburg, Florida

The potential for subsurface storage and recovery of treated effluent into the uppermost producing zone (zone A) of the Upper Floridan aquifer in St. Petersburg, Florida, is being studied by the U.S. Geological Survey, in cooperation with the city of St. Petersburg and the Southwest Florida Water Management District. A measure of the success of this practice is the recovery efficiency, or the quantity of water relative to the quantity injected, that can be recovered before the water that is withdrawn fails to meet water-quality standards. The feasibility of this practice will depend upon the ability of the injected zone to receive, store, and discharge the injected fluid. A cylindrical model of ground-water flow and solute transport, incorporating available data on aquifer properties and water quality, was developed to determine the relation of recovery efficiency to various aquifer and fluid properties that could prevail in the study area. The reference case for testing was a base model considered representative of the saline aquifer underlying St. Petersburg. Parameter variations in the tests represent possible variations in aquifer conditions in the area. The model also was used to study the effect of various cyclic injection and withdrawal schemes on the recovery efficiency of the well and aquifer system. A base simulation assuming 15 days of injection of effluent at a rate of 1.0 million gallons per day and 15 days of withdrawal at a rate of 1.0 million gallons per day was used as reference to compare changes in various hydraulic and chemical parameters on recovery efficiency. A recovery efficiency of 20 percent was estimated for the base simulation. For practical ranges of hydraulic and fluid properties that could prevail in the study area, the model analysis indicates that (1) the greater the density contrast between injected and resident formation water, the lower the recovery efficiency, (2) recovery efficiency decreases significantly as dispersion increases, (3) high formation permeability favors low recovery efficiencies, and (4) porosity and anisotropy have little effect on recovery efficiencies. In several hypothetical tests, the recovery efficiency fluctuated between about 4 and 76 percent. The sensitivity of recovery efficiency to variations in the rate and duration of injection (0.25, 0.50, 1.0, and 2.0 million gallons per day) and withdrawal cycles (60, 180, and 365 days) was determined. For a given operational scheme, recovery efficiency increased as the injection and withdrawal rate is increased. Model results indicate that recovery efficiencies of between about 23 and 37 percent can be obtained for different subsurface storage and recovery schemes. Five successive injection, storage, and recovery cycles can increase the recovery efficiency to about 46 to 62 percent. There is a larger rate of increase at smaller rates than at larger rates. Over the range of variables studied, recovery efficiency improved with successive cycles, increasing rapidly during initial cycles tyhen more slowly at later cycles. The operation of a single well used for subsurface storage and recovery appears to be technically feasible under moderately favorable conditions; however, the recovery efficiency is higly dependent upon local physical and operational parameters. A combination of hydraulic, chemical, and operational parameters that minimize dispersion and buoyancy flow, maximizes recovery efficiency. Recovery efficiency was optimal where resident formation water density and permeabilities were relatively similar and low.

Water-Resources Investigations Report↗

USGS1989

Simulation of steady-state ground water and spring flow in the upper Floridan aquifer of coastal Citrus and Hernando Counties, Florida

A digital groundwater flow model was developed to approximate steady-state predevelopment flow conditions in the Upper Floridan aquifer of coastal west-central Florida. The aquifer is the major source of water and natural spring flow in the area. The aquifer was simulated as a one-layer system with constant vertical recharge and discharge rates. Calibrated transmissivities ranged from 8,640 sq ft/day in the northern part of the area to nearly 13,000,000 sq ft/day near large springs. Calibrated inflows were about 2,708 cu ft/sec; of this, about 2,565 cu ft/sec discharged as natural spring flow and 137 cu ft/sec discharged as upward leakage along the coast. The model was used to show how the system might respond to large manmade stresses. Withdrawal of 116 cu ft/sec from a hypothetical regional well field resulted in potentiometric-surface drawdowns ranging from 0.1 to 1.7 ft and declines of generally less than 0.2 ft along the coast. Total spring flow decreased 5%, and the effect on individual springs varied from 0.1 to 8.0%. Withdrawal of 62 cu ft/sec from the 4-sq-mi node at each spring resulted in six of seven springs to the south of the Chassahowitzka River contributing 50% of their flow to pumpage. Springs located north of the Chassahowitzka River contributed as much as 18% of their flow to pumpage. (USGS)

Water-Resources Investigations Report↗

USGS1989

Effects of river discharge and high-tide stage on salinity intrusion in the Weeki Wachee, Crystal, and Withlacoochee River estuaries, southwest Florida

The Weeki Wachee, Crystal, and Withlacoochee Rivers are coastal streams flowing into the Gulf of Mexico that may be affected by either future surface water or groundwater withdrawals. Reduction of river discharge will affect the upstream extent of saltwater intrusion in the rivers; however, under certain reduced low-flow discharges, the estimated change in upstream extent of saltwater intrusion is on the order of several tenths of a mile and frequently is within the range of predicted error. Data on flow, tides, and salinity describe the physical characteristics of the Weeki Wachee, Crystal, and Withlacoochee River systems. Vertical and longitudinal salinity profiles indicate that salinity of the rivers increases downstream and varies substantially at any given location. The Weeki Wachee River system is the best mixed of the three. The Crystal River system exhibited the next best mixed system, and the Withlacoochee River system exhibited the most variation in its salinity regime. The daily maximum upstream extent of salinity intrusion is described by multiple linear-regression analysis based on daily mean streamflow of each river and high-tide stage of the gulf. The equations are used to show the effects of discharge on the daily maximum upstream extent of salinity intrusion in the rivers.

Florida↗

USGS1983

Trends and fluctuations in the potentiometric surface of the Floridan aquifer, west-central Florida 1961-80

Trends and fluctuations of water levels in wells tapping the Floridan aquifer in west-central Florida during 1961-80 are described in this report. Water levels in most of the study area have not changed appreciably, except in parts of Hardee, Hillsborough, Manatee, Polk, and Sarasota Counties. In these areas, ground-water pumpage by industry and agriculture caused long-term declines of water levels. The largest declines are centered in the agricultural area of southern Hillsborough and northern Manatee Counties where pumpage lowered water levels more than 30 feet since 1964. Hydrographs of 10 wells show that, during 1976-80, the downward water-level trend discontinued in areas of heavy pumpage and, in areas not affected by pumping, water levels remained fairly unchanged. Water levels rose more than 20 feet from May 1975 to May 1980 in southwest Polk, Hardee , northeast Sarasota, northeast Manatee, and southwest Hillsborough Counties. In the heavily pumped area of northern Hillsborough County, water levels rose 5 to 10 feet. From September 1975 to September 1980, water levels in southwest Polk County rose more than 10 feet. (USGS)

Florida↗

USGS1982

Ground-water levels in selected well fields and in west-central Florida, September 1981

The water table in the surficial aquifer and the potentiometric surface of the Floridan aquifer in a 1,200-square-mile area in west-central Florida are mapped semiannually by the U.S. Geological Survey. Maps are based on water levels measured in wells each May to coincide with seasonal low levels and each September to coincide with seasonal high levels. The mapped area shows 14 well fields that supplied 140.3 million gallons to municipalities on September 21, 1981. The water is withdrawn from the Floridan aquifer, the major aquifer in Florida. The effect of localized withdrawal on ground water is shown on the maps as depressions in both the potentiometric and water-table surfaces. In September 1981, ground-water levels were significantly higher than those of May 1981 and were unchanged or within a few feet of those in September 1980. Seasonal recharge from summer rains and reduced pumpage are factors in the water-level recovery from record and near record low levels of May 1981. (USGS)

Open-File Report↗

USGS1981

Potentiometric surface of the Floridan Aquifer, Southwest Florida Water Management District, May 1981

A May 1981 potentiometric-surface map of the Southwest Florida Water Management District depicts the annual low water-level period. Potentiometric levels decreased 10 to 45 feet between September 1980 and May 1981 in the citrus and farming sections of southern Hillsborough, northern Hardee, southwestern Polk, northwestern DeSoto, and Manatee Counties. Water levels in these areas are widely affected by pumping for irrigation and have the greatest range in fluctuations. Water-level decreases ranged from 0 to 1 feet in coastal, northern, and southern areas of the Water Management District. Water levels in all of the approximate 700 wells measured in May 1981 are lower than May 1980 because of the virtual absence of rainfall in April and May. (USGS)

Open-File Report↗

USGS1981

Ground-water levels in selected well fields and in west-central Florida, May 1981

The water table in the surficial aquifer and the potentiometric surface of the Floridan aquifer in a 1,200-square-mile area in west-central Florida are mapped semi-annually by the U.S. Geological Survey. Maps are based on water levels measured in wells each May to coincide with seasonal low levels and each September to coincide with seasonal high levels. The mapped area shows 14 well fields that supplied 200.7 million gallons to municipalities on May 18, 1981. The water is withdrawn from the Floridan aquifer, the major aquifer in Florida. The effect of localized withdrawal on ground water is shown on the maps as depressions in both the potentiometric and water-table surfaces. Water levels were lower in May 1981 than in May and September 1980. Annual change of water levels ranged from decreases of 19 feet at Sun City well field to less than 1 foot at Eldridge-Wilde well field. (USGS)

Open-File Report↗

USGS1980

Potentiometric surface of the Floridan Aquifer, Southwest Florida Water Management District, September 1980

A September 1980 potentiometric-surface map of the Southwest Florida Water Management District depicts the annual high water-level period. Potentiometric levels rose 1 to 31 feet between May 1980 and September 1980 in the citrus and farming sections of southern Hillsborough, northern Hardee, southwestern Polk, northwestern DeSoto, and Manatee Counties. Water levels in these areas are widely affected by reduced pumping for irrigation and have the greatest range in fluctuations. Generally, potentiometric levels were lower than previous September levels except in Citrus, eastern Levy, and western Marion Counties where levels were 0 to 8 feet higher. (USGS)

Open-File Report↗

USGS1980

Ground-water levels in selected well fields and in west-central Florida, September 1980

The water table in the surficial aquifer and the potentiometric surface of the Floridan aquifer in a 1,200-square-mile area in west-central Florida are mapped semiannually by the U.S. Geological Survey. Maps are based on water levels measured in wells each May to coincide with seasonal low levels and each September to coincide with seasonal high levels. The mapped area shows 14 well fields that supplied 141.8 million gallons to municipalities on September 18, 1980. The water is withdrawn from the Floridan aquifer, the major aquifer in Florida. The effect of localized withdrawal of ground water is shown on the maps as depressions in both the potentiometric and water-table surfaces. Potentiometric levels in the Floridan aquifer were higher in September 1980 than in May 1980 and generally lower than in September 1979. Annual change of water levels ranged from a decrease of 6 feet at Morris Bridge well field to an increase of 2 feet at Eldridge-Wilde well field. (USGS)

Open-File Report↗

USGS1979

Water table in the surficial aquifer and potentiometric surface of the Floridan Aquifer in selected well fields, west-central Florida, May 1979

The water table is the surficial aquifer and the potentiometric surface of the Floridan aquifer in a 1,200-square-mile area in west-central Florida are mapped semiannually by the U.S. Geological Survey. Maps are prepared showing water levels measured in wells each May to coincide with seasonal low levels, and each September to coincide with seasonal high levels. The mapped area shows 16 well fields which supplied 128 million gallons to municipalities on May 15, 1979. The water is withdrawn from the Floridan aquifer, the major aquifer in Florida. Water levels were significantly higher in May 1979 than in May 1978. Heavy rains on May 7 and 8th deluged the well-field areas with 2 to 18 inches of rain. The maximum increase in water levels from May 1978 to May 1979 was more than 8 feet at the Eldridge-Wilde well field. (USGS)

Open-File Report↗

USGS1979

Potentiometric surface of the Floridan Aquifer, Southwest Florida Water Management District, September 1979

A September 1979 potentiometric-surface map of the Southwest Florida Water Management District depicts the annual high water-level period. Potentiometric levels increased 1 to 20 feet between May 1979 and September 1979, in the citrus and farming sections of southern Hillsborough, northern Hardee, southwestern Polk, northwestern DeSoto, and Manatee Counties. Water levels in these areas are widely affected by pumping for irrigation and have the greatest range in fluctuations. Water-level increases ranged from 0 to 7 feet in coastal, northern, and southern areas of the Water Management District. Generally, potentiometric levels were higher than previous September levels due to heavy rains in August and September. (USGS)

Open-File Report↗