Search USGS⌕ Search

SEARCH · Search USGS

Results for “Scientific Monthly”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
USGS2018

The Ozark Plateaus Regional Aquifer Study—Documentation of a groundwater-flow model constructed to assess water availability in the Ozark Plateaus

Recent short-term drought conditions have emphasized the need to better understand the delicate balance between abundance, sustainability, and scarcity of groundwater in the Ozark Plateaus aquifer system. In 2014, the U.S. Geological Survey began construction of a groundwater-flow model as a tool for the assessment of groundwater availability in the Ozark Plateaus aquifer system. The model was developed to benefit concurrent and future investigations involving groundwater-pumping scenarios, optimization, particle transport, and groundwater-monitoring network analysis. The groundwater model simulates 116 years (1900–2015) of hydrologic conditions and the response of the groundwater system to changes in stress including changes in recharge and groundwater pumping for water supply. Semiseasonal stress periods were simulated from the later part of 1991 to 2015 and represent higher demand and lower recharge in the spring and summer months and lower demand and higher recharge in the fall and winter months. Groundwater pumping increases throughout the simulation period with a maximum rate of about 600 million gallons per day (Mgal/d). The process of matching historical hydrologic data for the Ozark Plateaus aquifer system model was accomplished by a combination of manual changes to parameter values and automated calibration methods. Observation data used in the development and evaluation of the model included 19,045 hydraulic-head observations from 6,683 wells within the model area. Observation data also included stream leakage estimates summed to calculate a net gain or net loss value for approximately 81 named streams. The majority (mean of over 95 percent) of the recharge component is discharged through streams simulated in the model. The total simulated discharge to streams fluctuates seasonally between 7,500 and 17,500 Mgal/d with a mean outflow of 11,500 Mgal/d. Much of the remaining balance between modeled recharge inflows and stream outflows is made up by water moving into or out of storage in the aquifer system resulting in changes in modeled groundwater levels. The goal of the model was to develop a model capable of suitable accuracy at regional scales. The intent was not to reproduce individual local-scale details, which are typically not possible given the uniform cell size of 1 square mile. Although the model may not represent each local-scale detail, the model can be applied for a better understanding of the regional flow system and to evaluate responses to changes in climate and groundwater pumping.

Ozark Plateaus aquifer system↗
USGS2008

Methods for and estimates of 2003 and projected water use in the Seacoast Region, Southeastern New Hampshire

New methods were developed to estimate water use in 2003 and future water demand in 2017 and 2025 in the Seacoast region in southeastern New Hampshire, which has experienced a 37-percent population increase during 1980 to 2000. Water-use activities for which estimates were developed include water withdrawal, delivery, demand, consumptive use, release, return flow, and transfer by registered and aggregated unregistered (less than 20,000 gallons per day (gal/d)) users at the census-block and town scales. Estimates of water use rely on understanding what influences water demand and its associated consumptive use, because changes in demand and consumptive use affect withdrawal and return flow. Domestic water demand was estimated using a per capita water demand model that related metered deliveries to domestic users with census block and block-group data. The model was used to predict annual, summer, and winter per capita water-demand coefficients for each census block. Significant predictors of domestic water demand include population per housing unit, median value of owner-occupied single family homes, median year of housing construction (with 1900 as the base value), population density, housing unit density, and proportion of housing units that are in urban areas. Mean annual domestic per capita water-demand coefficient in the Seacoast region was 75 gal/d; the coefficient increased to 91 gal/d during the summer and decreased to 65 gal/d during the winter. Domestic consumptive use was estimated as the difference between annual and winter domestic water demand. Estimates of commercial and industrial water demand were based on coefficients derived from reported use and metered deliveries. Projections of water demand in 2017 and 2025 were determined by using the housing and employee projections for those years developed through a Transportation Demand Model and applying current domestic and non-domestic coefficients. Water demand in 2003 was estimated as 25.8 million gallons per day (Mgal/d), 35 percent of which was during the summer months of June, July, and August. Domestic water demand was 18.6 Mgal/d (72 percent), commercial water demand was 3.7 Mgal/d (14 percent), industrial water demand was 2.9 Mgal/d (11 percent), irrigation water demand was 0.3 Mgal/d (1 percent), and mining and aquaculture water demand was 0.2 Mgal/d (1 percent). Domestic consumptive use for the Seacoast region was 16 percent of domestic water demand, which translates to a loss of 3 Mgal/d over the entire Seacoast region. In 2003, water withdrawal was 771.2 Mgal/d, of which 742.2 Mgal/d was instream use for hydroelectric power generation and thermoelectric power cooling. The remaining 29.0 Mgal/d was withdrawn by community water systems (22.6 Mgal/d; 72 percent), domestic users (6.4 Mgal/d; 21 percent), commercial users (1.0 Mgal/d; 3 percent), industrial users (1.0 Mgal/d; 3 percent), irrigation (0.2 Mgal/d; 1 percent) and other users (less than 0.1 Mgal/d). Return flow for 2003 was 772.2 Mgal/d, of which 742.0 Mgal/d was returned following use for hydroelectric power generation and thermoelectric plant cooling. The remaining 30.2 Mgal/d was returned by community wastewater systems (20.2 Mgal/d; 68 percent), domestic users (7.8 Mgal/d; 26 percent), commercial users (1.2 Mgal/d; 3 percent), industrial users (0.8 Mgal/d; 3 percent), and other users (0.1 Mgal/d). Domestic water demand is projected to increase by 54 percent to 28.7 Mgal/d from 2003 to 2025 based on projection of future population growth. Non-domestic (commercial, industrial, irrigation, and mining) water demand is projected to increase by 66 percent to 11.8 Mgal/d from 2003 to 2025.

Scientific Investigations Report↗
USGS2006

A Streamflow Statistics (StreamStats) Web Application for Ohio

A StreamStats Web application was developed for Ohio that implements equations for estimating a variety of streamflow statistics including the 2-, 5-, 10-, 25-, 50-, 100-, and 500-year peak streamflows, mean annual streamflow, mean monthly streamflows, harmonic mean streamflow, and 25th-, 50th-, and 75th-percentile streamflows. StreamStats is a Web-based geographic information system application designed to facilitate the estimation of streamflow statistics at ungaged locations on streams. StreamStats can also serve precomputed streamflow statistics determined from streamflow-gaging station data. The basic structure, use, and limitations of StreamStats are described in this report. To facilitate the level of automation required for Ohio's StreamStats application, the technique used by Koltun (2003)1 for computing main-channel slope was replaced with a new computationally robust technique. The new channel-slope characteristic, referred to as SL10-85, differed from the National Hydrography Data based channel slope values (SL) reported by Koltun (2003)1 by an average of -28.3 percent, with the median change being -13.2 percent. In spite of the differences, the two slope measures are strongly correlated. The change in channel slope values resulting from the change in computational method necessitated revision of the full-model equations for flood-peak discharges originally presented by Koltun (2003)1. Average standard errors of prediction for the revised full-model equations presented in this report increased by a small amount over those reported by Koltun (2003)1, with increases ranging from 0.7 to 0.9 percent. Mean percentage changes in the revised regression and weighted flood-frequency estimates relative to regression and weighted estimates reported by Koltun (2003)1 were small, ranging from -0.72 to -0.25 percent and -0.22 to 0.07 percent, respectively.

Scientific Investigations Report↗
USGS2015

Hydrology of the middle San Pedro area, southeastern Arizona

In the middle San Pedro Watershed in southeastern Arizona, groundwater is the primary source of water supply for municipal, domestic, industrial, and agricultural use. The watershed comprises two smaller subareas, the Benson subarea and the Narrows-Redington subarea. Early 21st century projections for heavy population growth in the watershed have not yet become a reality, but increased groundwater withdrawals could have undesired consequences - such as decreased base flow to the San Pedro River, and groundwater-level declines - that would lead to the need to deepen existing wells. This report describes the hydrology, hydrochemistry, water quality, and development of a groundwater budget for the middle San Pedro Watershed, focusing primarily on the elements of groundwater movement that could be most useful for the development of a groundwater model Precipitation data from Tombstone, Arizona, and base flow at the stream-gaging station on the San Pedro River at Charleston both show relatively dry periods during the 1960s through the mid-1980s and in the mid-1990s to 2009, and wetter periods from the mid-1980s through the mid-1990s. Water levels in four out of five wells near the mountain fronts show cyclical patterns of recharge, with rates of recharge greatest in the early 1980s through the mid-1990s. Three wells near the San Pedro River recorded their lowest levels during the 1950s to the mid-1960s. The water-level record from one well, completed in the confined part of the coarse-grained lower basin fill, showed a decline of approximately 21 meters. Annual flow of the San Pedro River, measured at the Charleston and Redington gages, has decreased since the 1940s. The median annual streamflow and base flow at the gaging station on the river near Tombstone has decreased by 50 percent between the periods 1968–1986 and 1997–2009. Estimates of streamflow infiltration along the San Pedro River during 1914–2009 have decreased 44 percent, with the largest decreases in the months June–October in the Benson subarea. In the Narrows-Redington subarea, streamflow infiltration has decreased about 65 percent during 1914–2009. The average annual outflow (27.6 hm 3 /year [cubic hectometers per year]) from the Benson subarea aquifer for water years 2001 through 2009 exceeded the inflows (20.0 hm 3 / yr) by 7.60 hm 3 /yr. In the Narrows-Redington subarea for the same period, the average annual outflow (15.7 hm 3 /yr) from the aquifer system exceeded the inflows (13.8 hm 3 /yr) by nearly 2 hm 3 /yr. The largest withdrawals of groundwater in both subareas are for irrigation; these withdrawals peaked in 1973 and have been steadily decreasing since then. Recharge from streamflow infiltration exceeded recharge from the mountain-front and from ephemeral channels in the Benson subarea. In the Narrows-Redington subarea, however, recharge from mountain-front and ephemeral channel recharge exceeded recharge from streamflow infiltration. Evapotranspiration by phreatophytes accounts for the largest outflow of groundwater for both subareas—78 percent of the outflow in the Narrows-Redington subarea and 62 percent of the outflow in the Benson subarea. Precipitation, surface-water, and groundwater chemistry and isotope data indicated the relative age and residence time of groundwater, the amount of interaction between geologic sources and groundwater, and how recharge elevation and season were related to the presence of modern water. The bedrock aquifer receives modern recharge (

Arizona↗
USGS2009

Potentiometric Surface of the Upper Floridan Aquifer, West-Central Florida, May 2009

The Floridan aquifer system consists of the Upper and Lower Floridan aquifers separated by the middle confining unit. The middle confining unit and the Lower Floridan aquifer in west-central Florida generally contain highly mineralized water. The water-bearing units containing fresh water are herein referred to as the Upper Floridan aquifer. The Upper Floridan aquifer is the principal source of water in the Southwest Florida Water Management District and is used for major public supply, domestic use, irrigation, and brackish water desalination in coastal communities (Southwest Florida Water Management District, 2000). This map report shows the potentiometric surface of the Upper Floridan aquifer measured in May 2009. The potentiometric surface is an imaginary surface connecting points of equal altitude to which water will rise in tightly-cased wells that tap a confined aquifer system (Lohman, 1979). This map represents water-level conditions near the end of the dry season, when ground-water levels usually are at an annual low and withdrawals for agricultural use typically are high. The cumulative average rainfall of 48.53 inches for west-central Florida (from June 2008 through May 2009) was 4.12 inches below the historical cumulative average of 52.65 inches (Southwest Florida Water Management District, 2009). Historical cumulative averages are calculated from regional rainfall summary reports (1915 to most recent complete calendar year) and are updated monthly by the Southwest Florida Water Management District. This report, prepared by the U.S. Geological Survey in cooperation with the Southwest Florida Water Management District, is part of a semi-annual series of Upper Floridan aquifer potentiometric-surface map reports for west-central Florida. Potentiometric-surface maps have been prepared for January 1964, May 1969, May 1971, May 1973, May 1974, and for each May and September since 1975. Water-level data are collected in May and September each year to show the approximate annual low and high water-level conditions, respectively. Most of the water-level data for this map were collected by the U.S. Geological Survey during the period May 18-22, 2009. Supplemental water-level data were collected by other agencies and companies. A corresponding potentiometric-surface map was prepared for areas east and north of the Southwest Florida Water Management District boundary by the U.S. Geological Survey office in Orlando, Florida (Kinnaman and Dixon, 2009). Most water-level measurements were made during a 5-day period; therefore, measurements do not represent a 'snapshot' of conditions at a specific time, nor do they necessarily coincide with the seasonal low water-level condition. The potentiometric contours are generalized to synoptically portray the head in a dynamic hydrologic system, taking due account of the variations in hydrogeologic conditions, such as differing depths of wells, nonsimultaneous measurements of water levels, variable effects of pumping, and changing climatic influence. The potentiometric contours may not conform exactly with the individual measurements of water levels.

Scientific Investigations Map↗
USGS2006

Water use and availability in the West Narragansett Bay area, coastal Rhode Island, 1995-99

During the 1999 drought in Rhode Island, belowaverage precipitation caused a drop in ground-water levels and streamflow was below long-term averages. The low water levels prompted the U. S. Geological Survey and the Rhode Island Water Resources Board to conduct a series of cooperative water-use studies. The purpose of these studies is to collect and analyze water-use and water-availability data in each drainage area in the State of Rhode Island. The West Narragansett Bay study area, which covers 118 square miles in part or all of 14 towns in coastal Rhode Island, is one of nine areas investigated as part of this effort. The study area includes the western part of Narragansett Bay and Conanicut Island, which is the town of Jamestown. The area was divided into six subbasins for the assessment of water-use data. In the calculation of hydrologic budget and water availability, the Hunt, Annaquatucket, and Pettaquamscutt River Basins were combined into one subbasin because they are hydraulically connected. Eleven major water suppliers served customers in the study area, and they supplied an average of 19.301 million gallons per day during 1995–99. The withdrawals from the only minor supplier, which was in the town of East Greenwich in the Hunt River Basin, averaged 0.002 million gallons per day. The remaining withdrawals were estimated as 1.186 million gallons per day from self-supplied domestic, commercial, industrial, and agricultural users. Return flows from self-disposed water (individual sewage-disposal systems) and permitted discharges accounted for 5.623 million gallons per day. Most publicly disposed water (13.711 million gallons per day) was collected by the Rhode Island Economic Development Corporation, and by the East Greenwich, Fields Point, Jamestown, Narragansett, and Scarborough wastewater-treatment facilities. This wastewater was disposed in Narragansett Bay outside of the study area. The PART program, a computerized hydrograph-separation application, was used to determine water availability in the study area on the basis of low flows measured at a nearby index station, the Pawcatuck River at Wood River Junction, Rhode Island. Water availability was defined as the 75th, 50th, and 25th percentiles of the total base flow; the base flow minus the 7-day, 10-year flow; and the base flow minus the Aquatic Base Flow at the index station. The base-flow contributions per unit area of sand and gravel deposits and of till were computed for June, July, August, and September for the index station and multiplied by the areas of sand and gravel and till in the subbasins. The calculated base flows at the index station were lowest in August at the 75th, 50th, and 25th percentiles for total base flow and for two additional low-flow scenarios. Because water withdrawals and use are greater during June, July, August, and September than at other times of the year, water availability was compared to water withdrawals in the subbasins for these summer months. Ratios were calculated by dividing the summer withdrawals by the water availability at the 75th, 50th, and 25th percentiles, and these percentiles of the base flow minus the two low flows for each subbasin. The closer this ratio is to one, the closer the withdrawals are to the estimated water available. These ratios allow comparisons of the use of water to the available water from one subbasin to another. The ratios were highest in July for the 50th percentile of the estimated gross yield minus the Aquatic Base Flow. The ratios ranged from 0.01 in the Providence and Seekonk subbasin to 0.38 in the Hunt-Annaquatucket-Pettaquamscutt subbasin for the 50th percentile of the gross yield minus the 7Q10 for August. A long-term (1941–2000) water budget was calculated for the study area to assess the basin inflows and outflows. The water withdrawals and return flows used in the budget were from 1995 through 1999. Inflow was assumed to equal outflow. The total water budget was 146.29 million gallons per day for the combined Hunt-Annaquatucket-Pettaquamscutt subbasin, 48.71 million gallons per day for the Greenwich Bay subbasin, 238.98 million gallons per day for the Providence and Seekonk Rivers subbasin, and 21.32 million gallons per day for the Conanicut Island subbasin. The estimated inflows from precipitation, streamflow from upstream basins, and wastewater return flow for the entire study area were 59.3, 38.5, and 2.2 percent, respectively. The estimated outflows for the study area from evapotranspiration, streamflow, and water withdrawals were 24.9, 73.9, and 1.2 percent, respectively.

Rhode Island↗
USGS2009

Variations in Withdrawal, Return Flow, and Consumptive Use of Water in Ohio and Indiana, with Selected Data from Wisconsin, 1999-2004

This report contains an analysis of water withdrawal and return-flow data for Ohio and withdrawal data for Indiana and Wisconsin to compute consumptive-use coefficients and to describe monthly variability of withdrawals and consumptive use. Concurrent data were available for most water-use categories from 1999 through 2004. Average monthly water withdrawals are discussed for a variety of water-use categories, and average water use per month is depicted graphically for Ohio, Indiana, and Wisconsin (public supply only). For most water-use categories, the summer months were those of highest withdrawal and highest consumptive use. For public supply, average monthly withdrawals ranged from 1,380 million gallons per day (Mgal/d) (November) to 1,620 Mgal/d (July) in Ohio, 621 Mgal/d (December) to 816 Mgal/d (July) in Indiana, and 515 Mgal/d (December) to 694 Mgal/d (July) in Wisconsin. Ohio and Indiana thermoelectric facilities had large increases in average monthly withdrawals in the summer months (5,520 Mgal/d in March to 7,510 Mgal/d in August for Indiana; 7,380 Mgal/d in February to 10,040 Mgal/d in July for Ohio), possibly because of increased electricity production in the summer, a need for additional cooling-water withdrawals when intake-water temperature is high, or use of different types of cooling methods during different times of the year. Average industrial withdrawals ranged from 2,220 Mgal/d (December) to 2,620 Mgal/d (August) in Indiana and from 707 Mgal/d (January) to 787 Mgal/d (August) in Ohio. The Ohio and Indiana irrigation data showed that most withdrawals were in May through October for golf courses, nurseries, and crop irrigation. Commercial water withdrawals ranged from 30.4 Mgal/d (January) to 65.0 Mgal/d (September) in Indiana and from 23.2 Mgal/d (November) to 49.5 Mgal/d (August) in Ohio; commercial facilities that have high water demand in Ohio and Indiana are medical facilities, schools, amusement facilities, wildlife facilities, large stores, colleges, correctional institutions, and national security facilities. Monthly livestock withdrawals were constant for Ohio but were more variable in Indiana and depended on whether the livestock facility operated on a seasonal schedule. Aquaculture withdrawals appeared to correlate with growing seasons and with aeration of ponds during the winter months. Mining withdrawals - specifically, those for nonmetallic mining - tended to be highest in April and may be related to dewatering. Consumptive use and consumptive-use coefficients were computed by two principal methods in this study: the return-flow and withdrawal method (RW; Ohio only) and the winter-base-rate method (WBR; Ohio, Indiana and Wisconsin). The WBR method was not suitable for the thermoelectric, industrial, irrigation, livestock, aquaculture, and mining water-use categories. The RW method was not used for public-supply facilities. A third method, the Standard Industrial Classification code method (SIC), was used only for certain industrial facilities. The public-supply annual average consumptive-use coefficient derived by use of the WBR methods ranged from 6 to 8 percent among Ohio, Indiana, and Wisconsin; the summer average consumptive-use coefficient was considerably higher, ranging from 16 to 20 percent. The commercial annual consumptive-use coefficient for both Ohio and Indiana was 30 percent by the WBR method, which fell within the Ohio annual median (17 percent) and annual average (42 percent) by the RW method. Thermoelectric consumptive use differs greatly by the type of cooling the facility uses; the Ohio annual median consumptive-use coefficient (RW method) was 2 percent for all thermoelectric facilities and facilities with multiple types of cooling, but exclusively once-through-cooling facilities had a median of 0 percent and exclusively closed-loop-cooling facilities had a median of 25 percent. Industrial consumptive-use coefficients varied by type of industry, as reflected by SIC code

Scientific Investigations Report↗
USGS2019

Assessment of the presence of sewage in the Mill River under low-flow conditions, Springfield, Massachusetts, 2010–11

The U.S. Geological Survey, in cooperation with the Pioneer Valley Planning Commission, the U.S. Environmental Protection Agency, and the Massachusetts Department of Environmental Protection Senator William X. Wall Experiment Station, assessed the presence of 14 commonly used human-health pharmaceutical compounds, fecal indicator bacteria, and other man-made compounds indicative of the presence of human sewage in the lower reach of the Mill River near its confluence with the Connecticut River in Springfield, Massachusetts. The study was part of the Tri-State Connecticut River Targeted Watershed Initiative and involved the collection and analysis of raw river water at three sites along the reach, extending from Watershops Pond to the mouth, over the course of a low-flow period, July through November 2010. Previous studies in the region indicated that nonpoint or undocumented sources of wastewater contributed a variety of organic contaminants and potentially harmful bacteria to rivers under both high- and low-flow conditions. Additional samples, including a raw sewage sample collected near a Mill River combined sewer overflow during a non-overflow period, were collected in March 2011. The study was designed to determine if city sewage or other domestic sources of wastewater were entering the river within this reach during low-flow conditions. No definitive evidence of sewage was measured in Mill River water samples collected during the study period. Fecal indicator bacteria, including Escherichia coli ( E. coli ) and enterococci bacteria, were detected in all Mill River water samples. In the DNA analysis of enterococci cultures from the Mill River, samples generally tested negative for the Enterococcus faecium ( esp ) human-specific genetic marker, whereas the raw sewage sample tested positive. Samples also generally tested negative in the human-specific rDNA marker assay for the anaerobic bacterium Bacteroidetes . Samples tested negative in 2010 for two Bacteroidetes human-specific genetic markers, HF134 and HF183, except samples from near the mouth of the Mill River, which tested positive. Samples collected in March 2011 from all three measurement sites tested positive for both markers. The results of bacterial analyses suggest that the fecal bacteria in summer and fall months are most likely of animal origin rather than human. Despite the urban setting, long history of development, and many potential sources of man-made contamination in the Mill River, none of the 12 water samples collected during the study contained targeted pharmaceutical compounds at concentrations greater than the analytical reporting levels. Other man-made compounds, like fluorescent whitening agents, were measured and detected in samples at low concentrations 4 out of 5 times the samples were collected; however, the other lines of evidence do not support a sewer source but rather other nonpoint sources upstream in the watershed. The results of this study do not support the hypothesis that aging sewer lines or combined sewer overflow infrastructure leak into the Mill River as tested during the low-flow conditions during sampling for this study. None of the results from Mill River samples offer conclusive evidence of the presence of sewage. Some low-level detections of pharmaceutical compounds, other man-made chemicals, and bacteria suggest an upstream, nonpoint source. A single raw sewage sample was collected, diluted, and examined for comparison with Mill River water samples and to ensure that the analytical methods could detect typical wastewater constituents. High levels of bacteria were measured, and low levels of three anthropogenic pharmaceutical compounds were detected, confirming the effectiveness of the sub-part-per-million method. The concentration of fluorescent whitening agent-1 in the sewage sample was 90,000 times greater than the median concentration in the Mill River samples.

Massachusetts↗
USGS2024

Phytoplankton, taste-and-odor compounds, and cyanotoxin occurrence in four water-supply reservoirs in the Triangle area of North Carolina, April–October 2014

Prior to 2014, local utilities and State agencies monitored for cyanotoxins and taste-and-odor (T&O) compounds and reported occasional detections in three water-supply reservoirs in Wake County, North Carolina. Comparable data for cyanotoxins and T&O compounds were lacking for other water-supply reservoirs in the Triangle area of North Carolina. This report assesses whether cyanotoxins and T&O compounds occurred in four previously unmonitored North Carolina Triangle area water-supply reservoirs at levels that exceed existing North Carolina and U.S. Environmental Protection Agency recreational and drinking water health advisory, guidance, and criterion levels based on data collected during the peak phytoplankton growth period in 2014. Samples were collected from five sites across the study reservoirs (Cane Creek Reservoir, West Fork Eno River Reservoir, B. Everett Jordan Lake, and University Lake) between April and October 2014 and analyzed for physical characteristics, chemical constituents, phytoplankton communities, cyanotoxins, and T&O compounds. Lake stratification during the sampling period in 2014 could indicate that the deep zones of the water column, during stratified anoxic conditions, may serve as possible sources of nutrients and metals for algal growth and other biogeochemical processes. Differences in phytoplankton communities were attributed to variability in environmental conditions across the sites and sampling events. Differences generally were greater among sites than among sampling events for phytoplankton communities and environmental conditions. Phytoplankton community assemblages, within reservoirs, often were dominated by cyanobacteria that contained genera capable of producing T&O compounds and cyanotoxins during summer and fall months. The occurrence and associated biovolumes of potential producers of cyanotoxins and T&O compounds varied across the sites and sampling events. Of 20 samples collected during the study, the T&O compound geosmin and the cyanotoxin microcystin were present in 19 and 18 samples, respectively. While not harmful, the aesthetically displeasing geosmin concentrations periodically exceeded the human detection threshold of 15 nanograms per liter at most sites. The T&O compound 2-methylisoborneol (MIB) was detected in 11 of 20 samples, with concentrations below the human detection threshold of 15 nanograms per liter in all but one sample. The cyanotoxin anatoxin-a was detected in two of the samples. No other cyanotoxins were detected during the study. In general, results did not indicate the biovolume of any given phytoplankton genera in the study was correlated with increased concentrations of MIB, geosmin, or microcystin. Results from this study indicated that microcystin concentrations in the water-supply reservoirs in the Triangle area were below EPA-recommended recreational level of 8 micrograms per liter, but periodically exceeded the EPA finished-water 10-day health advisory level of 0.3 microgram per liter for bottle-fed infants and preschool-age children. This suggests longer term data collection may be necessary to better understand the magnitude and frequency of cyanotoxin concentrations in these four water-supply reservoirs, particularly those with an elevated risk of exceeding the EPA 10-day health advisory levels in the finished drinking water or those with a higher frequency of T&O compound occurrence.

North Carolina↗
USGS2025

Hydrogeomorphic history, hydrodynamic conditions, and simulations of water levels and velocities from varying lake levels and streamflow for the Sheboygan Rivermouth and area of concern, Wisconsin

In 2011–13, the U.S. Geological Survey (USGS) conducted a study of the hydrogeomorphic setting and hydrodynamic conditions of the lower Sheboygan River and island complex within the backwater zone of Lake Michigan. Analyses of historical aerial photographs from 1938–2010 indicated that the Wildwood Islands complex had experienced mainly erosion and what was mainly one island in 1938 had eroded into about ten smaller islands and bars by 2010. Water levels, velocity and sedimentation patterns in the Sheboygan River mouth are affected by Lake Michigan water levels and seiche-related flow reversals for a potential river length of over 7 km. During the summer of 2012, when water levels in Lake Michigan were below the low water datum, seiche-related water-level fluctuations had a general range of 0.2 m and extended to just upstream of the Wildwood Islands complex, with greater variability in amplitude and frequency in the spring and fall months than in the summer. The low water level associated with the trough of a 60-90-minute seiche-related oscillation was sometimes 0.6 m lower than the low water datum. Runoff events produced river water levels during spring melt or storms that were 0.6 m above coincident Lake Michigan water levels. Frequent ice jams in the winter and early spring of 2012-13 raised river water levels to near the Lake Michigan ordinary high-water mark even though Lake Michigan water levels were at near record lows. Results from trends analyses from 1916 through 2008 indicated average annual streamflow and low flows were increasing in the Sheboygan River, but floods with an annual exceedance probability of 1 percent did not change. Simulations of a range of combinations of Lake Michigan water levels with river flows indicated that a variety of velocity patterns and water levels are possible near the Wildwood Islands complex. Simulated velocities ranged from 0 m/s during high lake levels and small river flows to 2 m/s during high lake levels and floods with an annual exceedance probability of 0.01. Silt deposition recorded in sediment cores matched locations of flow divergence in the model simulations. Time lapse photography confirmed flow reversals in the vicinity of the Wildwood Islands complex from frequent seiche oscillations. The study illustrates the large range in variability in water levels and velocities over short periods of time, and that the lake-effect zone can be greatly extended upstream during high lake levels for low-gradient rivermouth environments.

Wisconsin↗
USGS2007

Estimated water use and availability in the Pawtuxet and Quinebaug River basins, Rhode Island, 1995-99

Water availability became a concern in Rhode Island during a drought in 1999, and an investigation was needed to assess demands on the hydrologic system from withdrawals during periods of little to no precipitation. The low water levels during the drought prompted the U.S. Geological Survey and the Rhode Island Water Resources Board to begin a series of studies on water use and availability in each drainage area in Rhode Island for 1995–99. The study area for this report, which includes the Pawtuxet River Basin in central Rhode Island (231.6 square miles) and the Quinebaug River Basin in western Rhode Island (60.97 square miles), was delineated as the surface-water drainage areas of these basins. During the study period from 1995 through 1999, two major water suppliers withdrew an average of 71.86 million gallons per day (Mgal/d) from the Pawtuxet River Basin; of this amount, about 35.98 Mgal/d of potable water were exported to other basins in Rhode Island. The estimated water withdrawals from minor water suppliers were 0.026 Mgal/d in the Pawtuxet River Basin and 0.003 Mgal/d in the Quinebaug River Basin. Total self-supply withdrawals were 2.173 Mgal/d in the Pawtuxet River Basin and 0.360 Mgal/d in the Quinebaug River Basin, which has no public water supply. Total water use averaged 18.07 Mgal/d in the Pawtuxet River Basin and 0.363 Mgal/d in the Quinebaug River Basin. Total return flow in the Pawtuxet River Basin was 30.64 Mgal/d, which included about 12.28 Mgal/d that were imported from other basins in Rhode Island. Total return flow was 0.283 Mgal/d in the Quinebaug River Basin. During times of little to no recharge in the form of precipitation, the surface- and ground-water flows are from storage primarily in the stratified sand and gravel deposits; water also flows through the till deposits, but at a slower rate. The ground water discharging to the streams during times of little to no recharge from precipitation is referred to as base flow. The PART program, a computerized hydrograph-separation application, was used to analyze the data collected at two selected index stream-gaging stations to determine water availability on the basis of the 75th, 50th, and 25th percentiles of the total base flow; the base flow for the 7-day, 10-year low-flow scenario; and the base flow for the Aquatic Base Flow scenario for both stations. The index stream-gaging stations used in the analysis were the Branch River at Forestdale, Rhode Island (period of record 1957–1999) and the Nooseneck River at Nooseneck, Rhode Island (period of record 1964–1980). A regression equation was used to estimate unknown base-flow contributions from sand and gravel deposits at the two stations. The base-flow contributions from sand and gravel deposits and till deposits at the index stations were computed for June, July, August, and September within the periods of record, and divided by the area of each type of surficial deposit at each index station. These months were selected because they define a period when there is usually an increased demand for water and little to no precipitation. The base flows at the stream-gaging station Branch River at Forestdale, Rhode Island were lowest in August at the 75th, 50th, and 25th percentiles (29.67, 21.48, and 13.30 Mgal/d, respectively). The base flows at the stream-gaging station Nooseneck River at Nooseneck, Rhode Island were lowest in September at the 75th percentile (3.551 Mgal/d) and lowest in August at the 50th and 25th percentiles (2.554 and 1.811 Mgal/d). The base flows per unit area for the index stations were multiplied by the areas of sand and gravel and till in the studyarea subbasins to determine the amount of available water for each scenario. The water availability in the Pawtuxet River Basin at the 50th percentile ranged from 126.5 Mgal/d in August to 204.7 Mgal/d in June, and the total gross water availability for the 7-day, 10-year low-flow scenario at the 50th percentile ranged from 112.2 Mgal/d in August to 190.4 Mgal/d in June. The Scituate Reservoir safe yield was 83 Mgal/d in all scenarios. Water availability in the Quinebaug River Basin ranged from 13.94 Mgal/d in August to 30.53 Mgal/d in June at the 50th percentile. The total gross water availability for the 7-day, 10-year low-flow scenario at the 50th percentile ranged from 14.26 Mgal/d in August to 42.69 Mgal/d in June. Because water withdrawals and use are greater during the summer than other times of the year, water availability in June, July, August, and September was compared to water withdrawals in the basin and subbasins. The ratios of water withdrawn to water available were calculated for the 75th, 50th, and 25th percentiles for the subbasins; the closer the ratio is to 1, the closer the withdrawals are to the estimated water available, and the less net water is available. Withdrawals in July were higher than in the other summer months in both basins. In the Pawtuxet River Basin, the ratios were close to 1 in July for the estimated gross yield (from sand and gravel and from till and from the Scituate Reservoir safe yield), 7-day, 10-year low-flow scenario, and Aquatic Base Flow scenario at the 75th percentile and in August for all three scenarios at the 50th and 25th percentiles. In the Quinebaug River Basin, the ratios were close to 1 in August for the estimated gross yield; 7-day, 10-year low-flow scenario; and Aquatic Base Flow scenario. A long-term water budget was calculated for 1941 through 1999 to identify and assess the basin and subbasin inflow and outflows for the Pawtuxet and Quinebaug River Basins. The water withdrawals and return flows used in the budget were from 1995 through 1999. Inflow was assumed to be equal to outflow; total inflows and outflows were 574.9 Mgal/d in the Pawtuxet River Basin and 148.4 Mgal/d in the Quinebaug River Basin. Precipitation and return flow were 95 and 5 percent of the estimated inflows to the Pawtuxet River Basin, respectively. Precipitation was 100 percent of the estimated inflow to the Quinebaug River Basin; return flow was less than 1 percent of the inflow. Evapotranspiration, streamflow, and water withdrawals were 46, 41, and 13 percent, respectively, of the estimated outflows in the Pawtuxet River Basin. Evapotranspiration and streamflow were 49 and 51 percent, respectively, of the estimated outflows in the Quinebaug River Basin. Water withdrawals were less than 1 percent of outflows in the Quinebaug River Basin.

Rhode Island↗
USGS2026

Methods for estimating selected low-flow frequency and mean annual flow statistics at gaged and ungaged locations on streams in Georgia, North Carolina, and South Carolina

The U.S. Geological Survey, in cooperation with the Georgia Department of Natural Resources (Environmental Protection Division), North Carolina Department of Environmental Quality (Division of Water Resources), North Carolina Department of Public Safety (Office of Recovery and Resiliency), and South Carolina Department of Environmental Services, updated low-flow frequency, mean annual flow, and flow-duration statistics at 843 streamgages in and near Georgia, North Carolina, and South Carolina. The low-flow frequency statistics are annual minimum 1-day average flow with a 10-year recurrence interval (1Q10), annual minimum 7-day average flow for 2- and 10-year recurrence intervals (7Q2 and 7Q10, respectively), and annual minimum 30-day average flow with 2- and 3-year recurrence intervals (30Q2 and 30Q3, respectively). Monthly 1Q10 and 7Q10, and W7Q10 flow statistics for the winter period (November–March) also are presented. By using data from 604 of the streamgages on streams with streamflows that are not substantially affected by regulation or diversion and are not tidally influenced, regional regression equations were developed to predict flow statistics with prediction intervals at ungaged locations on streams with those same criteria. The regional regression analysis included data from 132 streamgages from adjacent States Alabama, Florida, Tennessee, and Virginia. The final regional regression equations include variables such as drainage area, streamflow variability, precipitation, percentage of impervious area, and percentage of the basin in various ecoregions. The low-flow statistics for the streamgages analyzed and the regional regression equations will be integrated into the U.S. Geological Survey StreamStats application ( https://www.usgs.gov/streamstats ) for Georgia, North Carolina, and South Carolina. StreamStats generates basin characteristics needed to compute low-flow frequency statistics for ungaged locations. A trend analysis of annual minimum 7-day average flows was done for 78 streamgages with at least 30 years of continuous record. Trends were evaluated for 30-, 50‑, 70-, and 90-year periods, ending in climate year 2021, and independence and short- and long-term persistence assumptions were considered. For all trend analysis assumptions, most streamgages did not exhibit significant trends in annual minimum 7-day average flows. Trends in annual precipitation and air temperature were similarly evaluated for the period 1895–2021 to assess the variability of climate for Georgia, North Carolina, and South Carolina.

Georgia, North Carolina, South Carolina↗
USGS2007

Winter ecology of the western burrowing owl ( Athene cunicularia hypugaea ) in southern Texas 1999-2004

This study examines the winter ecology of the western burrowing owl ( Athene cunicularia hypugaea ) in five Texas counties surrounding Corpus Christi, in southern Texas. There is a substantial gap in information on the owl's life cycle during migration and non-breeding winter months; almost all previous research on western burrowing owls has been conducted during the breeding season. The western burrowing owl currently is federally threatened in Mexico, federally endangered in Canada, and in the United States is considered a National Bird of Conservation Concern by the U.S. Fish and Wildlife Service. Topics investigated included status, effectiveness of public outreach, roost sites and use of culverts and artificial burrows, roost site fidelity, diet, contaminant burdens, body mass, and ectoparasites. Early ornithological reports and a museum egg set revealed that burrowing owls once bred in southern Texas and were common in winter; however, since the 1950's they have been reported in relatively low numbers and only during winter. In this study, public outreach increased western burrowing owl detections by 68 percent. Owls selected winter roost sites with small-diameter openings, including culverts less than or equal to 16 centimeters and artificial burrows of 15 centimeters, probably because the small diameters deterred mammalian predators. Owls showed strong roost site fidelity; 15 banded birds stayed at the same roost sites within a winter, and 8 returned to the same site the following winter. The winter diet was over 90 percent insects, with crickets the primary prey. Analyses of invertebrate prey and regurgitated pellets showed that residues of all but 3 of 28 carbamate and organophosphate pesticides were detected at least once, but all were below known lethal concentrations. Mean body mass of western burrowing owls was 168 grams and was highest in midwinter. Feather lice were detected in low numbers on a few owls, but no fleas or other ectoparasites were found.

Texas↗
USGS2021

Simulated effects of sea-level rise on the shallow, fresh groundwater system of Assateague Island, Maryland and Virginia

The U.S. Geological Survey, in cooperation with the National Park Service, developed a three-dimensional groundwater-flow model for Assateague Island in eastern Maryland and Virginia to assess the effects of sea-level rise on the groundwater system. Sea-level rise is expected to increase the altitude of the water table in barrier island aquifer systems, possibly leading to adverse effects to ecosystems on the barrier islands. The potential effects of sea-level rise were evaluated by simulating groundwater conditions under sea-level-rise scenarios of 20 centimeters (cm), 40 cm, and 60 cm. Results show that as sea level rises, low-lying areas of the island originally represented as receiving freshwater recharge in the baseline scenario are inundated by saltwater. This change from freshwater recharge to saltwater decreases the overall amount of freshwater recharging the system. As the water table rises in response to the higher sea levels, freshwater flow out of the system changes, with more freshwater leaving as submarine groundwater discharge and less freshwater leaving as seeps and evapotranspiration. At the current land-surface altitude, as much as 50 percent of the island may be inundated with a 60-cm rise in sea level, and the low-lying marshes may change from freshwater to saltwater. Groundwater levels at 32 wells were monitored for as long as 12 months between October 2014 and September 2015 on Assateague Island. Results from objective classification analysis of 14 shallow monitoring wells show two dominant processes affecting groundwater levels in two different settings on the island. On the western side of the island, between the primary dune and the inland bays, water levels clearly respond to precipitation events. This side of the island is more protected from ocean tides and typically is more vegetated than the eastern side. On the eastern side of the island, between the Atlantic Ocean and the primary dune, water levels clearly respond to tidal events. Specific conductance was measured at four wells, two on the western part of the island and two on the eastern part of the island. Specific conductance values in the two wells west of the primary dune show episodic decreases, coinciding with precipitation events. Specific conductance values in the two wells on the eastern side of the primary dune show episodic increases, coinciding with high-tide events. These high frequency monitoring data are intended to aid in designing a monitoring network that can document both short-term and long-term hydrologic processes on Assateague Island National Seashore. This study uses a modeling approach consistent with models developed for Gateway National Recreation Area, Sandy Hook Unit (New Jersey) and Fire Island National Seashore (New York). Combined, these models are meant to improve the regional capabilities for predicting climate-change effects on barrier islands and provide resource managers with a common set of tools for adaptation and mitigation of potentially adverse effects of sea-level rise.

Maryland, Virginia↗
USGS2018

Groundwater chemistry and water-level elevations in bedrock aquifers of the Piceance and Yellow Creek watersheds, Rio Blanco County, Colorado, 2013–16

The Piceance and Yellow Creek watersheds in Rio Blanco County, Colorado, are known to contain important energy resources (oil shale and natural gas) and mineral resources (nahcolite). The primary sources of fresh groundwater in the Piceance and Yellow Creek watersheds are bedrock aquifers in the Uinta and Green River Formations. The aquifers are divided into an upper and lower aquifer separated by a regionally extensive semiconfining layer. These aquifers provide water to streams and springs in the watersheds and are an important resource to people living and working in the area. Development of energy and mineral resources has the potential to affect the quality of groundwater in several ways. The Bureau of Land Management and the U.S. Geological Survey began groundwater monitoring in 2010 to characterize the groundwater quality and water-level elevations of shallow bedrock aquifers in the Piceance and Yellow Creek watersheds. The purpose of this report is to present ground-water chemistry and water-level elevations collected during 2013–16. Comparisons are made to data that were collected from the bedrock aquifers from 2010 to 2012 to identify the potential for changes in water quality and water-level elevations. Appreciable changes in water-level elevations and hydraulic gradient were observed in early April 2015 in two wells completed in the upper and lower aquifers. The hydraulic gradient between the two wells was consistently downward from the upper aquifer to the lower aquifer during 2010–15; however, in early April 2015, the gradient changed from downward to upward between the two aquifers. Overall, water-level elevations declined by about 14 and 11 feet in the upper and lower aquifers, respectively, from 2013 to 2016. Previously published data estimated groundwater ages at 1,200 years old in the upper aquifer and 9,600 years old in the lower aquifer. These groundwater ages indicate that ground-water was recharged over thousands of years. With such long periods of time for aquifer recharge, declines in water-level elevation over short time steps (a few months) have important implications for sustainable management of this resource. Solution mining activities or drilling for oil and natural gas in the area could be related to the changes observed in water-level elevations in these wells; however, further investigation would be needed to evaluate causation. Changes in major-ion chemistry were evaluated in the bedrock aquifer using time series plots of select major-ion data from 2010 to 2016. Major-ion chemistry was variable for a single well from 2010 to 2016 where alkalinity and sulfate were the most variable constituents. One possible explanation for the observed changes in major-ion chemistry may be that the sample depth for that well no longer represents the most appreciable flow in the borehole. On a larger scale, potential changes in flow within the borehole may indicate changes in the regional flow system. Methane and volatile organic compound concentrations were evaluated using a similar approach to that of major ions and had similar findings. Methane concentrations in wells sampled from 2010 to 2016 were generally constant. The only exception was observed at a single well where the range of methane concentrations was from 57.4 (2010) to 4.02 milligrams per liter (2013). This is the same well where changes in water-level elevation, hydraulic gradient, and major-ion chemistry were observed, providing multiple lines of evidence to indicate change in the bedrock aquifers. Sampling of a well located in an area with little energy development but where faults or fractures could provide a path for the migration of fluids indicate mixing of groundwater between the upper and lower aquifers.

Colorado↗
USGS2004

Trends in streamflow and comparisons with instream flows in the lower Puyallup River basin, Washington

The Puyallup Tribe of Indians is interested in better understanding the water resources of the lower Puyallup River Basin in order to ensure sufficient water to meet Tribal and hatchery needs and make future water-resource decisions. The U.S. Geological Survey, in cooperation with the Puyallup Tribe, conducted a study to identify trends in streamflow in the lower Puyallup River Basin and to compare streamflows in the Puyallup River with regulatory minimum instream flows. Daily mean streamflow, monthly mean streamflow for October, and annual mean streamflow records from 1980 through 2001 for two gaging stations on the lower Puyallup River and one each on Clarks Creek and Swan Creek in the lower Puyallup River Basin were analyzed for temporal trends. Daily mean streamflow records were divided into data sets for the wet period (November through June) and the dry period (July through October) for analysis. Annual precipitation records from three National Weather Service stations and ground-water-level records from five wells in the lower Puyallup River Basin were analyzed to determine possible relations with streamflow. Daily mean streamflow, daily minimum streamflow, and unit-streamflow records for the Puyallup River for 1991 and 1992 were evaluated for the instream-flow analysis. Significant temporal trends were not identified in daily mean streamflow records from the Puyallup River, Clarks Creek, or Swan Creek for the period of analysis. Trend analysis of monthly mean streamflow records for October at two gaging stations on the Puyallup River also indicated no significant trends for the period of analysis. Temporal trends were not evident in precipitation data from weather stations in the basin. A trend of decreasing depth to ground water with time (1995 through 1997) was identified in one well (20N/04E-34G01). This well is drilled to about 550 feet below land surface, and variations in water levels at this depth likely do not affect streamflow in the Puyallup River. Data limitations prevented the evaluation of possible correlations between streamflow in the Puyallup River and water use and land use in the study basin. Daily mean, daily minimum, and unit-streamflow values were evaluated to determine how each measure of streamflow compared with instream-flow values. The occurrence of excursions (streamflow below the instream-flow value) was greatest when unit-streamflow values were compared with instream-flow values. The use of daily mean streamflow records may underestimate the occurrence of excursions under certain streamflow conditions. The unit-streamflow hydrograph for the Puyallup River at Puyallup exhibits a distinct, regular pattern. The hydrograph closely mimics the hydrograph at Lake Tapps Diversion, on the White River, a tributary of the Puyallup River, which is the outflow from a power plant, suggesting that the power-plant outflow affects streamflow in the Puyallup River. Streamflow entering Lake Tapps through the White River Canal does not exhibit the same pattern as the Puyallup River or diversion. The influence of the White River Canal on streamflow in the Puyallup River appears to be obscured by operation of the Lake Tapps Diversion.

Washington↗
USGS2006

Simulation of daily pesticide concentrations from watershed characteristics and monthly climatic data

A time-series model was developed to simulate daily pesticide concentrations for streams in the coterminous United States. The model was based on readily available information on pesticide use, climatic variability, and watershed charac-teristics and was used to simulate concentrations for four herbicides [atrazine, ethyldipropylthiocarbamate (EPTC), metolachlor, and trifluralin] and three insecticides (carbofuran, ethoprop, and fonofos) that represent a range of physical and chemical properties, application methods, national application amounts, and areas of use in the United States. The time-series model approximates the probability distributions, seasonal variability, and serial correlation characteristics in daily pesticide concentration data from a national network of monitoring stations. The probability distribution of concentrations for a particular pesticide and station was estimated using the Watershed Regressions for Pesticides (WARP) model. The WARP model, which was developed in previous studies to estimate the probability distribution, was based on selected nationally available watershed-characteristics data, such as pesticide use and soil characteristics. Normality transformations were used to ensure that the annual percentiles for the simulated concentrations agree closely with the percentiles estimated from the WARP model. Seasonal variability in the transformed concentrations was maintained by relating the transformed concentration to precipitation and temperature data from the United States Historical Climatology Network. The monthly precipitation and temperature values were estimated for the centroids of each watershed. Highly significant relations existed between the transformed concentrations, concurrent monthly precipitation, and concurrent and lagged monthly temperature. The relations were consistent among the different pesticides and indicated the transformed concentrations generally increased as precipitation increased but the rate of increase depended on a temperature-dependent growing-season effect. Residual variability of the transformed concentrations, after removal of the effects of precipitation and temperature, was partitioned into a signal (systematic variability that is related from one day to the next) and noise (random variability that is not related from one day to the next). Variograms were used to evaluate measurement error, seasonal variability, and serial correlation of the historical data. The variogram analysis indicated substantial noise resulted, at least in part, from measurement errors (the differences between the actual concen-trations and the laboratory concentrations). The variogram analysis also indicated the presence of a strongly correlated signal, with an exponentially decaying serial correlation function and a correlation time scale (the time required for the correlation to decay to e-1 equals 0.37) that ranged from about 18 to 66 days, depending on the pesticide type. Simulated daily pesticide concentrations from the time-series model indicated the simulated concentrations for the stations located in the northeastern quadrant of the United States where most of the monitoring stations are located generally were in good agreement with the data. The model neither consistently overestimated or underestimated concentrations for streams that are located in this quadrant and the magnitude and timing of high or low concentrations generally coincided reasonably well with the data. However, further data collection and model development may be necessary to determine whether the model should be used for areas for which few historical data are available.

Scientific Investigations Report↗
USGS2014

Hydrogeology, water resources, and water budget of the upper Rio Hondo Basin, Lincoln County, New Mexico, 2010

The upper Rio Hondo Basin occupies a drainage area of 585 square miles in south-central New Mexico and comprises three general hydrogeologic terranes: the higher elevation “Mountain Block,” the “Central Basin” piedmont area, and the lower elevation “Hondo Slope.” As many as 12 hydrostratigraphic units serve as aquifers locally and form a continuous aquifer on the regional scale. Streams and aquifers in the basin are closely interconnected, with numerous gaining and losing stream reaches across the study area. In general, the aquifers are characterized by low storage capacity and respond to short-term and long-term variations in recharge with marked water-level fluctuations on short (days to months) and long (decadal) time scales. Droughts and local groundwater withdrawals have caused marked water-table declines in some areas, whereas periodically heavy monsoons and snowmelt events have rapidly recharged aquifers in some areas. A regional-scale conceptual water budget was developed for the study area in order to gain a basic understanding of the magnitude of the various components of input, output, and change in storage. The primary input is watershed yield from the Mountain Block terrane, supplying about 38,200 to 42,300 acre-feet per year (acre-ft/yr) to the basin, as estimated by comparing the residual of precipitation and evapotranspiration with local streamgage data. Streamflow from the basin averaged about 21,200 acre-ft/yr, and groundwater output left the basin at an estimated 2,300 to 5,700 acre-ft/yr. The other major output (about 13,500 acre-ft/yr) was by public water supply, private water supply, livestock, commercial and industrial uses, and the Bonito Pipeline. The residual in the water budget, the difference between the totals of the input and output terms or the potential change in storage, ranged from -2,200 acre-ft/yr to +5,300 acre-ft/yr. There is a high degree of variability in precipitation and consequently in the water supply; small variations in annual precipitation can result in major changes in overall watershed yield. Changing water-use patterns, concentrated areas of groundwater withdrawal, and variations in precipitation have created localized areas where water-table declines and diminished surface flow are of concern.

Lincoln, New Mexico↗