A groundwater system consists of a mass of water flowing through the pores or cracks below the Earth's surface. This mass of water is in constant motion. Water is constantly added to the system by recharge from precipitation, and water is constantly leaving the system as discharge to surface water and as evapotranspiration. Each groundwater system is unique in that the source and amount of water flowing through the system is dependent upon external factors such as rate of precipitation, location of streams and other surface-water bodies, and rate of evapotranspiration. The one common factor for all groundwater systems, however, is that the total amount of water entering, leaving, and being stored in the system must be conserved. An accounting of all the inflows, outflows, and changes in storage is called a water budget (Alley and others, 1999).
Estimation of the amount of groundwater that is available for use requires consideration of two key elements. First, the use of groundwater and surface water must be evaluated together on a system wide basis. This evaluation includes the amount of water available from changes in groundwater recharge, from changes in groundwater discharge, and from changes in storage for different levels of water consumption. Second, because any use of ground water changes the subsurface and surface environment (that is, the water must come from somewhere), the public should determine the tradeoff between groundwater use and changes to the environment and set a threshold at which the level of change becomes undesirable. This threshold can then be used in conjunction with a system wide analysis of the groundwater and surface-water resources to determine appropriate limits for consumptive use.
System wide hydrologic analyses typically use simulations (that is, computer models) to aid in estimating water availability and the effects of extracting water on the ground-water and surface-water system. Computer models attempt to reproduce the most important features of an actual system with a mathematical representation. If constructed correctly, the model represents the complex relations among the inflows, outflows, changes in storage, movement of water in the system, and possibly other important features. As a mathematical representation of the system, the model can be used to estimate the response of the system to various development options and provide insight into appropriate management strategies. However, a computer model is a simplified representation of the actual system, and the judgment of water-management professionals is required to evaluate model simulation results and plan appropriate actions (Alley and others, 1999).
Estimates of the inflow and outflow into the Long Island groundwater system were evaluated using a compilation of data from 2005-2010 where available. Previous estimates from earlier studies and numerical models are also presented in this section as a comparison to a 2005-2010 index period.
_______________________________
Table of Contents
State of the Aquifer, Long Island, New York - Introduction
- Precipitation
- NWIS - the USGS Data Archive
- Surface Water - Streamflow
- Groundwater Levels
- Water Table and Surface Maps
- Water Use
- Groundwater Budget
- Inflow to the Groundwater System
- Outflow from the Groundwater System
Below are other science projects associated with this project.
Long Island Water Availability
Long Island Precipitation
NWIS - the USGS Data Archive
Long Island Surface Water - Streamflow
Long Island Groundwater Levels
Long Island Water Table and Surface Maps
Long Island Water Use
Long Island Inflow to the Groundwater System
Long Island Outflow from the Groundwater System
Long Island Water Suitability
Long Island Water Suitability Case Studies
Long Island Groundwater System Potential Hazards
- Overview
A groundwater system consists of a mass of water flowing through the pores or cracks below the Earth's surface. This mass of water is in constant motion. Water is constantly added to the system by recharge from precipitation, and water is constantly leaving the system as discharge to surface water and as evapotranspiration. Each groundwater system is unique in that the source and amount of water flowing through the system is dependent upon external factors such as rate of precipitation, location of streams and other surface-water bodies, and rate of evapotranspiration. The one common factor for all groundwater systems, however, is that the total amount of water entering, leaving, and being stored in the system must be conserved. An accounting of all the inflows, outflows, and changes in storage is called a water budget (Alley and others, 1999).
Estimation of the amount of groundwater that is available for use requires consideration of two key elements. First, the use of groundwater and surface water must be evaluated together on a system wide basis. This evaluation includes the amount of water available from changes in groundwater recharge, from changes in groundwater discharge, and from changes in storage for different levels of water consumption. Second, because any use of ground water changes the subsurface and surface environment (that is, the water must come from somewhere), the public should determine the tradeoff between groundwater use and changes to the environment and set a threshold at which the level of change becomes undesirable. This threshold can then be used in conjunction with a system wide analysis of the groundwater and surface-water resources to determine appropriate limits for consumptive use.
System wide hydrologic analyses typically use simulations (that is, computer models) to aid in estimating water availability and the effects of extracting water on the ground-water and surface-water system. Computer models attempt to reproduce the most important features of an actual system with a mathematical representation. If constructed correctly, the model represents the complex relations among the inflows, outflows, changes in storage, movement of water in the system, and possibly other important features. As a mathematical representation of the system, the model can be used to estimate the response of the system to various development options and provide insight into appropriate management strategies. However, a computer model is a simplified representation of the actual system, and the judgment of water-management professionals is required to evaluate model simulation results and plan appropriate actions (Alley and others, 1999).
Estimates of the inflow and outflow into the Long Island groundwater system were evaluated using a compilation of data from 2005-2010 where available. Previous estimates from earlier studies and numerical models are also presented in this section as a comparison to a 2005-2010 index period.
_______________________________
Table of Contents
State of the Aquifer, Long Island, New York - Introduction
- Precipitation
- NWIS - the USGS Data Archive
- Surface Water - Streamflow
- Groundwater Levels
- Water Table and Surface Maps
- Water Use
- Groundwater Budget
- Inflow to the Groundwater System
- Outflow from the Groundwater System
- Science
Below are other science projects associated with this project.
Long Island Water Availability
The foundation of any groundwater analysis, including those analyses whose objective is to propose and evaluate alternative management strategies, is the availability of high-quality data. Some, such as precipitation data, are generally available and relatively easy to obtain at the time of a hydrologic analysis. Other data and information, such as geologic and hydrogeologic maps, can require...Long Island Precipitation
The National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC) offers several types of climate information generated from examination of the data in the archives. These types of information include record temperatures, record precipitation and snowfall, climate extreme statistics, and other derived climate products. A collection of statistical weather and climate...NWIS - the USGS Data Archive
As part of the U.S. Geological Survey's (USGS) program for disseminating water data within USGS, to USGS cooperators, and to the general public, the USGS maintains a distributed network of computers and fileservers for the acquisition, processing, review, and long-term storage of water data. This water data is collected at over 1.5 million sites around the country and at some border and...Long Island Surface Water - Streamflow
Surface water current conditions are based on the most recent data from on-site automated recording equipment. Measurements are commonly recorded at a fixed interval of 15 to 60 minutes and transmitted by satallite uplink or telephone telemetry to the USGS every hour. Values may include "Approved" (quality-assured data that may be published) and/or more recent "Provisional" data (of unverified...Long Island Groundwater Levels
Water-level measurements from observation wells are the principal source of information about the hydrologic stresses acting on aquifers and how these stresses affect groundwater recharge, storage, and discharge (Taylor and Alley, 2001). Water-level measurements are made by many Federal, State, and local agencies.Long Island Water Table and Surface Maps
The depth to the water table can be determined by installing wells that penetrate the top of the saturated zone just far enough to respond to water table fluctuations. Preparation of a water-table map requires that only wells that have their well screens installed near the water table be used. If the depth to water is measured at a number of such wells throughout an area of study, and if those...Long Island Water Use
The U.S. Geological Survey's National Water-Use Information Program (NWUIP) is responsible for compiling and disseminating the nation's water-use data. The USGS works in cooperation with local, State, and Federal environmental agencies to collect water-use information. USGS compiles these data to produce water-use information aggregated at the county, state, and national levels. Every five years...Long Island Inflow to the Groundwater System
Precipitation that infiltrates and percolates to the water table is Long Island's only natural source of freshwater because the groundwater system is bounded on the bottom by relatively impermeable bedrock and on the sides by saline ground water or saline bays and the ocean. About one-half the precipitation becomes recharge to the groundwater system; the rest flows as surface runoff to streams or...Long Island Outflow from the Groundwater System
The flow of water leaving, or discharging, the groundwater system of Long Island occurs naturally through streams, as base flow, at the coastline as shoreline discharge and sub-sea discharge, and through pumping wells as withdrawals. Estimates of each component of outflow from the groundwater system is presented and summarized in this section using streamflow measurements, and a compilation of...Long Island Water Suitability
Groundwater quality may be affected by natural and human factors (Johnston, 1988). Although the vulnerability of groundwater to contamination from the land surface is influenced by many factors, the degree of aquifer confinement, the depth of the well, and the surrounding land use are primary key factors that influence shallow groundwater quality.Long Island Water Suitability Case Studies
A collection of studies that focused on the quality of groundwater and surface water, are presented in this section. The reports associated with these areas of water quality concerns are linked as an online source for further reading.Long Island Groundwater System Potential Hazards
Hazards which may impact the ground water system adversely are presented in this web page. The impacts of these hazards are only shown here as a topic for further discussion and may need to be investigated with further details.