[1] The sustainability of human water use practices is a rapidly growing concern in the United States and around the world. To better characterize direct human interaction with hydrologic systems (stream basins and aquifers), we introduce the concept of the water use regime. Unlike scalar indicators of anthropogenic hydrologic stress in the literature, the water use regime is a two-dimensional, vector indicator that can be depicted on simple x-y plots of normalized human withdrawals (h out ) versus normalized human return flows (h in ). Four end-member regimes, natural-flow-dominated (undeveloped), human-flow-dominated (churned), withdrawal-dominated (depleted), and return-flow-dominated (surcharged), are defined in relation to limiting values of h out and h in . For illustration, the water use regimes of 19 diverse hydrologic systems are plotted and interpreted. Several of these systems, including the Yellow River Basin, China, and the California Central Valley Aquifer, are shown to approach particular end-member regimes. Spatial and temporal regime variations, both seasonal and long-term, are depicted. Practical issues of data availability and regime uncertainty are addressed in relation to the statistical properties of the ratio estimators h out and h in . The water use regime is shown to be a useful tool for comparative water resources assessment and for describing both historic and alternative future pathways of water resource development at a range of scales.

Abstract. Runoff-based indicators of terrestrial water availability are appropriate for humid regions, but have tended to limit our basic hydrologic understanding of drylands – the dry-sub-humid, semi-arid, and arid regions which presently cover nearly half of the global land surface. In response, we introduce an indicator framework that gives equal weight to humid and dryland regions, accounting fully for both vertical (precipitation + evapotranspiration) and horizontal (groundwater + surface-water) components of the hydrologic cycle in any given location – as well as fluxes into and out of landscape storage. We apply the framework to a diverse hydroclimatic region (the conterminous USA), using a distributed water-balance model consisting of 53 400 networked landscape hydrologic units. Our model simulations indicate that about 21% of the conterminous USA either generated no runoff or consumed runoff from upgradient sources on a mean-annual basis during the 20th century. Vertical fluxes exceeded horizontal fluxes across 76% of the conterminous area. Long-term average total water availability (TWA) during the 20th century, defined here as the total influx to a landscape hydrologic unit from precipitation, groundwater, and surface water, varied spatially by about 400 000-fold, a range of variation ~100 times larger than that for mean-annual runoff across the same area. The framework includes, but is not limited to classical, runoff-based approaches to water-resource assessment. It also incorporates and re-interprets the green-blue water perspective now gaining international acceptance. Implications of the new framework for hydrologic assessment and classification are explored.

A 14-month program of storm-precipitation and runoft-data collection was conducted in the Irondequoit Creek basin, a «+38-squarekilometer area along the south shore of Lake Ontario in north-central New York, from July 1980 through September 1981. The data form a basis for further study of nutrient inflow to Irondequoit Bay. This report describes the methods used to collect and verify the data and includes some representative examples of the data base. Stream-discharge and water-quality data were collected at 17 sites representing rural and urban land uses. Precipitation data were collected at five continuous-record gages and 11 daily-total gages. Evaporation data were collected at one site; chemical quality of precipitation and dustfall data were collected at four sites. Tables list watershed characteristics, precipitation data (including chemical quality of atmospheric deposition, monthly precipitation, and evaporation), and annual loadings of eight selected nutrients and heavy metals from the five major subbasins and three discrete land-use sites. Examples of computer printouts of streamflow, precipitation, and water-quality data available from the Geological Survey's WATSTORE computer system are included. WATSTORE-National Water Data Storage and Retrieval System maintained by the U.S. Geological Survey. A large-scale computerized storage, retrieval, and processing system for water data acquired through U.S. Geological Survey activities. * Intervening area between Linden Avenue site and the Thornell Road and Thomas Creek subbasins is 72.8 km2 .

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The contributing areas to six municipal ground-water supplies (Adams, Mannsville, Lacona-Sandy Creek, Pulaski, Orwell, and Camden) that tap the Tug Hill aquifer were estimated from surficial geologic maps and potentiometric-surface maps. Contributing areas to the individual water supplies ranged from 0.01 to 1.0 square mile (mi2) but may include as much as 17 mi2 of adjacent upland areas that contribute recharge to the aquifer through streambed infiltration and direct runoff. The potential for contamination within the contributing area is low because the region is predominantly rural.The contributing area to the Lacona-Sandy Creek well field was calculated by several methods for purposes of comparison. A finite-difference ground-water flow model and a post-processing particle-tracking program were used for a range of pumping, recharge, and hydraulic conductivity values. Ground-water budgets computed from steady-state simulation indicate that most of the water pumped by the wells is water that would be lost to springs and as evapotranspiration in the western flank of the aquifer. High pumping rates combined with low recharge rates may induce minor infiltration from Little Sandy Creek. Results of flow-path analysis indicate that (1) the size and shape of the contributing area differs significantly from the area of influence (the surface expression of the cone of depression), (2) flow paths from the eastern edge of the aquifer are less than 1 mile long, and (3) travel times to the supply well are generally between 500 and 1,000 days.Two modified analytical techniques also were used the Dupuit uniform-flow method and the Theis nonequilibrium method. Analytical methods are easier to apply than numerical methods but are constrained by limiting assumptions that, if not satisfied, can result in large errors. The Dupuit method, modified for a sloping water table, indicated a contributing area of 0.04 mi2 for a production well pumped at 200 gallons per minute and a horizontal hydraulic conductivity of 1,200 feet per day. This is smaller than the 0.13-mi2 contributing area obtained by numerical techniques for similar hydraulic properties, and its position differs also. The Theis method modified for partial penetration of the pumped well, dewatering of the aquifer, and a single linear impermeable boundary indicated a contributing area of 0.12 mi2, the size and shape of which is similar to the contributing area obtained by the numerical simulation.The selection of a technique for delineating a contributing area ultimately depends on the resources available for the analysis and the degree of accuracy required. Despite the uncertainties and incomplete information on the factors that affect the size of the contributing area, the four methods used in this study provide a more reliable estimate than the commonly used fixed-radius method.