1.1: Demand Balance

Equitably balance the multiple demands on the limited water resources of the Basin, while preserving and enhancing conditions in watersheds to maintain or achieve ecological integrity.

Other Information:

To equitably balance multiple demands, it is essential to understand the types of human and ecological demands being made on the hydrological system. To set realistic targets for preserving and enhancing conditions in watersheds to maintain or achieve ecological integrity, requires a clear understanding of existing conditions, and of the needs of aquatic and riparian populations. Those watersheds that currently approximate natural conditions should be protected to preserve their ecological and hydrological functions and those that have been degraded should be considered for restoration or enhancement. Assessing current water use. Improving our understanding of water use will help us to manage resources more effectively and focus our efforts to promote efficient water use. The generation of reliable data requires accurate and up-to-date records on all ground water and surface water withdrawal allocations, wastewater discharge permits, and connectivity among withdrawal, use, and discharge points. Data management problems currently hamper the development of a precise water use and discharge data set for all watersheds in the Basin. However, existing information for individual watersheds can be used to estimate water use in other watersheds with similar conditions. A summary of water withdrawals, exports and consumptive use in the Delaware River Basin based on data from 1996 is shown in Figure 3. There are two major exportations of water from the Basin. The largest (approximately 650 mgd) is to New York City, which obtains around half of its water supply from a system of upper Basin reservoirs that provide the water and make releases to the river designed to ensure a minimum rate of flow. The other major export (approximately 90 mgd) from the Basin is via the Delaware and Raritan Canal, which carries water to northeastern New Jersey. Limitations on these exports, of 800 mgd and 100 mgd respectively, were established by the Supreme Court Decree in 1954. The New York City aqueduct system and the Delaware and Raritan Canal are illustrated in Figure 4. The largest water using sectors in the Basin are those of power generation, industrial use and public water supply. In recent years, at the Basin-wide scale, industrial water use has declined whereas water demand for power generation has increased. For public water supply, conservation efforts have helped keep demands stable despite a growing population. In response to actual and projected increases in water demand for the power generating sector, Merrill Creek Reservoir was constructed in 1989. During low-flow periods releases are made from the reservoir to offset the consumptive use at facilities that have purchased storage capacity in the reservoir, thus allowing them to continue operation where cut-backs in production would otherwise have been required. Substantial capacity in the Merrill Creek Reservoir is currently unused and is thus available for future purchase to offset consumptive use at new facilities. Calculating water budgets. To help improve our understanding of how much water is safely available for use we need to understand water budgets on a watershed basis. A water budget is a description of the fate of water resources in a watershed, as illustrated in Figure 5. Budget “inputs” include precipitation and imports (transfers into the system). Water inputs will become: • Evapotranspiration into the atmosphere • Direct flows to surface water bodies (runoff) • Indirect contributions to stream flow through the soil and water table • Recharge to deeper ground water aquifers • Consumptive losses associated with human use • Exports from the watershed The proportion of water inputs that arrive at each destination is determined by climate; geology, soils and topography; by the land use attributes of a watershed; and the way we use water resources. Water budgets yield an average annual accounting of water volumes and do not reflect seasonal variation. Although the water budget approach has limitations, pilot studies are under way as part of state water supply studies and a USGS-DRBC partnership to assess the feasibility of using water budgets as a screening tool for watershed assessments. Assessing in-stream flow and freshwater inflow requirements. Understanding the needs of aquatic ecosystems is essential to several Goals of the Basin Plan, including: • Assessing the amount of water available for allocation • Setting standards for improving conditions in watersheds and restoring natural functions in stream corridors • Protecting threatened and endangered species • Improving operating plans for reservoirs • Setting appropriate criteria and standards for assessment and restoration within the Basin’s ecoregions are necessary to make sustainable water allocation decisions. Developing strategies for the allocation of water. Once both human and ecological needs are understood, the challenge of achieving an equitable balance of the multiple demands on the hydrological system can be addressed. Prudent allocation strategies may include curtailing water uses during drought conditions through allocation decisions or use restrictions, and allocating water to areas with limited water resources as determined by calculated water budgets and availability assessments. Allocation strategies also need to honor the rights of the parties defined in the 1954 U.S. Supreme Court Decree. Developing tools for assessing ecological integrity. The development of indices of ecological integrity that integrate the physical, biological and chemical requirements of healthy aquatic and riparian ecosystems is critical for realizing restoration and enhancement goals as well as for developing appropriate water allocation strategies. Key species or characteristics that are especially sensitive to changes in water availability or quality should be identified. Understanding the relationship of ecoregions, ecological communities, and watersheds is integral to the development and application of relevant assessment protocols.

Objective(s):

1.1.A: Integrated Resource Management Strategy

1.1.B: Ecological Integrity Assessment

1.1.C: Future Transfers

1.1.D: Transfer Assessment

1.1.E: Transfer Management

1.1.F: Transfer Assessment

1.1.G: Drought Allocations

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