Integrated Water Availability Assessments: Delaware River Basin

Science Center Objects

Integrated Water Availability Assessments examine water supply, use, and availability. In the Delaware River Basin, which serves over 13 million people, water availability can be affected by drought, river temperature, salinity, and more. The Delaware River Basin IWAAs will investigate these and other water quantity, quality, and use issues to assess available water and how it changes over time.

USGS scientist kneels in a shallow stream while taking a sediment sample

USGS scientist collects eDNA (environmental DNA) samples from sediment in New Jersey as part of the Delaware River Basin IWAAs Algal Assessment. (Credit: Pamela Reilly, USGS New Jersey Water Science Center)

Integrated Water Availability Assessments (IWAAs) examine the supply, use, and availability of water. These assessments evaluate water quantity and quality in both surface and groundwater, as related to human and ecosystem needs and as affected by human and natural influences. When fully implemented, IWAAs will conduct regional water-availability assessments in each of ten medium-sized watersheds selected as Integrated Water Science (IWS) basins. These regional intensive assessments in reference basins, like the Delaware River Basin (DRB), form the mechanism to develop and evolve nationally integrated assessment and prediction capacity and applications.

The Delaware River is an interstate river, forming parts of the border for the states of New York, Pennsylvania, New Jersey and Delaware. In 2016, the DRB was providing drinking water for over 8 million people within the basin and an additional 5 million people which rely on freshwater diverted from the basin, to New York City, for example. These diversions, and water released for other purposes from reservoirs in the upper DRB, are managed by the states and the USGS Office of the Delaware River Master. Reservoir releases in the DRB have implications for both water quantity and quality. When and how water is released affects downstream conditions, like the potential for drought, river temperature variations, and the location of the salt front, which is where freshwater from the Delaware River mixes with salty water from the Delaware Bay. The "Water Science and Management in the Delaware River Basin" data visualization story describes these issues and their connectivity in the DRB.

In addition to the basin water quantity and quality challenges related to reservoir releases, the mainstem of the Delaware River contains both non-tidal (upper basin) and tidal (lower basin) segments, and thus is affected by traditional inland surface water issues, like temporal and spatial variability in streamflow and changing water quality, and by coastal processes, like saltwater intrusion of groundwater resources and the migration of the salt front into the tidal segment of the river. The IWAAs and Next Generation Water Observing Systems (NGWOS) Programs, taking into account the priorities of basin stakeholders, are currently collaborating to combine existing and new data collection with integrated assessments to address these and other water availability issues.

The DRB IWAAs project is divided into a pilot, which began in 2019, and three additional phases. The components of the pilot are currently underway and are described below in more detail. While the work of the pilot preceded the development of the larger IWAAs strategy, these efforts are valuable because they provide a foundation for the study of critical issues in the DRB.


Components of the Delaware River Basin Regional IWAAs pilot

The DRB IWAAs pilot project was launched in 2019 in response to the initiation of the NGWOS Program’s activities in the basin. The resulting studies were developed to address stakeholder concerns and to create the foundation for future work of the IWAAs Program.

Water availability and water quality trends are of interest to DRB stakeholders who want to identify streams that are experiencing water quality degradation and the causes of that degradation, and to track the progress and effectiveness of conservation efforts. The Multisource Surface-Water-Quality Status and Trends Assessment compiled and harmonized discrete surface-water-quality data from the Water Quality Portal including data collected by the USGS, U.S. Environmental Protection Agency, Delaware River Basin Commission, and other DRB stakeholders. This fact sheet describes the data harmonization process and the resulting dataset, containing over 1.5 million data records. These data were used to generate long-term trends in water quality for 16 priority parameters. This foundational dataset provides the information needed to summarize surface-water-quality trends for the DRB, explore how changing water quality affects water availability, and investigate the influence of streamflow trends and potential water-quantity changes on water quality. (Ongoing)

USGS scientist stands in a chest-high stream, in the rain, holding a sampler.

USGS scientist deploys a Solid Phase Adsorption Toxin Tracking (SPATT) sampler in New Jersey as part of the Delaware River Basin IWAAs Algal Assessment.(Credit: Heather Heckathorn, USGS New Jersey Water Science Center)

Harmful algal blooms (HABs) pose threats to humans and aquatic ecosystems by creating aquatic conditions which can produce toxins, reduce dissolved oxygen concentrations, and alter aquatic food webs. The DRB Algal Assessment is focusing on characterizing algal communities and the likelihood of nuisance/harmful algal bloom occurrence within four sub-watersheds of the DRB in New Jersey by measuring algal biomass, the presence of algal groups responsible for toxins and nuisance blooms, nutrients, and other parameters. This project also explored novel sampling techniques including Solid Phase Adsorption Toxin Tracking (SPATT) samplers and, in collaboration with the USGS Leetown Science Center, new sampling methods and processing techniques for eDNA. Results will be used to develop algal stressor models to predict the responses of algal communities to nutrients, flow, temperature, and other potential variables in these watersheds. (Ongoing)

Understanding baseflow, which is groundwater that seeps to the surface and sustains many streams and rivers, and how much, when, and where it is present, is necessary to assess the vulnerability and potential response of aquatic systems to changes in environmental conditions. The DRB Assessment of Baseflow Contributions to Streamflow, which generated a daily and monthly time series of baseflow estimates at reference locations in the DRB, improves our understanding of how and when groundwater is sustaining surface-water supply. This pilot study supports the future development of basin-wide estimates and maps of baseflow for integrated predictions of water supply and the factors that influence supply, and inform questions about the effects of natural and human-induced changes in the environment, like drought. (Ongoing)

Quantifying and predicting water quantity in the DRB enhances our understanding of many related hydrologic processes - including expanding our ability to predict drought and low flow conditions. The Simulation and Analysis of Groundwater Dynamics component of the DRB pilot will create a basin-specific groundwater flow model able to hindcast and forecast monthly variability in groundwater conditions in the DRB. The DRB model will more accurately capture conditions in the shallow subsurface of the basin, thus improving the ability to predict the potential effects of climate variability and drought on groundwater contributions to streamflow. The utility of the model to represent groundwater conditions at local scales will be tested using recently developed methods to enhance model discretization and resolution. (Ongoing)

Understanding drought history in the DRB can contextualize current conditions and help identify drivers of drought in the future. A characterization of the long-term history of the magnitude, frequency, duration, and severity of droughts in the DRB was conducted and published in the article Hydro-climatic drought in the Delaware River Basin. This work used both the instrumented record and paleo-reconstructions to determine climatic drivers of drought. (Completed)


Delaware River Basin Regional IWAAs Phases

In addition to the pilot, Phase 1, which began in October of 2020, will last two years and will focus on identifying existing data and modeling tools and strategic planning. Phase 2 of the project will include the development of integrated assessments and predictions, and Phase 3 will focus on product delivery.

Table showing the timing of the Delaware River Basin IWAAs pilot and three phases

The Delaware River Basin IWAAs pilot was conducted in 2019 and 2020, and the 10-year regional IWAAS project began in 2021. Completion is anticipated by 2031.

The core objectives of Phase I - understanding relevant past and current work in the basin, and making data discoverable and usable - are crucial for Phase 2 activities as well as activities being conducted through other projects working in the basin.  The main tasks of Phase 1 can be grouped into two broad categories – (1) data and model compilation and assessment and (2) science plan development.

Specific objectives related to data and model compilation and assessment include:

  1. Conducting a retrospective analysis of existing data, water-availability assessments, and prediction tools
  2. Cataloging and developing an access structure to historic data sets and current observation networks relevant to the topics noted above. 
  3. Creating multisource harmonized and screened data sets for use in water-availability assessment, model building, and assessment of trends and drivers. 
  4. Development of a streamlined process to provide regular updates to the data sets (#3).

Objectives related to science planning include:

  1. Developing a detailed strategic modeling plan to improve the water-availability integration and prediction capacity for IWAAs core and regionally relevant water-availability components and metrics.
  2. Creating a detailed strategic plan to improve representation of trends, and identify drivers of those trends, of IWAAs core and external and internal stakeholder-priority availability components.

Currently underway, Phase 1 is preparing the launching pad from which IWAAs will assess water supply, demand, and the factors that influence water availability in the DRB toward the eventual delivery of water availability forecasts, both in the region and nationally. Successful completion of Phase 1 requires substantial coordination with other projects working in the basin to ensure that components of water availability assessments being conducted by those projects are developed in a way that facilitates eventual development of an integrated water availability assessment and prediction capacity. The activities of the DRB pilot are also currently active and will be incorporated into the future science planning for the basin.