Delaware River Basin Focus Area Study: Ecological Flow Science

Science Center Objects

The Riverine Environmental Flow Decision Support System (REFDSS), models of river temperature, and evaluation of methods of determining Habitat Suitability Criteria were all products of the ecological-flow science component of the Delaware Focus Area Study.

National Water Census  •  Delaware River Basin  •  Process-Based Streamflow  •  Statistical Streamflow  •  Water Use  •  Ecological Flow

 

Environmental flow DSS

The Delaware River Basin Focus Area Study modified an existing decision support system to develop the Riverine Environmental Flow Decision Support System (REFDSS) for the Upper Delaware River, a system that is regulated by three headwater reservoirs. In regulated river systems, managers must develop flow release scenarios that attempt to balance both human and ecosystem needs. Meeting these natural flow needs is complex due to the myriad of interacting physical and hydrologic factors that affect river systems. Tools that synthesize the large amount of scientific data, and models developed to evaluate  these factors, support water resource professionals and help facilitate management of these systems.

Example output from REFDSS showing a “Flow Versus Habitat Chart”, which is a means of visualizing the habitat area as a function

Example output from REFDSS showing a “Flow Versus Habitat Chart”, which is a means of visualizing the habitat area as a function of streamflow (discharge).

 The REFDSS was designed to enable side-by-side evaluation of different flow management scenarios and compare their potential effects on habitat availability, allowing managers to make informed decisions on the best flow scenarios.

Key Findings and Results

  • The Upper Delaware REFDSS provides a user-friendly platform for evaluating alternative flow scenarios allowing flow managers to make informed decisions that support human and ecosystem water needs.
  • Read the report

 

Temperature modeling

In addition to flow, releases from impoundments can have a large influence on the water temperature downstream. The Focus Area Study developed and tested a suite of models to predict river temperature in the Upper Delaware River (upstream of the USGS stream gage at Lordville, NY). This section of the Delaware River is managed as a coldwater fishery, and the flow and temperature of this portion of the river is affected by the operation of three reservoirs (Cannonsville, Pepacton, and Neversink) in the headwaters. Total releases and whether the release comes from the bottom or top of the reservoir are important factors.

These models found that air temperature, upstream water temperatures, and upstream discharge are important determinants of water temperature. Upstream discharge and river temperatures reflect reservoir operations and the models indicate that reservoir management strongly influences the temperature regime in the upper basin.

The Focus Area Study also developed a regression model to predict thermally stressful events in the mainstream Delaware River near Lordville, NY, incorporating the effects of releases from Cannonsville and Pepacton reservoirs. Changes in temperature patterns are known to affect populations of fish and macroinvertebrates in river systems; therefore, models like the ones developed in the Delaware River can assist reservoir managers with making informed decisions about flow releases as they balance competing demands for water.

Key Findings and Results

  • Temperature models developed for the Delaware River were successful in predicting daily mean temperature across a broad range of conditions and will serve as important tools for managing thermal releases in regulated river systems such as the Delaware River.
  • Read the report

 

Methods to establish Habitat Suitability Criteria

REFDSS was used to examine alternative habitat suitability criteria (HSC) for aquatic life, a key component of environmental flow science. HSC for water depth and velocity were developed by the Delphi method (expert opinion) and by two primary literature meta‐analyses and compared to assess whether these independent methods produce analogous criteria for multiple fish species (e.g., rainbow trout, brown trout, American shad), and life stages (e.g., juvenile). The different HSC were then used in REFDSS to calculate habitat availability under three alternative reservoir management scenarios. The analysis pointed out the desirability of defining the environmental flow goal as either tolerance limits for the species of interest, or optimal habitat conditions when determining HSC.

Key Findings and Results

  • Habitat suitability criteria (HSC) in the Delaware River based on three reservoir management scenarios were evaluated using the REFDSS to assess how the Delphi and literature-derived HSC values would affect the amount of potentially available habitat for a suite of fish species and life stages. Some consistent and important differences were found in HSC generated using the different methodologies.
  • Read the report

 

(below) The Delaware River near Callicoon, NY. As a result of stormflow and water-management operations, stretches of the Delaware River can rapidly change from low-flow conditions with extensive areas of the riverbed exposed, to highly turbulent conditions during high-flow events. These rapid changes may negatively affect the abundance and distribution of riverine fauna and flora.

 

Delaware River near Callicoon, NY - low flow

Delaware River near Callicoon, NY - low flow conditions in late September 2010 (653 cubic feet per second). Facing downstream from the Callicoon bridge. (Credit: Kelly Maloney, USGS.)

Delaware River near Callicoon, NY - median flow

Delaware River near Callicoon, NY - median flow conditions in late August 2010 (1,430 cubic feet per second), facing upstream from the Callicoon bridge.

 

Delaware River near Callicoon, NY - high flow

Delaware River near Callicoon, NY - high flow during October 2010 (63,814 cubic feet per second), facing upstream from the Callicoon bridge. (Credit: Kelly Maloney, USGS)

 

 

 

 

 

 

 

 

 

 

 

 

 

National Water Census  •  Delaware River Basin  •  Process-Based Streamflow  •  Statistical Streamflow  •  Water Use  •  Ecological Flow