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Great Falls of the Passaic River at Paterson, N.J

Great Falls of the Passaic River at Paterson, N.J.

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Data Model of Stream Flows: Baseline Identification & Analysis for the Ecological Flow Goals

Project Title: Data Model of Stream Flows: Baseline Identification & Analysis for the Ecological Flow Goals
Project Number: 2454C2R
Project Chief:
Project Start Date: 01-JUN-2005
Project End Date: 30-SEP-2007

Project Objectives

The objectives of the project is to identify a series of baseline hydrographs for surface water gaging stations with greater than 20 years of flow record and calculate the stream characteristic data for these baseline periods using the NJHAT software.

Statement of Problem

It is the goal of NJDEP to evaluate potential impacts of a proposed water withdrawal by determining the change in streamflow characteristics. This is done by:

  1. obtaining a daily streamflow hydrograph at the site of interest;
  2. analyzing the daily hydrograph during a 'baseline' period to determine the natural variability of selected streamflow characteristics;
  3. creating an impacted daily hydrograph that shows the net effect of the proposed withdrawal;
  4. analyzing the impacted hydrograph to determine impacted streamflow characteristics;
  5. comparing the impacted streamflow characteristics to the variability of those characteristics during the baseline period. This baseline period is considered to be a period during which the stream has supported a non-impaired or acceptable ecology.

The recent 4-year joint USGS/NJDEP research project 'Ecological Flow Goals' has resulted in the New Jersey Hydrologic Assessment Tool (NJHAT). This analysis software determines streamflow characteristics and variability based on a daily hydrograph. The project proposed here supplies additional information and tools identified as necessary during that earlier project.

Strategy and Approach

Task 1) Identify baseline periods for rivers

A minimum length of record to generate statistically significant results will be determined. Stream gages with an acceptable length of record and that are suitable for NJHAT analysis will be identified. For each eligible gage, a baseline period will be determined during which streamflow is considered to be least impaired by anthropogenic changes such as impoundments, withdrawals, and/or land-use changes. This determination will be based on statistical analysis of flows during different time periods, research on historic changes in the watershed, and the best professional knowledge of the staff of USGS and NJDEP. It is understood that many portions of NJ changed considerably between pristine conditions and the start of streamflow measurements. In such cases the year 1921 (earliest stream gages) will be considered as the start of the baseline period.

Task 2) Establish natural variability of baseline period for all gages

For all of the eligible gages and associated baseline periods identified in step 1, flows will be analyzed using the New Jersey Hydrological Assessment Tool and the 25%, 50%, and 75% values of all evaluation parameters that support this determination will be calculated.

Task 3) Deliverables

The results of Task 1 and 2 will be presented on the USGS web site and all results will be provided to the NJDEP in an Excel file.

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