NUTRIENT PLANNING AND MANAGEMENT FOR LONG ISLAND SOUND
WATER QUALITY IMPROVEMENTS
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Client: HydroQual, Inc. Mahwah, NJ, and
CT Dept of Environmental Protection, Hartford, CT
Nutrient loadings from watersheds
within the state of Connecticut have
a significant impact on the water
quality and aquatic health of Long
Island Sound (LIS). In this study,
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funded by EPA and the Connecticut
Department of Environmental
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Protection (CT DEP), AQUA
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TERRA, under subcontract to
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HydroQual, Inc. developed a
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statewide watershed model using the
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Rivers
Lon
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CT State Boundary
Management Zones
U.S. EPA Hydrological Simulation
Test Basins
Calibration Basins
Program - FORTRAN (HSPF) and
the U.S. Geological Survey's
graphical user interface, GenScn, to evaluate nutrient loadings to the LIS. The study
objectives were to (1) quantify all sources of key nutrients within each of the six nutrient
management zones that lie primarily within the state of Connecticut, and their delivery
efficiency to LIS; (2) identify nonpoint source management opportunities within each
zone; and (3) compile data within a watershed model framework that allow load and
delivery analysis of management options and other variables.
AQUA TERRA had the lead role in all tasks related to the development of the CT
Watershed Model (CTWM) including: data review and application database
development, model application on test watershed(s), expansion of the model from the
test watersheds to a state-wide model, identifying appropriate BMPs, evaluating nutrient
loadings under current and future buildout scenarios and alternative BMP
implementation, and providing major portions of the final report, as well as the final
model code and associated files. AQUA TERRA worked closely with CT DEP staff in
evaluating appropriate GIS databases and other data including land use/land cover, soils,
topography, natural basin boundaries, dams, diversions, pollution sources, atmospheric
deposition, snow depth, hydrography, channel cross-sections, and lake/reservoir
operations and characteristics. The data were incorporated into an application database
using the companion database system for HSPF, the Watershed Data Management
(WDM) file, within the GenScn user interface framework.
HydroQual developed estuary models for three estuaries to
assess delivery efficiency, or pollutant attenuation, to assess
estuary losses and subsequent delivery to LIS.
The CTWM evolved by first performing calibration and validation on three small test
basins across the state (Norwalk, Quinnipiac, and Salmon) representing a range of land
uses, including urban, agriculture, and forest/natural conditions. The model was then
extended to three major calibration river basins (Farmington, Housatonic, and
Quinebaug) and subsequently expanded to a statewide model by using the most spatially
applicable set of calibrated watershed parameters for the non-calibrated areas. Based on
urban growth rates predicted to occur by the year 2020, full buildout scenarios and
resulting loads to LIS were developed for the six management zones to assess the impacts
of potential growth scenarios.
To evaluate potential impacts of alternative best management practices (BMPs), AQUA
TERRA extracted pollutant removal efficiencies from various literature sources (e.g.
National Pollutant Removal Performance Database for Stormwater Treatment Practices)
for generalized BMP categories determined to be technically feasible and effective at
removing the pollutants of concern. Composite pollutant removal efficiencies were then
derived to cover the range of appropriate efficiencies for BMPs applicable to urban and
agricultural lands. Three alternative levels of BMP implementation were represented by
defining increasing percentages (10%, 30%, 50%) of the subwatershed landuses and areas
controlled by BMPs. Ultimately, these three nonpoint source BMP implementation
scenarios were developed and simulated, in addition to the full buildout scenario with and
without BMPs; and the associated nutrient reductions were evaluated. The user-friendly
interface and framework of the CTWM was specifically designed to promote continuing
use by CT DEP staff to assess additional BMPs, implementation levels, and point source
controls for nutrient reductions to LIS.
In addition to having the major role in the CTWM development, AQUA TERRA further
supported the project by preparing major portions of the final report, participating in a
training workshop for state personnel, attending meetings, and providing the model setup
and associate data files for use by CT DEP staff.