Nutrient Planning and Management For Long Island Sound Water Quality Improvements
Client: HydroQual, Inc., Mahwah, NJ
Nutrient loadings from watersheds within the state of Connecticut
have a large impact on the water quality and aquatic health of
Long Island Sound (LIS).
In this study, funded by EPA and the
Connecticut Department of Environmental Protection (CTDEP),
a statewide watershed model was developed by AQUA TERRA Consultants
using the U.S. EPA Hydrological Simulation Program - FORTRAN (HSPF)
and the U.S. Geological Survey's graphical user interface GenScn
to quantify all sources of key nutrients to the LIS.
The Connecticut Watershed Model (CWM) was developed to evaluate
nutrient sources and loadings within each of six nutrient
management zones that lie primarily within the state
of Connecticut, and assess their delivery efficiency to LIS.
The Connecticut Watershed Model evolved by first performing
calibration and verification on three small test basins across the
state (Norwalk, Quinnipiac, and Salmon) representing a range of
land uses, including urban, forest, and agricultural. The model
was then extended to three major river calibration basins
(Farmington, Housatonic, and Quinebaug) and subsequently expanded
to a statewide model by using the most spatially applicable set of
calibrated watershed parameters in 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 evaluate potential impacts of
alternative best management practices (BMPs), pollutant removal
efficiencies were extracted from the National Pollutant Removal
Performance Database for Stormwater Treatment Practices for
BMP categories determined to be technically feasible and effective
at removing the pollutants of concern.
Composite pollutant removal efficiencies were then computed based
on an assumed mix of BMPs for both urban and agricultural lands.
Alternative levels of BMP implementation were represented by
defining increasing fractions of the subwatershed landuses and
areas served by BMPs. Ultimately, 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 CWM was specifically designed to
promote continuing use by CTDEP staff to assess additional BMPs,
implementation levels, and point source controls for nutrient
reductions to LIS.