Neuse Watershed_Model Selection Memo Final.docx

respec.com RSI(RAP)-W0392.22001/3-23/2

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Rapid City, SD 57703
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EXTERNAL MEMORANDUM
To: Pam Behm Modeling and Assessment Branch Chief North Carolina Department of Environmental Quality 217 West Jones Street Raleigh, NC 27603
cc: Project Central File W0392.22001
From: Seth Kenner
Project Manager RESPEC P.O. Box 725 Rapid City, SD 57709
Date: March 1, 2023
Subject: Selection of HSPF Watershed Model for the Neuse River
This memorandum discusses the selection of the watershed model to support the North
Carolina Department of Environmental Quality’s Division of Water Resources (DWR’s)
adaptive management efforts to protect and restore the Neuse River Estuary. The selected
model must be capable of the following:
/ Determining transport and delivery factors for point-source discharges and nutrient
offset credits
/ Ensuring a scientifically sound modeling system that represents each component of
the Neuse River Watershed (e.g., land areas, stream channels, waterbodies, point
sources, and diversions)
/ Representing nutrient transport and enabling the calculation of delivery factors.
Based on these criteria, RESPEC Company, LLC (RESPEC) selects U.S. Environmental
Protection Agency's (EPA's) Hydrological Simulation Program – FORTRAN (HSPF) as the
modeling software to develop the Neuse River Watershed model. This memorandum provides
additional details of the rationale behind the selection of HSPF for the Neuse River modeling
project.

HSPF OVERVIEW AND RATIONALE FOR SELECTION
A calibrated watershed model is a standard tool for the developing and evaluating modern
nutrient strategies. This model will be a core product that DWR staff, stakeholders, and the
Environmental Management Commission rely on in continually refining the Neuse Nutrient
Strategy rules. Therefore, the selected watershed model must be widely accepted,
defensible, freely obtained, and transparent in its algorithm representations.
Pam Behm // 2
March 1, 2023

RESPEC staff possess comprehensive knowledge of a wide range of watershed and water quality
models. For this model selection, RESPEC also consulted the EPA-sponsored report, TMDL Model
Evaluation and Research Needs [Shoemaker et al., 2005]. Among the watershed models referenced in
the report, HSPF is the only one listed as a detailed watershed model. Along with the Loading Simulation
Program in C++ (LSPC), which is derived from HSPF, HSPF is noted as one the few watershed models
capable of simulating land processes and receiving water processes simultaneously. The report also
notes that HSPF has been widely reviewed and applied throughout its long history [Hicks, 1985;
Ross et al., 1997; Tsihrintzis et al., 1996]. One of the largest applications of the model was to the
Chesapeake Bay Watershed as part of the EPA’s Chesapeake Bay Program’s management initiative
[Donigian et al., 1990; Donigian and Patwardhan, 1992]. HSPF has demonstrated its effectiveness
through a long history of successful model applications. The model is free and nonproprietary, and its
source code is available through GitHub (https://github.com/respec/FORTRAN).

HSPF was first publicly released in 1980 and was developed by HydroComp, Inc. [Johanson et al., 1980]
under contract with EPA. HSPF is a continuous watershed simulation model that runs on an hourly
timestep and produces a time series of water quantity and quality at any point in a watershed. The HSPF
model represents the dynamic and complex soil, groundwater and surface water processes, and
impacts from point and nonpoint sources of pollution. The model is an extension and reformulation of
several previously developed models: the Stanford Watershed Model (SWM) [Crawford and Linsley,
1966]; the HSP, including HSP Quality [HydroComp, Inc., 1977]; the Agricultural Runoff Management
(ARM) model [Donigian and Davis, 1978]; and the Nonpoint Source Runoff (NPS) model [Donigian and
Crawford, 1977]. HSPF Release 12.5 will be used for the Neuse River modeling.

HSPF uses several software tools developed by the U.S. Geological Survey for providing interactive
capabilities on model input, data storage, input-output analyses, and calibration. The modeling program
was incorporated into EPA’s BASINS modeling system. BASINS was initially developed by Tetra Tech,
Inc., and has been maintained and enhanced by RESPEC staff since 1998. The main purpose of BASINS
is to analyze and develop TMDL standards and guidelines nationwide. The most recent version is
BASINS 4.5 [EPA, 2019], which is based on an open-source code concept and includes numerous
models as plug-in components (e.g., HSPF, SWAT).

RESPEC is uniquely qualified to support the entire process of applying HSPF. Our staff are among the
principal scientists and engineers who participated in the original development of HSPF. Since 1981,
our staff members have performed all the HSPF code maintenance for the EPA, and our responsibility
continues today. In this capacity, we are widely regarded as the premier experts in all operational,
software, and application aspects of the model. Our staff members have also been the principal authors
of all versions of the HSPF User’s Manual [Bicknell et al., 2001] and the HSPF Application Guide, as well
as the customized HSPF guidance manual that was created to address the Minnesota Pollution Control
Agency’s current requirements for HSPF model applications. We also developed the EPA Technical
Notes, as posted on the EPA BASINS modeling system website, to help watershed modelers properly
select, apply, and parameterize model applications. We have a long history of developing and applying
models and ensuring that the models are well documented and that training is available to build end-
user capacity.

RESPEC also recommends using the Scenario Application Manager (SAM) for this project. RESPEC’s
HSPF SAM is a user-friendly, comprehensive decision-support tool for planning and implementing
targeted actions to restore or protect water quality. The framework of the HSPF SAM includes a
Geographic Information System (GIS) for best management practice (BMP) site selection; a BMP
database with pollutant-removal efficiencies and associated costs; and scenario analysis, optimization,
Pam Behm // 3
March 1, 2023

and reporting capabilities. SAM facilitates planning to achieve the water quality goals established
through watershed protection and restoration programs. SAM also assists in understanding watershed
conditions and identifying priority areas and BMPs that will provide the greatest water quality benefits
for each dollar invested. The HSPF SAM combination is uniquely suited for calculating pollutant
transport and delivery factors from any modeled source, including wastewater, to the outlet of every
modeled subwatershed. The delivery transport factors at a selected point of interest can be calculated
for each combination of modeled subwatershed and source. The transport factors are calculated by
dividing the loads delivered to the point of interest by the local loads directly from the source. The local
loads and the delivered loads that reach any modeled endpoint can be output using the HSPF SAM
software. The delivered loads output from HSPF SAM include gains and losses from instream
processes as the water flows through the watershed.

RESPEC has been providing in-person HSPF training for as long as we have been using the HSPF model
(i.e., 40 years), and in recent years, our training sessions for HSPF and SAM were virtual as well. Our staff
are seasoned at delivering such sessions and have trained many HSPF and HSPF SAM users in
Minnesota and Connecticut. Staff trained to use HSPF SAM will meet agency standards for regulatory
use and support in the Neuse River Watershed.
REFERENCES
Bicknell, B. R., J. C. Imhoff, J. L. Kittle, Jr., T. H. Jobes, and A. S. Donigian, Jr., 2001. HYDROLOGICAL SIMULATION PROGRAM - FORTRAN, Version 12, User’s Manual, prepared by Aqua Terra Consultants, Mountain View, CA. Crawford, N. H. and R. K. Linsley, 1966. Digital Simulation in Hydrology: Stanford Watershed Model IV, Technical Report No. 39, prepared by the Department of Civil and Environmental Engineering, Stanford
University, Stanford, CA. Donigian, Jr., A. S. and N. H. Crawford, 1977. Simulation of Nutrient Loadings in Surface Runoff with the NPS Model, EPA 600/3 77/065, prepared by HydroComp, Inc., Palo Alto, CA, for the U.S. Environmental Protection Agency, Athens, GA.
Donigian, Jr., A. S. and H. H. Davis, 1978. User’s Manual for Agricultural Runoff Management (ARM) Model, EPA-600/3-78-080, prepared by the U.S. Environmental Research Laboratory, Athens, GA. Donigian, A. S. Jr., and A. S. Patwardhan, 1992. “Modeling nutrient loadings from croplands in the Chesapeake Bay Watershed,” Proceedings of Water Resources Sessions at Water Forum ‘92, Baltimore, Maryland, August 2-6, 1992, pp. 817-822.
Donigian, A. S., Jr., B. R. Bicknell, L. C. Linker, J. Hannawald, C. Chang, and R. Reynolds, 1990. Chesapeake Bay Program Watershed Model Application to Calculate Bay Nutrient Loadings: Preliminary Phase I Findings and Recommendations, prepared by Aqua Terra Consultants, Mountain View, CA, for the U.S. EPA Chesapeake Bay Program, Annapolis, MD.
Hicks, C. N., 1985. Continuous Simulation of Surface and Subsurface Flows in Cypress Creek Basin,
Florida, Using Hydrological Simulation Program - FORTRAN (HSPF), Publication No. 86, prepared by Water Resources Research Center, University of Florida, Gainesville, FL. HydroComp, Inc., 1977. HydroComp Water Quality Operations Manual, prepared by HydroComp, Inc., Palo Alto, CA.
Pam Behm // 4
March 1, 2023

Johanson, R. C., J. C. Imhoff, and H. H. Davis, 1980. User’s Manual for the Hydrologic Simulation Program - FORTRAN (HSPF), EPA-600/9-80-105, prepared by the U.S. Environmental Protection Agency, Environmental Research Laboratory, Athens, GA. Ross, M.A., P. D. Tara, J. S. Geurink, and M. T. Stewart, 1997. FIPR Hydrologic Model: User’s Manual and Technical Documentation, prepared by the University of South Florida, Tampa, FL, for the Florida
Institute of Phosphate Research, Bartow, FL, and Southwest Florida Water Management District, Brooksville, FL. Shoemaker, L., T. Dai, and J. Koenig, 2005. TMDL Model Evaluation and Research Needs, EPA/600/R-05/149, prepared by Tetra Tech, Inc., Fairfax, VA, under the sponsorship of the U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Cincinnati, OH.

Tsihrintzis, V. A., H. R. Fuentes, and R. Gadipudi, 1996. “Modeling Prevention Alternatives for Nonpoint Source Pollution at a Wellfield in Florida,” Water Resources Bulletin, Journal of the American Water Resources Association (AWRA), Vol. 32, No. 2, pp. 317-331. U.S. Environmental Protection Agency, 2019. Better Assessment Science Integrating Point and Nonpoint Sources, BASINS Version 4.5 User’s Manual, prepared by the U.S. Environmental Protection
Agency, National Exposure Research Laboratory, Research Triangle Park, NC.
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