st andrews bay hydrodynamic and water quality modeling report€¦ · analysis simulation package...

St Andrews Bay Hydrodynamic and Water Quality Modeling Report

Prepared By: Tetra Tech, Inc. 2110 Powers Ferry Rd. Suite 202 Atlanta, GA 30339 770-850-0949 www.tetratech.com

Prepared For: Environmental Protection Agency – Region 4 61 Forsyth St Atlanta, GA 30303

September 2009

St Andrews Bay Hydrodynamics and Water Quality Model

TABLE OF CONTENTS TABLE OF CONTENTS.............................................................................................................. 2

LIST OF FIGURES....................................................................................................................... 4

LIST OF TABLES......................................................................................................................... 5

1.0 INTRODUCTION............................................................................................................ 6

1.1 MODELING APPROACH................................................................................................................. 6 1.2 PROJECT LOCATION ..................................................................................................................... 7

2.0 EFDC HYDRODYNAMIC MODEL ............................................................................. 8

2.1 MODEL SELECTION ...................................................................................................................... 8 2.2 MODEL HISTORY.......................................................................................................................... 8

3.0 EFDC APPLICATION ON ST ANDREWS BAY ...................................................... 10

3.1 HYDRODYNAMIC DATA.............................................................................................................. 10 3.3 MODEL SEGMENTATION............................................................................................................. 11 3.4 MODEL BOUNDARY CONDITIONS............................................................................................... 13

3.4.1 Surface Water Elevation ....................................................................................................... 14 3.4.3 Meteorological...................................................................................................................... 14 3.4.4 Salinity and Temperature Boundary..................................................................................... 14

4.0 EFDC CALIBRATION ................................................................................................. 15

4.1 WATER SURFACE ELEVATION CALIBRATION ............................................................................. 15 4.2 TEMPERATURE CALIBRATION .................................................................................................... 17 4.3 SALINITY CALIBRATION............................................................................................................. 17

5.0 WASP WATER QUALITY MODEL........................................................................... 19

5.1 MODEL SELECTION .................................................................................................................... 19 5.2 MODEL HISTORY........................................................................................................................ 19

6.0 WASP APPLICATION ON ST ANDREWS BAY...................................................... 20

6.1 INCORPORATION OF THE HYDRODYNAMIC MODELING RESULTS ............................................... 20 6.2 MODEL BOUNDARIES ................................................................................................................. 20

6.2.1 Offshore Boundary ............................................................................................................... 20 6.2.2 Intracoastal Boundaries ....................................................................................................... 20 6.2.3 Freshwater Boundaries ........................................................................................................ 21

6.3 MODEL LOADS........................................................................................................................... 21 6.3.1 Point Source Loads............................................................................................................... 21 6.3.2 Marsh Loadings.................................................................................................................... 21

6.4 MODEL KINETICS ....................................................................................................................... 22 6.4.1 Decay rate K1 (1/day) for Carbonaceous BOD ................................................................... 23 6.4.2 Ammonia Reaction Rates...................................................................................................... 23 6.4.3 Sediment Oxygen Demand.................................................................................................... 23 6.4.4 Reaeration ............................................................................................................................ 23 6.4.5 Chlorophyll a and Light parameters .................................................................................... 24 6.4.6 Atmospheric Deposition........................................................................................................ 24

7.0 WASP MODEL CALIBRATION................................................................................. 24

7.1 CBOD NUTRIENT,AND CHLOROPHYLL A COMPARISON .......................................................... 25 U,

7.2 DISSOLVED OXYGEN COMPARISON............................................................................................ 25

8.0 SUMMARY AND CONCLUSIONS............................................................................. 27

Prepared by Tetra Tech 2


9.0 REFERENCES ............................................................................................................... 28

APPENDICES ............................................................................................................................. 30



LIST OF FIGURES

Figure 1-1 ........................................................................... 7 St Andrews Bay LocationFigure 3-1 .................................................................... 11 St Andrews Bay BathymetryFigure 3-2 ................................................................................ 12 St Andrews Bay GridFigure 3-3 ............................................................ 13 St Andrews Bay Grid BathymetryFigure 4-1 .......................... 15 Hydrodynamic Model Calibration Comparison StationsFigure 4-2 ........... 16 2003-2007 Water Surface Elevation Comparison at Panama CityFigure 4-3 ........ 16 August 2007 Water Surface Elevation Comparison at Panama CityFigure 4-4 ............................. 17 Temperature Salinity Comparison at St Andrews BayFigure 4-5 .................................................. 18 Salinity Comparison at St Andrews BayFigure 7-1 .. 25 Modeled and Measured Ammonia (mg/l) at Escatawpa River Mile 7.7Figure 7-2 ............ 26 Modeled and measured DO (mg/l) at Escatawpa River mile 7.7.



LIST OF TABLES

Table 6-1 .............................................. 21 Model Inputs for NPDES Permitted FacilitiesTable 6-2 ............................................................................. 22 Model Input Marsh LoadsTable 6-3 .......................................................... 22 Seasonal Distribution of Marsh LoadsTable 6-4 ............................................... 24 Phytoplankton Coefficients in WASP ModelTable 6-5 ..................................... 24 Phytoplankton Light Coefficients in WASP Model



1.0 INTRODUCTION Tetra Tech, Inc. (Tetra Tech) was contracted by the Environmental Protection Agency (USEPA) Region 4 to develop a three-dimensional hydrodynamic and water quality model using the Environmental Fluid Dynamics Code (EFDC) for the hydrodynamic and the Water Quality Analysis Simulation Package (WASP) for the water quality modeling.

This report includes both the hydrodynamic and water quality modeling results. The calibration of the models was performed to data spanning the years 2003-2007 for the hydrodynamics and the years 2005-2007 for the water quality model, periods with the most comprehensive dataset.

The goal of the hydrodynamic and water quality models was to produce a defensible and accurate model that EPA Region 4 and the State could use to make management decisions for St Andrews Bay.

1.1 Modeling Approach

Accepted water quality modeling procedures were used to calibrate the St Andrews Bay model. The water quality model incorporated normal oxygen dynamics, including reaeration, sediment oxygen demand (SOD), Carbonaceous Biochemical Oxygen Demand (CBOD) and uptake, Nitrogenous Biochemical Oxygen Demand (NBOD) and uptake, and algal activity. The modeling approach was a five step process:

1. Incorporation of the hydrodynamic modeling results. 2. Determination of upstream and ocean boundary conditions. 3. Development of point sources loadings, marsh loadings, and tributary loadings. 4. Determination of the instream modeling parameters and kinetic rates. 5. Calibration to measured water quality data.



1.2 Project Location

The St Andrews Bay watershed is the only major basin that lies entirely within the Florida Panhandle (Figure 1-1). The bay system consists of four coastal plain interconnected estuaries: St Andrews Bay, East Bay, West Bay, and North Bay. St Andrews bay is connected to the Gulf of Mexico through a main pass and branches inland into the East and North Bays. The East and West Bays are connected to the Intracoastal Waterway. The St Andrews Bay watershed covers about 750,000 acres in Walton, Washington, Jackson Calhoun, Gulf and Bay counties with 61% located in Bay County. Deer Point Lake Reservoir is included in the watershed discharging into the North Bay, being the primary source of drinking water for Bay County.

Figure 1-1 St Andrews Bay Location



Deer Point Lake Reservoir fresh water discharge into Norht Bay is the primary source of freshwater to the system and is critical to the ecology of the estuary. Surface tides in the Gulf of Mexico at the entrance of the St Andrews Bay are predominantly diurnal with an average range of 1 foot, or 30 cm. Water temperatures range from highs of 86 to 92o F (30o-33o C) to a low of 50o F (10o C).

The St Andrews Bay watershed supports extensive habitat for many terrestrial and aquatic species. The populations of wildlife and plants found in the basin are very diverse and unique due to the different habitats found in it, including the coastal marshes and estuaries. The water quality is highly influenced by its natural geographic location, weather patterns, and human uses.

2.0 EFDC HYDRODYNAMIC MODEL

2.1 Model Selection

The EFDC was selected to perform the hydrodynamic simulations because it was able to fulfill all of the requirements presented in the goals of the study. EFDC has been applied on many waterbodies within USEPA Region 4 for TMDL and permitting modeling projects including complex systems such as Mobile Bay, AL, Neuse River and Estuary, NC, Brunswick Harbor, GA, Fenholloway River and Estuary, FL, Loxahatchee River and Estuary, FL, Indian River Lagoon, FL, Lake Worth Lagoon FL, Florida Bay, Lake Okeechobee, FL, Cape Fear River, NC, and St. Johns River, FL. EFDC has proven to capture the complex hydrodynamics in similar systems.

The EFDC model is a part of the USEPA TMDL Modeling Toolbox due to its application in many TMDL-type projects. As such, the code has been peer reviewed and tested and has been freely distributed and supported by Tetra Tech. EFDC was developed by Dr. John Hamrick and is currently supported by Tetra Tech for USEPA Office of Research and Development (ORD), USEPA Region 4, and USEPA Headquarters. The EFDC model is nonproprietary and publicly available through USEPA Region 4 and USEPA ORD from the Watershed and Water Quality Modeling Technical Support Center (http://www.epa.gov/athens/wwqtsc/index.html). The models, tools, and databases in the TMDL Modeling Toolbox are continually updated and upgraded through TMDL development in Region 4.

2.2 Model History

The EFDC model comprises an advanced three-dimensional surface water modeling system for hydrodynamic and reactive transport simulations of rivers, lakes, reservoirs, wetland systems, estuaries, and the coastal ocean. The modeling system was originally developed at the Virginia Institute of Marine Science as part of a long-term research program to develop operational models for resource management applications in Virginia's estuarine and coastal waters (Hamrick, 1992). Since the EFDC model is public domain, with current users including universities, governmental agencies and engineering consultants. The following sub-sections describe the model's capabilities and previous applications and its theoretical and computational formulations.

The EFDC model’s hydrodynamic model component is based on the three-dimensional shallow water equations and includes dynamically coupled salinity and temperature transport. The basic physical process simulation capabilities of the EFDC hydrodynamic component are similar to those of the Blumberg-Mellor or POM model (Blumberg & Mellor, 1987), the U.S. Army Corps of Engineers' (USACOE) CH3D-WES model (Johnson, et al., 1993), and the TRIM model. Notable extensions to the EFDC hydrodynamic model include representation of hydraulic



structures for controlled flow systems, vegetation resistance for wetland systems (Hamrick and Moustafa, 1996), and high frequency surface wave radiation stress forcing for nearshore coastal simulations.

EFDC is a multifunctional, surface-water modeling system, which includes hydrodynamic, sediment-contaminant, and eutrophication components. The EFDC model is capable of 1, 2, and 3-dimensional spatial resolution. The model employs a curvilinear-orthogonal horizontal grid and a sigma or terrain following vertical grid. The EFDC model’s hydrodynamic component employs a semi-implicit, conservative finite volume-finite difference solution scheme for the hydrostatic primitive equations with either two or three-level time stepping. (Hamrick, 1992). The semi-implicit scheme is based on external mode splitting with the external mode being implicit with respect to the water surface elevation and the internal mode being implicit with respect to vertical turbulent momentum diffusion. Advective and Coriolis-curvature accelerations in both the external and internal modes are represented by explicit conservative formulations. Salinity and temperature transport are simultaneously solved with the hydrodynamics and dynamically coupled through an equation of state. The hydrodynamic component includes two additional scalar transported variables, a reactive variable which can be used to represent dye or pathogenic organisms, and a shell fish larvae variable which includes a number vertical swimming behavior options. Scalar transport options include a number of high accuracy advection schemes including flux corrected MPDATA and flux limited COSMIC. Additional hydrodynamic component features include, the Mellor-Yamada turbulence closure formulation, simulation of drying and wetting, representation of hydraulic control structures, vegetation resistance, wave-current boundary layers and wave induced currents, and dynamic time stepping. An embedded single and multi-port buoyant jet module is included for coupled near and far field mixing analysis.

The EFDC hydrodynamic model can run independently of a water quality model. The EFDC model simulates the hydrodynamic and constituent transport and then writes a hydrodynamic linkage file for a water quality model such as the WASP7 model. This model linkage, from EFDC hydrodynamics to WASP water quality, has been applied on many USEPA Region 4 projects in support of TMDLs and has been well tested (Wool et al., 2003). EFDC is also directly linked to Waterways Experiment Station CE-QUAL-ICM (Cerco and Cole, 1993).



3.0 EFDC APPLICATION ON ST ANDREWS BAY

3.1 Hydrodynamic Data

The simulation period for the purposes of the current study for the hydrodynamic model was the period from January 2003 to December 2007. The data utilized in the development of hydrodynamic boundary conditions and for the purpose of model calibration consists of the following types:

Measured salinity and temperature at stations throughout the system

Freshwater flow discharges from Deer Point Reservoir,

Immediate watershed flow determination using the LSPC model

Measured tides at Panama City,

Measured meteorological data,

Data collection of salinity and temperature were conducted by the Florida DEP as well as other organizations such as USEPA and USGS.

Deer Point Reservoir discharge to North Bay was obtained from water mass balance calculation of the lake watershed.

Bathymetry data for the Gulf of Mexico adjacent area, St Andrews, North, East and West Bays were obtained from the National Geophysical Data Center. This bathymetry is presented in Figure 3-1.



Figure 3-1 St Andrews Bay Bathymetry

3.3 Model Segmentation

The Gulf of Mexico in the vicinity of St Andrews Main Pass and St Andrews, North, East and West Bays were segmented into curvilinear orthogonal computational grid cells representing horizontal dimensions for the hydrodynamic model. The hydrodynamic model utilizes a sigma coordinate system that allows for a fixed number of layers in the vertical direction, and as depth changes, the vertical layers stretch or shrink. The waterbody was segmented into 777 horizontal grid cells with 4 layers (Figure 3-2).

In the Gulf of Mexico, the average dimensions of the cells are 3450 ft by 2460 ft (1,050 by 750 meters). In St Andrews Bay the average cell is 1380 ft (420 m) long by 1480 ft (450 m) wide, in the North Bay 1540 ft (470 m) long by 1740 ft (530 m) wide, in the East Bay 2625 ft (800 m) long by 2625 ft (800 m) wide, and in the West Bay 4100 ft (1250 m) long by 3120 ft (950 m) wide.

The bathymetry data was interpolated into the grid resulting in the grid bathymetry shown in Figure 3-3.



Figure 3-2 St Andrews Bay Grid



Figure 3-3 St Andrews Bay Grid Bathymetry

3.4 Model Boundary Conditions

Deterministic time variable models predict conditions within the computational domain of the model based upon perturbations within the model grid caused by outside forcing functions, or boundary conditions. These forcing functions need to be described to the model in order to predict the perturbations that occur within the model grid. The forcing functions that are required in the hydrodynamic model include:

Water surface elevation (tides),

Freshwater inflow,

Meteorological conditions (wind, solar radiation, etc.),

Salinity and temperature (density).



For calibration purposes, time dependent or constant values for each of these parameters must be applied at each of the appropriate boundaries for the entire model simulation period. These values were applied at all of the boundaries within the system including:

Open boundary in the Gulf of Mexico (water surface elevation),

Open boundary with the Intracoastal Waterway at the East and the West Bays,

Deer Point Lake discharge, and

Adjacent watersheds Creek freshwater inflows.

The following presents discussions of how the boundary conditions were determined and applied for the model calibration simulations.

3.4.1 Surface Water Elevation

Water surface elevation data were not available as direct measurements within the Gulf of Mexico at the open boundary of the model domain or at the East and West Bay connection with the Intracoastal Waterway. In order to generate the water surface elevation boundary forcing conditions, tidal measurements at Panama City in St Andrews Bay were utilized to generate the water surface elevation boundary values. The time series at the open boundary was time shifted and the amplitude adjusted until the simulated tide at the tidal gauge location in Panama City matched the measurements.

3.4.3 Meteorological

The meteorological data needed for the hydrodynamic model were obtained from the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC) from 1997 to 2008. Meteorological parameters collected at Panama City Bay County Airport station (WBAN 03882) in Panama City, FL used in the modeling effort were air temperature, dew point temperature, cloud cover, precipitation, and wind direction and speed. These conditions were considered spatially uniform throughout the modeled domain.

3.4.4 Salinity and Temperature Boundary

Temperature boundary conditions were generated based on in stream measurements. Salinity on the open boundary was based on values in the Gulf of Mexico measured close to St Andrews Main Entrance. Direct measurements for the boundaries were not available.



4.0 EFDC CALIBRATION The hydrodynamic model was calibrated to available data from January 2003 to December 2007. Figure 4-1 illustrates the location of calibration stations throughout the modeled area.

The calibration objectives for the hydrodynamic model were to adequately represent the physics of the system by propagating momentum and energy throughout the system based upon freshwater inflow, tides, and wind. Another calibration objective was to have the ability to predict salinity and temperature that affect the hydrodynamics through density changes.

Figure 4-1 Hydrodynamic Model Calibration Comparison Stations

4.1 Water Surface Elevation Calibration

Water surface elevation data were compared for the only available station at Panama City which was also used to generate the boundary conditions. Water surface elevations in the area are affected by the astronomical tides, freshwater inflows, local wind as well as meteorological tides or wind surges in the Gulf of Mexico. Tides are caused by the gravitational attraction of the moon and the sun on the earth, for this reason they are called astronomical tides. Direct tides are influenced by the depth of ocean basins, by the Earth's rotation, and by the continental boundaries they touch. The actual tide at any location is therefore an indirect tide.

Figures 4-2 and 4-3 illustrate the observed versus predicted water surface elevation for the simulation period at Panama City.



Figure 4-2 2003-2007 Water Surface Elevation Comparison at Panama City

Figure 4-3 August 2007 Water Surface Elevation Comparison at Panama City



4.2 Temperature Calibration

The simulation of the time varying temperature was compared to measurements. Figure 4-4 and Figures A-1 through A-9 present time series of the simulated versus measured temperature for the simulation period of 2003-2007. The model captures the range and fluctuations of temperature throughout the system well.

Figure 4-4 Temperature Salinity Comparison at St Andrews Bay

4.3 Salinity Calibration

Time series plots were generated to compare model simulations to measured data of salinity. The time series comparisons for the simulation period 2003-2007 are shown in Figures 4-5 and A-10 through A-18. Time series of bottom and surface model salinity were compared to measured data. The plots reveal that the measured data is encompassed by the surface and bottom simulations for most of the stations following in general the trend and magnitude of the salinity intrusion. Time series comparisons were made with both surface and bottom simulations in order to provide the modeled range.



Figure 4-5 Salinity Comparison at St Andrews Bay



5.0 WASP WATER QUALITY MODEL

5.1 Model Selection

The Water Quality Analysis Simulation Program Version 7.0 (WASP7) was used for the water quality model based on it comparative advantages explained below. WASP7 is an enhanced Windows version of the USEPA Water Quality Analysis Simulation Program (WASP) (Di Toro et al., 1983; Connolly and Winfield, 1984; Ambrose, R.B. et al., 1988), with many upgrades to the user’s interface and the model’s capabilities. The major upgrades to WASP have been the addition of multiple BOD components, addition of sediment diagenesis routines, and addition of periphyton routines. WASP7 has features including a pre-processor, a rapid data processor, and a graphical post-processor that enable the modeler to run WASP more quickly and easily and evaluate model results both numerically and graphically. With WASP7, model execution can be performed up to ten times faster than the previous USEPA DOS version of WASP. Nonetheless, WASP7 uses the same algorithms to solve water quality problems as those used in the DOS version of WASP. The hydrodynamic file generated by EFDC is compatible with WASP7 and it transfers segment volumes, velocities, temperature and salinity, as well as flows between segments. The time step is also set in WASP7 based on the hydrodynamic simulation.

WASP7 helps users interpret and predict water quality responses to natural phenomena and man-made pollution for various pollution management decisions. WASP7 is a dynamic compartment-modeling program for aquatic systems, including both the water column and the underlying benthos. The time-varying processes of advection, dispersion, point and diffuse mass loading, and boundary exchange are represented in the basic program. Water quality processes are represented in special kinetic subroutines that are either chosen from a library or written by the user. WASP is structured to permit easy substitution of kinetic subroutines into the overall package to form problem-specific models. WASP7 comes with two such models, TOXI for toxicants and EUTRO for conventional water quality.

5.2 Model History

WASP7 is an enhancement of the original WASP (Di Toro et al., 1983; Connolly and Winfield, 1984; Ambrose, R.B. et al., 1988). WASP has a long history of application to various problems. Some applications have been validated with field data, or verified by model experiments and reviewed by independent experts. Earlier versions of WASP have been used to examine eutrophication of Tampa Bay; phosphorus loading to Lake Okeechobee; eutrophication of the Neuse River and estuary (Wool et al., 2003); eutrophication and PCB pollution of the Great Lakes (Thomann , 1975; Thomann et al., 1976; Di Toro and Connolly, 1980), eutrophication of the Potomac Estuary (Thomann and Fitzpatrick, 1982), Kepone pollution of the James River Estuary (O'Connor et al., 1983), volatile organic pollution of the Delaware Estuary (Ambrose, 1987), and heavy metal pollution of the Deep River, North Carolina (JRB, 1984). In addition to these, numerous applications are listed in Di Toro et al., 1983.



6.0 WASP APPLICATION ON ST ANDREWS BAY

6.1 Incorporation of the Hydrodynamic Modeling Results

The EFDC was used to perform the hydrodynamic simulations for the Escatawpa River and Estuary. The model and the application to St Andrews Bay are documented in the previous sections of this report. The water quality model was calibrated for the period ranging from January 2005 to December 2007.

The EFDC hydrodynamic model provides to WASP:

Ocean flow and tidal dynamics,

Freshwater inflows,

Three dimensional model cell structure and volumes,

Cell volumes and transport,

Salinity, and Temperature

The hydrodynamic modeling information is incorporated into the WASP model through the hydrodynamic linkage file.

6.2 Model Boundaries

The data that were available was used to establish the ocean boundary conditions, as well as the open boundaries with the Intracoastal Waterway in the East and West Bays and the upstream and freshwater inflows.

6.2.1 Offshore Boundary

Limited data were available to establish the ocean boundaries for dissolved oxygen (DO), carbonaceous biochemical oxygen demand (CBOD), and nutrients concentrations. Available measured data in the Gulf of Mexico near St Andrews bay entrance was used to determine the open boundary concentrations.

Ocean boundary DO levels were set at 7 mg/L. CBODu was set at 5.36 mg/L and ammonia at 0.03 mg/L. Total nitrogen and total phosphorous set at 0.26 and 0.04 mg/L respectively.

6.2.2 Intracoastal Boundaries

CBOD, ammonia, and DO boundary conditions at the Intracoastal waterway were determined from available water quality data measured at instream station close to these boundaries. Limited CBOD5 and ammonia data were available.

At the West Bay boundary CBODu was set to 5.36 mg/L, ammonia to 0.033 mg/L, and DO was set at 7.3 mg/L. Total nitrogen and total phosphorous were set at 0.997 and 0.06 mg/L respectively.

At the East Bay boundary CBODu was set to 5.36 mg/L, ammonia to 0.03 mg/L, and DO was set at 5 mg/L. Total nitrogen and total phosphorous were set at 0.75 and 0.04 mg/L respectively.



6.2.3 Freshwater Boundaries

Time series of CBOD and nutrient boundary conditions for the freshwater inflows were obtained from the LSPC model developed for the adjacent watershed. DO was set to 7 mg/L for all the watershed inflows.

Deer Point Lake discharge concentration values were determined from available water quality data measured in North Bay at the spillway discharge. CBODu was set to 5.36 mg/L, ammonia to 0.03 mg/L, and DO was set at 6 mg/L. Total nitrogen and total phosphorous were set at 0.93 and 0.04 mg/L respectively.

6.3 Model Loads

6.3.1 Point Source Loads

Point source CBOD and ammonia were obtained from available USEPA Permits. Long term BOD analyses were not available therefore and f-ratio was used to convert the 5-day BOD (BOD5) measurements to ultimate CBOD (CBODu) inputs for the water quality model. The value of the f-ratio, ratio between CBODu and CBOD5, was determined based on the carbonaceous decay rate K1.

A summary of permitted falicities discharging to the modeling domain and the respective loads are included in Table 6-1. The following calculations and nomenclature were used:

CBODu (Ultimate CBOD) = BOD5*f-ratio

Table 6-1 Model Inputs for NPDES Permitted Facilities

Facility Name Permit

Number Flow

(MGD) BODu (mg/L)

DO (mg/L)

TN (mg/L)

TP (mg/L)

St Andrews WWTF

FL0020451 3.38 7.02 7.58 2.54 1.25

Panama City Beach WWTP

FL0021512 2.25 7.21 6.87 6.2 0.6

Military Point Regional WWTF

FL0167959 3.92 7.81 7.02 3.62 1.6

Lynn Haven WWTF

FL0169978 1.42 39.5 6.28 3.67 0.52

Millville WWTF FL0170909 2.64 5.1 7.35 2.38 1.6 FL0002631 39.84 10.9 6.5 3.67 0.52

6.3.2 Marsh Loadings

The adjacent marsh areas in the West Bay play a significant role on the dissolved oxygen concentrations. These marsh areas provide a CBODu loadings that is necessary to account for. A seasonal varying marsh load was therefore added to the West Bay.

Based on literature values a marsh load of 6 kg/day/acre (recommended for brackish marshes) was used and three marsh areas were identified. Table 6-2 presents the value and locations of these marsh loads.

To address seasonality of the marsh loads, a reference paper was used that measured dissolved inorganic carbon (DIC) in tidal freshwater marshes in Virginia and the adjacent estuary



(Neubauer and Anderson, 2003). The percentages for the seasonal distribution are shown in Table 6-3.

No extra external Ammonia loads were added to represent the marsh load into the system.

Table 6-2 Model Input Marsh Loads

Marsh Name Cell where marsh load

CBODu kg/day

1 6 40 22500 2 3 40 15000 3 6 45 30000

Table 6-3 Seasonal Distribution of Marsh Loads

Month Percent of Total Load January 20

February 20 March 40 April 40 May 60 June 80 July 100

August 100 September 80

October 60 November 40

6.4 Model Kinetics

Model kinetics and parameters determine the decay of the pollutants and the oxygen uptake amount in the system. These kinetic rates and parameters were determined based on the measured data and standard water quality modeling assumptions.

The main rates and parameters are:

Decay rate K1 (1/day) for Carbonaceous BOD, Decay rate Kn (1/day) for Ammonia and Rest of Nitrogen Series, Sediment Oxygen Demand (g/m2/day), Reaeration (1/day), and Chlorophyll a or phytoplankton kinetics and light (solar radiation, light extinction

coefficient).



6.4.1 Decay rate K1 (1/day) for Carbonaceous BOD

The CBOD represents the oxygen demanding equivalent of the complex carbonaceous material present in the system. Thus CBOD is the concentration of organic material and the oxidation of the organic carbon in a body of water that will utilize oxygen at a rate equivalent to the decrease of CBOD (Thomann and Mueller, 1987). The CBODu and the CBOD decay rates were determined through model calibration.

A temperature correction factor, 1.047, was used to adjust the CBOD decay rate for the changes in temperature.

The St Andrews Bay is a complex system which receives wastewater with various types of BOD characteristics, concentration, and f-ratio. There have been multiple discussions on how to assign an appropriate decay rate that accurately accounts for the impact of these different BOD decay rate waters. One method would be to assume each wastewater discharge acts independently in the receiving water and assign a unique CBOD decay rate to each wastewater discharge that is equivalent to their respective bottle rate. The other method is to assume the wastewater and receiving waters’ concentration of organic material combine and the oxidation of the organic carbon in a body of water is a single rate that decays the combine CBODu. The second approach is the method used in the St Andrews Bay modeling.

Based on calibration, a K1 rate of 0.1/day at 20 degrees C was assigned to the entire system.

6.4.2 Ammonia Reaction Rates

A uniform ammonia Kn rate of 0.1/day at 20 degrees C was used. A temperature correction factor 1.08 was used to adjust the Kn rate for the changes in temperature.

6.4.3 Sediment Oxygen Demand

The sediment oxygen demand (SOD) in rivers and estuaries may result from the discharge of settleable organic solids, urban runoff, and upstream non-point sources of organic materials. A system wide SOD rate of 0.75 1/day was used for modeled domain. A temperature correction factor 1.05 was used to adjust the SOD rate for the changes in temperature.

6.4.4 Reaeration

Oxygen transfer in natural waterbodies depends on internal mixing and turbulence due to velocity gradients and fluctuations, temperature, wind mixing, waterfalls, dams and rapids, and surface films (Thomann and Mueller, 1987). For the St Andrews Bay system, a time varying tidal reaeration using O’Connor Dobbins formulation, incorporating the model’s surface layer predicted depths and velocities were used to calculate this oxygen transfer. The wind induced reaeration option was also included in the oxygen transfer calculation. O’Connor Dobbins reaeration formulation was developed to be applied to estuaries using average tidal velocity and depth. A temperature correction factor 1.022 was used to adjust the reaeration rate for the changes in temperature.



6.4.5 Chlorophyll a and Light parameters

Default kinetic parameters were used for chlorophyll a kinetics and calibration was obtained by varying the algal growth rate. Table 6-4 shows the WASP7 Chlorophyll a parameters.

Daily solar radiation was obtained from nearby weather station. Table 6-5 shows light input parameters and a light extinction coefficient of 0.3 1/ft (0.9 1/m) was used based on limited available data.

Table 6-4 Phytoplankton Coefficients in WASP Model

Model Parameter Model Rate Phytoplankton Maximum Growth Rate @20c 2 Phytoplankton Growth Temperature Coefficient 1.07 Phytoplankton Carbon::Chlorophyll Ratio 112 Phytoplankton Half-Saturation Constant for Nitrogen 0.025 Phytoplankton Half-Saturation Constant for Phosphorus 0.001 Phytoplankton Endogenous Respiration Rate @20c 0.1 Phytoplankton Respiration Temperature Coefficient 1.05 Phytoplankton Death Rate Non-Zooplankton Predation 0.02 Phytoplankton Zooplankton Grazing Rate 0 Nutrient Limitation Option 0 Phytoplankton Phosphorus::Carbon Ratio 0.025 Phytoplankton Nitrogen::Carbon Ratio 0.17 Phytoplankton Half-Sat. for Recycle of Nitrogen and Phosphorus 0.005

Table 6-5 Phytoplankton Light Coefficients in WASP Model

Model Parameters Model Rate Phytoplankton Maximum Quantum Yield Constant 720 Phytoplankton Optimal Light Saturation 350

6.4.6 Atmospheric Deposition

Also considered sources of nutrients are the wet and dry deposition of micro-nutrients, which can directly impact the ecophysiology and nutrient balance of the ecosystem within St Andrews Bay. Measurements of nutrient input from wet and dry deposition specific to St Andrews Bay were not available and a value was determined based on measurement done in Tampa Bay. The values considered for atmospheric deposition were 0.3 mg/m2/day for Nitrate/Nitrite, 0.3 mg/m2/day for Ammonia and 0.1 mg/m2/day for Orthophosphate.

7.0 WASP MODEL CALIBRATION The calibration was performed using the period ranging from January 2005 to December 2007 for calibration. As illustrated in the previous sections, the majority of the model kinetic parameters have been defined by the measured data. The model loading and boundary conditions were also measured and inputted directly into the model. The main calibration parameters were adjustments to SOD and the carbonaceous decay ratio K1. These adjustments were determined based on the time series DO results.



7.1 CBODu, Nutrient,and Chlorophyll a Comparison

The predicted model CBODu, Ammonia, Total Nitrogen, Total Phosphorus, and Chlorophyll a outputs were compared to the measured values from data collected during the period 2005-2007. Figure 7-1 shows the comparison of simulated and measured ammonia at St Andrews Bay station.

Figure 7-1 Modeled and Measured Ammonia (mg/l) at St Andrews Bay

Data available of CBOD5 (converted to CBODu), Ammonia, Total Nitrogen, and Total Phosphorus at the available stations is very scarce during the calibration period. Figures B-1 to B-8 in Appendix B presents these comparisons.

7.2 Dissolved Oxygen Comparison

The predicted model DO output was compared to the measured values from data collected during the calibration period. Figure 7-2 and Figures B-9 to B-13 in Appendix B illustrates that the calibrated model is yielding reasonable DO values.

As stated before the main calibration parameters were decay rate K1 and SOD. These were adjusted to allow the model to match the DO time series.



Figure 7-2 Modeled and measured DO (mg/l) at St Andrews Bay



8.0 SUMMARY AND CONCLUSIONS The 3-dimensional model setup for St Andrews Bay successfully ran to determine dissolved oxygen in the system. The model was critical to capture the differences in the system.

The following goals were defined for the hydrodynamic and water quality model:

The models need to be able to simulate the conditions in the St Andrews Bay system.

The models must be interconnected to the more complex offshore areas to better assess the effects of the Gulf of Mexico.

Longitudinal and vertical gradients of salinity affect residual transport; as such, the model must be able to handle the degree of stratification within the estuarine region.

Critical conditions to dissolved oxygen must be simulated to determine daily and monthly average dissolved oxygen under natural conditions when anthropogenic sources are removed.

In general, the model presented within this report meet the goals outlined above. The model is able to simulate the overall conditions throughout the region in water surface elevation, temperature and salinity for the hydrodynamics and dissolved oxygen, BOD, nutrients and phytoplankton for the water quality.



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APPENDICES

Appendix A EFDC Calibration Appendix B WASP Calibration

st andrews bay hydrodynamic and water quality modeling report€¦ · analysis simulation package...

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