Lower Cape Fear River Estuary Model Progress Report

Lower Cape Fear River Estuary

Model Progress Report

Jim Bowen, UNC Charlotte

August 15, 2007

Raleigh, NC

Description of Model Application

Open Boundary

Elevation Cond.

Lower Cape Fear River

Estuary Schematic

Black River,

FlowBoundary Cond.

Cape Fear R.

Flow Boundary Cond.

NE Cape Fear

Flow Boundary Cond.

DO Conceptual Model

BOD Sources

Sediment Sediment O2 Demand

Cape Fear

BOD Load

NECF & Black R.

BOD Load

Muni & Ind.

BOD Load

decaying

phytopl.

DO Conceptual Model

BOD Sources, DO Sources

Cape Fear

BOD Load

NECF & Black R.

BOD Load

Ocean Inflows

Surface

Reaeration

Phytoplank.

ProductivityMuni & Ind.

BOD Load

decaying

phytopl.

MCFR Inflows

Consumption

DO Conceptual Model

BOD Sources, DO Sources & Sinks

Cape Fear

BOD Load

NECF & Black R.

BOD Load

Ocean Inflows

Surface

Reaeration

Input of NECF &

Black R. Low DO

Phytoplank.

ProductivityMuni & Ind.

BOD Load

decaying

phytopl.

MCFR Inflows

Modeling Developments

(Hydrodynamic model)

1. Moved model boundary for NECF up to

Burgaw monitoring station

2. Created flow boundary conditions for

2003-2005 for Black and NECF using

station pairs (Tomahawk and Currie,

Chinquapin and Burgaw)

3. Created calibration database of all

available hydrodynamic data (DWQ

Ambient, LCFRP, special study, USGS)

More model developments (Hydro)

4. Created scripts and monitoring data filesto compare long-term daily and short-termhourly hydrodynamic data

5. Created new shortwave solar radiation fileusing observed to replace data estimatedfrom meteorological forcings

6. Delineated NECF watersheds in estuary toimprove placement of freshwater loadings

1. Added new cells to extend model

to Burgaw monitoring station

• 950 horizontal cells in old grid, 1004 cellsin new grid

• 8 vertical layers

• Average cell dx = 300 m, dy = 400 m

• Separate cells for channel and adjoiningmarshes

• ** show grids w/Google Earth

2. Created new Black R. and

NECF R. flow boundary

conditions• Needed flows at model boundary for Black

and NECF rivers

• Had two stations in each watershed for

approximately one year

• Used lagged and scaled flows (@

Tomahawk, Chinquapin) to estimate

missing data for model boundaries

Flows at Burgaw

• High flow event from Hurricane Charlie seen Q3,2004

5. Created new short-wave solar

radiation file• Had previously used estimated short-wave solar

using met data (cloud cover, day of year) forestimation

• Previous data set produced overpredictions oftemperature during summer

• Discovered a Wilmington short wave data setexisted from NWS

• Found these data gave much improvedtemperature predictions

Example temperature time series

• Predicted temps near 40 deg C much higher thanobservations

6. Added new freshwater sources

for NECF, Black, Cape Fear

• Area between Burgaw and mouth of NECF

includes a signficant portion of watershed

drainage area (approx. 10% of total)

• Need to add additional water inputs to correctly

account for location of freshwater inputs

• Also made corrections for Black and Cape Fear

Rivers (show w/ google earth)

• Estimated flows by scaling NECF flows at

Burgaw

Example: 6 additional NECF

sources added

River Watershed I J

Estimated

Area (sqmi)

multiplier multiplier addition #

NECF 10 43 93 329.0 0.347 0.347 3

NECF 9 43 89 44.5 0.045

NECF 11 43 87 32.4 0.033 0.110 4

NECF 8 43 86 32.3 0.032

NECF 7 43 82 6.3 0.007

NECF 12 43 81 72.7 0.078

NECF 6 43 79 1.5 0.002 0.118 6

NECF 13 43 78 27.3 0.028

NECF 5 43 73 4.7 0.005

NECF 14 43 50 36.6 0.040

NECF 1 43 47 19.7 0.020 0.211 5

NECF 2 43 45 142.5 0.151

NECF 3 43 38 3.0 0.003

NECF 4 43 35 3.5 0.004 0.007 2

NECF 15 43 22 4.4 0.005

NECF 16 43 21 10.8 0.012 0.034 1

NECF 17 43 17 17.2 0.018

NECF Total N/A N/A 788.4 0.826

NECF Total N/A N/A 790

Additional Estuary Sources:

Summary

Northeast Cape Fear 6 760 10.0

Cape Fear below NECF 3 260 3.5

Cape Fear above Navassa 3 250 3.3

Black River 2 120 1.6

Total 14 1390 18.4%

River # Srcs Sq. Mi. DA%

More model developments (Hydro)

7. Developed new downstream boundaryelevation file NOAA measured elevationsat Southport

8. Created downstream boundary salinity datausing Marker 12 salinity continuous monitoring

9. Calibrated hydrodynamic model by runningmodel w/ various bottom roughnesses andassumed bottom elevations

Hydrodynamic Model Results

• Show temperature and salinity time seriescomparisons

• Also show statistical measures of model fitto data

• Use all available salinty and temperaturedata sources (LCFRP, USGS, DWQ)

• Use 2003 model startup, make comparisonfor April - November 2004

April - November 2004 Temperature

Statistical Measures of Fit (units of deg C)

mean(pred-obs) =0.10046

ME_norm =0.0043473

RMSE =0.96224

MAE =0.71269

MAE_norm =0.030841

RMSE_norm =0.041639

r_squared =0.97272

num data comparisons = 4150

r2 adjusted for bias = 0.96465

April - November, Hourly

Temperatures

Fit Statistics (units are deg C)

mean(pred-obs) =-0.075693

ME_norm =-0.0032593

RMSE =0.88541

MAE =0.64122

MAE_norm =0.027611

RMSE_norm =0.038126

r_squared =0.97935

num data comparisons =

r2 adjusted for bias = 0.96956

April - November 2004 Salinity

Statistical Measures of Fit (units of PSU)

mean(pred-obs) =-0.25797

ME_norm =-0.043321

RMSE =2.6493

MAE =1.6424

MAE_norm =0.27581

RMSE_norm =0.4449

r_squared =0.87049

1-mse/var(obs) = 0.84804

July 2004 Salinity, Hourly Data,

Bottom

Fit Statistics (salinity units)

ME_norm =0.11916

RMSE =3.2932

MAE =2.4755

MAE_norm =0.1866

RMSE_norm =0.24824

r_squared =0.79945

1-mse/var(obs) = 0.67269

July 2004 Salinity, Hourly Data, Top

Hydrodynamic Calibration -

Summary

• Calibration essentially complete

• Excellent agreement w/ temperature and

salinity

• Elevation agreement (not shown) still needs

some work to get predicted tidal amplitude

attenuation to match observed attenuation

More Model Developments

(Water Quality Model)

1. Reviewed long-term BOD data to

determine organic matter decay rates

2. Created new point source load files w/

additional NECF sources and variable

organic matter decay rates

Long-term BOD measurements,

data sources

1. IP long-term BOD tests (BOD vs. time)

2. Wilmington long-term tests (BOD vs.

3. DWQ special study data (BOD30/BOD5

ratio)

4. LCFRP data (BOD20/BOD5 ration,

partial data set)

IP and Wilmington long-term

BOD measurements

• Multiple measurements, BOD exerted vs.

• Fit data to determine ultimate BOD and

BOD decay rate

IP Measurements,

7/20: BODU = 110 mg/L, K = 0.03 day-1

7/27: BODU = 90 mg/L, K = 0.03 day-1

Wilmington Measurements

Wilmington NS: BODU = 32 mg/L, K = 0.05 day-1

Wilmington SS: BODU = 118 mg/L, K = 0.13 day-1

DWQ and LCFRP long-term

BOD data

• Have BOD 5 + BOD20 or BOD30 data

• Have multiple times and locations

• Use ratio of BOD’s to determine BOD

decay rates

BOD exerted for 2 decay rates

Ratio decreases as k increases

BOD30/BOD5 ratio

Given BOD30/BOD5 ratio, k can be found

from curve

LCFRP data

• Based on July ‘02 - June ‘03 monthly data at 3boundary stations (NC11, B210, NCF117) = 36measurements w/ BOD5 and BOD20

• Mean = 0.054 day-1

• Expect to get additional data for later years

DWQ Special Study Data

• 7 stations, 2 measurements during July 2004

• BOD 30 and BOD 5 measurements

• Use BOD30/BOD5 ratio to determine K

(data not shown)

Average k = 0.07 day-1

Standard deviation = 0.01 day-1

Long-term BOD data - summary

• IP WW has lowest decay rate (0.03 day-1)

• River water has intermediate decay rates

(0.05 - 0.07 day-1)

• Wilmington WWTP decay rates quite

variable (0.05 - 0.13 day-1)

• Using two DOC types, labile (k = 0.1 day)

and refractory (k = 0.03 day)

• Most sources will have some of both labile

and refractory

DO model results so far

Fit statistics (units are mg/L)

ME_norm =0.16725

RMSE =1.5

MAE =1.1671

MAE_norm =0.20109

RMSE_norm =0.25846

r_squared =0.49312

1-mse/var(obs) = 0.025191

Upcoming Work

• Finish assigning decay rates and redefining loadsonce additional BOD data are available

• Work on incorporating SOD data in a moredetailed way

• Do additional model/data comparisons w/ DWQspecial study data

• Plan to finish water quality calibration by end ofSeptember and begin to consider how to doscenario tests

Lower Cape Fear River Estuary Model Progress Report

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