lower cape fear river basin cape fear do issuesjdbowen/lcfr/sep03_tmdl_wkshop/b… · 1.water...

Lower Cape Fear River BasinCape Fear DO Issues

byJim Bowen, Assoc. Professor

Civil Engr. Dept., UNC Charlotte

Cape Fear Basin TMDL ConferenceRaleigh, NC

September 9, 2003

Outline of Talk1. Water Quality Models - The Analysis Tool of

the TMDL Analysis2. An Example TMDL - Neuse River Estuary,

Nitrogen TMDL3. Contrasting DO Conceptual Models - Neuse

and Lower Cape Fear River Estuaries4. Special Challenges in Modeling DO

Dynamics in the Lower Cape Fear RiverEstuary

The TMDL Analysis

Pollutant LoadNutrients (N,P),BOD, etc.

4321

Scenario

The TMDL Analysis


4321

Scenario

Water Quality

4321

ScenarioWaterQualityGoal

The TMDL Analysis


4321

Scenario

Water Quality

4321


Water Quality Model

TMDL’s Use Water Quality Models

Estuary PhysicalCharacteristics: e.g. length,width, depth,roughness

Water Quality ModelAdjustable Parameters:(growth, death, decay,sinking rates, temperature,nutrient, light functions.)

HydrologicConditions

RiverFlows,Temp’s,Conc’sTides Time

“Met” DataAir temps,precip,wind,cloudiness

Time

State Variables

nutrientsDO,chlorophyllorganic C Time

PollutantLoads

2. An Example TMDL - NeuseRiver Estuary, Nitrogen TMDL

Nitrogen Loadto Estuary

4321

Scenario



4321

Scenario

Chlorophyll-a Conc.

4321




4321

Scenario

Chlorophyll-a Conc.

4321


Neuse Estuary Eutrophication Model

Neuse and Cape Fear Models are“Mass Balance” Models

MassOutflow

Volume of Water

Internalsources

InternalSinks

StateVariable

Accumulation = Mass In - Mass Out

MassInflow

What Should the State Variables,Sinks, and Sources Be?

MassOutflow

Volume of Water

Internalsources

InternalSinks

StateVariable

MassInflow

What Should the State Variables,Sinks, and Sources Be?

MassOutflow

Volume of Water

Internalsources

InternalSinks

StateVariable

MassInflow

“Conceptual Model” ofSystem

Surface Layer

Bottom Layer

Neuse Estuary Conceptual Model

Sediment

Surface Layer

Bottom Layer


Sediment

RiverineNutrient Load

Long water residence time

Surface Layer

Bottom Layer


Sediment

Algal Blooms, High DORiverineNutrient Load

Long water residence time

Surface Layer

Bottom Layer


Sediment

Algal Blooms, High DO

Sediment O2 Demand


Surface Layer

Bottom Layer


Sediment


Sediment O2 Demand


withoutstratification

Surface Layer

Bottom Layer


Sediment


Sediment O2 Demand


withoutstratification

Acceptable DO

Surface Layer

Bottom Layer


Sediment


Sediment O2 Demand


withstratification

Surface Layer

Bottom Layer


Sediment


Sediment O2 Demand


withstratification

Anoxic BottomWaters

Model Developed for Nutrient TMDLNEEM = Neuse Estuary

Eutrophication Model

Neuse River Estuary

NEEM Divides Water Body intoSegments

Divide Segments into Layers (6-18)Layers may have varying widths

Layer 2

Layer 5

Water Column

NEEM Water Quality State Variables

1. Temperature 2. Salinity3. Suspended Solids

Oxidants/Reductants

Nutrients

Organic Matter

Phytoplankton

4. Diatoms & Dinoflagg’s5. Chloros & Cryptos6. Blue-Green Algae

7. LPOM 8. RDOM9. RPOM 9. Part Si10. LDOM

11. NH312. NO2+ NO313. Dissolved Silica14. Ortho Phosphate

9. Dissolved Oxygen10. Benthically Derived Oxygen Demand

Sediment Organic Matter

Physical Properties

18. Labile SOM19. Refr. SOM

NEEM Predicted and ObservedSalinities near New Bern

1998-2000

NEEM Predicted and ObservedChl-a near New Bern

1998-2000

NEEM Predicted and ObservedDO Conc. near New Bern

1998-1999

Load Reduction Needed to MeetWater Quality Standards (3 Models)

Summary of model results used to recommend a 30% reduction in NitrogenLoading from the 1995 baseline loading.

0 10 20 30 40 50

Percent TN Reduction Required to Meet

Chlorophyl-a Standard

Neu-BERN w/ dummy

Neu-BERN no dummy

NEEM

WASP

Neuse TMDL Load Reduction Results

3. LCFR Estuary, OrganicMatter (BOD) TMDL

BOD Loadto Estuary

4321

Scenario


BOD Loadto Estuary

4321

Scenario

DO Conc.

4321



BOD Loadto Estuary

4321

Scenario

DO Conc.

4321


LCFR Estuary Model

Vertically Mixed WaterColumn

LCFR Estuary DO Conceptual Model

Sediment

Cape FearNutrient Load

Shorter water residence time



Sediment


NECF & Black R.Color Load


MonitoringStationsMap

LowerCapeFearRiverProgram

2001-2002 Salinity, LCFRP Data

NC11

Riverine OceanLCFR

2000-2001 Light Attenuation,LCFRP Data

Riverine OceanLCFR

2001-2002 Turbidity, LCFRPData

Riverine OceanLCFR



Sediment

Fewer phytoplankton

Sediment O2 Demand


NECF & Black R.Color Load


2001-2002 Chl-a, LCFRP Data

Riverine OceanLCFR

2000-2001 Orthophosphate,LCFRP Data

Riverine OceanLCFR

2000-2001 NOx, LCFRP Data

Riverine OceanLCFR

LCFR Estuary DO Conceptual ModelBOD Sources, DO Sources & Sinks

Sediment


Sediment

Cape FearBOD Load

NECF & Black R.BOD Load


Sediment

Cape FearBOD Load


Muni & Ind.BOD Load


Sediment

Cape FearBOD Load


Muni & Ind.BOD Load

decaying phyto.


Sediment

Cape FearBOD Load


SurfaceReaeration

Phytoplank. ProductivityMuni & Ind.

BOD Load

decaying phyto.


Sediment

Cape FearBOD Load


Ocean Inflows

SurfaceReaeration

Input of NECF &Black R. Low DOWater


BOD Load

decaying phyto.


Sediment Sediment O2 Demand

Cape FearBOD Load


Ocean Inflows

SurfaceReaeration



BOD Load

decaying phyto.

BOD Consumption


Sediment Sediment O2 Demand

Cape FearBOD Load


Ocean Inflows

SurfaceReaeration



BOD Load

decaying phyto.

2001-2002 DO, LCFRP Data

Riverine OceanLCFR

95-01 DO @ NC 11 (Cape Fear),LCFRP Data

95 96 97 98 99 00 01

95-01 @NCF 117 (NortheastCape Fear), LCFRP Data

95 96 97 98 99 00 01

Special Challenges of ModelingLCFR Estuary

1. Three dimensional variability (longitudinal,lateral, vertical) in state variables

2. Mixing regimes vary significantly fromupstream (riverine) to mouth (energetic tidalmixing)

3. Many significant sources of DO to surfacewaters

– algal productivity,– surface reaeration,– lateral inflows from ocean)


4. Many significant sinks of DO that affectsurface waters

• sediment oxygen demand• low DO water input from Black and NE Cape

Fear River,• municipal and industrial wastewater loads,• BOD inputs from adjacent swamps & Black

and NE Cape Fear Rivers


5. Widely varying decomposition rates ofdifferent organic matter sources

• Decaying phytoplankton biomass• Industrial, municipal BOD loads• Refractory organic matter from “black

water” sources

BOD decomposition rates varywidely

DO Consumed(mg/l)

Decayingphytoplanton biomass

Black waterorganic matter

Municipal,industrialBOD loads

Time 5 days

BOD5

BOD decomposition rates varywidely

Time 50 days5 days

Black waterorganic matter

Municipal,industrialBOD loadsDO

Consumed(mg/l) Decaying

phytoplanton biomass

Conclusions Regarding LCFRTMDL1. Challenging system to model2. Model must properly account for changing

physical regimes through the estuary(river to mouth)

3. Model must account for all of DO sourcesand sinks

4. Model must properly account for differingqualities of BOD sources to estuary

lower cape fear river basin cape fear do issuesjdbowen/lcfr/sep03_tmdl_wkshop/b… · 1.water...

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