Development of a Sediment Transport Model for the Chesapeake Bay: Supporting Physical Data

Development of a Sediment Transport Model for the Chesapeake Bay:

Supporting Physical Data

Co-PIs:Co-PIs:Lawrence P. SanfordLawrence P. Sanford11

Carl T. FriedrichsCarl T. Friedrichs22

Jerome P.-Y. MaaJerome P.-Y. Maa22

11University of Maryland Center for Environmental University of Maryland Center for Environmental Science, Horn Point Laboratory, Cambridge MDScience, Horn Point Laboratory, Cambridge MD

22College of William and Mary, Virginia Institute of College of William and Mary, Virginia Institute of Marine Science, Gloucester Point, VAMarine Science, Gloucester Point, VA

Overall Project DescriptionOverall Project Description Year 1, 2004Year 1, 2004

Deliver physical data from previous studiesDeliver physical data from previous studies 4 seasonal axial surveys of upper half of Potomac4 seasonal axial surveys of upper half of Potomac 5 d process study (3 vessels) near Gunston Cove5 d process study (3 vessels) near Gunston Cove All surveys complete, data return good (not perfect), All surveys complete, data return good (not perfect),

data mostly processeddata mostly processed Year 2, 2005Year 2, 2005

Deliver Year 1 dataDeliver Year 1 data 4 seasonal axial surveys of upper half of Potomac4 seasonal axial surveys of upper half of Potomac 5 d process study (3 vessels) of Potomac ETM region5 d process study (3 vessels) of Potomac ETM region All surveys complete, data return very good, data All surveys complete, data return very good, data

partially processedpartially processed Year 3, 2006Year 3, 2006

Complete data processing and analysisComplete data processing and analysis Deliver Year 2 dataDeliver Year 2 data

-77.4 -77.3 -77.2 -77.1 -77 -76.9 -76.8

Longitude, [deg]

-77.4 -77.3 -77.2 -77.1 -77 -76.9 -76.8

38.3

38.4

38.5

38.6

38.7

38.8

38.9

39

Latit

ude,

[deg

]

38.3

38.4

38.5

38.6

38.7

38.8

38.9

39

-34

-30

-26

-22

-18

-14

-10

-6

-1

1

4

17

35

65

100

Elev., [m]

12

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km]

25

20

15

10

5

0

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km ]

25

20

15

10

5

0

Dep

th, [

m]

051015202530405060708090100125150200

Potomac River Salt & TSS Axial Contours: August 19, 2004 Main (DC) Channel

TSS, [mg/l]

Salin ity, [PSU ]

Ft. W

.

301

B.

W.W

.B.

I.H.

MD

Pt.

Salin ity, [PSU ]

Transmissometer

OBS

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km]

25

20

15

10

5

0

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km]

25

20

15

10

5

0

Dep

th, [

m]

051015202530405060708090100125150200

Potomac River Salt & TSS Axial Contours: November 16, 2004 Main (DC) Channel

TSS, [m g/l]

Salin ity, [PSU ]

Ft. W

.

W.W

.B.

I.H.

MD

Pt.

Salinity, [PSU ]

Transm issometer

OBS

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km]

25

20

15

10

5

0

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km]

25

20

15

10

5

0

Dep

th, [

m]

051015202530405060708090100125150200

Potomac River Salt & TSS Axial Contours: March 22, 2005 Main (DC) Channel

TSS, [mg/l]

Salin ity, [PSU ]

Ft. W

.

W.W

.B.

I.H.

MD

Pt.

Salin ity, [PSU]

Transmissometer

OBS

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km ]

25

20

15

10

5

0

0 10 20 30 40 50 60 70 80 90 100 110 120 130

River distance from Little Falls, [km ]

25

20

15

10

5

0

Dep

th, [

m]

051015202530405060708090100125150200

Potomac River Salt & TSS Axial Contours: September 20, 2005 Main (DC) Channel

TSS, [mg/l]

Salin ity, [PSU]

Ft. W

.

W.W

.B.

I.H.

MD

Pt.

Salin ity, [PSU ]

Transm issom eter

OBS

Conclusions, part 1Conclusions, part 1

-34

-30

-26

-22

-18

-14

-10

-6

-1

1

4

17

35

65

100

Elev., [m]

-77 .4 -77.3 -77.2 -77.1 -77 -76 .9 -76.8

Longitude, [deg]

-77 .4 -77.3 -77.2 -77.1 -77 -76 .9 -76.8

38.3

38.4

38.5

38.6

38.7

38.8

38.9

39

Latit

ude,

[deg

]

38.3

38.4

38.5

38.6

38.7

38.8

38.9

39

2004

2005

-15

-13

-11

-9

-7

-5

-3

-1

1

3

5

7

9

11

13

15

Elev., [m]

-77.17 -77 .16 -77.15 -77.14 -77.13 -77.12 -77.11 -77.1 -77.09

Longitude, [deg]

-77.17 -77 .16 -77.15 -77.14 -77.13 -77.12 -77.11 -77.1 -77.09

38.63

38.64

38.65

38.66

38.67

38.68

Latit

ude,

[deg

]

38.63

38.64

38.65

38.66

38.67

38.68

M ooring

ucosm 1

ucosm 2&SC2ucosm 3SC 1ucosm 3&SC 3

2004 Intensive Erosion Testing Sites2004 Intensive Erosion Testing Sites

-15

-13

-11

-9

-7

-5

-3

-1

1

3

5

7

9

11

13

15

Elev., [m ]

-77.3 -77.25 -77.2 -77.15 -77.1

Longitude, [deg]

-77.3 -77.25 -77.2 -77.15 -77.1

38.3

38.32

38.34

38.36

38.38

38.4

38.42

38.44

38.46

38.48

38.5

Latit

ude,

[deg

]

38.3

38.32

38.34

38.36

38.38

38.4

38.42

38.44

38.46

38.48

38.5

ucosm 1&M ooring

ucosm 2

SC1

SC2

2005 Intensive Erosion Testing Sites2005 Intensive Erosion Testing Sites

Stress Limited, Locally Linear ErosionStress Limited, Locally Linear Erosion

0

0.05

0.1

0.15

0.2

0.25

0 5000 10000 15000Time (s)

Erod

ed M

ass

(kg

m-2

)

0

0.2

0.4

0.6

Shea

r Stre

ss (P

a)

observed fit Shear

1.E-06

1.E-05

1.E-04

2450 4450 6450 8450Elapsed time (s)

Eros

ion

Rate

(kg

s-1 m

-2)

0

0.2

0.4

0.6

Shea

r Stre

ss (P

a)

GP1 fit Shear

2005 Site 1 in the ETM channel, compared to2005 Site 1 in the ETM channel, compared to all all 2002 CB ETM cores is remarkably similar2002 CB ETM cores is remarkably similar

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0503 exp 1 cores 1&2c , [Pa]

Ero

ded

Mas

s, [k

g . m-2

]

core 1core 2

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.1

0.2

0.3

0.4

0.5

pr0503 exp 1 cores1 & 2

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m-2

]

core 1core 2

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4Critical stress, c (Pa)

Erod

ed m

ass

(kg

m-2

)

y = -.0014+1.5688x1.6070

R2 = .78

0

0.1

0.2

0.3

0.4

0.5

0 0.001 0.002 0.003Erosion rate constant, M(kg s-1 Pa-1 m-2)

Erod

ed m

ass

(kg

m-2

)

2005 Site 1 in the ETM channel, compared to 2005 Site 2 in 2005 Site 1 in the ETM channel, compared to 2005 Site 2 in the channel downstream of the ETM. Site 2 is less erodible.the channel downstream of the ETM. Site 2 is less erodible.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0503 exp 1 cores 1&2c , [Pa]

Ero

ded

Mas

s, [k

g . m-2

]

core 1core 2

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0503 exp 2 cores 5&6

c , [Pa]

Ero

ded

Mas

s, [k

g . m

-2]

core 5core 6

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.1

0.2

0.3

0.4

0.5

pr0503 exp 2 cores5 & 6

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m

-2]

core 5core 6

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.1

0.2

0.3

0.4

0.5

pr0503 exp 1 cores1 & 2

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m-2

]

core 1core 2

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0503 exp 3 cores 7&8c , [Pa]

Ero

ded

Mas

s, [k

g . m

-2]

core 7core 8

2004 Site 2 opposite Gunston Cove, compared to 2005 Site 3 2004 Site 2 opposite Gunston Cove, compared to 2005 Site 3 at same location. 2005 is similar, slightly less erodibleat same location. 2005 is similar, slightly less erodible

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0404 exp 2 cores 4&5c , [Pa]

Ero

ded

Mas

s, [k

g . m

-2]

core 4core 5

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0503 exp 3 cores7 & 8

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m

-2]

core 7core 8

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.1

0.2

0.3

0.4

0.5

pr0404 exp 2 cores4 & 5

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m

-2]

core 4core 5

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0404 exp 3 cores 6&7c , [Pa]

Ero

ded

Mas

s, [k

g . m

-2]

core 6core 7

2004 Site 1 inside Gunston Cove, compared to 2004 Site 3 on 2004 Site 1 inside Gunston Cove, compared to 2004 Site 3 on the inside channel edge. Site 1 is similar to Site 2, not very the inside channel edge. Site 1 is similar to Site 2, not very

erodible. Site 3 is similar to 2005 Site 1, in the ETM channel.erodible. Site 3 is similar to 2005 Site 1, in the ETM channel.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

pr0404 exp 1 cores 1&3

c , [Pa]

Ero

ded

Mas

s, [k

g . m-2

]

core 1core 3

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.1

0.2

0.3

0.4

0.5

pr0404 exp 3 cores6 & 7

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m

-2]

core 6core 7

0 0.5 1 1.5 2 2.5 3 3.5

x 10-3

0

0.1

0.2

0.3

0.4

0.5

pr0404 exp 1 cores1 & 3

M, [kg . s-1 . m-2 . Pa-1]

Ero

ded

Mas

s, [k

g . m

-2]

core 1core 3

Conclusions, part 2Conclusions, part 2

Modeling resuspension and deposition with a Modeling resuspension and deposition with a dynamically varying mixed sediment beddynamically varying mixed sediment bed

Consolidation causes Consolidation causes cc to increase rapidly with depth into to increase rapidly with depth into the bed and with time after deposition.the bed and with time after deposition.

Example critical stress (shear strength) profile from Example critical stress (shear strength) profile from laboratory tests by Parchure and Mehta (1985)laboratory tests by Parchure and Mehta (1985)

Erodibility can change significantly in response to disturbance.Erodibility can change significantly in response to disturbance.Passage of a tropical storm, upper Chesapeake Bay, Sept 1992. Passage of a tropical storm, upper Chesapeake Bay, Sept 1992.

Dredged sediment disposal site, 5 m depth. Dredged sediment disposal site, 5 m depth.

Stn 6, 1m

Stn 8, 3m

Stn 6, 1m

Howell Pt. Buoy

September 1992

17 18 19 20 21 22 23 24 25 26 27 28 29

Spe

ed (c

m/s

)

0102030405060

RM

S P

(mb)

02468

10

TSP

(mg/

l)

0

50

100

150200

(Win

d S

peed

)2

050

100150200250

10 cm

Physical disturbance overwhelms bioturbation at upper York River site

Bioturbation dominates fine sediment fabric at Chesapeake Bay site

Interactions between physical and biological disturbance of the sea bed can lead to distinct layering or near homogeneity

( x-radiographs courtesy of Linda Schaffner)

Increasing physical disturbance of sea bed

Present approach:Present approach: Use a layered bed model with continuous profiles of Use a layered bed model with continuous profiles of cc, layer-averaged , layer-averaged

erosion constant M and sand fraction ferosion constant M and sand fraction fss Use sediment bed mass m as independent variable instead of depth Use sediment bed mass m as independent variable instead of depth

(better for consolidation)(better for consolidation) 2-component mixture of sand and mud2-component mixture of sand and mud

Separate erosion parameters for sand and mud (interaction effects Separate erosion parameters for sand and mud (interaction effects not yet incorporated)not yet incorporated)

Erosion rates proportional to fractions at interfaceErosion rates proportional to fractions at interface Mud erosion follows Sanford and Maa (2001)Mud erosion follows Sanford and Maa (2001) Sand erosion follows Harris and Wiberg (2001)Sand erosion follows Harris and Wiberg (2001) Assume constant Assume constant c,sandc,sand Assume that Assume that c,mudc,mud approaches an equilibrium profile at a first order rate approaches an equilibrium profile at a first order rate Allow for sediment mixing (bioturbation, bedload transport)Allow for sediment mixing (bioturbation, bedload transport) Subtract or add active bed layers to follow the interface during erosion or Subtract or add active bed layers to follow the interface during erosion or

depositiondeposition Only mix mass between layers when a threshold is exceeded (minimizes Only mix mass between layers when a threshold is exceeded (minimizes

numerical dispersion)numerical dispersion) Model evolution of Model evolution of c, mud c, mud and f and fss as a function of m and time as a function of m and time

Critical Stress and Erosion Rate Constant, Critical Stress and Erosion Rate Constant, all upper Chesapeake Bay UMCES microcosm all upper Chesapeake Bay UMCES microcosm

data from 2001-02data from 2001-02

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4Critical stress, c (Pa)

Erod

ed m

ass

(kg

m-2

)

y = -.0014+1.5688x1.6070

R2 = .78

0

0.1

0.2

0.3

0.4

0.5

0 0.001 0.002 0.003Erosion rate constant, M(kg s-1 Pa-1 m-2)

Erod

ed m

ass

(kg

m-2

)

Example: Erosion, deposition, and consolidation of Example: Erosion, deposition, and consolidation of a pure mud and a sand-mud mixturea pure mud and a sand-mud mixture

Bed consists of 20 layers 0.075 kg mBed consists of 20 layers 0.075 kg m-2-2 thick thick Critical stress profile initiated with average of upper Critical stress profile initiated with average of upper

Chesapeake Bay microcosm profiles, also assumed to be Chesapeake Bay microcosm profiles, also assumed to be equilibrium profileequilibrium profile

Assume M=constant=0.001 kg mAssume M=constant=0.001 kg m-2-2 s s-1-1 Pa Pa-1-1

Spring-Neap cycle of tidal shear stress, max varies Spring-Neap cycle of tidal shear stress, max varies between 0.15-0.25 Pabetween 0.15-0.25 Pa

A 2-day event from day 20-22 doubles the max stress A 2-day event from day 20-22 doubles the max stress A 2-day event from day 34-36 triples the max stressA 2-day event from day 34-36 triples the max stress Very low sediment mixing of 0.01 cmVery low sediment mixing of 0.01 cm22 yr yr-1-1

wwsmsm = 36 m d = 36 m d-1-1, h = 2 m, h = 2 m Consolidation rate = 1.0 dConsolidation rate = 1.0 d-1-1, swelling rate = 0.05 d, swelling rate = 0.05 d-1-1

wwssss = 363 m d = 363 m d-1-1, , csandcsand = 0.125 Pa (fine sand) = 0.125 Pa (fine sand)

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

TSS

(g/

l)

0 10 20 30 40 50 600

0.2

0.4

0.6

0.8

App

lied

Stre

ss (

Pa)

Bed

mas

s (k

g/m

2)

0 10 20 30 40 50

0

0.5

1

Bed

mas

s (k

g/m

2)

0 10 20 30 40 50

0

0.5

1

Critical Stress (Pa)

Sand fraction

All mud, very low sediment mixingAll mud, very low sediment mixing

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

TSS

(g/

l)

0 10 20 30 40 50 600

0.2

0.4

0.6

0.8

App

lied

Stre

ss (

Pa)

Bed

mas

s (k

g/m

2)

0 10 20 30 40 50

0

0.5

1

Bed

mas

s (k

g/m

2)

0 10 20 30 40 50

0

0.5

1

Critical Stress (Pa)

Sand fraction

50/50 sand-mud, very low sediment mixing50/50 sand-mud, very low sediment mixing

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

TSS

(g/

l)

0 10 20 30 40 50 600

0.2

0.4

0.6

0.8

App

lied

Stre

ss (

Pa)

Bed

mas

s (k

g/m

2)

0 10 20 30 40 50

0

0.5

1

Bed

mas

s (k

g/m

2)

0 10 20 30 40 50

0

0.5

1

Critical Stress (Pa)

Sand fraction

50/50 sand-mud, sediment mixing 10 cm50/50 sand-mud, sediment mixing 10 cm22 yr yr-1-1

ConclusionsConclusions Layered bed model for critical stress profile in Layered bed model for critical stress profile in

terms of bed mass simplifies formulation. terms of bed mass simplifies formulation. Specification of equilibrium conditions based on Specification of equilibrium conditions based on

observed erosion behavior promising, but may observed erosion behavior promising, but may need tweaking.need tweaking.

““Consolidation” formulation predicts reasonable Consolidation” formulation predicts reasonable behavior with little computational effort, but behavior with little computational effort, but needs more validationneeds more validation

Mud-sand mixture and diffusive mixing schemes Mud-sand mixture and diffusive mixing schemes lead to realistic complex bed structures and lead to realistic complex bed structures and directly affect resuspensiondirectly affect resuspension

Conclusions, continuedConclusions, continued Need to incorporate sand-mud interaction Need to incorporate sand-mud interaction

effects on erodibilityeffects on erodibility Need to simplify code, translate into Need to simplify code, translate into

Fortran subroutine(s) for incorporation into Fortran subroutine(s) for incorporation into sediment transport modelssediment transport models

Community modeling/open source code Community modeling/open source code approach favoredapproach favored