Channel Erosion and Water Quality Modeling using SWAT

Channel Erosion and Water Quality Modeling

using SWAT

North Central TexasWater Quality Project

Balaji Narasimhan, Peter M. Allen, Mark Ernst, John A. Dunbar, Steve Bernardz,

Jeff Arnold, and Raghavan Srinivasan

North Central TexasWater Quality Project

•TWDB lake volumetric surveys (1995 and 2005)•Average loss of volume (Sedimentation Rate):

–1032 ac.ft/year•Density of sediments??

Input Data Sources

Reservoir Cores and Sediment Survey

Compute Average Density

Sediment Volume byDifferential Bathymetry

Multi-frequency Acoustic Survey System

Preliminary Sub-bottom Survey: uniform thickness 1-2ft.

Reservoir Cores and Sediment Survey

Compute Average Density

North Central TexasWater Quality Project

•Sediment Coring–Average sediment dry density 344.5 kg/m3 (21.5 lbs/ft3)–Average Sediment thickness 1.29 ft–446,558 Metric Tons/yr (Total sediment yield)

•Watershed Survey–Channel Erosion

Lake and Watershed Survey – Baylor

North Central TexasWater Quality Project

Lake and Watershed Survey

Historical Air Photographs: Scale/Resolution and Availability

1995 2004

Channel Erosion in Watershed

Field Survey and Limited Air Photo Assessment

Example Survey

Assigned Field Loss RatesLateralRecession Rate(ft/yr.)

Average(ft./year)

Category Description

0.01-0.12 .0675 Slight Some bare bank but active erosion not readily apparent. Some rills but no vegetative overhang. No exposed tree roots.

0.2-0.8 .5 Moderate Bank is predominantly bare with some rills and vegetative overhang. Some exposed tree roots. No slumps.

0.5-1.4 .94 Severe Bank is bare with very noticeable vegetative overhang. Many tree roots exposed and some fallen trees. Slumping or rotational failures are present. Some changes in cultural features such as missing fence posts and realignment of roads.

Channel Erosion Methods:

Griener Method (1982)

Channel/Gully Rate*Delivary Ratio

Wilkinson Method 0.5 Length *Height*Er*Density

Integration Method Same above except allow for change width with length

SEDNET Method .0001pgQS Stream Power

Gaged Data Method

Estimates Based on Simon’s Sediment Yeild Eq. and % channel erosion

Method Modeled Channel Erosion (tons/year)

Griener Method (1982)

129,357 (adjusted for upstream reservoirs)

Wilkinson Method 168,182 (SWAT channel lengths)

Integration Method 151,359 (Drainage Area/Length )

SEDNET Method 197,684 (bare channel condition)

Gaged Data Method 225,922 (Assume Blackland 1/3 basin)

Mean (All Methods) 168,182 (152,572 Metric tons/year)

Summary of All Methods

Field SurveyChannel Erosion Category

North Central TexasWater Quality Project

• Total Erosion–446,558 Metric Tons/yr

•Channel Erosion–152,572 Metric Tons/yr– 35% of total sediment from channel erosion

North Central TexasWater Quality Project

Lake and Watershed Survey – BaylorCedar Creek Sedimentation

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

1966

01

1968

08

1971

03

1973

10

1976

05

1978

12

1981

07

1984

02

1986

09

1989

04

1991

11

1994

06

1997

01

1999

08

2002

03

2004

10

Mill

ions

Date

Sedi

men

t (t)

PREDICTED MEASURED Linear (PREDICTED)

2005 Estimate

Baylor Field Estimation:Total Sediment Load: 446,558 Metric Tons/yrChannel Erosion : 152,572 Metric Tons/yrOverland Erosion : 293,986 Metric Tons/yr

SWAT Predictions:Total Sediment load : 467,730 Metric Tons/yrChannel Erosion : 162,528 Metric Tons/yrOverland Erosion : 305,046 Metric Tons/yrTotal sediment reaching the reservoir : 451,600 Metric Tons/yr(Trapping by upstream dams/PL655 structures: 16,130 Metric T / )

Coefficients related to sediment RSDIN Initial soil residue cover 1000 kg/ha *.hru USLE_C Minimum "C" value for pastureland in

fair condition 0.007 - crop.dat

SPCON Linear parameter for calculating the maximum amount of sediment that can be reentrained during channel sediment routing

0.01 - basins.bsn

SPEXP Exponent parameter for calculating sediment reentrained in channel sediment routing

1.4 - basins.bsn

CH_COV Channel cover factor 0.1 to 1.0 - *.rte CH_EROD Channel erodibility factor 0.3 to 0.8 - *.rte

Sediment Load

Rangeland0.39%

Urban7.40%

Channel34.75%

WWTP0.03%

Forest0.75%Pasture

15.78%

Cropland40.78%

Wetland0.10%

0.11%

0.77%

4.84%

0.10%

6.73%

13.82%

4.18%

0.20%

4.47%0.13%

21.98%

14.46%

2.45%0.08%

6.47% 0.53%

12.08%

6.47%

Cedar Creek

Kings Creek

All other creeks

97% reaches lake

97% reaches lake

100% reaches lake

89% reaches lake

Total sediment load: 467,730 Metric Tons/yr

26.43%

45.49%

28.08%

North Central TexasWater Quality Project

Nutrient Calibration

Soil Nutrient Initialization• Default nutrient initialization

– Based on organic carbon– C:N ratio of 14:1 – orgN– N:P ratio of 8:1 – orgP

• Pasture – 60%– However, historically they were cropland till 1980’s– Cotton, corn, sorghum– Nutrient build up at the top layer

• Especially phosphorus

Mineral Phosphorus Buildup in the top soil layer

0

50

100

150

200

250

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

Year

Min

P (k

g/ha

)

PastureCropland

Organic Phosphorus (Top soil layer)

0

50

100

150

200

250

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

Year

Org

P (k

g/ha

)

PastureCropland

Soil nutrient initialization run

• Pastures were assumed to be cropland with sorghum– Conventional Tillage– Fertilizer - 67 kg N and 34 kg P per hectare

• Model run for 37 years• Soil nutrient at the end of the simulation

was used to initialize the nutrients in pasture land soils

Data source: TRWD, Kings Intensive Study, September 16, 2002

TOTAL N - KINGS CREEK 9/16/2002

0.0

5.0

10.0

15.0

20.0

25.0

30.0

SUB 13-KC279

SUB 15

SUB 19

SUB 32-KC987

SUB 34-KC34

SUB 80-KC138

8

SUB 45

SUB 52-KC403

4

SUB 54

SUB 89-KC274

MG

/L

Observed QUAL2E SWAT

Variable Definition QUAL2E-Espey SWAT-SSL

Name Cal. Coef Cal. Coef.

LAO Light averaging option 2 2

IGROPT Algal specific growth rate option 2 2

AI0 Ratio of chlorophyll-a to algal biomass [µg-chla/mg algae] 10 10

AI1 Fraction of algal biomass that is nitrogen [mg N/mg alg] 0.090 0.090

AI2 Fraction of algal biomass that is phosphorus [mg P/mg alg] 0.020 0.020

AI3 The rate of oxygen production per unit of algal photosynthesis [mg O2/mg alg)] 1.600 1.400

AI4 The rate of oxygen uptake per unit of algal respiration [mg O2/mg alg)] 2.300 2.000

AI5 The rate of oxygen uptake per unit of NH3-N oxidation [mg O2/mg NH3-N] 3.500 3.000

AI6 The rate of oxygen uptake per unit of NO2-N oxidation [mg O2/mg NO2-N] 1.000 1.000

MUMAX Maximum specific algal growth rate at 20º C [day-1] 1.800 1.000

RHOQ Algal respiration rate at 20º C [day-1] 0.100 0.300

TFACT Fraction of solar radiation computed in the temperature heat balance that is photosynthetically active 0.300 0.300

K_L Half-saturation coefficient for light [kJ/(m2·min)] 0.418 0.418

K_N Michaelis-Menton half-saturation constant for nitrogen [mg N/lL] 0.400 0.400

K_P Michaelis-Menton half-saturation constant for phosphorus [mg P/l] 0.040 0.040

LAMBDA0 Non-algal portion of the light extinction coefficient [m-1] 1.500 1.500

LAMBDA1 Linear algal self-shading coefficient [m-1·(µg chla/l)-1)] 0.002 0.002

LAMBDA2 Nonlinear algal self-shading coefficient [m-1·(µg chla/l)-2] 0.054 0.054

P_N Algal preference factor for ammonia 0.100 0.100

Tributary Samples

North Central TexasWater Quality Project

• Data source: TRWD, Tributary Samples, 1989-2002

Total Nitrogen

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Caney

SWAT

Cedar-

1391

SWAT

Cedar-

243

SWATClea

r

SWATKing

s

SWATLa

cy

SWATLy

nn

SWATN.Twin

SWAT

S. Twin

SWATPrai

rieSWAT

mg/

Ln=18 n=27 n=13 n=19 n=40 n=10 n=5 n=24 n=20 n=13

Total Phosphorus

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Caney

SWAT

Cedar-

1391

SWAT

Cedar-

243

SWATClea

r

SWATKing

s

SWATLa

cy

SWATLy

nn

SWATN.Twin

SWAT

S. Twin

SWATPrai

rieSWAT

mg/

L

n=20 n=29 n=13 n=20 n=42 n=12 n=7 n=26 n=22 n=15

Data source: TRWD, Tributary Samples, 1989-2002

SWAT - QUAL2E

parameterDescription Espey-

QUAL2ESSL-

SWAT

RS1 Local Algal Settling (0.15 to 1.82) (Default=1.0) 0.01 0.01

RS2 Benthos Source Rate for Dissolved P (Default=0.05) 0 0.001

RS3 Benthos Source Rate for NH4-N (Default=0.5) 0 0.001

RS4 Org N Settling Rate (0.001 to 0.10) (Default=0.05) 0.1 0.01

RS5 Org P Settling Rate (0.001 to 0.10) (Default=0.05) 0.1 0.01

RK1 CBOD deoxygenation rate (0.02 to 3.4) (Default=1.71) 0.055 0.1-0.5

RK2 Reaeration Rate (0.01 to 100) (Default=50.0) 1.4-15.89 0.5-1.5

RK3 CBOD Settling loss Rate (-0.36 to 0.36) (Default=0.36) 0.01-0.1 0.025-0.25

RK4 Benthic Oxygen Demand (Default=2.0) 0.8 0.8

North Central TexasWater Quality Project

R2 of the Medians

Parameter R2

TSS 0.177NH3 0.775NOX 0.498ON 0.536OrgP 0.745OPO4 0.804TOTAL N 0.697TOTAL P 0.835

*R2 values highlighed in Red are significant at p = 0.05

Total N

Urban14.40%

Rangeland1.39%

Channel5.40%WWTP

7.21%

Forest3.53%

Pasture44.08%

Cropland23.44%Wetland

0.55%

0.39%

2.21%

0.27% 0.36%

18.22%

0.65%2.75%1.99%

0.26%

6.03%

6.43%

0.62%10.06%

0.60%

16.31%

2.72%

0.82%

5.77%

0.38%

15.80%

2.28%

4.39%0.69%

Cedar Creek

Kings Creek

All other creeks86% reaches lake

85% reaches lake

91% reaches lake

73% reaches lake

Total Nitrogen:1,666,005 kg

26.84%

43.03%

30.14%

Total P

Urban13.30%

Rangeland0.10%

Channel9.20%

WWTP12.12%

Forest0.22%Pasture

22.59%

Cropland42.43%

Wetland0.03%

0.03%

1.95%

0.66%

7.54% 0.04%

10.51%

3.50%

10.01%

5.73%

0.05%

6.74%

0.04%

19.77%

4.26%

1.45%

5.62%

0.03%

8.30% 0.14%

12.15%

1.44%

Cedar Creek

Kings Creek

All other creeks87% reaches lake

88% reaches lake

94% reaches lake

73% reaches lake

Total Phosphorus: 218,202 kg

24.24%

46.63%

29.13%

North Central TexasWater Quality Project

SWAT to WASP: Non-point source file from SWAT output

WASP SWAT SWATSegment Subbasin Output File

1 91 .bsb2 93 .bsb3 96 .bsb4 97 .bsb5 99 .bsb6 102 .bsb15 101 .rch16 100 .rch17 98 .rch18 95 .rch19 94 .rch20 92 .rch21 90 .rch22 89 .rch

• Highlights– Water routing

• Bucket type to iterative approach– Rapid geomorphologic assessment

• Total sediment yield and Channel Erosion– Soil nutrient initialization– Independent verification of SWAT and

QUAL-2E– Nutrient contribution from channel

erosion

North Central TexasWater Quality Project

Improved physically based approaches for Channel Erosion Modeling in SWAT

Balaji Narasimhan, P. M. Allen, J. G. Arnold, and R. Srinivasan

Friday August 7: 10:15-12:00PMSession H1-Model DevelopmentRoom 386