channel erosion and water quality modeling using swat
TRANSCRIPT
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