TIn this study, the hydrology and land management within the Sand Creek Watershed was simulated and BMP effects on discharge and sediment yield were evaluated. The results indicate that the SWAT can be used to evaluate many different BMPs, however, it is important to understand how the model conceptualizes the BMP to properly interpret the simulation results.
3. Assessing Potential Solutions
TMDL
“How do I determine the app
effectiveness of BMPs on a
BASINS
regional watershed scale?”
“There’s an app for that!” “There’s a model for that!”
4. A Predictive Model Approach
Monitoring and
Conceptualization
BMP Implementation Model Design and
BMP Simulation
9. SWAT Model Design
Land Management
Row Crop (C‐S) or
Livestock (C‐C‐A‐A)
Point Sources
5 point sources
3 WWTP, 1 WTP, 1 Industrial
Hydrology
Hand digitized channel,
PWI Ponds, NWI Wetlands
Climate
4 Precipitation Stations
2 Meteorological Stations
Landuse
NLCD (2001)
Soils
NRCS STATSGO
Elevation / Slope
10‐meter DEM
10. SWAT Model Calibration
• Calibration relies on most sensitive parameters,
adjusted within appropriate ranges
• Used autocalibration tool called PEST to calibrate the model at the 5 monitoring sites
• Calibrated Targets included:
o Annual Water Budget
o Daily Discharge
o Monthly Sediment
CNII ESCO AWC SOLK SLOPE
SWAT Model Input Parameter Controls
11. Calibration: Annual Water Budget
Long Term Average Conceptual vs. Model Simulated Annual Water Budget for the SCW
GW Tile
Surface Contribution Water
Precipitation Contributions Drainage ET PET
Runoff to Aquifer Yield
to Stream to Stream
Avg. Conceptual 29” – 32” 6” 6” – 8” 4” – 6” 20% 21” – 22” 40” 6” – 8”
8‐yr Avg. Simulated 32” 2.4” 2.29” 5” 28% 24” 42” 6”
12. Calibration: Average Daily Discharge
2750
2500 Measured vs. SWAT Simulated Daily Discharge at Jordan
Average Daily Discharge (ft3/sec)
2250
2000 Measured Discharge
1750 Simulated Discharge
1500
1250
1000
750
500
250
0
Jan‐01
Apr‐01
Oct‐01
Apr‐02
Sep‐02
Mar‐03
Jun‐03
Sep‐03
Mar‐04
Jun‐04
Sep‐04
Mar‐05
Jun‐05
Sep‐05
Mar‐06
Jun‐06
Sep‐06
Mar‐07
Jun‐07
Sep‐07
Mar‐08
Jun‐08
Sep‐08
Jul‐01
Dec‐01
Jul‐02
Dec‐02
Dec‐03
Dec‐04
Dec‐05
Dec‐06
Dec‐07
Dec‐08
Entire Simulation Period (2001‐2008) R2 Nash ‐Sutcliffe Vol. Difference
Acceptable Range of Statistic 0.50 1.00 ‐‐‐
Sand Creek at Jordan (Outlet) 0.83 0.74 ‐ 12%
13. Calibration: Monthly TSS Load
Calibrate to Upland
Edge of Field Contributions
‐ 40% of Monthly Measured Load
Calibrate to Upland
Watershed Channel Contributions
‐ 60% of Monthly Measured Load
Calibrate to Subwatersheds
Below Knick Point
‐ 25% (Field) of Monthly Measured Load
‐ 75% (Non‐Field) of Monthly Measured Load
14. Calibration: Monthly TSS Load
2.25E+06 Measured vs. Simulated TSS Load (Field and Non-Field) at Jordan (Middle Sand Creek)
2.00E+06 Simulated Non‐Field
1.75E+06 Simulated Field
Measured Non‐Field
1.50E+06
TSS Load (lbs)
Measured Field
1.25E+06
1.00E+06
7.50E+05
5.00E+05
2.50E+05
0.00E+00
Jan‐01
May‐01
Sep‐01
Jan‐02
May‐02
Sep‐02
Jan‐03
May‐03
Sep‐03
Jan‐04
May‐04
Sep‐04
Jan‐05
May‐05
Sep‐05
Jan‐06
May‐06
Sep‐06
Jan‐07
May‐07
Sep‐07
Jan‐08
May‐08
Sep‐08
Field Export Non‐Field Export Total
R2 NSE % Diff R2 NSE % Diff R2 NSE % Diff
Acceptable Range of Statistic 0.50 1.00 ‐‐‐ 0.50 1.00 ‐‐‐ 0.50 1.00 ‐‐‐
Sand Creek at Jordan 0.69 0.47 ‐ 1% 0.69 0.59 ‐ 21% 0.71 0.57 ‐ 12%
16. Sand Creek BMPs
BMPs are relative to 2030 conditions
Agricultural Buffer Strips 1
Highly Erodible Land
Current Conditions 2030 Conditions 2
Conversion
(2001‐2008) “Predictive Basecase”
Porter Creek Agricultural
3
Land Conversion
• Additional 6% (~10,000 acres) urban land
• 2030 permitted point source discharge
Pond Construction / 4
Wetland Restoration
Channel Improvements 5
17. 1 Agricultural Buffer Strips (30‐feet)
(1) Buffer Strip BMP = 2030 Conditions + 30ft Buffer
• Buffer Strip BMP = 2030 Conditions + 30‐ft Buffer
• Impedes sediment, nutrients, bacteria, and pesticides
• Applied to all Agricultural HRUs within Sand Creek
Sediment Reduction after
Location
Installation of 30‐ft Buffer*
Average Edge‐of‐Field Reduction 47% (6,065,000 lbs)
Loss
Average Upland Watershed Reduction 11% (457,600 lbs) of
Sand Creek Watershed Outlet Reduction 0% (2,760 lbs) Investment
* As compared to 2030 Predictive Basecase
18. 2 Highly Erodible Land (HEL) Conversion
(2) HEL Land Conversion = 2030 Conditions + 50% of HEL converted to Switchgrass
• Conversion of 5,020 acres of agricultural HEL
• Corn / Soybean (CN = 66) Switchgrass (CN = 50)
HEL Simulated Land
HEL Conversion
HEL Land (Not Converted)
Sediment Reduction after
Location
HEL Land Conversion *
Average Edge‐of‐Field Reduction 11% (1,490,000 lbs)
Average Upland Watershed Reduction 5% (256,500 lbs)
Sand Creek Watershed Outlet Reduction 3% (2,300,524 lbs)
* As compared to 2030 Predictive Basecase
19. 3 Porter Creek Agricultural Land Conversion
(3A) Porter Creek Ag. Land Conversion = 2030 Conditions + 30% switchgrass conversion
(3B) Porter Creek Ag. Land Conversion = 2030 Conditions + 50% switchgrass conversion
(3C) Porter Creek Ag. Land Conversion = 2030 Conditions + 80% switchgrass conversion
Total cropped acres = 15,176 acres
30% = 4,574 acres to grass
50% = 7,674 acres to grass
80% = 12,143 acres to grass
Grassland /
Agriculture Rural Residential
Sediment Reduction Sediment Reduction Sediment Reduction
Location 30% Conversion * 50% Conversion * 80% Conversion *
Porter Creek Edge‐of‐Field Reduction 32% (6,913,500 lbs) 52% (11,365,000 lbs) 90% (19,640,000 lbs)
Porter Creek Watershed Reduction 10% (684,700 lbs) 16% (1,146,000 lbs) 26% (1,849,500 lbs)
Sand Creek Watershed Outlet Reduction 3% (2,257,500 lbs) 5% (3,592,700 lbs) 9% (6,698,500 lbs)
* As compared to 2030 Predictive Basecase
20. 4 Pond Construction & Wetland Restoration
(4A) Pond and Wetland Restoration = 2030 Conditions + Scott County New Pond / Wetland
(4B) Pond and Wetland Restoration = 2030 Conditions + 3‐County New Pond / Wetland
• Relied on Ducks Unlimited drained wetland inventory and
Scott County flood control study as model input
• Scenario 4A = 60 ponds / wetlands in Scott County
Scenario 4B = 120 ponds / wetlands (three counties)
• Modeled as wetlands, ponds, or reservoirs depending Scott County Restored
on location within stream network. Rice and Le Sueur
Counties Restored
Scott County Pond / 3‐County Pond /
Location Wetland Restoration * Wetland Restoration *
Average Edge‐of‐Field Reduction 1% (112,200 lbs) 14% (2,034,700 lbs)
Average Upland Watershed Reduction 19% (679,400 lbs) 31% (1,603,038 lbs)
Sand Creek Watershed Outlet Reduction 10% (7,799,679 lbs) 21% (15,688,100 lbs)
* As compared to 2030 Predictive Basecase
21. 5 Channel Improvements
(5) Channel Improvement = 2030 Conditions + Middle Sand Channel Improvements
• Improved channel cover and decreased channel
erodibility potential within model
Sediment Reduction after Middle
Location
Sand Channel Improvement*
Average Edge‐of‐Field Reduction 0% (0 lbs)
Average Upland Watershed Reduction 0% (0 lbs)
Sand Creek Watershed Outlet Reduction 26% (19,110,200 lbs)
* As compared to 2030 Predictive Basecase
23. Conclusions
SWAT Model
• Simulated BMPs only as good as the our conceptualization of the system
• Choosing a tool for BMP evaluation requires:
o Monitoring data detail
o Type and locations of potential BMPs
o Understanding of suite of models and their limitations
• Sediment source allocation between field and non‐field is challenging with current model
Future model updates will trace sediment through watershed with greater ease
• Regional models can be coupled with local‐scale models such as APEX and CONCEPTS
Sand Creek Watershed
• A combination of water retention and channel improvements led to the greatest sediment
reduction, but reduction still exceeded state turbidity standard for Sand Creek at Jordan.
• Need to contain the water as much as the sediment due to non‐field contributions
• Benefits from BMPs observed in upland watersheds of Sand Creek were mitigated by
downstream problems
24. Questions?
Adam Freihoefer, Environmental Analyst
Metropolitan Council
651‐602‐1056
adam.freihoefer@metc.state.mn.us
25. Study Site: Sand Creek Watershed
• 51% Agriculture, 28% Grassland,
9% Forest, 7% Urban (low‐medium)
• 5 point source contributions
• Porter and Sand Creek impaired
for Turbidity
2001 NLCD Land Use
Agriculture
Forest
Grassland
Urban
Water
Hydrologic Network
Turbidity Impairment
Point Source
26. SWAT Model Design
Subwatersheds 58
HRUs 893
Warm‐Up Period 4 years (1997‐2000)
Calibration Period 8 years (2001‐2008)
Daily (Discharge),
Time Step
Monthly( Sediment)
ET Method Hargreaves
Agricultural HRUs
Tile Drainage
with 0‐5% Slope
27. BMPs TSS Concentration vs. Turbidity Standard
Middle Sand Creek at Jordan
400
Total Suspended Sediment Conc.
350
300
250
(mg/l)
200
150
100
50
0
2030 1 2 3A 3B 3C 4A 4B 5
Average Sediment Concentration
Turbidity Standard (TSS ‐ 111/mg/L)
28. BMPs TSS Concentration vs. Turbidity Standard1,2
10% Exceedence Concentrations for Modeled Scenarios (mg/L)
Raven Upper Sand Sand Creek Porter Sand Creek
Scenario
Creek Creek Tributary Creek at Jordan
Target Concentration 46 62 41 63 111
2030: Predictive Basecase 119 183 122 117 350
1: Buffers 101 176 100 115 350
2: HEL Conversion 118 178 118 114 347
3A: Porter 30% 119 181 122 111 343
3B: Porter 50% 119 180 122 104 344
3C: Porter 80% 119 181 122 96 336
4A: Scott Wetlands 110 180 64 109 336
4B: 3‐County Wetlands 104 160 57 108 314
5: Middle Sand Channel 119 180 122 116 258
4B + 5: Combination 104 160 57 79 226
(1): Target Concentration is based on TSS equivalent to turbidity at 25 NTUs (Minnesota Standard)
(2): Modeled concentrations represent an 8‐yr monthly flow weighted mean concentrations
