# Presentation: 177777

## BMP Evaluations Using SWAT Model and Associated Uncertainties

- A. Shirmohammadi and T. W. Chu.
- Biological Resources Engineering Department
- University of Maryland, College PArk

## “Forests and wetlands trap sediments and help slow the flow of pollutants into the Bay.  Their loss, coupled with the decline of grasses and oysters in the 1970s and 1980s, caused the Bay to lose much of its resilience.”

- Chesapeake Quarterly
- MD Sea Grant College, Vol. 3, Num. 3
- October 2004

## Ecological Resilience: Provides a measure of the amount of disturbance that an ecosystem can withstand without shifting into an “alternate stable state”

## For Bay: “The shift from a food web dynamic driven by benthic processes- such as underwater grasses and oysters- to one driven by phytoplankton in the water column is a classic example of regime shift, a shift between stable states.” 

## Slide 5

## Identifying Thresholds: “Researchers must develop a systematic way to anticipate when a system is getting close to a threshold or tipping point and prevent it from going over the edge.  They also need to develop methods to turn around the state of a system such as the Chesapeake Bay from undesirable to desirable!” ---Load Reduction! 

## Background

- Hydrologic/ water quality models are the main tools used to tabulate total maximum daily loads (TMDLs)
- Procedure for tabulating TMDLs
- Use monitored data as input into model to represent base conditions
- Simulate alternate management scenarios
- Choose management scenario that meets water quality standards
- Determine total load and allocate load among sources

## Background

- General expression for TMDL allocations:
- 	TMDL=ΣWLA + ΣLA + Future Growth + MOS
- Waste Load Allocations (WLA)- point source contributions
- Load Allocations (LA)- non-point source contributions including background sources
- Margin of Safety (MOS)- accounts for uncertainties about the relationship between pollutant loads and receiving water quality (USEPA, 1999a)

## Background

- Types of Uncertainty in Modeling
- Model Structure
- Parameter Values
- Natural Variability (Spatial and Temporal)
- Data Uncertainty
- Model Prediction

**Notes:**
Model Structure
Inaccurate representation of dynamic behavior of the system
Parameter Values
Inability to accurately quantify parameters of a model
Natural Variability (spatial and temporal)
Inherent randomness of natural processes
Data Uncertainties
e.g., Measurement error, Data layers and resolution (GIS), Data handling, Inconsistency of data
Model Prediction
Inaccurate representation of future behavior of the system

## Watershed/Basin Scale Model

**Watershed/Basin Scale Model**
**SWAT**
**(Arnold et al., 1998)**

## Data Source:

- Study Site:
- Warner Creek Watershed

## Data Collection:

- Precipitation
- Stream flow
- Sediment
- NO3-N
- NH4-N
- TKN
- PO4-P
- TP

## Location: Frederick County, Maryland

- Location: Frederick County, Maryland
- Area: 346 ha (856 acres)
- Soil Type: 1/3 Area:  Manor-Edgemont-Brandywine; 2/3 Area: Penn-Readington-Croton
- Slope: 95% Area:  Slope <15%,  5% Area:    Slope between 15 and 25%
- Erodibility: 65% Area:  Moderately erodible; 12% Area:  Severely erodible; 23% Area: classified not erodible
- Land Use: Pasture, Dairy, Beef, Cropland

## Background on SWAT Model

## Components of SWAT Model

- Hydrology
- Sedimentation (Erosion)
- Nutrients
- Pesticides
- Bacteria

## Slide 17

- Calibration period (1994-1995).
- Validation period (1996-2002).

## Slide 19

## Table. Statistical results comparing measured and simulated flow data at station 2A after adjustment to the subsurface flow contribution from outside the watershed. 

| Hydrologic measurements | No. of samples | r | r2 | R2
(Nash-Sutcliffe) | RMS (mm) |
| --- | --- | --- | --- | --- | --- |
|  |  | Calibration Period (April,1994-1995) |  |  |  |
| Stream flow | 21 | 0.92 | 0.84 | 0.83 | 11.7 |
| Surface runoff | 21 | 0.72 | 0.52 | 0.46 | 10.2 |
| Subsurface flow | 21 | 0.90 | 0.82 | 0.81 | 7.7 |
|  |  | Validation period  
(1996-2002) |  |  |  |
| Stream flow | 72 | 0.82 | 0.68 | 0.68 | 25.8 |
| Surface runoff | 84 | 0.81 | 0.66 | 0.66 | 17.6 |
| Subsurface flow | 72 | 0.70 | 0.49 | 0.39 | 17.2 |
|  |  | Validation period  
(1997-2002) |  |  |  |
| Stream flow | 60 | 0.86 | 0.73 | 0.73 | 18.8 |
| Surface runoff | 72 | 0.77 | 0.60 | 0.48 | 12.0 |
| Subsurface flow | 60 | 0.78 | 0.61 | 0.60 | 14.6 |

**Table. Statistical results comparing measured and simulated flow data at station 2A after adjustment to the subsurface flow contribution from outside the watershed. **

## Slide 21

## Slide 22

## Slide 23

## -

**NO****3 ****- N Statistics**

## Slide 25

## List of BMPs Simulated

| Background  | up and downhill planting with conventional tillage  |
| --- | --- |
| BMP1 | contour planting with conventional tillage  |
| BMP2 | contour planting with conservation tillage  |
| BMP3 | contour planting with no-till  |
| BMP4 | contour stripcropping with no-till  |

## Total areas for row crops planting within Warner watershed

| Year | Total watershed area (ha) | Area under row crop (ha) | Area % of total |
| --- | --- | --- | --- |
| 1994 | 346 | 143.57 | 41.5 |
| 1995 | 346 | 137.93 | 39.9 |
| 1996 | 346 | 144.62 | 41.8 |
| 1997 | 346 | 177.53 | 51.3 |
| 1998 | 346 | 171.24 | 49.5 |
| 1999 | 346 | 158.34 | 45.8 |
| 2000 | 346 | 173.02 | 50.0 |
| 2001 | 346 | 151.46 | 43.8 |
| 2002 | 346 | 139.35 | 40.3 |
| Average | 346 | 155.23 | 44.9 |

## Results of BMP Simulation 

## Comparison of annual total streamflow at the outlet of the watershed based on different BMP implementations.

|  | Scenarios |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  | Background | BMP1 | BMP2 | BMP3 | BMP4 |
| Year | Total Streamflow (mm) |  |  |  |  |
| 1994 | 419 | 417 | 421 | 423 | 423 |
| 1995 | 334 | 331 | 321 | 320 | 320 |
| 1996 | 1014 | 1014 | 1013 | 1004 | 1004 |
| 1997 | 314 | 313 | 314 | 315 | 315 |
| 1998 | 459 | 458 | 455 | 459 | 459 |
| 1999 | 436 | 434 | 426 | 428 | 428 |
| 2000 | 381 | 379 | 366 | 368 | 367 |
| 2001 | 156 | 157 | 155 | 158 | 158 |
| 2002 | 233 | 232 | 219 | 221 | 221 |
| Average | 416 | 415 | 410 | 411 | 411 |
| % Change from Background |  | -0.3 | -1.5 | -1.3 | -1.4 |

- *Background: up and downhill planting with conventional tillage
-  BMP1: contour planting with conventional tillage
-  BMP2: contour planting with conservation tillage
-  BMP3: contour planting with no-till
-  BMP4: contour stripcropping with no-till

## Comparison of annual surface runoff at the outlet of the watershed based on different BMP implementations.

- *Background: up and downhill planting with conventional tillage
-  BMP1: contour planting with conventional tillage
-  BMP2: contour planting with conservation tillage
-  BMP3: contour planting with no-till
-  BMP4: contour stripcropping with no-till

|  | Scenarios |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  | Background | BMP1 | BMP2 | BMP3 | BMP4 |
| Year | Surface Runoff (mm) |  |  |  |  |
| 1994 | 172 | 163 | 154 | 151 | 151 |
| 1995 | 158 | 153 | 129 | 122 | 122 |
| 1996 | 544 | 537 | 503 | 462 | 462 |
| 1997 | 119 | 117 | 109 | 93 | 93 |
| 1998 | 158 | 155 | 134 | 132 | 132 |
| 1999 | 232 | 230 | 195 | 188 | 188 |
| 2000 | 200 | 197 | 168 | 161 | 161 |
| 2001 | 78 | 77 | 64 | 62 | 62 |
| 2002 | 106 | 105 | 78 | 74 | 74 |
| Average | 196 | 193 | 170 | 161 | 161 |
| % Change from Background |  | -1.9 | -13.2 | -18.2 | -18.2 |

## Comparison of annual surface runoff at the outlet of the watershed based on different BMP implementations without winter crop planting .

- *Background: up and downhill planting with conventional tillage
-  BMP1: contour planting with conventional tillage
-  BMP2: contour planting with conservation tillage
-  BMP3: contour planting with no-till
-  BMP4: contour stripcropping with no-till

|  | Scenarios |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  | Background | BMP1 | BMP2 | BMP3 | BMP4 |
| Year | Surface Runoff (mm) |  |  |  |  |
| 1994 | 207 | 203 | 199 | 181 | 181 |
| 1995 | 180 | 175 | 172 | 155 | 155 |
| 1996 | 566 | 557 | 544 | 509 | 509 |
| 1997 | 127 | 124 | 122 | 108 | 108 |
| 1998 | 175 | 172 | 165 | 154 | 154 |
| 1999 | 247 | 244 | 227 | 214 | 214 |
| 2000 | 212 | 209 | 193 | 180 | 180 |
| 2001 | 83 | 82 | 74 | 69 | 69 |
| 2002 | 115 | 115 | 95 | 88 | 88 |
| Average | 212 | 209 | 199 | 184 | 184 |
| % Change from Background |  | -1.6 | -6.4 | -13.3 | -13.3 |

## Comparison of annual sediment loading at the outlet of the watershed based on different BMP implementations.

- *Background: up and downhill planting with conventional tillage
-  BMP1: contour planting with conventional tillage
-  BMP2: contour planting with conservation tillage
-  BMP3: contour planting with no-till
-  BMP4: contour stripcropping with no-till

|  | Scenarios |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  | Background | BMP1 | BMP2 | BMP3 | BMP4 |
| Year | Sediment Loading (kg/ha) |  |  |  |  |
| 1994 | 7658.96 | 6589.60 | 3468.21 | 3430.64 | 3338.15 |
| 1995 | 6647.40 | 5260.12 | 4075.14 | 3757.23 | 3621.39 |
| 1996 | 21156.07 | 18526.01 | 16994.22 | 13303.47 | 13000.00 |
| 1997 | 4884.39 | 4219.65 | 3757.23 | 3447.98 | 3384.39 |
| 1998 | 5924.86 | 4682.08 | 4190.75 | 4164.74 | 4083.82 |
| 1999 | 7312.14 | 5462.43 | 4508.67 | 4329.48 | 4219.65 |
| 2000 | 7138.73 | 5028.90 | 4046.24 | 3838.15 | 3783.24 |
| 2001 | 1612.72 | 1274.57 | 1147.40 | 1143.64 | 1121.97 |
| 2002 | 3901.73 | 2806.36 | 2147.40 | 2056.36 | 2035.26 |
| Average | 7359.67 | 5983.30 | 4926.14 | 4385.74 | 4287.54 |
| % Change from Background |  | -18.7 | -33.1 | -40.4 | -41.7 |

## Comparison of annual nitrate nitrogen loading at the outlet of the watershed based on different BMP implementations.

- *Background: up and downhill planting with conventional tillage
-  BMP1: contour planting with conventional tillage
-  BMP2: contour planting with conservation tillage
-  BMP3: contour planting with no-till
-  BMP4: contour stripcropping with no-till

|  | Scenarios |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  | Background | BMP1 | BMP2 | BMP3 | BMP4 |
| Year | Nitrate-N Loading (kg/ha) |  |  |  |  |
| 1994 | 6.879 | 6.358 | 6.301 | 6.321 | 6.309 |
| 1995 | 9.798 | 8.382 | 7.283 | 6.821 | 6.725 |
| 1996 | 38.728 | 33.526 | 32.659 | 27.913 | 27.723 |
| 1997 | 3.728 | 3.497 | 3.295 | 2.968 | 2.951 |
| 1998 | 12.081 | 10.954 | 9.017 | 8.908 | 8.876 |
| 1999 | 12.890 | 11.532 | 9.451 | 9.361 | 9.269 |
| 2000 | 14.971 | 13.671 | 9.769 | 9.254 | 9.231 |
| 2001 | 2.382 | 2.275 | 1.642 | 1.635 | 1.630 |
| 2002 | 12.197 | 11.965 | 8.150 | 7.798 | 7.789 |
| Average | 12.628 | 11.351 | 9.730 | 8.998 | 8.945 |
| % Change from Background |  | -10.1 | -23.0 | -28.7 | -29.2 |

## Comparison of annual soluble phosphorus loading at the outlet of the watershed based on different BMP implementations.

- *Background: up and downhill planting with conventional tillage
-  BMP1: contour planting with conventional tillage
-  BMP2: contour planting with conservation tillage
-  BMP3: contour planting with no-till
-  BMP4: contour stripcropping with no-till

|  | Scenarios |  |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  | Background | BMP1 | BMP2 | BMP3 | BMP4 |
| Year | Soluble P loading (kg/ha) |  |  |  |  |
| 1994 | 4.769 | 4.046 | 3.266 | 3.127 | 3.043 |
| 1995 | 10.173 | 7.457 | 6.329 | 6.038 | 5.734 |
| 1996 | 32.081 | 25.289 | 26.503 | 24.162 | 23.535 |
| 1997 | 5.347 | 4.104 | 3.728 | 3.725 | 3.616 |
| 1998 | 7.948 | 5.838 | 5.231 | 5.367 | 5.234 |
| 1999 | 11.763 | 8.844 | 7.399 | 7.656 | 7.324 |
| 2000 | 11.329 | 8.353 | 7.254 | 7.214 | 7.075 |
| 2001 | 2.633 | 2.087 | 1.694 | 1.621 | 1.567 |
| 2002 | 5.173 | 4.017 | 2.919 | 2.798 | 2.751 |
| Average | 10.135 | 7.782 | 7.147 | 6.856 | 6.653 |
| % Change from Background |  | -23.2 | -29.5 | -32.4 | -34.4 |

## Slide 35

## Slide 36

## Slide 37

## Slide 38

## Slide 39

## Comparison of average annual (1994-2002) model prediction at the outlet of the watershed based on different BMP implementations with and without winter crop planting

| Average annual prediction (1994-2002) | BACKGROUND |  | BMP1 |  | BMP2 |  | BMP3 |  | BMP4 |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  | no winter crop | with winter crop | no winter crop | with winter crop | no winter crop | with winter crop | no winter crop | with winter crop | no winter crop | with winter crop |
| Streamflow (mm) | 420 | 416 | 419 | 415 | 418 | 410 | 418 | 411 | 418 | 411 |
| % reduce |  | -0.9 |  | -0.9 |  | -2.0 |  | -1.7 |  | -1.7 |
| Surface runoff (mm) | 212 | 196 | 209 | 193 | 199 | 170 | 184 | 161 | 184 | 161 |
| % reduce |  | -7.6 |  | -7.9 |  | -14.3 |  | -12.8 |  | -12.8 |
| Sediment loading (kg/ha) | 11120.75 | 7359.67 | 9215.48 | 5983.30 | 8751.77 | 4926.14 | 7672.13 | 4385.74 | 7460.82 | 4287.54 |
| % reduce |  | -33.8 |  | -35.1 |  | -43.7 |  | -42.8 |  | -42.5 |
| Nitrate-N loading (kg/ha) | 13.814 | 12.628 | 12.521 | 11.351 | 11.454 | 9.730 | 10.356 | 8.998 | 10.286 | 8.945 |
| % reduce |  | -8.6 |  | -9.3 |  | -15.1 |  | -13.1 |  | -13.0 |
| Soluble P loading (kg/ha) | 12.322 | 10.135 | 9.647 | 7.782 | 9.376 | 7.147 | 8.965 | 6.856 | 8.735 | 6.653 |
| % reduce |  | -17.7 |  | -19.3 |  | -23.8 |  | -23.5 |  | -23.8 |

## Latin Hypercubic Sampling

- For Model Uncertainty

## Latin Hypercube Sampling (LHS)

- Divided into *n* non-overlapping intervals on the basis of equal probability.
- One value from each interval is then selected randomly with respect to the probability density in the interval.

- n=5

- Normal distribution

- Uniform distribution

## Model output distribution of Streamflow at the watershed outlet

## Model output distribution of  Sediment loading at the watershed outlet

## Model output distribution of Nitrate loading at the watershed outlet

## Model output distribution of Streamflow at the watershed outlet

- BMP4
- BMP4 (1996)

**1004**

## Model output distribution of Nitrate loading at the watershed outlet

- BMP4 (1996)
- BMP4 (1996) without winter crop

## Acknowledgement

- Our Cooperator,
- Dr. Linda Abbot of USDA/OCE/ORACBA

## Model output distribution of  Sediment loading at the watershed outlet

- BMP2
- BMP4 (1996)