1.
SWAT modeling of nutrient response to BMPs
in the Beargrass Creek Watershed
Katrin Bieger, Douglas R. Smith, and Jeffrey G. Arnold
2016 SWCS Annual Conference
Louisville, KY
July 24‐27, 2016

2.
Outline
1. Introduction
2. Input data and model setup
3. Preliminary results
4. Outlook

3.
Soil and Water Assessment Tool
• Arnold et al. (1998), http://swat.tamu.edu/
• Predict the impact of land management practices on water
quantity and quality in large complex watersheds
• Subdivision of the watershed into subwatersheds and
Hydrologic Response Units (HRUs)
• Limited capability to identify critical source areas
1. Introduction

4.
SWAT+
• Expected to facilitate
– maintenance of code and input files
– linkage of SWAT and other models
– addition of new process subroutines
• Flexible spatial representation of interactions and processes
within a watershed using “connect” files
• Routing of runoff, sediment and nutrients across the
landscape
1. Introduction

5.
Watershed delineation and stream definition
2. Input data and model setup
10 m DEM Resampling
to 5 m
Processing
using TauDEM
• Predefined watershed and streams?
• Delineate riparian areas?

6.
HRU definition
2. Input data and model setup
Land use SSURGO
Dominant soils
Land use digitized from
aerial photosHydrologic Response Units
• Soil properties
• Management schedules
• Tile drains

7.
Climate and streamflow
2. Input data and model setup
Observed Q at
watershed outlet:
6/10/2014‐
5/16/2016
→ calibra on

8.
Observed and simulated streamflow
3. Preliminary results
Daily
NSE: 0.70
R2: 0.75
PBIAS: ‐16.4
Monthly
NSE: 0.88
R2: 0.94

9.
Water balance 2014‐2015
3. Preliminary results
Amount [mm] % of precipitation
Precipitation 1084 100
ET 609 56
Water yield 353 33
Surface runoff 242 22
Lateral flow 51 5
Tile flow 61 6
Unaccounted for 122 11
too high
too low
I have no idea what is going on here…
• Error in writing output?
• Error in model calculations? Source: Sanford & Selnick, 2013

10.
“A major challenge of the ongoing evolution of the model will
be meeting the desire for additional spatial complexity while
maintaining ease of model use.” (Gassman et al. 2007)
HRU routing
4. Outlook
Challenges:
1. Circular routing
2. Roads

11.
Implementation of BMPs
4. Outlook
Reduction
efficiencies
or simulation
of processes?
Why use SWAT?
• Identification of most effective combination of management
practices
• Prediction of long‐term effects of management practices
• Consideration of climate change?

12.
Moving forward…
1. Spatial extent/parameterization of tile drains
2. Management schedules and plant growth
3. Soil parameterization
4. Calibration of water balance and streamflow
5. Calibration of nitrogen concentrations/loads
6. Implementation of BMPs in the model
7. HRU routing
4. Outlook

13.
Thank you for your attention!
kbieger@brc.tamus.edu