TOPAGNPS is a tool that enhances topographic analysis to support watershed assessments in AnnAGNPS. It automatically delineates watersheds and identifies ephemeral gullies, riparian buffers, and wetlands to allow evaluation of various conservation practices. It was demonstrated on a case study watershed, showing how buffers and land use changes reduced sediment loads from sheet and rill erosion at the subwatershed outlet over time.

1. Enhanced topographic analysis tools for
watershed assessment of integrated
conservation management practice
Ronald L. Bingner
Robert R. Wells
USDA-ARS-National Sedimentation Laboratory
Oxford, Mississippi
Henrique G. Momm
Department of Geosciences
Middle Tennessee State University
Murfreesboro, Tennessee
Yongping Yuan
USEPA
Las Vegas, Nevada
Jurgen Garbrecht
USDA-ARS-Grazinglands Research Laboratory
El Reno, Oklahoma

2. Outline
• Overview of USDA TOPAGNPS topographic
analysis technology for use with AnnAGNPS
• Overview of ephemeral gully, riparian buffer,
wetland watershed enhancements
• Example watershed applications for
integrated conservation practice evaluation
and assessment.
• Summary

3. Watershed Management Planning
What practices to use & where to place them?
Cover
Crops
Buffers
Grass
Waterways
Constructed
Wetlands
No-Till

4. AnnAGNPS – Annualized Agricultural Nonpoint
Source Pollution Model
 Evaluates the integrated effect of
agricultural conservation
practices, riparian buffers and
wetlands for watershed
management planning.
 Uses RUSLE2 science and
databases.
 Tracks pollutants from their
source (sheet & rill, gully, channel,
point source, feedlot).

5. TOPAZ
Topographic Parameterization Tool v3.2
(Garbrecht & Martz, 1997)
AN AUTOMATED DIGITAL LANDSCAPE ANALYSIS TOOL FOR:
• TOPOGRAPHIC EVALUATION
• DRAINAGE IDENTIFICATION
• WATERSHED SEGMENTATION
• SUBCATCHMENT PARAMETERIZATION

6. Automatically Determined Watershed Delineation
AnnAGNPS CELLS
CONNECTED BY THE
CHANNEL NETWORK

7. TOPAZ Enhancements ‐ TOPAGNPS
• Linked with AnnAGNPS
• Utilizes 64‐bit OS for increased speed and memory
• Allows submeter DEM resolution
• Utilizes a graphical user interface
• Incorporates standard GIS input and output capabilities
• Defines RUSLE LS‐factor values
• Integrates all TOPAZ and TOPAGNPS modules into a
single program
• Adds ephemeral gully, riparian buffer, constructed &
pothole wetland identification & characterization.

8. RUSLE Landscape
(AnnAGNPS Cells)
Overland flow
Interrill
Rill
Ephemeral
Gully
(Concentrated
flow)
Erosion Types

9. Integrating Gully, Wetland & Buffer
Components within Watershed Models
Cell F
Cell E
Cell D
Cell CCell A
Cell B
watershed
outlet
feedlot
gully
A wetland is located on reach 2, buffer in reach 1, more wetlands
can be constructed on other reaches such as reach 1 and 3

10. Tillage-Induced Ephemeral Gully Erosion Formation
August 26, 2005
In an USA Wheat Field in Kansas
Ephemeral Gully
October 17, 2005
Ephemeral Gully
Hidden by Wheat
Cover Conditions Can Hide Ephemeral Gullies

11. TOPAGNPS
• Ephemeral Gullies
– AnnAGNPS uses the concept of “potential ephemeral gully”
– Despite the available gully modeling capabilities, a critical AnnAGNPS
input is the location of downstream gully channel initiation (existing or
potential)
– On watershed scale the identification of these locations is difficult and
time‐consuming
– TOPAGNPS identifies & characterizes EGs
11

12. March 2013 Watershed‐Scale Characterization of Riparian Vegetation as Potential Filter Strips using Multi‐Source Remote Sensing
12
Influence of natural and/or planted riparian
(streamside) vegetative buffer strips
The amount of sediment/chemicals trapped by buffers is
affected by:
• Width of the riparian buffer
• Type of vegetation cover
• Amount and intensity of rainfall
• Runoff characteristics
• Local terrain slope

13. Trapping Efficiency
A quantitative measure of the sediment transport
reduction by riparian buffers

14. March 2013 Watershed‐Scale Characterization of Riparian Vegetation as Potential Filter Strips using Multi‐Source Remote Sensing
14
TOPAGNPS
Riparian Buffer GIS representation
AnnAGNPS cells &
reaches
Buffer

15. March 2013 Watershed‐Scale Characterization of Riparian Vegetation as Potential Filter Strips using Multi‐Source Remote Sensing
15
Trapping Efficiency
Existing models
Flow
Buffer
Local slope
One‐dimensional representation: Proxy Two‐dimensional representation:
TOPAGNPS

16. March 2013 Watershed‐Scale Characterization of Riparian Vegetation as Potential Filter Strips using Multi‐Source Remote Sensing
16
TOPAGNPS
TE Estimation in AnnAGNPS Cells includes the effect of
concentrated flow paths through buffers (short‐circuits)
A
0
0
0
1 2
3 4
5 6 TE = 97%
Potential short‐
circuits
TE = 90%
TE = 47%
Varying widths & lengths

17. TOPAGNPS Wetland Feature
For more info: Momm et al. 2016 article in Transactions of the ASABE
TOPAGNPS estimates
wetland/pond extents
AnnAGNPS determines wetland
sediment trapping efficiency
AnnAGNPS tracks pollutants from their
source to any point in the watershed

18. Goodwin Creek Experimental Watershed - Station #14
Subarea Analysis
Subarea for Analysis

19. Goodwin Creek Subarea AnnAGNPS System Characterization
1979 Image
Conventional
Tillage
AnnAGNPS
Subarea
Boundary
AnnAGNPS
Reach
Ephemeral
Gully
Installed
Managed
Buffer
Natural
Buffer

20. Goodwin Creek Subarea Changes
2012 Conventional Tillage to Pasture – Buffer Expansion
Natural
Buffer
1979
Natural
Buffer
2012
Pasture
Ephemeral
Gully
Controlled

21. Sheet & Rill Source Sediment Loads to Subarea Outlet - Buffer Effects
No Buffers
Natural Buffer Effects
Natural & Managed Buffer Effects

23. Summary
• Technology has been developed within AnnAGNPS to
evaluate integrated sheet & rill, gully, and channel
erosion control practices including wetland and
riparian buffer effects on pollutant loads at a
watershed‐scale
• AnnAGNPS incorporates pollutant source load
technology to assess the origin of pollutant loads
transported to any point in the watershed, including
wetland and buffer capability to reduce pollutant
loads at any location within a watershed

24. Thank you

25. Questions