Assessing the Integrated Impact of
Riparian Buffers, Ponds, and
Ephemeral Gullies on Pollutant
Loads in Goodwin Creek
Lindsey Yasarer, PhD
Research Hydrologist, USDA-ARS, National
Sedimentation Laboratory, Oxford, MS
Co-authors: Ronald Bingner, Henrique Momm
November 2016 AWRA Conference - Orlando, FL
Watershed Modeling Applications
AnnAGNPS Watershed Model
Annualized Agricultural NonPoint Source Model
A joint effort between the USDA –
Agricultural Research Service
and
Natural Resource Conservation Service
A tool to evaluate the integrated effects of conservation
practices within ungauged watersheds on:
• Water Quantity
• Sheet and rill erosion
• Gully erosion
• Chemical water quality
AnnAGNPS
• AnnAGNPS components:
• TOPAGNPS  generates cell and stream network
• SCS curve number daily runoff
• RUSLE  generates daily sheet and rill erosion
• Critical Inputs:
• Land-use and management
practices
• Soil profile characteristics
• Daily climate parameters
• Topographic information
Integrated Tools for
Watershed Assessment in
AnnAGNPS
Goodwin Creek
Watershed
- Located in Panola County,
Mississippi
- USDA-CEAP: Conservation Effects
Assessment Program Watershed
Simulation Inputs:
- Land-use 1982-1996
- SSURGO Soils
- 1m hydrologically corrected DEM
- Corrected precipitation data
PEG: Potential Ephemeral Gully
Tool
•Ephemeral
CompoundGully:
Topographic Index:
NRCS:
“an𝐴 ephemeral
cropland gully is larger than a rill and
𝐶𝐶𝐶 =
∙
𝑡𝑡𝑡
𝛽
∙
PLANC
𝑑
smaller
a [classic]
“It usually appears on a
2)
• 𝐴𝑑 =than
upstream
area (mgully”…
cultivated
field
during the planting or growing season and is
• β = slope
(m/m)
erased
by cultivation”…
“They frequently form in well• PLANC
= Planform
curvature
defined,
shallow depressions in
natural drainage ways upstream
from incised channels or gullies”
Location of Gully Mouth
Effects of Potential Ephemeral Gullies
on Sediment Yield
With Gullies
No Gullies
26% increase
AGBUF: Riparian Buffer Tool
Calculates trapping efficiency through
buffer including effect of
concentrated flow paths
Momm et al., 2013
Impact of
Riparian Buffer
on Sediment
Loads
Without Buffer
With Buffer
No Buffer
56% decrease
Buffer
AGWET: Wetland/Pond Tool
Step 1:AGWET estimates wetland/pond extents
A
B
User-provides points User-provided lines on
on a reach
a reach with height
Model generates
barrier line and height
C
User-provided
threshold and model
generated potential
wetland points using
wetness index
Potential constructed
Existing constructed
Potential constructed
wetland or pond with wetland or pond with
wetland or pond and
pre-determined location
known location
unsure of ideal locations
For more info: Momm et al. 2016 article in Transactions of the ASABE
Using combination of approaches A and B
AGWET: Wetland/Pond Tool
Step 2: Run the model with AGWET input and AnnAGNPS
determines wetland/pond sediment trapping efficiency
Nitrate-nitrogen removal can also be estimated
For more info: Momm et al. 2016 article in Transactions of the ASABE
Pond sediment trapping efficiency
At Outlet:
• 2% decrease in sediment load
• 5% decrease in streamflow
Module Integration
Average Annual sediment load Mg/ha
• AnnAGNPS (no modules)
4.5
• AGWET
4
3.5
• PEG
3
2.5
• AGBUF
2
1.5
• AGBUF + PEG
1
0.5
• AGWET +AGBUF
0
• AGWET + PEG
• AGWET +AGBUF +PEG
clay
silt
sand
Interesting Findings
• Pond areas were well-represented by AGWET tool
• Sediment trapping efficiencies of wetlands were
high, but there was not a large impact on overall
watershed sediment loads
• Next step: Improve sediment and phosphorus trapping
algorithms in AGWET
• Potential for a great number of ephemeral gullies in
watershed  sensitivity analysis needed
• Buffer predicted to drastically reduce sediment
loads  how accurate is this? Analysis needed
AGNPS References
• Website: Google AGNPS – executables, source code and
technical documentation all available for download
• Momm et al. 2012. AGNPS GIS-Based Tool for WatershedScale Identification and Mapping of Cropland Potential
Ephemeral Gullies. Applied Engineering in Agriculture
• Momm et al. 2013. Effect of Topographic Characteristics on
Compound Topographic Index for Identification of Gully
Channel Initiation Locations. Transactions of the ASABE
• Momm et al. 2014. Spatial Characterization of Riparian
Buffer Effects on Sediment Loads from Watershed Systems.
Journal of Environmental Quality
• Momm et al. 2016. Characterization and Placement of
Wetlands for Integrated Conservation Practice Planning.
Transactions of the ASABE
Thank you!
Lindsey Yasarer
USDA-ARS
National Sedimentation Laboratory
Oxford, MS
[email protected]