Estimating Field-Scale Runoff and Sediment Delivery Seth M. Dabney, USDA-ARS Dalmo A. N. Vieira, USDA-ARS Daniel C. Yoder, Univ. of Tennessee
Organization Buffers for concentrated flow control Distributed erosion estimation A reality check
NRCS practices to control concentrated flow erosion Buffer Practice NRCS code Purpose Field Border 386 + Riparian Forest Buffer 391 + Grassed Waterway 412 + Vegetative Barrier 61 + Related Practices With Buffering Attributes Channel Vegetation 322 + Farm-ponds/in-stream wetlands 378 * Grade Stabilization Structure 41 + Terrace 6 + Water and Sediment Cont. Basin 638 + + indicates a purpose for which practice may be designed; * reflects an area of potential impact, but not a design purpose
Narrow stiff-grass barriers can cause backwaters over a foot deep, spreading runoff
Here sediment deposited 1-15 ft upslope of grass. How wide is this.5 ft buffer?
Elevation (cm) 4 3 1 4 6 8 Distance Above Barrier (cm)
Manning s Equation V = 2/3 1 R s n 1/ 2 V = average velocity (m s -1 ) n = a hydraulic resistance parameter (s m -1/3 ) R = hydraulic radius (m) s = ground slope
1 Filter Strip Vegetative Barrier Grassed Waterway (s m -1/3 ) n 1 Vetiver D C B Switchgrass with residues A.1 1, m -2 E Bristle bunches 2,5 m -2.1.1.1.1 1 1 VR ~ q (m 2 s -1 )
Tillage Erosion Tillage operations cause more soil to be moved downslope than upslope Progressive erosion of hilltops and accumulation of soil near slope bottoms Erosion of hilltops may lead to exposure of unproductive subsoil
Deep Hollow Lake, Mississippi Delta an oxbow of the Yazoo River Riparian Ephemeral.5 m Contours
Filter Strip without traffic
Slotted-Inlet pipe and pad grade control structures slow surface runoff and limit gully formation Soil/pad surface
Slotted-inlet on pipes are resistant to fouling with crop residues carried in runoff and drains hydrograph tails faster than a square cut pipe.
Pipe reduces peak flow from 7 ha cotton, increases ponded depth; could create sheet flow over broad buffer/spillway
Distributed erosion estimation
RUSLE2 computes sheet and rill erosion, not concentrated flow erosion
Ephemeral gully channels end RUSLE hillslopes (AH 73)
http://www.ars.usda.gov/research/docs.htm?docid=222
http://www.ars.usda.gov/research/docs.htm?docid=222
http://www.ars.usda.gov/research/docs.htm?docid=222
http://www.ars.usda.gov/research/docs.htm?docid=222
Example: Treynor, IA, WS 11 1975 2; Hedges starting 1992 HISTORY CT 1975-1997 Hedges established starting 1992 NT 1997-2
Example: Treynor, IA, WS 11 Flow measurement and sampling
Treynor, IA, WS 11 1975 1991; plowed corn averaging 121 bu/a; RUSLE2 profile 2 Observed RUSLE2 Simulated Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 CT - No Hedge 1975-1991 A 16 14 1 1 8 6 4 Rainfall (mm) Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 CT - No Hedge B 16 14 1 1 8 6 4 Rainfall (mm) 1 3 5 7 9 11 1 3 5 7 9 11
Uncalibrated Runoff Event Depths, Treynor Iowa epy=18, α=.31, σ=1.3 epy=15,α=.5, σ=9.1
Uncalibrated Monthly Runoff and Erosion, Treynor Iowa Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 Observed RUSLE2 Simulated CT - No Hedge 1975-1991 A 16 14 1 8 15 6 1 4 5 1 Rainfall (mm) Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 CT - No Hedge B 16 14 1 8 15 6 1 4 5 1 Rainfall (mm) 1 3 5 7 9 11 1 3 5 7 9 11 Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 CT - Hedge 1991-1997 C 16 14 1 1 8 6 4 Rainfall (mm) Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 CT - Hedge D 16 14 1 1 8 6 4 Rainfall (mm) 1 3 5 7 9 11 1 3 5 7 9 11
Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 Observed CT - No Hedge 1975-1991 A 16 14 1 1 8 6 4 Rainfall (mm) Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 RUSLE2 Simulated CT - No Hedge B 16 14 1 1 8 6 4 Rainfall (mm) 1 3 5 7 9 11 1 3 5 7 9 11 Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 CT - Hedge 1991-1997 C 16 14 1 1 8 6 4 Rainfall (mm) Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 CT - Hedge D 16 14 1 1 8 6 4 Rainfall (mm) 1 3 5 7 9 11 1 3 5 7 9 11 Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 NT - Hedge 1997-2 E 16 14 1 1 8 6 4 Rainfall (mm) Runoff (mm) or Sediment Yield (Mg ha- 1 ) 4 35 3 25 15 1 5 Runoff Sed. Yield Rain NT - Hedge F 16 14 1 1 8 6 4 Rainfall (mm) 1 3 5 7 9 11 1 3 5 7 9 11 Month Month
Flow measurement and sampling
Distributed erosion using high resolution topographic data (e.g. LiDAR) GIS tools to identify flow network and channel locations API RUSLE2 calls with slope length calculated from runoff ratios RUSLE2 runoff event sequence linkage with a concentrated flow (ephemeral gully) erosion model
Terrain Analysis Define areas of concentrated flow (channels) Define cell connectivity and catchments
Slope length calculated as ratio of runoff leaving to runoff generated within cell
2D-RUSLE2 API example Distributed soil loss (3 m cells) 35 Mg ha -1 y -1
EphGEE Ephemeral Gully Erosion Estimator
A reality check
Switchgrass (Panicum virgatum) roots contribute to soil cohesion, but need time to grow.
Summary RUSLE2 is being optimized to use LiDAR data. The representative runoff event sequence allows distributed sheet and rill erosion estimation and outputs are suitable for linkage with an ephemeral gully model. Buffers and structural conservation practices can control concentrated-flow erosion but maintenance is necessary.
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