Sensitivity and Stability of Iowa Daily Erosion Project 2 to Variable Landscape and Rainfall

Intensity

Soil and Water Conservation Society Annual MeetingJuly 27, 2015Brian Gelder

R.M. Cruse, K. Gesch, D. James, D. Herzmann, T. Sklenar, J. Opsomer, J. Laflen, D. Flanagan

What Is the Iowa Daily Erosion Project?

• Estimates daily sheet and rill hill slope erosion spatially across Iowa;

• Gen 1 Debut 2002;• WEPP model is the ‘engine.’

IDEP Gen 1• Cox, C.; Hug, A.; Bruzelius, N. Losing Ground; Environmental

Working Group: Ames, IA,USA, 2011.• Soil erosion threatens Iowa agriculture. Kathleen Masterson.

Harvest Public Media. April 12, 2011. http://harvestpublicmedia.org/article/519/soil-erosion-threatens-iowa-agriculture/5

• High prices sow seeds of erosion. William Neuman. New York Times. April 12, 2011

• Cruse, R.M., D. Flanagan, J. Frankenberger, B. Gelder, D. Herzmann, D. James, W. Krajewski, M. Kraszewski, J. Laflen, J. Opsomer, and D. Todey 2006. Daily estimates of rainfall, water runoff, and soil erosion in Iowa. J. Soil Water Conserv. 61:191-198. – Best Research Paper Award for Impact and Quality (Honorable Mention)

2011 Journal of Soil and Water Conservation

– Soils– Slopes– Management

WEPP and IDEP

WEPP

WEPP and IDEP1

WEPP

NRINEXRAD Precipitation

WEPP

NEXRAD Precip

LiDAR Elevation

gSSURGO Soils

Field-scale Land-use & Management

WEPP and IDEP2

Presentation Objectives

• For IDEP2– Test output for • Stability• Accuracy

• Implicitly test input data accuracy suitability for supporting ‘accurate’ sheet and rill erosion estimates

IDEP2 Database• 1,647 HUC12 watersheds• 14,944,400+ Hectares• >430,000 fields in Iowa

Major Geo-Spatial Components by HUC12• Soils - gSSURGO – 10m raster• Land Use - 2008-2013 NASS Crop Data Layer • Elevation - LiDAR-based, 3m resolution• 2009 crop-specific field boundaries

IDEP 2 Hillslope Profiles

• WEPP OFEs break at Land-use and Soils boundaries• Slope estimated for each OFE from DEM

OFE 2

OFE 3

OFE 1

OFE 4

15

HUC 12 Boundary

Stratified sampling units – subcatchments

SubcatchmentBoundary

13

CatchmentBoundary

Flowpath

Research Question: Is one flow path per subcatchment a sufficient sampling density to give a representative

HUC 12 average? CatchmentBoundary

Flowpath

Procedure

• Select 3 HUC12 watersheds per MLRA (10)• In 30 HUC12s, generate up to10 flowpaths per

sub-catchment• Run DEP using 1 through 10 flowpaths

Select HUC12s

Results

Results

Does IDEP Give Representative Soil Erosion Estimates?

• Compare to NRI– RUSLE technology– Long term average rainfall product– Linear hill slopes– Periodic site visits to determine management– Statewide average sheet and rill detachment &

delivery to base of hill slope

8.8 T/A

2.8 T/A 8.8 T/A

3.6 T/A 10.6 T/A

4.8 T/A 1.6 T/A

5.4 T/A5.4 T/A 8.0 T/A

State Wide Average 5.7 T/A/YR

Loss

NRI Comparison

YearSoil loss

(tons/acre) NRI (95%CI)2007 2.84 5.25 (4.78-5.72)2008 8.832009 3.552010 10.60 5.42 (4.97-5.87)2011 4.762012 1.752013 5.382014 8.00

Average 5.71

NRI Comparison

• Average IDEP annual erosion = 5.71 tons/acre• 2007 and 2010 NRI = 5.25 and 5.42 ton/acre• Conclusions:– Over multiple years IDEP agrees with NRI– IDEP better captures annual & spatial variability

Conclusions

• IDEP long-term statewide averages agree with NRI (statewide average) suggesting estimates are realistic and inputs data are defendable.

• Increasing number of flowpaths modeled per sub-catchment has little impact on estimates across a representative sample of HUC 12s suggesting one flow path per subcatchment is suitable.