Boll, Jan - Soil and Water Conservation Society

Evaluation of Conservation
Practices in a Mixed-Land
Use Watershed using
Interdisciplinary Analyses
Jan Boll 1 , Erin S. Brooks 1 , Brian Crabtree 1 Naga S. Tosakana 2 , J.D. Wulfhorst 2 ,
Larry van Tassel 2 , and Robert Mahler 3
1
Biological and Agricultural Engineering, University of Idaho, Moscow, ID
2
Agricultural Economics and Rural Sociology, University of Idaho, Moscow, ID
3
Plant, Soil and Entomological Sciences, University of Idaho, Moscow, ID

Paradise Creek Watershed
•5000 ha watershed
•Mixed land use
watershed with urban,
agricultural and forested
lands
•Exceeds TMDL for
sediment loading (need
85% reduction)
Funded by USDA-CSREES-
Conservation Effectiveness Assessment
Program (CEAP)

Research & Objectives
Our research includes: 1) combination of
monitoring and modeling, 2) participatory
component with local operators/managers
Objectives:
To modify a distributed erosion model to model
hydrology correctly
To target agricultural fields from physical data
( sediment transport model)
To target agricultural fields using physical and
socio-economic data ( optimization)

Hydrology
• Variable source hydrology
– The majority of runoff exiting a watershed is driven by
a relatively small portion of the watershed.
– The abundance of these runoff generating areas may
increase and decrease depending on temporal and
spatial variability.

Saturated areas

Water Erosion Prediction Project
(WEPP) Model
• Uses readily available data sources (DEM,
soils, land use, climate)
• We modified WEPP to simulate variable
source area hydrology
• Addition of 20 overland flow elements per
hillslope
– Allows subsurface lateral flow to become
surface runoff at toe slopes within a hillslope

Elevation map
Slope map

GeoWEPP generated
hillslopes
• Up to 1000 hillslopes
allowed per watershed
• 20 Overland flow elements
per hillslope (maximum)

5 crops:
• winter wheat
• spring wheat
• barley
• peas
• lentils
3 tillage practices:
• conventional
• conservation (mulch till)
• direct seed (no-till)
•CRP
Land use map

Water and Sediment Control Structure
Gully Plug
photo: Bill Dansert ISCC

Rock Chute
Filter Strip
Diversion
Roof
management

Hillslope Diagram
With multiple OFE’s
water can exit the
hillslope when lower
OFE’s become
saturated

Historic Data Points
2006 points

RESULTS
• WEPP: quick validation review
• WEPP: 30 yr simulations for different
tillage practices
• WEPP: mean vs median for management
• Optimization: maximum returns while
reducing sediment delivery to stream

Observed versus Simulated Streamflow
40
35
WEPP Simulated
Observed
30
Streamflow (mm)
25
20
15
10
5
0
1/9/01 6/8/01 11/5/01 4/4/02 9/1/02 1/29/03 6/28/03 11/25/03 4/23/04

Streamflow and Sediment Load
40
35
WEPP Simulated Streamflow
Observed
WEPP Simulated Sediment Load
10000
9000
8000
Streamflow (mm)
30
25
20
15
7000
6000
5000
4000
Del. Sediment (Tonnes)
3000
10
2000
5
1000
0
0
11/5/01 3/10/02 7/13/02 11/15/02 3/20/03 7/23/03 11/25/03 3/29/04 8/1/04

Grass Direct Seed Mulch Till Conventional
0.07 Tons/ac
0.1 tons/ac
0.9 tons/ac
2.5 tons/ac
614 Tons
1100 tons
10,000 tons
24,000 tons
Winter Wheat
Spring Barley
Spring Peas
Rotation
Sediment
Delivery
by
Hillslope
***30 year Averages

photo: Bill Dansert ISCC

Gully Plugs
Severely eroded spots
- Areas where on the average 75
percent or more of the original surface
layer has been lost from accelerated
erosion. Typically 2 to 5 acres.
Escarpments
A relatively continuous and steep slope or
cliff generally produced by erosion, but can
be produced by faulting breaking the
continuity of more gently sloping land
surfaces. Exposed nonbedrock material is
nonsoil or very shallow, poorly developed
soil.

Sediment load: Yearly variations
1000000.00
100000.00
Conv. WW-Barley-Pea
Mulch WW-Barley-Pea
Direct Seed WW-Barley-Pea
Grass
Total Sediment Load (Tons)
10000.00
1000.00
100.00
10.00
1.00
1977 1978 1979 1980 1981 1982 1983 1984

30 Year WEPP Simulated Sediment Load
Rotation
Tillage Practice
Average
(Tons)
Median
(Tons)
WW-Barley-Pea Conventional 46,300 23,500
WW-Barley-Pea Mulch 10,658 2,800
WW-Barley-Pea Direct Seed 1,213 300
WW-Barley Conventional 34,106 16,856
WW-Barley Mulch 4,428 365
WW-Barley Direct Seed 3,946 275
WW-Pea Conventional 79,700 37,200
WW-Pea Mulch 12,400 2,700
WW-Pea Direct Seed 2,100 200
Grass Grass 600 100

2003
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
1975
8
7
6
5
4
3
2
1
0
Sediment load: Average and Median
Mulch tillage Winter Wheat-Barley Rotation
Average
Median
30 Year Average = 0.9 tons/ac
30 Year Median = 0.01 tons/ac
Sediment Delivered to Streams (tons/ac)

Sediment Load: Average and Median
100%
90%
1998 Mulch Till WW-Barley-Pea
Cumulative Percentage of Fields
80%
70%
60%
50%
40%
30%
20%
Median = 0.8 Tons/Field
Average = 7.1 Tons/Field
10%
0%
0 1 2 3 4 5 6 7 8 9 10
Sediment Delivered to Streams (Tons/Field)

Load reduction efficiency: by field
100%
90%
80%
Cumulative Percent Load
70%
60%
50%
40%
30%
20%
10%
0%
Grass
NT WW-B-P
NT WW-P
NT WW-B
MT WW-B
MT WW-B-P
MT WW-P
CT WW-B
CT WW-B-P
CT WW-P
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Cumulative Percent of Fields

Load reduction efficiency: by area
100%
Cumulative Percent of 30 Year Average Load
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Grass
NT WW-B-P
NT WW-P
NT WW-B
MT WW-B
MT WW-B-P
MT WW-P
CT WW-B
CT WW-B-P
CT WW-P
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Cumulative Percent Area

Optimization Model
• To evaluate various options to achieve sediment
reduction goals while optimizing the farm income
• The objective function is to maximize the net
returns subjected to constraints of land availability
and soil loss reduction:
Max Π = ( PC
* Y − C,
F
CC,
F
) X
C,
F
C,
F
Subject to the constraints:
Σ X
C , F
=
C
Σ eC
, F
X
C , F
L
≤
F
E

Data
• Operators provided crop/tillage/machinery/
fertilizer/pesticide/harvest practices, BY
FIELD
• The yield data for the model were
generated by using the CROPSYST
simulation model
• Sediment delivery was provided by the
WEPP model

Optimization results
Crop distribution
Soil loss
reduction
(%)
Area
(ac)
Variable
profit
($/ac)
Rotations
Wwheat
(ac)
Barley
(ac)
Lentil
(ac)
Peas
(ac)
CRP
(ac)
0
4943
142
Rotation 2 & 3
2471
0
2016
461
0
10
4943
133
Rotation 1, 2, 3 & 4
2237
9
1772
456
469
20
4943
131
Rotation 1, 2, 3 & 4
2178
9
1700
468
587
30
4943
127
Rotation 1, 2, 3 & 4
2039
9
1562
468
865
40
4943
124
Rotation 1, 2, 3 & 4
1913
9
1448
461
1128
50
4943
119
Rotation 1, 2, 3 & 4
1837
23
1377
438
1268
60
4943
118
Rotation 1, 2, 3 & 4
1837
23
1359
456
1311
Rotations: 1 = CRP, 2 = Winter wheat-Peas, 3 = Winter wheat-Lentil, 4 = Winter wheat-Barley

Optimization results
Net returns ($/ac) vs Soil loss reduction (%)
Net returns ($/
160
140
120
100
80
60
40
20
Variable profit ($/ac)
0
0 10 20 30 40 50 60
Soil loss reduction (%)

0% Reduction 10% Reduction 30% Reduction 50% Reduction 60% Reduction
0% CRP 9% CRP 18% CRP 26% CRP 27% CRP
Optimization
-maximize profit while reducing sediment load
Available Options
- Winter Wheat, Spring Wheat, Barley, Peas, Lentils, CRP
- Mulch Tillage

0% Reduction 10% Reduction 30% Reduction 50% Reduction 60% Reduction
Optimization
-maximize profit while reducing sediment load
Available Options
- Winter Wheat, Spring Wheat, Barley, Peas, Lentils, CRP
- Conventional Tillage, Mulch Tillage

Targeting Talking Points
• How do we manage agricultural landscapes:
median conditions or w/ extreme events?
• How to include non-agricultural effects when
managing agricultural landscapes?
• How do landowner/operator relationships affect
our ability to manage agricultural landscapes?
• What level of cost-share is needed to
adequately target ‘hot spots’ in the watershed?
Thank you!