United States
Environmental Protection
Agency
vvEPA
Great Lakes National
Program Office
536 South Clark Street
Chicago, Illinois 60605
GLNPO # 87-8
EPA-905/2-87-003
June 1987
Tri-State
Tillage Project
Modeling Component
Applying the Answers
Model to Assess the
Impacts of Conservation
Tillage on Sediment and
Phosphorus Yields to
Lake Erie
Do not WEED. This document
should be retained in the EPA
Region 5 Library Collection.
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FOREWORD
The U.S. Environmental Protection Agency (USEPA) was created because of
increasing public and governmental concern about the dangers of pollution
to the health and welfare of the American people. Noxious air, foul water,
and spoiled land are tragic testimony to the deterioration of our natural
environment.
The Great Lakes National Program Office (GLNPO) of the USEPA was established
in Region V, Chicago, Illinois to provide specific focus on the water
quality concerns of the Great Lakes. The Section 108(a) Demonstration
Grant Program of the Clean Water Act (PL 92-500) is specific to the Great
Lakes drainage basin and thus is administered by the Great Lakes National
Program Office.
Several sediment erosion-control projects within the Great Lakes drainage
basin have been funded as a result of Section 108(a). This report describes
one such project supported by this Office to carry out our responsibility
to improve water quality in the Great Lakes.
We hope the information and data contained herein will help planners and
managers of pollution control agencies to make better decisions in carrying
forward their pollution control responsibilities.
Valdas V. Adamkus
Administrator, Region V
National Program Manager for the Great Lakes
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EPA-905/2-87-003
June 1987
GLNPO #87-8
TRI-STATE TILLAGE PROJECT
"Modeling Component Applying The Answers Model to Assess The Impacts
of Conservation Tillage on Sediment and Yields to Lake Erie"
Final Report
Prepared by:
David B. Beasley, Ph.D., P.E.
Associate Professor
Agricultural Engineering Department
Purdue University
West Lafayette, IN 47907
Great Lakes Grant No. R005717
For
GLNPO# 87-8
U.S. Environmental Protection Agency
Great Lakes National Program Office
230 South Dearborn Street
Chicago, Illinois 60604
September 1984
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Disclaimer
This report has been reviewed by the Great Lakes National Program
Office, U.S. Environmental Protection Agency and approved for pub-
lication. Approval does not signify that the contents necessarily
reflect the views and policy of the USEPA, nor does mention of
trade names or commercial products constitute endorsement or rec-
ommendation for use.
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TABLE OF CONTENTS
Section Page
INTRODUCTION 1
PROJECT AREA 2
STUDY METHODOLOGY 6
PROJECT RESULTS 13
SUMMARY AND CONCLUSIONS 17
REFERENCES 23
m
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LIST OF TABLES
Table Page
1. Major Soil Group Descriptions and Spatial
Extent 4
2. Land Use and Management Descriptions 9
3. Cropping Distribution for the Major Soil
Groups (from CTIC) 10
4. Scenarios Used in the Simulation Study 10
5. General Watershed Information (First
0.5 Percent Sample) 14
6. General Watershed Information (Second
0.5 Percent Sample) 15
7. Predicted Sediment and Phosphorus Yields for
Each Scenario on Each Watershed - First 0.5%
Sample 16
8. Predicted Sediment and Phosphorus Yields for
Each Scenario on Each Watershed - Second 0.5%
Sample 17
9. Predicted Sediment and Phosphorus Yields for
Eight Scenarios on Each Soil Group — Western
Basin Totals 18
10. Unit Area Loading Information 21
IV
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LIST OF FIGURES
Figure Page
1. Study Area Drainage and Site Location Map 3
2. Study Area Soil Groups Map 5
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Final Report of the
Modeling Component — Tri-State Tillage Project
"Applying the ANSWERS Model to Assess the Impacts of Conservation
Tillage on Sediment and Phosphorus Yields to Lake Erie"
David B. Beasley, Ph.D., P.E.
Associate Professor
Agricultural Engineering Department
Purdue University
West Lafayette, IN 47907
INTRODUCTION
In late 1981, a modeling study was proposed as a part of the Tri-State
Tillage project. This study had two major objectives. The primary goal of
the program was to provide basin scale projections of sediment and phosphorus
yield reductions in the Western Basin of Lake Erie attainable from various
degrees (i.e., spatial extent) and types of tillage management. Secondarily,
a study of the size of the sample area needed to make accurate projections was
to be undertaken.
Two stratified 0.5% samples (based on soil association groupings) were
simulated for a number of tillage management scenarios. Basin-wide projec-
tions of sediment and phosphorus yield were compared to observed river mouth
data for the study area. Finally, the projections were refined based on
actual conservation tillage implementation rates to provide data for tracking
purposes. Data for 1982 and 1983 land use patterns in the project area (on
each major Soil Group) were obtained from the Conservation Tillage Information
1
-------
Center (CTIC) and used to better describe the actual patterns and percentages
of cover and management in the simulations. The "potential" scenarios were
also modified to correspond to the CTIC information.
The yields predicted from each Group, as well as from the Basin as a
whole, are consistent with long-term river mouth and tributary monitoring of
sediment yields in the project area. Predicted unit area loads of phosphorus
indicate that major reductions in diffuse phosphorus loading will be rather
difficult to obtain. This is due to the fact that the amount of phosphorus
reduction required by Annex III of the International Joint Agreement is of a
similar magnitude to the unit area agricultural loading.
Descriptions of the project area, study objectives, and developed metho-
dology are included. The results of the final simulations are described in
detail and emphasized in the Summary and Conclusions section.
PROJECT AREA
The Tri-State Tillage Project encompasses approximately 24,200 square
kilometers in Northwest Ohio, Northeast Indiana and Southeast Michigan (Figure
1). The Maumee, Portage, and Sandusky River basins make up the majority of
the study area. Some "near lake" drainage area is also included. Thirty-one
counties in the three states are participating in the project. The locations
of all of the watersheds simulated in the study are shown in Figure 1.
The methodology developed in this project is based on the premise that
"representative" samples of the basin could be identified and modeled using a
"stratified" sampling technique. The stratification would be based on simi-
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larities in the drainage characteristics of the numerous soil associations
within the basin. The distribution of the major soil associations (Soil
Groups) in the study area is depicted in Figure 2 and a description of the
characteristics of each Group appears in Table 1. Soils in the study area
vary from sands to loams to clays to organic mucks.
Table 1. Major Soil Group Descriptions and Spatial Extent
Group
1
2
3
4
5
6
7
8
Drainage
Class
SPD-VPD
WD-SPD
VPD
MWD-VPD
SPD-VPD
WD-MWD
WD-VPD
WD-VPD
Surface USDA-SCS
Soil Hydrologic
2
Texture Group
SiCL-C
L-SiCL
Muck
L-SiL
SiL-SiCL
L-SiL
FS-SiL
SL-SiL
D
C-D
A-D
B-D
B-D
B-C
A-B
B-D
Parent Percent of
Material Basin Area
Lacustrine-Till
Till
Organic
Outwash
Lacustr ine
Ou twa sh- Al 1 uv ia 1
Outwa sh-Al 1 uv ial
Till
28.6
50.5
0.2
4.6
9.3
0.5
4.5
1.8
1 Drainage class abbreviations are: VPD—very poorly drained, SPD—somewhat
poorly drained, MWD—moderately well drained, WD—well drained.
2 Some groups (particularly 3 and 4) contained soils which were listed as
drained/undrained, thus the large range.
3 Groups 4 and 6 were later combined.
Cropping patterns are also variable. However, the predominant agricul-
tural crops are corn, soybeans and small grains. Much of the area is composed
of soils with less than adequate internal drainage and very little slope.
Thus, both surface and subsurface drainage systems are numerous.
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in
c:
-5
rv
3=
-5
fD
CT5
-s
o
MAUMEE
PORTAGE
SANDUSKY
BASIN
SOIL
GROUPS
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STUDY METHODOLOGY
The ANSWERS (Areal Nonpoint Source Watershed Environment Response Simula-
tion) model, developed at Purdue University (Beasley, 1977; Beasley and Hug-
gins, 1982), was chosen as the predictive tool for the study. Since ANSWERS
is an event-oriented, distributed parameter model, simulation of the entire
study area was deemed both unreasonable and unnecessary. Instead, a strati-
fied sample of the area was described, simulated and the results extended to
the much larger study area.
The methodology required that a number of "representative" subwatersheds
be selected and simulated. Ideally, these subwatersheds would have an area of
1,000 to 1,800 hectares so that sediment and nutrient yields at their outlets
could be eventually expected to reach the larger receiving body of water
(stream, river or lake). This size of watershed normally would be expected to
support a second- or even third-order stream system. It would, therefore,
drain to a well defined, continuously flowing channel system that should pro-
vide for ultimate delivery to the receiving body. Originally, a 0.5 percent
sample of the area was chosen. This corresponded to 9 watersheds of the size
mentioned above. Later work in the project included selecting and describing
an additional 0.5 percent sample and comparing simulation results with those
from the first sample. In doing so, a determination was made of the adequacy
of the different size samples (0.5 and 1.0 percent) to describe the entire
basin response of the different Soil Groups as indicated by monitored informa-
tion.
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The watersheds, mentioned above, were chosen based on a stratified sam-
pling criteria. The stratification involved grouping soils (actually associa-
tions) with similar water movement characteristics (internal drainage, surface
texture, hydrologic group, and parent material) in order to simplify and "nor-
malize" data collection and expand applicability of simulation results. The
application of this classification and stratification scheme resulted in 8
major Soil Groups. The Soil Groups (shown in Figure 2) were planimetered to
determine the areas in each grouping. The Soil Group descriptions and their
areal extent are shown in Table 1. These major Soil Groups included more than
75 soil types. Since neither Group 3 nor 8 accounted for more than 4 percent
of the area (both less than 2 percent), they were eliminated from further con-
sideration. Since Groups 4 and 6 were similar, they were combined to form an
area large enough to require one watershed.
Watersheds were then selected from areas mapped as belonging to a partic-
ular Soil Group. The maps used in this original site selection were the state
soil association maps for Ohio, Indiana, and Michigan. Care was taken to
select drainage areas in counties that were participating in the project and
that had modern soil surveys. The topography and detailed soils information
from the selected areas were then collected and assembled, using USGS topo-
graphic and SCS Soil Survey maps, into detailed watershed data files as
described in the ANSWERS Users Manual (Beasley and Huggins, 1982). Based on
the watersheds selected to represent the various groups, 9 were required for
both of the 0,5 percent samples.
The cropping data, including management, was selected using a statistical
process which "populated" the watershed in a manner consistent with cropping
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patterns on the group being represented. Once the percentages of the various
land uses were known, a randctn number generator was used to "populate" the
watersheds with land uses so that the divisions of land uses in the watersheds
and the entire county were the same. The cropping and management assumptions
are detailed in Table 2. Information derived from the Conservation Tillage
Information Center (CTIC) data base was used to describe the land use and
managenent patterns on the various Soil Groups throughout the study area for
the final simulations. Those percentages, upon which the conclusions of this
study are based, are shown in Table 3. The scenarios chosen for simulation
are presented in Table 4. There were two actual years (1982 and 1983)
included along with the 6 potential or hypothetical scenarios (which were
based on modifications to the 1982 percentages). The 1982 data is considered
the baseline, since that year has been so designated by USEPA. 'The 1983 data
is the first complete year of CTIC data.
For the simulations, an element size of 1 hectare (100 meters on a side)
was chosen. This led to 1,000 to 1,800 overland flow elements plus somewhere
between 125 and 300 channel flow elements for a chosen watershed. The time
step chosen for the simulation was one minute. The rainfall event simulated
corresponded to an 8-year return period, 1.5-hour duration storm with the
antecedent soil moisture at field capacity. This storm typically produced
sediment and total P yields that corresponded well with observed average
annual yields on a number of watersheds within the basin (Black Creek area of
Allen Co., IN). The definitive work on this "design storm" concept was per-
formed by Conrad Heatwole (1980) and was utilized in both the Indiana Model
Implementation Project (MIP) and Allen County Special ACP Projects.
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Table 2. Land Use and Management Descriptions
Land
Use
Row Crop
Other Crop
Hay-Pasture
Woods
Built-up
Tillage Area in
Management Vegetation
Conventional
Chisel Plow
Mini Till
No-till
Conventional
Chisel Plow
No- till
- % -
25
30
60
80
60
60
85
90
85
60
Max. Roughness Residue
Height Cover
- on -
5.1
6.4
6.4
7.6
4.6
5.1
6.4
3.8
7.6
3.8
< 30%
30% to 60%
40% to 70%
> 70%
< 30%
30% to 60%
> 60%
USLE
"C"4
0.50
0.10
0.05
0.02
0.10
0.08
0.02
0.04
0.01
0.20
Row crop values depict corn, other crop values describe a combination
between small grains and truck crops.
o
Conventional consists of fall turn plow and spring disk, chisel plow
is fall tillage with spring harrow or similar, mini-till is either
ridge plant after field cultivation or standard till-plant technique.
For other crop categories, these definitions really only designate
differences in residue cover.
Residue covers are based on high predictivity. Thus, lesser yields
would probably produce more erosion and sediment yield.
The values are reported for crop stage 1 - the period after planting
until the plants reach 1 month in age.
The 75-plus soil types were sorted for similarities based on hydrologic
group, textural class, parent material, internal drainage, soil erodibility -
"K", and permeability. The result was 13 different soils response classes.
When conservation tillage was applied on a specific soil, the infiltration
capacity of that soil was assumed to increase. The more conservative the til-
lage systems and the more residue that remained on the surface, the higher the
infiltration rates (Beasley and Huggins, 1982).
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Table 3. Cropping Distribution for the Major Soil Groups (from CTIC).
Group
1
2
4+6
5
7
Row Crops
63
58
63
50
55
Crop
Other Crops
19
18
16
15
16
or Cover*
Pasture
5
10
8
15
10
Forest
8
9
8
15
14
Built-up
5
5
5
5
5
* Row crops include: corn, soybeans, sorghum, etc. Other crops include:
small grains, beets, berries, etc. Pasture includes hay crops. Forest
includes: brushland and swamp. Built-up includes: homesteads, farmsteads,
and other semi-pervious, smooth areas.
Table 4. Scenarios Used in the Simulation Study
Scenario Description
1 Baseline. 1982 basin averages for conventional, chisel
plow, reduced till, and no-till on row and other cropland.
2 1983 basin averages for conventional, chisel plow, reduced
till, and no-till on row and other cropland.
3 1/4 of the conventional tillage on both row and other crops
replaced with fall chisel plowing.
4 1/4 of the conventional tillage on row crops only replaced
by till-plant minimun tillage techniques.
5 1/4 of the conventional tillage on both row and other crops
replaced with no-till techniques.
6 1/2 of the conventional tillage on both row and other crops
replaced with fall chisel plowing.
7 1/2 of the conventional tillage on both row and other crops
replaced with no-till techniques.
8 All conventionally tilled areas switched to no-till techniques
(most conservative scenario).
10
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The phosphorus projections used in this study are the result of an equa-
tion which relates particulate phosphorus yield (85% - 90% of Total P) to sed-
iment yield. This equation was the result of an extensive data analysis of
the water quality information gathered in the Black Creek Project (Lake and
Morrison, 1977) by Dr. Darrell W. Nelson, formerly of the Agronomy Department
at Purdue. The equation used was:
P = ,00058*SED**1.12
where: P = particulate phosphorus yield in kg/ha,
SED = predicted sediment yield in kg/ha.
The predicted particulate P yield was then divided by 0.85 to produce an esti-
mate of Total P yield.
When the representative watersheds had been described and crop and soils
information supplied to the model, a number of scenarios were simulated.
These scenarios described the "as is" or baseline conditions in the watersheds
as well as potential conditions involving the changing of management to forms
of tillage with greater conservation potential. Thus, a planner could study
the impact of various levels of conservation tillage application (all the way
to 100 percent no-till) and compare them to existing levels.
11
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PROJECT RESULTS
The primary reason for conducting this study was to provide accurate
estimates of the efficacy of a large-scale application of conservation tillage
on sediment and phosphorus yields in the Western Basin of Lake Erie. However,
other questions also needed to be answered. The question of how large an area
to simulate to arrive at consistent results is quite important. >From a
planner's standpoint, the question of how much time must be allotted to apply
the methodology described herein is also very important.
The work conducted in the first two years of the study involved the
selection and simulation of two 0.5 percent samples of the total basin.
Numerically, this involved 9 watersheds in each year. While project personnel
spent large amounts of time defining the basin, detailing how Soil Groups
would be described, selecting appropriate watersheds for simulation, and
entering data, we believe that a routine application of this methodology could
be done much more efficiently. Selection of watersheds, data preparation, and
simulation should be possible on a 3.5 to 5.0 days per 1,000 elements basis.
Thus, it should be possible to complete work on a 1,500 element watershed in
less than two weeks. Although cost information and data on individual com-
puter requirements is generally not applicable to other systems, the simula-
tions presented herein typically cost $8 to $14 on Purdue's CDC-6600 and
required 200 to 350 CPU seconds. Simulations were also run on a Digital
Equipment Corporation VAX 11/780 and typically required 500 to 800 CPU
seconds.
12
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The Group 1 and Group 2 soils were represented by multiple watersheds.
Two catchments were used for Group 1 and four for Group 2. The output from
the individual watersheds were combined to give a Group average. Each of the
watersheds that made up the two 0.5 percent samples are described in Tables 5
and 6.
In an effort to more closely detail the cropping and management systems
presently in use, the CTIC Data Base was utilized. Table 3 displays the land
use percentages for the baseline (1982) scenario for each of the major soil
groups.
The simulation results for the 8 scenarios for both of the 0.5 percent
samples are shown in Tables 7 and 8. Watersheds composed primarily of Group 2
soils stand out as sources of sediment and phosphorus in both samples. Since
the soils in this Group are typically more erodible, the topography more vari-
able, and the infiltration rates fairly low, it is quite logical that these
soils would have the highest erosion and phosphorus yields. Each of the other
Groups had at least one factor which lessened its impact when compared to
Group 2. All other Groups had lower average values of slope, and several had
much higher infiltration capacities. Also, other Groups contained soils which
were more resistant to erosion than soils classified in Group 2.
When the information in Table 1 is combined with that in Tables 7 and 8,
the problem with the Group 2 soils becomes even more evident. Since these
soils make up over 50 percent of the basin, any large-scale reduction in the
phosphorus yields to the Western Basin of Lake Erie will have to be achieved
by reducing Group 2 phosphorus yields. Table 9 highlights this information by
13
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Table 5. General Watershed Information (First 0.5 Percent Sample)
No.
Name
Location
Description
Edgerton-Carson and
Miller Ditches
Unnamed Tributary to
Auglaize River
Bottern, Kurtz, and
Roth Ditches
East Branch
19 Aurand Run
20 Kyle Prairie Creek
7 Unnamed Tributary to
Maumee River
3 Cartwright Run
Harris Ditch
Allen Co., IN
Allen Co., OH
Allen Co., IN
Seneca Co., OH
Hancock Co., OH
Mercer Co., OH
Henry Co., OH
Putnam Co., OH
Lucas, Henry, and
Fulton Co., OH
Group 1 soils, 1,164 hectares,
0.21 percent average slope.
Group 1 soils, 1,118 hectares,
0.44 percent average slope.
Group 2 soils, 1,366 hectares,
1.16 percent average slope.
Group 2 soils, 1,192 hectares,
1.74 percent average slope.
Group 2 soils, 1,573 hectares,
0.66 percent average slope.
Group 2 soils, 1,372 hectares,
0.68 percent average slope.
Groups 4 and 6 soils, 1,827 hectares,
0.53 percent average slope.
Group 5 soils, 1,234 hectares,
0.62 percent average slope.
Group 7 soils, 1,606 hectares,
0.66 percent average slope.
14
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Table 6. General Watershed Information (Second 0.5 Percent Sample)
No.
Name
Location
Description
10 Unnamed Tributary to
Auglaize River
11 Town Creek
21 Beaver Run
22 Unnamed Tributary to
Black Creek
23 Harrison Creek
24 Lick Creek
16 Coon and Lick
Creeks
17 Owl Creek
18 Unnamed Tributary to
Beaver Creek
Putnam Co., OH
Van Wert Co., OH
Allen Co., OH
Mercer Co., OH
Seneca Co., OH
Williams Co., OH
Henry Co., OH
Williams Co., OH
Wood Co., OH
Group 1 soils, 1,628 hectares,
0.23 percent average slope.
Group 1 soils, 1,263 hectares,
0.31 percent average slope.
Group 2 soils, 1,535 hectares,
0.69 percent average slope.
Group 2 soils, 1,057 hectares,
0.76 percent average slope.
Group 2 soils, 1,560 hectares,
0.72 percent average slope.
Group 2 soils, 1,284 hectares,
1.59 percent average slope.
Groups 4 and 6 soils, 930 hectares,
0.56 percent average slope.
Group 5 soils, 1,661 hectares,
0.38 percent average slope.
Group 7 soils, 1,311 hectares,
0.37 percent average slope.
* Land use was broken into five categories: row crops, other crops, hay or pasture,
woodlands, and built-up areas. For this table, cropland includes the first two
categories.
15
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Table 7. Predicted Sediment and Phosphorus Yields for Each Scenario on Each Watershed - First 0.5% Sample.
#1
#2
#3
#6
#19
#20
#7
#8
#9
Soil
Watershed Group
- Edger ton-Car son and 1
Miller Ditches
- Unnamed Tributary to 1
Auglaize River
- Bottern, Kurtz, and 2
Roth Ditches
- East Branch 2
- Aurand Run 2
- Kyle Prairie Creek 2
- Unnamed Tributary to 4+6
Maumee River
- Cartwright Run 5
- Harris Ditch 7
Parameter
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
1
210
0.27
600
0.88
1,330
2.14
2,210
3.80
680
1.02
840
1.28
400
0.55
530
0.77
130
0.17
2
210
0.27
600
0.87
1,250
2.01
2,060
3.51
640
0.95
790
1.20
370
0.52
530
0.76
130
0.15
3
210
0.24
520
0.75
1,140
1.81
1,880
3.17
600
0.88
730
1.10
350
0.48
450
0.65
120
0.15
Seen;
4
U-n/l
Kg/ 1
170
0.22
500
0.72
1,100
1.74
1,820
3.06
570
0.84
700
1.05
340
0.46
420
0.60
120
0.14
ario
5
160
0.21
480
0.68
1,060
1.66
1,760
2.94
540
0.78
670
0.99
320
0.44
410
0.58
110
0.14
6
170
0.21
440
0.63
940
1.45
1,540
2.54
510
0.74
620
0.91
290
0.40
380
0.53
100
0.12
7
120
0.15
350
0.48
770
1.16
1,280
2.06
400
0.56
490
0.70
250
0.33
300
0.41
80
0.10
8
50
0.06
110
0.13
220
0.29
350
0.48
150
0.19
160
0.21
90
0.11
90
0.11
30
0.04
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Table 8. Predicted Sediment ard Phosphorus Yields for Each Scenario on Each Watershed - Second 0.5% Sample.
#10
#11
#21
#22
#23
#24
#16
#17
#18
Soil
Watershed Group
- Unnamed Tributary to 1
Auglaize River
- Town Creek 1
- Beaver Run 2
- Unnamed Tributary to 2
Black Creek
- Harrison Creek 2
- Lick Creek 2
- Coon and Lick 4+6
Creeks
- Owl Creek 5
- Unnamed Tributary to 7
Beaver Creek
Parameter
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
1
210
0.27
170
0.21
690
1.04
860
1.31
940
1.45
1,750
2.92
550
0.80
380
0.54
140
0.17
2
200
0.26
170
0.21
660
0.97
810
1.23
880
1.36
1,620
2.68
510
0.74
380
0.53
130
0.16
3
190
0.24
150
0.19
620
0.91
740
1.11
810
1.24
1,470
2.41
470
0.67
340
0.47
130
0.16
Scena
4
kn/V
Kg/r
180
0.23
140
0.18
590
0.86
710
1.06
780
1.19
1,420
2.32
450
0.64
320
0.43
130
0.15
irio
5
170
0.21
140
0.17
550
0.81
680
1.02
750
1.12
1,360
2.21
430
0.61
310
0.42
120
0.15
6
180
0.23
130
0.17
520
0.75
640
0.94
710
1.07
1,240
1.99
400
0.56
290
0.39
110
0.14
7
130
0.17
100
0.12
410
0.58
520
0.75
580
0.85
1,030
1.61
320
0.44
230
0.30
90
0.11
8
60
0.06
40
0.04
140
0.18
160
0.21
200
0.26
280
0.38
130
0.16
90
0.10
50
0.06
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Table 9. Predicted Sediment and Phosphorus Yields for Eight Scenarios on Each Soil Group — Western Basin Totals.
1 o
Group Sample
1 A
B
2 A
B
4+6 A
CO
B
5 A
B
7 A
B
Parameter
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
Sed
P
1
280,300
400
131,500
165
1,546,000
2,520
1,295,400
2,055
49,400
65
67,900
100
119,300
175
85,500
120
14,200
20
15,200
20
2
280,300
395
128,000
165
1,448,200
2,345
1,212,900
1,905
45,700
65
62,900
90
119,300
170
85,500
120
14,200
15
14,200
15
3
252,600
345
117,700
150
1,329,000
2,125
1,112,100
1,730
43,200
60
58,000
85
101,300
145
76,500
105
13,000
15
14,200
15
Scenario
4
231,900
325
110,700
140
1,280,100 1,
2,045
1,069,300 1,
1,660
42,000
55
55,500
80
94,500
135
72,000
95
13,000
15
14,200
15
5
221,500
310
107,300
130
231,300
1,945
020,500
1,575
39,500
55
53,100
75
92,300
130
69,800
95
12,000
15
13,100
15
6
211,100
290
107,300
140
1,102,900
1,725
950,200
1,450
35,800
50
49,400
70
85,500
120
65,300
90
10,900
15
12,000
15
7
162,600
220
79,600
100
898,200
1,370
776,000
1,160
30,900
40
39,500
55
67,500
90
51,800
70
8,700
10
9,800
10
8
55,400
65
34,600
35
268,800
355
238,300
315
11,100
15
16,000
20
20,300
25
20,300
25
3,300
5
5,400
5
1 Groups 1 and 2 utilized multiple watershed simulations. Figures reported are averages.
2 A and B samples correspond to the first and second 0.5 percent samples.
-------
showing Basin-wide tonnages for each major Soil Group. Several of the
scenarios indicate reasonable reduction levels can be achieved without extreme
changes in management. Obviously, levels of reduction approaching 50 percent
or more (unless all cropland goes to no-till) will only be achieved with a
mixture of tillage and structural (terraces, sediment basins, waterways, etc.)
BMPs.
A notable result is that the baseline (1982 scenario) yield for the 0.5
and 1.0 percent samples were within 85 kg/ha (10 percent) of each other. This
indicates that the information gained from the 0.5 percent sample would have
been essentially the same as that gained from the full 1.0 percent sample.
An uncertainty analysis was conducted on the 1.0 percent sample (since
each Soil Group had at least 2 observations) using the 90% Confidence Interval
as the test criteria. The analysis looked at the uncertainties (based on sam-
ple standard deviation and Student's t) both within Soil Groups and for the
entire, basin-wide estimation. Both sediment and phosphorus yields were sub-
jected to the analysis. The results indicated that for the 1.0 percent sample
(18 watersheds) the uncertainty associated with sampling ranged from 26%
(Scenario 8) to 28% (Scenario 1) for sediment estimations and from 25%
(Scenario 8) to 32% (Scenario 1) for phosphorus estimations. This translated
to 745 _+ 207 kg/h
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Sediment yields in the basin are low. The predicted baseline average
(1.0 percent sample) of 745 kg/ha compares very well with the area weighted
averages of the Maumee (average of water years 1975-1978), Portage (average of
water years 1975-1978), and Sandusky (average of water years 1975-1979) basins
of 680 kg/ha/yr (USAGE, 1982).
The data from both 0.5 percent samples were used to produce the informa-
tion shown in Table 10. Long-term monitoring information (USAGE, 1979) indi-
cates that the mean annual unit-area P loads (both agriculture and non-
agriculture) for the basin average approximately 1.07 to 1.21 kg/ha. The
modeling program indicates that the predominantly agricultural study area
ranges from 1.16 to 1.31 kg/ha (with individual Soil Groups ranging from 0.17
to 2.06 kg/ha). Hence, the observed basin average and the simulated average
are essentially the same. While the Group 2 soils have unit area loads of P
approaching 2 kg/ha, the entire basin is closer to 1 kg/ha. Even though these
yields are relatively high when compared to some other agricultural situa-
tions, they are certainly not out of line with highly fertile and highly agri-
cultural areas in other parts of this country. Tables 7 and 8 indicate that
substantial reductions in sediment and phosphorus yields will only occur with
large changeovers to more conservative tillage types (or addition of struc-
tural measures) .
SUMMARY AND CONCLUSIONS
A model ing study was undertaken to help in assessing the effectiveness of
increasing amounts of conservation tillage for reducing phosphorus and sedi-
ment yields to Lake Erie. The study area included the Maumee, Portage, and
20
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Table 10. Unit Area Loading Information
kg-P/ha
Mean Annual Monitoring Data
(from LEWMS reports)
1975 Basin Average 1.21
1976 Basin Average 1.10
1977 Basin Average 1.07
ANSWERS Predictions
0.5 percent sample 1.31
1.0 percent sample 1.17
Sandusky River basins and near-lake areas. The ANSWERS model was combined
with a stratified sampling procedure to produce estimates, based on represen-
tative watersheds, for major Soil Groups. These estimates were then area
weighted to yield basin-wide predictions.
Predictions for two 0.5 percent samples of the study area were produced.
The second sampling was used to make an overall 1.0 percent sample.
Statistical cropping and management data from county Soil Surveys were
originally used in the watershed data files. However, CTIC data was used to
update the tillage management scenarios and produce more representative
descriptions for the final simulations presented herein.
There are a number of important results and conclusions that can be drawn
from this project:
1. Since both the 0.5 and 1.0 percent sample results compared closely with
monitored information, a 0.5 percent sample appears to be adequate for
the region under consideration.
21
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2. The Group 2 soils predominate in both areal extent and sediment and
phosphorus yields. These soils must be the primary target in any major
reduction program.
3. The "representative watershed" concept produced results that ware con-
sistent with both USGS and LEWMS information. Thus, the projected
impacts of tillage management changes should be quite reasonable.
4. The cost of producing these simulations is only a very small fraction of
what a continuous monitoring program would cost. Watershed description
is the major cost and is a "one-time" expense. In addition, results are
available much more quickly than monitoring data and can be obtained for
hypothetical as well as actual conditions.
5. The amount of reduction achievable from conservation tillage only is
probably not adequate for the Annex III goals. The 1,000 + metric
tonnes required of the study area could only be achieved if almost 50%
of the basin changes over to no-till. If only the Group 2 soils were
treated, approximately 60% of all Group 2 soils in the row crop or other
crop categories would have to be switched over to no-till to achieve the
sought after reduction.
6. A realistic, short-term expectation might be a 50 percent switchover to
chisel plowing (scenario 6). This would indicate a reduction of 837
tonne over 1982 yields (against an approximate 1,100 tonne goal), assum-
ing all cropland in the basin was treated equally.
22
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7. The model used for phosphorus prediction produces an estimate of total
phosphorus. Monitoring data suggests that as much as half of the bio-
logically available P is soluble. While the estimation technique gives
credit to some soluble P, it may not be accurate for small, low sediment
yield events. Hence, the weight given to soluble P may not be great
enough.
8. ANSWERS produces estimates of total sediment yield. Most monitoring
programs are reporting results based on suspended sediment monitoring.
While bedload is not a significant problem in some parts of this coun-
try, it should certainly be considered in the upper Midwest! Many of
the particles moving through saltation are aggregates that are almost
entirely made up of clay and silt particles. These particles carry P in
almost exactly the same concentrations as the primary particles. Their
large weight, when compared to dispersed, suspended particles, indicates
the importance of adequately accounting for their presence in the sedi-
ment and P loading sampling programs.
REFERENCES
1. Beasley, D.B. 1977. ANSWERS: A mathematical model for simulating the
effects of land use and management on water quality. Ph.D. Thesis, Pur-
due University, West Lafayette, IN. 266 pp.
2. Beasley, D.B. and L.F. Huggins. 1982. ANSWERS Users Manual. EPA-
905/9-82-001. U.S. Environmental Protection Agency, Region V, Chicago,
IL. 54 pp.
23
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3. Heatwole, C. 1980. Simulation of watershed response to determine a
design storm. Project Report for CE 642 (Fall 1979) for Dr. R.A. Rao.
Purdue University. West Lafayette, IN. 42 pp.
4. Lake, J. and J. Morrison. 1977. Environmental impact of land use on
water quality, final report of the Black Creek project — technical
volume. EPA-905/9-77-007-B. U.S. Environmental Protection Agency,
Region V. Chicago, IL. 274 pp.
5. U.S. Army Corps of Engineers. 1979. Lake Erie management study.
Methodology Report. Buffalo, NY. 146 pp.
6. U.S. Army Corps of Engineers. 1982. Lake Erie wastewater management
study. Final Report. Buffalo, NY. 241 pp.
-------
TECHNICAL REPORT DATA
(Please readInilructions on the reiersL before completing!
1 REPORT NO
EPA-905/2-87-003
3 RECIPIENT'S ACCESSION-NO
4. TITLE ANDSU8TITLE
Modeling Component-Tri-State Tillage Project
"Applying the ANSWERS Model to Assess the Impacts of
Conservation Tillage on Sediment and Phosphorus Yields
5 REPORT DATE
May 1987
6. PERFORMING ORGANIZATION CODE
" 5GL
7. AUTHOR(S)
David B. Beasley, Ph.D., P.E.
8. PERFORMING ORGANIZATION REPORT NO
GLNPO # 87-08
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Agricultural Engineering Department
Purdue University
West Lafayette, Indiana 47907
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Grant No. R005717-01
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Great Lakes National Program Office
230 South Dearborn Street
Chicago, Illinois 60604
13. TYPE OF REPORT AND PERIOD COVERED
Final 1982-1984
14. SPONSORING AGENCY CODE
Great Lakes National Program
Office, USEPA, Region V
15. SUPPLEMENTARY NOTES
Ralph G. Christensen, Project Officer
Great Lakes Program
16. ABSTRACT ~~~
This modeling study was undertaken to help in the assessing the effectiveness of
increasing amounts of conservation tillage for reducing phosphorus and sediment yields
to Lake Erie. The study area included the Maumee, Portage, and Sandusky River basins
and the near-lake areas. The ANSWERS model was combined with a stratified sampling
procedure to produce estimates, based on representative watersheds, for major Soil
Groups. These estimates were then area weighted to yield basin-wide predictions.
Predictions for two 0.5 percent samples of the study area were produced. The second
sampling was used to make an overall l.O percent sample. Simulations of the data
collected are reported in the report. Eight different scenarios were done with
varying residue cover and tillage methods with the different soil types.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATi Field/Group
Modeling
Sediment
Phosphorus
Tillage
No-till
Conservation tillage
Conventional tillage
Uater quality
Runoff
Yields
Unit area
loads
8. DISTRIBUTION STATEMENT
Document is available to the public throug
National Technical Information Service
(NTIS), Springfield, VA 22161
19 SECURITY CLASS (This Report)
21 NO. OF PAGES
32
20 SECURITY CLASS (This page)
22. PRICE
EPA Form 2220-1 (3-73)
25
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