AGNPS USER`S GUIDE
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What is AGNPS
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AGNPS development
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Basic Theory of AGNPS
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How to Prepare Data of AGNPS
What Is AGNPS
Name:
Developed by:
The Function:
Data Input:
Output:
Agricultural Non-Point Source Pollution Model
USDA-ARS:
North Central Soil Conservation Research Laboratory
Southeast Watershed Research Station
Minnesota Pollution Control Agency
Hydrological calculation: Rainfall and Runoff;
Water contamination: sediment and chemical contamination;
Water pollution control: point and non-point pollution.
Data Input is rather complicated: it needs input 22 data
for each cell. There are also many operations.
Can obtain 24 Output value at the watershed outlet in
Hydrology and Nutrient items:
Input Data
1. Cell number (from)
2. Receiving cell number (to)
3. SCS curve number (CN)
4. Land slope
5. Land slope shape factor
6. Field slope length
7. Channel slope
8. Channel sideslope
9. Manning`s roughness coefficient
10. Soil erodibility factor
11. Cover and management factor
12. Support practice factor
13. Surface condition constant
14. Aspect (direction of drainage)
15. Soil texture
16. Fertilization level
17. Fertilization availability factor
18. Point source indicator
19. Gully source level
20 Chem. Oxy. Demand. (COD) factor
21. Impoundment factor
22 Channel indicator
Output Data
Hydrology:
Nutrient:
1. Runoff volume (inches)
2. Peak runoff rate (cf s)
3. Fraction of runoff within the cell
4. Sediment (by part. size and in total)
5. Sediment yield (tons)
6. Sediment concentration (ppm)
7. Sediment particle size distribution
8. Upland erosion (tons/acre)
9 Chemical erosion (tons/acre)
10. Amount of deposition (%)
12 Enrichment ratio
13. Delivery ratio
1. Nitrogen
2. Sediment associated mass (lbs/acre)
3. Concentration of soluble material
4. Mass of soluble material in runoff
5. Phosphorous
6. Sediment associated mass (lbs/acre)
7. Concentration of soluble material
8. Mass of soluble material in runoff
9. Chemical Oxygen Demand
10. Concentration (ppm)
11. Mass (lbs/acre)
AGNPS Development
Agricultural Non-Point Source Pollution Control
1. The problem appeared in 1970s. The 1970 Clean Water Act (cwa) AND
ITS SUBSEQUENT Amendments clearly considered NPS pollution as one of
the most serious water quality problems.
2. In The Netherlands, Dr. Fedders, a professor in Wageningen Agricultural
University, researched water models SWATRO and SALTBL from 1972. So
far, they developed integrated model SWACROP.
3. After 1980s many countries pay attention to research Water models. And
they gradually developed many advanced models, such as TANK model
(Japan), STANFORD model, Sacramento Model (America), CROPWAT
(Italy, FAO).
4. In China, the model research started from 1970s. The most famous models
are Full Store Runoff model, Over Ratio Runoff model (River & Sea Univ.)
and SPAC model (QingHua Univ.). In 1990, World Bank financed us to build
a Non-Point Source Pollution laboratory in River and Sea University. This
laboratory is largest one in Asia. Now, they are researching Yangzsi River
pollution.
Basic Theory of AGNPS
AGNPS developed based on Stanford Watershed Model
The basic theories of AGNPS are:
1. Curve Number Method developed by Soil Conservation Service (
USDA SCS, 1972 and 1986) is a well-known hydrological method in
the world. There are many hydrological models were developed based
on the method (such as SWACROP, SWATRE, SALTBAL) and
2. Universal Soil Loss Equation (USLE): developed by Wischneier and
Smith, 1978, is another well-known model for predicting soil erosion
from agricultural fields. However, recently we found it was not
suitable to the conditions of our country especially in our province and
the formula is too general, it is influenced by many factors. So, we are
looking for another good method to calculate soil erosion.
Both Models are empirical approach with a focus on past
experiences and large scale field tests are needed for parameters.
SCS Curve Number Model
The function was set up from great deal of data test
The formula:
P
F/S=Q/(P-Ia)
Therefor,
P=Ia+F+Q
Q=(P-Ia)2/(P+S-Ia), P>=Ia
Q=0
P<Ia
Normally
Ia= 0.2
S= 25400/CN- 254
CN ( curve number) value varied depend on
hydrological conditions, soil type, land
use, vegetation, and crop pattern.
F
P
Ia
Q
S
Time
P:
Q:
Ia:
F:
S:
precipitation;
Surface Runoff
initial loss
Current loss
Potential loss, = max. value of F
Universal Soil Loss Equation (USLE)
USLE formula :
A=RKLSPC
A= annual soil loss
R=rainfall factor
K=soil erodibility factor
L=field slope length factor
S=field slope factor
P=supporting practice factor
C=cover and management factor
Although the formula is simply
proportional to six parameters,
each factor is based on a separate
set of variables
Each parameter is analyzed by
statistical or experimental
methods and experiences.
Factors include topographic
factors and land management
factors considers crop rotation,
tillage and planting methods,
and cover residues.
How to Prepare Data-Initial Data
How to Prepare Data-Initial Data
An Example of Data Input
Cell Number, Receiving cell Number
Increase o’clock
direction
How divide
cells and
sub-divided
cells
Slope shape factor
Flow
direction
8
1
2
N
7
1 = Uniform
3
2 = convex
6
5
4
3 = Concave