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AGNPS USER `S GUIDE. * What is AGNPS * AGNPS development * Basic Theory of AGNPS * How to Prepare Data of AGNPS. What Is AGNPS. Name: Agricultural Non-Point Source Pollution Model Developed by : USDA-ARS: North Central Soil Conservation Research Laboratory

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agnps user s guide


* What is AGNPS

* AGNPS development

* Basic Theory of AGNPS

* How to Prepare Data of AGNPS

what is agnps

Name:Agricultural Non-Point Source Pollution Model

Developed by:USDA-ARS:

North Central Soil Conservation Research Laboratory

Southeast Watershed Research Station

Minnesota Pollution Control Agency

The Function:Hydrological calculation: Rainfall and Runoff;

Water contamination: sediment and chemical contamination;

Water pollution control: point and non-point pollution.

Data Input: Data Input is rather complicated: it needs input 22 data

for each cell. There are also many operations.

Output: 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

Input Data
output data

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)

Output Data
agnps development
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
Basic Theory of AGNPS

AGNPS developed based on Stanford Watershed Model

The basic theories of AGNPS are:

1. Curve Number Methoddeveloped bySoil 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
SCS Curve Number Model

The function was set up from great deal of data test


The formula:




Q=(P-Ia)2/(P+S-Ia), P>=Ia

Q=0 P<Ia

NormallyIa= 0.2

S= 25400/CN- 254

CN( curve number) value varied depend on hydrological conditions, soil type, land use, vegetation, and crop pattern.







P: precipitation;

Q: Surface Runoff

Ia: initial loss

F: Current loss

S: Potential loss, = max. value of F

universal soil loss equation usle
Universal Soil Loss Equation (USLE)

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.

USLE formula :


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


Cell Number, Receiving cell Number

Increase o’clock


How divide

cells and

















Slope shape factor



8 1 2


7 3

6 5 4

1 = Uniform

2 = convex

3 = Concave