AGNPS USER`S GUIDE

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AGNPS USERS GUIDE
What is AGNPS AGNPS development
Basic Theory of AGNPS How to Prepare
Data of AGNPS
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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

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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. Mannings 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

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Output Data

• Hydrology
• 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

• Nutrient
• 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)

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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.

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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.

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SCS Curve Number Model
The function was set up from great deal of data
test
P

• The formula
• F/SQ/(P-Ia)
• Therefor,
• PIaFQ
• Q(P-Ia)2/(PS-Ia), PgtIa
• Q0 PltIa
• 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 precipitation Q Surface Runoff Ia
initial loss F Current loss S Potential
loss, max. value of F
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Universal Soil Loss Equation (USLE)

• USLE formula
• ARKLSPC
• A annual soil loss
• Rrainfall factor
• Ksoil erodibility factor
• Lfield slope length factor
• Sfield slope factor
• Psupporting practice factor
• Ccover 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.
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How to Prepare Data-Initial Data
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How to Prepare Data-Initial Data
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An Example of Data Input
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Cell Number, Receiving cell Number
Increase oclock direction
How divide cells and sub-divided cells
3221
3222
3210
3100
3223
3224
3230
3240
3310
3320
3400
3330
3340

Slope shape factor
8 1 2
N
7 3
6 5
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Flow direction
1 Uniform
2 convex
3 Concave