AGNPS Presentation

8/2/2019 AGNPS Presentation

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HYDROLOGICAL MODEL~AGNPS~

Agricultural Non-Point SourcePollution Model


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I. Watershed

Hydrological Mode(1) HEC-1 with WMS,(2) SHE,(3) TOPOG,(4) TOPMODEL,(5) ANSWERS and(6) AGNPS


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II. Objectives Predicting Volume of SurfaceRunoff and Surface Soil Erosion

Predicting Rate of Sedimentatiodue to Surface Soil Erosion

Predicting Erosion of nutrientelement


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.Matters

Computer and Printer Software of AGNPS (Ag r i c u l t u r a l Non -P

Sou r c e P o l l u t io n Mode l) Topography Map for Research Area Soil Map for Research Area Land Use/Land Cover Map for Research Pen, Ruler, Calculator, etc


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IV. TheoryModel is representation of s t a t e s , ob j e c t s and eveThe representations have to be expressed in thesimple form (eliminate or minimize indirect andcomplex variables).AGNPS Model constitutes a combination of distribuand sequential model. In the distributed model, thmass equilibrium of all cells is processedsimultaneously; while in the sequential model,pollutant will be routed in the surface run-off andriver channel


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AGNPS Model is one of Hydrologic Modeldeveloped by USDA-ARS, USDA-SCS, MPLCMR and EPA.

This model has been used by manycountries such as America, Canada and tEuropean Union countries (Yoon, 1996 inNugroho, 2000)


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AGNPS consists a number of cells and eacell could accommodate 22 parameters

Thus, data format from AGNPS Model is the form of raster or cells.

The area of cell depends on size of the

watershed area; the area of cell should b< 10 acre if area of watershed is equal oless than 2000 acre, and it should be 40acre or larger if size of watershed is > 20

acre.


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V o l u m e o f S u r fa c e R u n o f f can bepredicted with Curve Number from the S

( )

( )SP

SPQ

8.0

2.02

+

=

101000

=CN

S


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Peak Discharge

The first method is used if the river chan

is triangular form:

The second method used if the the riverchannel is rectangular form:

19.082.016.07.0 )(48.807.0

= LWROCSAQpA

[ ]Q

AQp

TcCTcCC

= ++

64010

2.210 )(log)(loglog


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Su r f a c e e r o s i o n is loss of materials of surface due to surface runoff.

)()( SSFKLSCPEISL =


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V. The AGNPS Model Procedur


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5.1. Preparing Data Collecting the Thematic Maps (Topography, Soil,Use/Land Cover)

* Correcting the system of map projection1. UTM2. Latitude/Longitude

* Matching the Thematic Map Scale1. Fraction: (ex. 1:50,000; 1:100,000)2. Bar Scale


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Delineating the watershed boundary* Making the river network basedon TopographicMap

* * Plotting the location ofhydrometric station* Making the boundary ofwatershed* Overlay The Watershed Map witThe Soil and


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Making the grid on Thematic Map

* Making the grid on all thematic map of research area

* Giving the number of grid on all thematic map

Soil Map Land Use Map Topography Map


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1. Cell Number 2. Receiving Cell Number 3. Cell Division 4. Receiving Cell Division 5. Aspect of Runoff Drainage 6. SCS Curve Number 7. Land Slope 8. Slope Shape Factor 9. Field Slope Length 10. Mannings Roughness Coefficient 11. Soil Credibil i ty Factor (K)

Identifying the data on each grid


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12. Cropping Factor (C) 13. Practice Factor (P) 14. Surface Condition Constant 15. Soil Texture 16. Fertil ization Level 17. Availabil ity Factor 18. Point Source Indicator 19. Gully Source Level 20. COD Factor 21. Impoundment Factor 22. Channel Indicator


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The Sort Description of AGNPS Param1. Cell Number

Each cell in the watershed has to beidentified by a number. The cells arenumbered consecutively, beginning at the

cell in the northwest corner, and sweepinfrom west to east, north to south.1

543

2


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2. Cell Division

The base cell can be divided into 4 sub cells and in this

program the name of sub cell is the cell division.

3 100

3 400

3 310 3 320

3 3403 330

3 210

3 230 3 240

3 221 3 222

3 223 3 224


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3. Receiving cell number: Represent the drainage direction and it isdetermined by cell topography. The receiving cell number for the watershedoutlet must be a number greater than the totnumber of cells in the watershed.

1

543

2

The receiving cell number of c

is cell-2 because Cell-2 receives

water from cell-1

The receiving cell number of c

is cell-5

The greatest number is 5


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4. Receiving Cell Division:

The division indicator for the receiving cell is an integer whspecifies which division of the receiving cell is the cell which

actually drained into. Each division of a cell is one quarter the area of its base cell. The numbering scheme is as follo

100

543

2200

400300

The receiving cell division o

sub cell-100 is sub cell-200

The receiving cell division o

sub cell-200 is cell-2


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5. Aspect

A single digit indicates the

principal direction ofdrainage from the cell. Thiscan be one of eight possibledirections, 1 being north

and proceeding clockwise, 8being northwest. If there isno drainage from the cell,input a 0.


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6. SCS curve number:

The runoff curve number or hydrologic socover complex number used in the SoilConservation Service equation for estimatdirect runoff from the storm rainfall.

(see D:\CAMBODIA\Paper AGNPS \Curve Number.Doc)


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7. Land slope

The primary slope, in percent, of the cell. Thcan be obtained from topographic maps,existing data or actual measurements. Assuman average slope if the cell is irregular. If the

cell is predominantly water or marsh, enter avalue of 0.


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8. Slope shape factor

An identification number used to indicatethe dominant slope shape of the cell. Ona uniform slope; two, a convex slope; andthree, a concave slope.


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9. Field slope length

Field slope length can be found by usintopographic map or the result of fieldsurvey. If the cell is predominantly wat

marsh, enter a value of 0.


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10. Manning's roughness coefficient

A roughness coefficient can be found by using MannTable. Example:

To Natural streams Clean and straight, no rifts or deep pools Clean and winding, some pools and shoals Clean and winding, some weeds, stones and pools Sluggish reaches with weeds and deep pools


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11. Soil erodibility factor

The soil erodibility factor is the parameter used in theuniversal soil loss equation (K), obtained from Soil ConseService soils data. If the cell is predominantly watermarsh, enter a value of 0.

12. Cropping factorThe Cropping factor (c factor) used in the universal soil

equation (see Wischmeier and Smith, 1978).13. Practice factor

The parameter used in the universal soil loss equation (examine a worst case situation, assume a practice factor Other values for various conservation practices can be

found in USDA Agricultural Handbook 537.


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14. Surface condition constantA value based on land use at the time of the stormmake adjustments for the time it takes overlandrunoff to channelize. Values are shown in thefollowing table.

15. Soil textureThe major soil texture classif ication for the cell. Tmajor soil texture can be determined from thetexture triangle.


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16. Fertilization levelA single digit indication of the level of fertilization onfield. The number to be input and the levels are:

Assumed fertilization (lb/a): Level N P Input ------------------------------------------------------------- No fertilization 0 0 0 Low fertilization 50 20 1 Average fertilization 100 40 2 High fertilization 200 80 3 User Defined Level Input Input 4


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17. Availability factor

18. Point source indicator 19. Gully source level

20. Chemical oxygen demand factor

21. Impoundment factor

22. Channel Indicator

AGNPS Presentation

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