GIS-Assisted Approach in Soil Erosion Assessment using Manifold Software

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• GIS-Assisted Approach in Soil Erosion Assessment
  using Manifold Software

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Introduction

• Soil erosion research is a capital-intensive and
  time-consuming activity.
• However, the advent of computer technology leads
  to a new approach in dealing with soil erosion in
  a watershed.
• GIS has the capability of integrating spatial and
  analytical functionality of spatially distributed
  data.

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Introduction

• Soil Erosion
• The removal of soils from their original site
• Removes top fertile soil
• Source of sediment that pollutes streams and
  fills reservoirs.
• Contributes to non-point source pollution.
• Composed of three subprocess (detachment,
  transport and deposition)
• Types of Soil Erosion
• Sheet erosion
• Rill erosion
• Gully erosion
• Stream channel erosion

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Soil Erosion Models

• Universal Soil Loss Equation (USLE)
• Empirical model
• Estimates soil erosion by raindrop impact and
  surface runoff
• Modifield Soil Loss Equation (MUSLE)
• Revised Universal Soil Loss Equation (RUSLE)
• WEPP
• Rose Erosion Model
• CREST
• Others

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What are the Factors of USLE?

• Critical Factors
• The critical factors affecting soil erosion were
  based on the empirical formula developed by
  Wischmeir and Smith (1978) widely known as USLE.
• Erosive power of rainfall (R)
• Soil erodibility (K)
• Topographic Factor (LS)
• Vegetative cover (C)
• Erosion measures (P)

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Universal Soil Loss Equation

• The USLE is expressed by the formula with some
  modifications
• A R K LS C P
• where
• A Annual soil loss
• R Erosivity
• (EI30 10.8 4.15Rm)
• K Erodibility
• (K (0.043pH)(0.0621/OM)
  (0.0082S)-(0.0062C)Si
• L Slope length factor
• S Slope gradient factor
• C Cover factor
• P Erosion control factor

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The Factors of USLE .
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The Factors of USLE .
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The Factors of USLE .
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The Factors of USLE .
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The Factors of USLE .
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The Factors of USLE .
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The GIS-Assisted Approach (using USLE)
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The GIS-Assisted Model
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GIS-Assisted Approach in Soil Erosion Assessment
Here is the simplified procedure in calculating
areas vulnerable to soil erosion of the sample
watershed

1. Generation of Input Maps as Drawing using Manifold

Commands Generate of thematic maps (areas, lines
and points) affecting soil erosion following the
procedures described in the previous topics
(either from a georegistered scanned image and
then proceed with digitizing or by using the GPS
readings and create a table and then create a
drawing from the table). In the example, the
following are considered a) contours, b) soil
map, c) landuse map (vegetation and erosion
control practices), and d) rainfall erosivity
from different stations. Commands Press File ?
Create ? Drawing.. R Isohyte Map K Map LS
Map C Map P Map
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

LS Factor

• Generate a Surface from Contours (DEM)

Commands Right click on the drawing (with
contours) and press Copy. In the Project Pane,
right click and select Paste As ? Surface, then a
Paste as Surface Dialog Box will appear. Input
Height as Elev, Type as Floating-point (single),
Pixel Size as 10 or higher depending on the size
of watershed, and Method as Triangulation (flat),
and press OK. In this example, 10 x 10 pixel size
is used.
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

LS Factor

• Generate the LS Factor from Slope

Commands Select any Surface Component in the
Map and press Surface ? Transform and a Transform
Dialog Box will appear. Press the pull down menus
for Scope and select All Pixels. In the Formula
Field, use this formula to compute for LS
Factor LS (Ls/22.13)0.5(0.0650.045s0.0065s
2)
(pow((10/22.13),0.5))(0.065(0.045(slope(DEM)))
(0.0065(pow((slope(DEM)),2))))
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

Soil Erodibility (K)

• Add a Column in the Table for Erodibility Values

Commands Double click the Table component (Soil
Map) in the Project Pane. Then, right click on
the column of the Table and press Add ? Column
and the Add Column Dialog Box will appear. Type
the Name (K values) and Type (Floating-point
(double)) of the column and press OK. Input the K
values and these will depend on the nature of
soil.
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

Soil Erodibility (K)

• Generate a Surface from Soil Map with K Values

Commands Right click on the Drawing (Soil Map
with K values) in the Project Pane and press
Copy. In the Project Pane, right click and select
Paste As ? Surface, then a Paste as Surface
Dialog Box will appear. Input Height as K values,
Type as Floating-point (double), Pixel Size as 10
or higher depending on the size of watershed, and
Method as No Interpolation (default), and press
OK. In this example, 10 x 10 pixel size is used
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

Cover Factor (C)

• Add a Column in the Table for C Values

Commands Double click the Table component
(Landuse Map) in the Project Pane. Then, right
click on the column of the Table and press Add ?
Column and the Add Column Dialog Box will appear.
Type the Name (C values) and Type (Floating-point
(double)) of the column and press OK. Input the C
values and these will depend on the nature of
landuse/vegetation cover.
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

Cover Factor (C)

• Generate a Surface from Landuse Map with C Values

Commands Right click on the Drawing (Landuse
Map with C Values) in the Project Pane and press
Copy. In the Project Pane, right click and select
Paste As ? Surface, then a Paste as Surface
Dialog Box will appear. Input Height as C Values,
Type as Floating-point (double), Pixel Size as 10
or higher depending on the size of watershed, and
Method as No Interpolation (default), and press
OK. In this example, 10 x 10 pixel size is used
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

Erosion Control (P)

• Add a Column in the Table for P Values

Commands Double click the Table component
(Landuse Map) in the Project Pane. Then, right
click on the column of the Table and press Add ?
Column and the Add Column Dialog Box will appear.
Type the Name (P values) and Type (Floating-point
(double) of the column and press OK. Input the P
values and these will depend on the nature of
erosion control measures.
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

Erosion Control (P)

• Generate a Surface from Landuse Map with P Values

Commands Right click on the Drawing (Landuse
Map with P values) in the Project Pane and press
Copy. In the Project Pane, right click and select
Paste As ? Surface, then a Paste as Surface
Dialog Box will appear. Input Height as P values,
Type as Floating-point (double), Pixel Size as 10
or higher depending on the size of watershed, and
Method as No Interpolation (default), and press
OK. In this example, 10 x 10 pixel size is used
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GIS-Assisted Approach in Soil Erosion Assessment

1. Generation of Surfaces from Drawings of Factors
   using Manifold as Input to Soil Erosion VA

R Isohytes (R)

• Generate Surface from Rainfall Amount Map

Commands Right click on the Drawing (Rain
Station Map with R values) in the Project Pane
and press Copy. In the Project Pane, right click
and select Paste As ? Surface, then a Paste as
Surface Dialog Box will appear. Input Height as R
values, Type as Floating-point (double), Pixel
Size as 10 or higher depending on the size of
watershed, and Method as Kriging, and press OK.
In this example, 10 x 10 pixel size is used.
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GIS-Assisted Approach in Soil Erosion Assessment

1. Calculation of Areas Vulnerable to Soil Erosion

• Calculate the Soil Erosion Vulnerability

Commands Select any Surface Component in the
Map and press Surface ? Transform and a Transform
Dialog Box will appear. Press the pull down menus
for Scope and select All Pixels. In the Formula
Field, input the following
(R Isohyte Factor)(K Factor)(LS
Factor) (C Factor)(P Factor)
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Thank you