NR505 – Concepts in GIS

Introduction

Location Map

Base Map

Database Schema

Conventions

GIS Analyses

Flowchart

GIS Concepts

Results

Conclusion

References

To create a soil erosion index for the Tekeze River watershed, we chose to implement the Universal Soil Loss Equation (USLE). USLE was created to predict long-term average annual erosion rates. Originally used for agricultural purposes, USLE has been turned to for predicting erosion rates for many other landuses. One flaw of USLE, is that it does not take into account erosion from gully, wind, or tillage practices, but only accounts for sheet and rill erosion occurrences on a slope. Despite this, USLE is considered to be widely-used and a potentially accurate predictor of long-term soil erosion.

USLE is made up of six factors of which each factor plays an important role in the soil erosion process. The equation and its factors are as follows:

*A = RKSLCP*

Where A = Average Annual Soil Loss in (Mg/ha)

R = Rainfall – Runoff erosive index factor(MJ mm/ha hr yr)

K = Soil Erodibility factor (ton ha hr/ha MJ mm)

S = Slope steepness factor (dimensionless)

L = Slope length factor (dimensionless)

C = Crop-Management factor (dimensionless)

P = Conservation Practice Factor (dimensionless)

Each of the factors was used in an overlay analysis within GIS to create the resulting USLE values as an erosion distribution map and erosion index map. Below you will find a list of each factor, the exact equations used in calculating the factor value, and the steps taken within GIS to create each factor. Also included below is the first step in the process, delineating the Tekeze River Watershed.

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Delineation of Tekeze River Watershed

**Crop Management Factor (C) and Management Practice Factor (P) **

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Delineation of the Tekeze River Watershed

Steps taken in GIS to Delineate Tekeze River Watershed

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**Slope Steepness Factor, S**

Equation used to Calculate Slope Steepness Factor

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Steps taken in GIS to Calculate Slope Steepness Factor

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**Slope Length Factor, L **

Equation used to Calculate Slope Length Factor

Steps taken in GIS to Calculate Slope Length Factor

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**Rainfall Erosivity Factor, L**

Equation used to Calculate Rainfall Erosivity Factor

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Steps taken in GIS to Calculate Rainfall Erosivity Factor

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**Crop Management Factor (C) and Management Practice Factor, (P) **

Values used to Calculate Crop Management Factor, and Management Practice Factor

Steps taken in GIS to Calculate **Crop Management Factor (C) and Management Practice Factor, (P) **

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**Soil Erodibility Factor, K **

Equation used to CalculateSoil Erodibility Factor, K

Steps taken in GIS to** Calculate Soil Erodibility Factor, K **

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