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Calculation of Abstractions Using GIS. Gaurav Garg CVEN 689 Dept Of Civil Engg. Presentation Objectives. Definition of Abstractions. Methodology Data Gathering Data Processing using GIS Analysis using MS-Excel Interpretation with GIS Results. Abstractions.

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Calculation of abstractions using gis

Calculation of Abstractions Using GIS

Gaurav Garg

CVEN 689

Dept Of Civil Engg


Presentation objectives
Presentation Objectives

  • Definition of Abstractions.

  • Methodology

    • Data Gathering

    • Data Processing using GIS

    • Analysis using MS-Excel

    • Interpretation with GIS

  • Results


Abstractions
Abstractions

The part of the precipitation that does not contribute

to the runoff.

It includes-

  • Infiltration

  • Depression Storage

  • Interception

  • Evapo-Transpiration


Infiltration techniques
Infiltration Techniques

  • Richard’s Equation

  • Horton’s Method

  • Green and Ampt Method

  • SCS Curve Number Method

  • Initial loss plus Constant loss Method


Data collection
Data Collection

  • DEM for delineating watersheds

  • STATSGO – Soils Data Polygons

  • NWS – Weather Stations Points

  • Green-Ampt parameters ( Clapp and Hornberger 1978)

  • Assumed Uniform Precipitation


Delineating watersheds
Delineating Watersheds

Using CRWR-Prepro

Main steps involved: -

  • Flow Direction

  • Flow Accumulation

  • Stream Network

  • Delineate Watersheds


Guadalupe Watershed

Texas STATSGO

Intersection



Procedure of calculating infiltration
Procedure of Calculating Infiltration

  • Green-Ampt Model

    Assumptions:

  • Soil is homogeneous with depth.

  • Infiltration wetting front is perfectly sharp and is same everywhere in horizontal.

    For this project a constant precipitation of 6cms for 2 hrs has been assumed.


Green ampt equation
Green-Ampt Equation

  • f(t) = Kh [1+( |Ψf|*(Φ-θ0)]

    F(t)

    f(t) = infiltration at time t

    F(t) = cumulative infiltration

    Kh = Hydraulic conductivity

    |Ψf|= Suction Head

    (Φ-θ0)= Change in moisture content






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