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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
slide7

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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