Hydrology & Water Resources Engineering - Vol 1 | 9. Theissen’s and Isohyetal Methods by Abraham | Learn Smarter
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Knowledge
9. Theissen’s and Isohyetal Methods

Estimating average precipitation over a catchment area is vital for hydrological tasks such as flood estimation and water resource planning. This chapter discusses two primary methods for estimating rainfall spatially: the Theissen Polygon Method and the Isohyetal Method. Each method's construction, assumptions, advantages, limitations, and applications are explored, highlighting their importance in accurately assessing rainfall distribution.

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Sections

  • 9

    Theissen’s And Isohyetal Methods

    This section discusses the Theissen Polygon and Isohyetal Methods for estimating average precipitation over a catchment area.

    Learning Practice

  • 9.1

    Theissen Polygon Method

    The Theissen Polygon Method is a geometrical approach used to estimate area-weighted average rainfall based on point observations from rain gauge stations.

    Learning Practice

  • 9.1.1

    Concept And Purpose

    The Theissen Polygon Method estimates area-weighted average rainfall by assigning rain gauges to specific polygons, aiding in hydrological design and planning.

    Learning Practice

  • 9.1.2

    Steps Of Construction

    This section outlines the procedural steps necessary to implement the Theissen Polygon Method for estimating area-weighted average rainfall.

    Learning Practice

  • 9.1.3

    Assumptions

    This section outlines the assumptions underlying the Theissen Polygon Method for estimating rainfall.

    Learning Practice

  • 9.1.4

    Merits

    The merits of the Theissen Polygon Method highlight its simplicity and effectiveness for estimating average rainfall in small to medium catchments.

    Learning Practice

  • 9.1.5

    Demerits

    The section details the demerits of the Theissen Polygon Method in hydrology, noting its limitations regarding topographical influences and station distribution.

    Learning Practice

  • 9.2

    Isohyetal Method

    The Isohyetal Method is a contouring technique used to estimate areal precipitation by drawing isohyets, which are lines connecting points of equal rainfall depth.

    Learning Practice

  • 9.2.1

    Concept And Purpose

    The Isohyetal Method is a contouring technique used to estimate average rainfall over a catchment area by connecting points of equal rainfall depth.

    Learning Practice

  • 9.2.2

    Steps Of Construction

    The section outlines the systematic steps for constructing Isohyetal maps to estimate areal precipitation across a catchment area.

    Learning Practice

  • 9.2.3

    Key Considerations In Isohyetal Drawing

    Isohyetal drawing requires careful interpolation to accurately represent rainfall contours, ensuring logical patterns and a dense network of stations for reliability.

    Learning Practice

  • 9.2.4

    Merits

    The merits of the Isohyetal Method highlight its accuracy and ability to consider spatial rainfall variations.

    Learning Practice

  • 9.2.5

    Demerits

    This section outlines the demerits associated with the Isohyetal Method in estimating average rainfall over a catchment area.

    Learning Practice

  • 9.3

    Comparison Between Theissen And Isohyetal Methods

    This section compares the Theissen Polygon and Isohyetal Methods, highlighting their differences in basis, accuracy, data requirements, computation time, subjectivity, and spatial distribution.

    Learning Practice

  • 9.4

    Application Scenarios

    This section discusses the contexts in which the Theissen and Isohyetal methods for estimating rainfall are applied.

    Learning Practice

  • 9.5

    Modern Enhancements And Gis Integration

    This section discusses modern enhancements in hydrology, focusing on the integration of GIS tools to improve rainfall estimation methods.

    Learning Practice

References

Chapter_9_Theiss.pdf

Class Notes

Memorization

What we have learnt

  • The Theissen Polygon Method...
  • The Isohyetal Method relies...
  • GIS tools can enhance the a...

Final Test

Revision Tests