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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What we have learnt
- The Theissen Polygon Method uses geometric divisions to estimate average rainfall based on point observations.
- The Isohyetal Method relies on drawing isohyets for superior accuracy, accounting for spatial rainfall gradients.
- GIS tools can enhance the accuracy and efficiency of both methods by automating processes and reducing subjectivity.
Key Concepts
- -- Theissen Polygon Method
- A geometrical approach to estimate area-weighted average rainfall from point observations at rain gauge stations.
- -- Isohyetal Method
- A contouring technique for estimating areal precipitation by connecting points of equal rainfall depth.
- -- Isohyets
- Lines that connect points of equal rainfall on a map.
- -- Areaweighted average rainfall
- A calculation that accounts for the area of influence of each rain gauge station in determining average precipitation.
- -- Spatial interpolation
- A method used to estimate values at unmeasured locations based on values from surrounding measured points.
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