If area and rainfall in respective rainguage station are given which method is usefull..

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Examoogle · Accepted Answer

Option B: Theissen polygon method

Explanation & Concepts:
The Thiessen polygon method calculates the average rainfall over a catchment area by assigning weights to each rain gauge station based on the area of the polygon surrounding it. The area is determined by drawing perpendicular bisectors between adjacent gauges to form unique influence zones.

Working Principle: The catchment is divided into polygons such that any point within a polygon is closer to the rain gauge located inside it than to any other gauge. The average rainfall is then computed as the weighted average of the rainfall at each station, where weights are the proportions of the total area covered by each polygon.

Key Formulas: $P_{avg} = \frac{\sum P_i A_i}{\sum A_i}$ — Average areal rainfall

Key Points: Accounts for non-uniform distribution of rain gauges.; More accurate than the arithmetic mean method.; Does not account for orographic effects (unlike Iso-Hyetal method).; Once the network is established, the polygons remain fixed.

Advantages: Superior to arithmetic average in handling non-uniform spatial distribution.; Mathematically objective and repeatable process.

Disadvantages: Does not consider elevation or topographical changes.; Rigid structure; requires re-calculation if a rain gauge is added or removed.

Applications: Catchment areas with flat topography.; Hydrological modeling where gauge spatial weight is required.

Additional Info: The Thiessen polygon method is essentially a weighted average method where the weights are the Thiessen coefficients.. Option A (Arithmetic average) assumes uniform distribution; Option C (Iso-Hyetal) uses lines of equal rainfall and is generally considered the most accurate but complex.

Answer: B is correct — The Thiessen polygon method determines the areal average rainfall by weighting individual gauge readings based on their surrounding polygonal influence area.

Exam Tip: If the problem mentions 'topographical influence' or 'elevation', the Iso-Hyetal method is usually the preferred choice over the Thiessen method.

Examoogle · Answer

Option A: aerithmetic average method

Examoogle · Answer

Option C: Iso-Hyetal Method

Examoogle · Answer

Option D: all of the above

Feature	Arithmetic Method	Thiessen Method
Requirement	Simple Mean	Thiessen Polygon
Spatial Bias	Ignores Area	Weights by Area

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