T2 Rainfall data 2

How many methods are used to determine the average rainfall depending upon area of basin in rain gauging?

• 2

• 3

• 4

• 5

Answer explanation

When there are more basins, three of the following methods are used to determine the average of rainfall depending upon the area of basin. They are Arithmetic

1) Mean method

2)Thiesson method

3)iso-hyetal method

In which of the following rain gauging methods are the values of rainfalls of all stations added?

• Arithmetic mean method

• Thiesson method

• Iso-hyetal method

• Recording type

Answer explanation

In arithmetic mean method, the values of rainfalls of all the stations are added and the sum is divided by the number of gauging stations. This can be represented in the mathematical term as:
h_a = h1+h2…….hnn=Ʃhn.

Which among the following method is very accurate of rain gauging?

• Recording type

• Thiesson method

• Iso-hyetal method

• Arithmetic mean method

Answer explanation

Thiesson method is very accurate compared to other methods and is generally used when the catchment area lies between 500 to 5000km square. Assume that there are stations in the given basin names=d as 1, 2, 3, 4, 5, 6, 7, and 8. It is very important to divide the total basin area in such a way that each located station in the basin represents that area in the true.

Thiesson method is better result than arithmetic mean method because _________

• Small procedure

• It is highly accurate

• Gives better detail about records

• It is shorter time consuming

Answer explanation

The mean rainfall of the basin in thiesson method is given by:
h_a = h1A1+h2A2+h3A3+h4A4+h5A5+h6A6+h7A7+h8A8A1+A2+A3+A4+A5+A6+A7+A8
This method gives better result than arithmetic mean method because it is very accurate and each point on a perpendicular bisector of the line joining the two gauging stations will be equidistant from both the stations. If one moves slightly this or that side of the bisector, the position will distinctly fall in the domain of that station of which ones position is now near.

In which of the following rain gauging method is contour joining the points of equal rainfall is done?

• Recording type

• Thiesson method

• Iso-hyetal method

• Arithmetic mean method

Iso-hyetal method is commonly used for the basin area above 500sq.km.

• True

• False

Answer explanation

Iso-hyetal method is commonly used for the basin above 500sq.km. The analysis of rainfall for power generation purposes is usually more concerned with dry years rather than wet years. For the assessment of storage requirements, it is often necessary to determine the driest period for which provision must be made.