Past Year Questions: Precipitation & General Aspects of Hydrology | Topic wise GATE Past Year Papers for Civil Engineering - Civil Engineering (CE) PDF Download

Question 1. A catchment may be idealised as a rectangle. There are three rain gauges located inside the catchment at arbitrary locations. The average precipitation over the catchment is estimated by two methods:     [2019 : 1 Mark, Set-I]
(i)    Arithmetic mean (P_A), and
(ii)   Thiessen polygon (P_T). Which one of the following statements is correct?
(a)    P_A is always smaller than P_T
(b)    P_A is always equal to P_T
(c)    There is no definite relationship between P_A and P_T
(d)    P_A is always greater than P_T 
Answer: (c)
Solution: The result from Thiessen polygon method is more accurate than arithmetic mean method. But there is no any close relationship between values obtained by Thiessen polygon method and Arithmetic mean method.
∴ There is no any relation between P_A and P_T.

Question 2. Rainfall depth over a watershed is monitored through six number of well distributed rain gauges. Gauged data are given below:

The Thiessen mean value (in mm, up to one decimal place) of the rainfall is______      [2018 : 2 Marks, Set-I]
Solution: Thiessen mean value of rainfall;


Question 3. A catchment is idealized as a 25 km x 25 km square. It has five rain gauges, one at each corner and one at the center, as shown in the figure.

During a month, the precipitation at these gauges is measured as G₁ = 300 mm, G₂ = 285 mm, G₃ = 272 mm, G₄ = 290 mm and G₅ = 288 mm. The average precipitation (in mm, up to one decimal place) over the catchment during this month by using the Thiessen polygon method is      [2017 : 2 Marks, Set-II]
Solution: 

Let sides of square be, a = 25 km Now area of the polygon is calculated as,


Question 4. In a catchment, there are four rain-gauge stations, P, Q, Ft and S. Normal annual precipitation values at these stations are 780 mm, 850 mm, 920 mm and 980 mm, respectively. In the year 2013, stations Q, R and S, were operative but P was not. Using the normal ratio method, the precipitation at station P for the year 2013 has been estimated as 860 mm. If the observed precipitation at stations O and P for the year 2013 were 930 mm and 1010 mm, respectively; what was the observed precipitation (in mm) at station S for that year?      [2015 : 2 Marks, Set-I]
Solution:  Let P_p = Precipitation in 2013 at station P
N_p = Normal annual precipitation at station P


Question 5. An isohyet is a line joining points of     [2013 : 1 Mark]
(a) equal temperature
(b) equal humidity
(c) equal rainfall depth
(d) equal evaporation
Answer: (c)