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# Irrigation (161-180)

Updated: Apr 25, 2020

161. Instantaneous unit hydrograph is a hydrograph of

i) unit rainfall excess

ii) infinitely small duration

162. For a catchment area of 120 km², the equilibrium discharge in m³hour of an S

curve obtained by the summation of 6 hour unit hydrograph is

0.2 x 10

163. A unit hydrograph has one unit of rainfall excess

164. The peak of a 4 hour flood hydrograph is 240 m³/sec . If the rainfall excess is 80 mm and base flow which is constant is 40, m³/sec, then the peak of 4-hours unit hydrograph will be 25 m³/sec

165. A 4-hour direct runoff hydrograph of a catchment is triangular in shape with a

time base of 100 hours and peak flow of 50 m³/sec. The catchment area is 360 km². The peak flow of this catchment area for a 4-hour unit hydrograph is

20 m³/sec

166. To estimate the magnitude of a flood with a return period of T years, Gumbel's

distribution method requires the following data pertaining to annual flood series

i) mean value

ii) standard deviation

iii) length of record

167. For an annual flood series arranged in descending order of magnitude, the return for a magnitude listed at position period m in a total data N is (N+l)/m

168. If the risk of a flood occurring in the next 10 years is accepted to 10%, then the

return period for design should be 1/(1-0.9¹/¹⁰)

169. Partial duration series is mostly used for rainfall analysis

170. If storage, inflow rate and out flow rate are denoted by S, I and Q respectively, then the value of S in Muskingham method of flood routing is given by the expression

K (XI -XQ-Q)

where K and X are coefficients

171. Which of the following are Saint Venant's equations for unsteady open-channel flow ?

continuity equation,momentum equation

172. In case of channel routing, the storage is a function of

a) inflow discharge only

b) outflow discharge only

173. Muskingham method of flood routing is

channel routing method

174. Which of the following equations are used in hydrological flood routing methods ? continuity equation

175. In linear reservior, storage varies linearly with outflow rate

176. The dimensions of storage coefficient is dimensionless

177. The porosity of a sand sample is 50%. The specific yield of an aquifer containing this sand will be less than 50%

178. Discharge per unit drawdown at a well is called specific capacity

179. Permeability of a soil sample at a temprature of 20°C is 0.5 mm/sec. If the

temperature is decreased to 15°C, the permeability of the same soil sample is

less than 0.5 mm/sec

180. Due to decrease in pressure, the water level in a well penetrating a confined aquifer will increase