Irrigation (221-248)

Updated: Apr 25, 2020

221. Which one of the following constitutes the basic assumption of unit-hydrograph theory? Time invariance and linear response

222. The following parameters relate to the design of weirs on permeable foundations:

1. exit gradient.

2. uplift pressure.

Design of the downstream end pile of the

weir depends upon

223. Given that the base period is 100 days and the duty of the canal is 1000 hectares per cumec, the depth of water will be 86.4 cm

224.A pumped storage plant is a peak load plant

225.If p is the precipitation, a is the area represented by a rain gauge, and n is the

number of rain gauges in a catchment area, then the weighted mean rainfall is

226.Depth-Area-Duration curves of precipitation are drawn as maximising envelopes through the appropriate data points


A. Conservation reservoirs-Controlled outlets B. Retarding basins-Uncontrolled outlets C. Flood plains-Temporary storage of flood water D. Flood walls-Flood-fighting

228.The following four hydrological features have to be estimated or taken as inputs before one can compute the flood hydrograph at any catchment outlet

1. rainfall hydrograph

2. infiltration index

3. unit hydrograph

4. base flow

The correct order in which they have to be employed in the computations is


Tailwater curve much above jump height curve-Sloping apron Tailwater curve slightly above jump height curve-Ski jump bucket Tailwater curve coinciding with jump height curve-Basin at bed level Tail water curve below the jump height curve-Sunk basin

230.The Standard Project Flood is derived from the probable maximum

precipitation in the region


A.Canal drop-Control of bed grade B. Canal escape-Control of full supply level C. Canal cross regulator-Control of flow depth D. Canal outlets-Control of discharge

232.For medium silt whose average grain size is 0.16 mm, Lacey's silt factor is likely to be 0.70


A. Minor irrigation work-Surplus weir B. Medium irrigation project in interior area-Syphon spillway C. Earth dam across main river-Saddle spillway D. Masonry dam on good rock-Ogee spillway

234. Mean precipitation over an area is best obtained from gauged amounts by

orographically weighted isohyetal method

235. The following steps are involved in arriving at a unit hydrograph

1. Separation of base flow

2. Estimating the surface runoff in volume

3. Estimating the surface runoff in depth

4. Dividing surface runoff ordinates by depth of runoff

236. Probability of a 10-year flood to occur at least once in the next 4 years is


237. The following data were recorded from an irrigated field

1. Field capacity : 20%

2. Permanent wilting point: 10%

3. Permissible depletion of available soil

moisture : 50%

4. Dry unit weight of soil :1500kgf/m3

5. Effective rainfall: 25 mm

Based on these data, the net irrigation requirement per metre depth of soil will be

50 mm

238. Depth-area-duration curves would seem to resemble arcs of a circle concave upwards with duration increasing outward

239. The spacing of tile drains to relieve waterlogged land is directly proportional

to the coefficient of permeability of the soil to be drained

240. The maximum permissible suction lift for centrifugal pump in practice (at sea level and at 30°C) is 6 m

241. An aquifer confined at top and bottom by impermeable layers is stratified into three layers as follows:

The transmissivity (m /day) of the aquifer is


242. In a flow-mass curve study, the demand line drawn from a ridge does not intersect the mass curve again. This implies that

the demand cannot be met by the inflow as the reservoir will not refill

243. The following rainfall data refers to stations A and B which are equidistant

from station 4X

The value of P will be 200

244. Consider the following statements :

1. A 100-year flood discharge is greater than a 50-year flood discharge.

2. 90% dependable flow is greater than 50% dependable flow.

3. Evaporation from salt-water surface is less than that from fresh-water surface

245.If a 4-hour unit hydrograph of a certain basin has a peak ordinate of 80 m³/s, the peak ordinate of a 2-hour unit hydrograph for the same basin will be

greater than 80 m³/s


A. Dalton-Evaporation B. Snyder-Synthetic unit hydrograph C. Blaney Criddle-Consumptive use equation D. Sherman-Unit hydrograph

247. A culvert is designed for a peak flow Q on the basis of rational formula. If a storm of the same intensity as used in the design and twice the duration occurs, then the resulting peak discharge will be Q


A. Specific yield-Volume of water drained by gravity per unit volume of aquifer B. Specific capacity-Well yield per unit drawdown C. Specific retention-Volume of water retained per unit volume of aquifer D. Specific storage-Volume of water released from unit volume of aquifer for unit decline in piezometric head

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