Test 4 - Rain-Gauge Network Design and Rainfall Data Analysis

Question 1 ప్రశ్న 1

Which principle is most important when planning a rain-gauge network for a catchment?

A All gauges should be clustered near the catchment outlet for easy access B The network should represent the important spatial variability of precipitation while satisfying the intended hydrological purpose at reasonable cost C Gauge locations should depend only on catchment area and never on topography D The maximum possible number of gauges should always be installed regardless of data requirements

Question 2 ప్రశ్న 2

In a mountainous basin with strong orographic rainfall, which station-placement strategy is generally most appropriate?

A Place all gauges at one elevation so that their records are directly comparable B Distribute gauges so that important elevation zones, windward and leeward areas, and major rainfall gradients are represented C Place gauges only beside roads, irrespective of topography D Use one centrally located gauge because mountain rainfall is normally uniform

Question 3 ప్రశ్న 3

A 2400 km² catchment is monitored by six rain gauges. If network density is expressed as catchment area represented per station, what are the present density and the density after two additional gauges are installed?

A 400 km²/station and 300 km²/station B 400 km²/station and 480 km²/station C 600 km²/station and 300 km²/station D 2400 km²/station and 1200 km²/station

Question 4 ప్రశ్న 4

In the traditional statistical adequacy criterion for a rain-gauge network, which expression gives the required number of stations N when Cv is the coefficient of variation of station rainfall values in percent and e is the allowable percentage error in estimated basin mean rainfall?

A N = Cv/e B N = (Cv/e)^2 C N = Cv^2/e D N = e^2/Cv

Question 5 ప్రశ్న 5

According to N = (Cv/e)^2, if the allowable percentage error is reduced from 10% to 5% while Cv remains unchanged, how does the required number of gauges change?

A It is halved B It doubles C It becomes four times as large D It remains unchanged

Question 6 ప్రశ్న 6

A catchment has six operating rain gauges. The coefficient of variation of the relevant rainfall values is 30%, and an allowable error of 10% is specified. Using N = (Cv/e)^2, how many gauges are required in total and how many additional gauges are needed?

A 6 total; no additional gauges B 9 total; 3 additional gauges C 12 total; 6 additional gauges D 30 total; 24 additional gauges

Question 7 ప్రశ్న 7

Three existing stations record comparable-period rainfalls of 80, 100 and 120 mm. Using the sample standard deviation, the mean is 100 mm and the standard deviation is 20 mm. For an allowable error of 10%, what does the traditional adequacy criterion indicate?

A Cv = 10% and three stations are sufficient B Cv = 20%, N = 4, so one additional station is indicated C Cv = 20%, N = 2, so one station should be removed D Cv = 40%, N = 16, so thirteen additional stations are required

Question 8 ప్రశ్న 8

For an existing network of m gauges, the relation N = (Cv/e)^2 may be rearranged to estimate the percentage error associated with m stations as e = Cv/sqrt(m). If Cv = 24% and m = 9, what is the estimated error?

A 2.67% B 8% C 24% D 72%

Question 9 ప్రశ్న 9

Under which condition is the arithmetic-mean method most appropriate for estimating mean areal rainfall over a catchment?

A Gauges are reasonably uniformly distributed and their rainfall values do not show large spatial variation B All gauges are clustered in one corner of the basin C Rainfall has a strong elevation gradient but no topographic information is used D Only one rain gauge exists

Question 10 ప్రశ్న 10

Four representative rain gauges record storm depths of 80, 100, 120 and 100 mm. Using the arithmetic-mean method, what is the mean areal rainfall?

A 90 mm B 100 mm C 105 mm D 120 mm

Question 11 ప్రశ్న 11

What is the fundamental basis of the Thiessen-polygon method for estimating catchment-average rainfall?

A Every gauge is assigned equal weight irrespective of its location B Each station is weighted according to the catchment area closer to that station than to any other station C Weights are proportional only to station elevation D Rainfall contours are drawn first and all polygon areas are ignored

Question 12 ప్రశ్న 12

Three gauges record 80, 100 and 140 mm of rainfall. Their Thiessen area weights are 0.20, 0.30 and 0.50 respectively. What is the Thiessen-weighted catchment rainfall?

A 100 mm B 110 mm C 116 mm D 140 mm

Question 13 ప్రశ్న 13

Which statement concerning Thiessen weights is correct?

A For a fixed network and catchment boundary, the area weights are determined by station geometry and normally sum to unity B The weights must be recalculated from rainfall magnitude during every storm even if the station network is unchanged C All station weights must be identical D Thiessen polygons automatically account fully for orographic rainfall variation

Question 14 ప్రశ్న 14

What is an important limitation of the Thiessen-polygon method in a mountainous basin?

A It does not explicitly account for rainfall variation caused by topography or orographic effects B It cannot assign different weights to different gauges C It can be used only when all gauges have identical rainfall D It cannot use a gauge lying near the basin boundary

Question 15 ప్రశ్న 15

Which procedure best describes the isohyetal method of estimating mean areal rainfall?

A Draw contours of equal rainfall, determine the areas between successive isohyets, assign each zone a representative rainfall, and compute an area-weighted average B Assign equal weight to every station and ignore spatial variation C Draw perpendicular bisectors between every pair of gauges and use only polygon centroids D Use only the largest rainfall recorded in the basin

Question 16 ప్రశ్న 16

An isohyetal analysis divides a 100 km² catchment into three zones: 20 km² between 0 and 50 mm, 30 km² between 50 and 100 mm, and 50 km² between 100 and 150 mm. Using the arithmetic mean of bounding isohyets for each zone, what is the mean areal rainfall?

A 75 mm B 90 mm C 100 mm D 125 mm

Question 17 ప్రశ్న 17

Which method is generally most capable of incorporating a known strong spatial rainfall gradient caused by topography, provided sufficient station data and hydrological judgment are available?

A Arithmetic mean method B Isohyetal method C Simple unweighted averaging of only the lowest-elevation gauges D Ignoring all gauges outside the centre of the catchment

Question 18 ప్రశ్న 18

A rainfall value is missing at one station for a particular storm. When nearby stations have similar long-term normal precipitation and lie in the same rainfall regime, which simple estimation approach is reasonable at introductory engineering-hydrology level?

A Use the arithmetic mean of rainfall at representative neighbouring stations B Set the missing rainfall automatically equal to zero C Use the maximum neighbouring rainfall regardless of station characteristics D Multiply the nearest rainfall by catchment area

Question 19 ప్రశ్న 19

Rainfall at a station is missing for a storm. Three climatologically similar neighbouring stations record 40, 46 and 44 mm. Using the simple arithmetic-average estimate, what is the missing rainfall?

A 40.0 mm B 43.3 mm C 44.0 mm D 46.0 mm

Question 20 ప్రశ్న 20

Why is the normal-ratio method useful for estimating missing rainfall when neighbouring stations have substantially different normal precipitation?

A It adjusts each neighbouring event rainfall according to the ratio of the missing station's normal rainfall to the neighbour's normal rainfall B It assumes that all stations always receive exactly the same rainfall C It ignores long-term rainfall differences between stations D It uses only the station having the largest normal rainfall

Question 21 ప్రశ్న 21

The normal annual precipitation at a station with missing storm rainfall is 1000 mm. Three neighbouring stations have normal annual precipitation of 800, 1000 and 1250 mm and record storm depths of 48, 55 and 70 mm respectively. Using the normal-ratio estimate Px = (1/3)Σ[(Nx/Ni)Pi], what is the missing rainfall?

A 55 mm B 57 mm C 60 mm D 64 mm

Question 22 ప్రశ్న 22

What is the principal purpose of a double-mass curve in rainfall-data analysis?

A To detect changes in the consistency of a station record by comparing its cumulative rainfall with cumulative rainfall of a stable reference group B To determine rainfall intensity directly from individual raindrop diameters C To calculate catchment area from a topographic map D To determine evaporation from a reservoir

Question 23 ప్రశ్న 23

Which change is most likely to create an artificial break in the slope of a rainfall double-mass curve?

A Relocation of the test rain gauge to a site with different exposure B A regional wet year affecting both the test station and surrounding stations similarly C Using cumulative rainfall on both axes D Extending the record by another year under unchanged measurement conditions

Question 24 ప్రశ్న 24

In a double-mass plot with cumulative reference rainfall on the x-axis and cumulative rainfall at the test station on the y-axis, an inconsistent segment has slope 0.75 but should be adjusted to a reference-consistent slope of 0.90. What correction factor should be applied to rainfall values in that segment, and what does an observed 800 mm become?

A 0.833; 667 mm B 1.20; 960 mm C 1.65; 1320 mm D 0.15; 120 mm

Question 25 ప్రశ్న 25

A double-mass curve of cumulative rainfall at a test station against cumulative mean rainfall of stable neighbouring stations remains approximately a straight line with unchanged slope over the complete record. What is the most appropriate interpretation?

A The test record is broadly consistent relative to the reference group over that period B Every annual rainfall value at the test station must be identical to neighbouring rainfall C The station record contains no random measurement error whatsoever D The test station must be removed from the network

Question 26 ప్రశ్న 26

Consider the following statements about rain-gauge network design and rainfall analysis: I. Increasing spatial rainfall variability generally increases the number of gauges needed for a specified statistical accuracy. II. Thiessen weights are based on areas represented by individual gauges. III. Isohyetal analysis can explicitly represent spatial rainfall gradients through contours of equal precipitation. IV. A persistent change in double-mass-curve slope can indicate inconsistency in a station record. Which option is correct?

A I and II only B I, II and III only C II, III and IV only D I, II, III and IV

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