Page 1 : oO, , Oo @, , i, &, , © & © 8 © 08 ® © @ © aoaoaooo0o6e ©aG eo, , , , Fa, cS), @, &, , , , , , , , DOWNLOADED FROM www. CivilEnggForAll.com _, , PREGIRITATION AND ITS MEASUREMENT, , from », but if no record of rainfall is available beyond the catchment, A, may be assume to correspond to P,, only, If however, rainfall record of area beyond catchment is available we can find the rainfall depth for area,, , A, by interpolation. Similar logic applies for area A,., , Example 7], , , , , , , , , , , , that duration is sélég ni {followings steps are taken:, Step 1: From. the dataof rail at different places of a catchment for a particular storm, isohyetal map is, Prepared., Step 2: Area between the i isohyets are determined using planimeter. ., Step 8: Area between two isohyets is multiplied by the average of the wcodepandiag ‘gshiyeta sid fe volume, of rainfall in that area is: found., Step 4; Cumulative volume and cumulative area are calculated., , Step 6: Cumulative volume is divided by cumulative area to know the average depth of rainfall over the, cumulative area for the chosen duration of rainfall. The same procedure is repeated for other durations also., , , , , , a | E S M. ASTER . Office: F-126, Katwaria Sarai, New Delhi- 110016, Bir eS ae oe Website: www.iesmaster.org, E-mail:
[email protected], NESIGATERSUS Phone: 011-41013406, 7838813406, 9711853908,
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DOWNLOADED FROM www. CivilEnggForAll.com, , HYDROLOGY, Step 6: Average'depth for a particular duration is plotted against the cumulative area to obtain the DAD curve, for that duration of rainfall., , Thus average depth of rainfall for a patticular area can be calculated from DAD curve., For a given duration of rainfalls (say 6-hr rainfall) column’, (D), (2), (8) will be known and from this (4), (5), 6), (7) are, , calculated. Thus curve is plotted with (7) as ordinate a (6), as abscissa., , , , , , , , , , , , , , DAD curve can also be obtained from emperical equation like, , , , : Pp = Average depth in catchment over an area A (km?), , P, = Highest amount of rainfall in catchment at the, ‘storm centre, , K, n = constant for a given region. They can be ob, by regression analysis., , But it is unlikely that the storm centre coincides wit, is not possible. i, , However, Py can be calculated from the assumplio, is the average depth over an area of 25 km?.\, , ingauge station. Hence exact determination of P,, , ghest rainfall over a raingauge in the catchmient, , , , From this P, can be calculated., , , , , , , , , , , , , , , , , , , , , , , , , , , , . Now average depth is plotted against cumulative area to get depth area curve fora particular duration., , my 1.E.S MASTER ~ Office: F-126, Katwaria Sarai, New Deihi- 110016, , , , Trstivte for Engineers: Website: www.iesmaster.org, E-mail: ies_master®yahoo.co.in, IESIGATE/PSUs Phone: 011-41013406, 7838813406, 971853908
Page 3 : if, ‘TOWNLOADED FROM www.CivilEnggForAll.com, , PRECIPITATION AND ITS MEASUREMENT 27, , , , IMUM. DEPTH AREA DURATION. CURVE, , , , In the design of hydraulic structures, we need to determine the design flood. The design fldod: will be determined, , 4 _ from the design storm. To find out the design storm we need to know the maximum rainfall of a particular, , duration over a particular area. This is found from Max. DAD curve., , Due to various storms of a particular duration (i.e. say various storms of 24 hr duration) depth area curve is, found. Then area is plotted w.r. to Max depth of rainfall corresponding £9 arious storms of 24 hr duration., This is max DAD curve:, , , , f rainfall of various days), , , , , , , , , , , , , , , , , , , , , , , , , When the above maximum depth of rainfa wt area we get maximum DAD curve. Max. DAD curve, can also be plotted in terms of point rai ‘entage with area., , Point rainfall percentage means : over an area is how much percentage of point rainfall, recorded by raingauge., , , , , , , , , , , , LESMASTER | oc F128 Kalvara Sara, , , , , , Website: www.iesmaster.org, E-mail:
[email protected], ae or Er, IESIGATEPSUs, Phone: 011-41013406, 7838813406, 9711858908, , , , @®@60 ©O G8 6 SGC
