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<br />b. Plate 2. BPS IDdex Ra1lar&U. 'l'be 1soh~es OD Plate 2 <br />represent the lIIlI,'.1...... avenae depth or re.1.Ilrall 1a 24 hours over 200 <br />square miles durillg the ste.n4Ard proJect stom, wh1ch is equal to approxi- <br />mtely 40 to 60 percent ot tbe MAy1__ posdble r&Wall 1l1d1cated on <br />Plate 1, vith a g~ average or about 50 percent. Plate 2 vas prepared <br />by reduc1Jlg 1soh~ts on Plate 1 to 50 percent ot orig1nal values llDd re- <br />shap1Jlg tbe 1aohyets 1n c erta1n regiolUl by moderate lIlIIOunts to cont01'lll <br />vi th supplementary stuclies or re.1.Ilrall characterist1cs 111 those reglolUl <br />During development stucliee s1lll1lar charts were prepared tor selected areu <br />l'lUIg1Jlg trom 10 to 20,000 square miles and stom durat10Dl1 troIII 6 to 96 <br />hours. It vas tound that deptb-area-durat1OD values tor these seve:raJ. <br />charts bore a reasonably cOlUl1stent relat1onsb1p to values shown on <br />PlJLte 2.. Accord1.llg1y, Plate 2 vas adopted as tbe "SPS Il:Idex Ra1J1tall. <br />chart, tbe use ot wh1ch 1s expla1J1ed here1natter. <br /> <br />c. Plate 3. SPS Index :Rainfall Isobyets VII Actual Storm <br />Values. Th1s chart sbovs graph1cally a cOlllp&rison betveen tbe selected <br />SPS Index Ra1J1tall 1sohyets and re.1.Ilrall values recorded durillg actual <br />stonDS 1.11 various geographical locations tor cOlllJl8.rable durat10ns and <br />areas. Data trom all st01'lll stuclies cOlllpleted to date (approx, 400) are <br />sbown on the chart. <br /> <br />d. Plate 4. . Ratio ot Actual St01'lll Values to SPS Indax Ra1J:I.tall. <br />In Figure (a) ot Plate 4 the rainfall values recorded in actual stOl'lllll, as <br />sbown on Plate 3, are plotted aga1.l1st values 1l1d1cated by SPS Index Ra1Jl- <br />tall 1sobyets tor correspond.1Dg geographical locat10ns. The nlllllber ot <br />actual storm values exceed.1Dg various percentages ot the SPS Index Rain- <br />tall are shown graphically 111 Fig\l1'e (a) lIDd the percentages ot actual <br />storm values that equalled or exceeded various SPS Index :Rainfall ratios <br />are 1I1d1cated in Figure (b). To demonstrate the relat1ve cODs1stency ot <br />re!.stionships 1:0 clifferent geograph1cal areas, separate curves are plotted <br />1:0 F1gur(' (b) tor tour areas, delineated by SPS IDdex Rainfall lIIobyets as <br />inclicated on Plate 4, as vell as tor the total area east ot 1050 longitude. <br />It may be observed tbat on the average approximately 10 percent ot tbe <br />storms studied to date have equalled or exceeded tbe SPS Index Ra1Dfall. <br />This percentage vill ot course vary as edclitional storm stuclies are com- <br />pleted, but serves to illustrate that the standard proJect stom is not ot <br />unprecedented magnitude regionally, althOUgh it 1s det1n1tely ot a major <br />category. <br /> <br />e. Plate 5. Tabulation, Precipitation During Major Storms ot <br />Record, ~ressed 111 Percent ot SPS IDdex Ra1l1tall. ID preparing this <br />table the geographical location ot maximUm ra1ntall durillg each storm ot <br />record vas dete1'lll1ned by 2-degree latitude-long1tude quadrengles, and tbe <br />corresponding SPS Index Rainfall value vas scaled trom PlJLts 2; the avena. <br />depths ot re.1ntall over selected areas 111 variCN.I periods ot t1llle vere <br />obtained tor the Corps ot Engineers publ1catiolUl entitled "Storm Ra1ntall <br />111 the Eastern United States", lIDd converted to percent ot SPS Index Rain- <br />:'all, as shovn 111 Plats 5. For study purposes, the data vere tabulated <br />by geographical zones as delineated on Plate 2. Plate 5 includes 105 ot the <br />more outst"I'<li"g norms ot the 400 investigated 111 detail. <br /> <br />8 <br /> <br />e <br /> <br />e <br /> <br />e: <br />