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<br />Q <br />IA <br /> <br />Q /DEPTH OF RA:) <br /> <br />. <br />~ <br />4 <br />~ <br /> <br />IF <br />tJ <br /> <br />DETERMINE ~ t;\ DEPTH RUNOFFVOUJlIE <br />VOLUME OF ~ \V OF . <br />RUNOFF RUNOFF WATERSHEll AREA <br /> <br />o <br /> <br />UNIT HYDROGRAPH <br />DETERMINED OF <br />DURATION tit" <br /> <br />j <br />~ <br />4 <br />4 <br />, <br />. <br />) <br /> <br /> <br />t <br /> <br /> <br />~ <br />~ <br />I <br />~ <br />4 <br />~ <br />. <br /> <br />REMOVE GROUNDWATER <br /> <br />t <br /> <br />t <br />... <br />. <br /> <br />LlNEARITY <br /> <br />SUPERPOSITION <br /> <br />J <br />~, <br />1 <br />~ <br />.. <br /> <br />~, <br />j <br /> <br />Figure II-2.--Unit hydrograph determination procedure. <br /> <br />runoff volume is then distributed over <br />the entirc watershed (divided by the <br />watershcd area) to determine the equiva- <br />lcnt runoff depth, (4) The ordinates of <br />the runoff hydro graph are divided by <br />this runoff depth to produce the unit <br />hydrograph for the storm duration. <br /> <br />The unit hydrograph can be used with <br />the concepts of linearity and superposi- <br />tion to predict the watershed response <br />to a design rainfall with a specified <br />return period. Linearity implies that <br />if the unit hydrograph represents a basin's <br />response to I-inch of runoff for a given <br /> <br />TIME <br /> <br /> <br />"FLOW <br /> <br /> <br />,.....-, <br />I '-- COMPOSITE <br />/ \ HYOROORAP~ <br /> <br />I \ <br />I \ <br />\ , <br />,- _.-- --rim of Rio <br />\ <br />\-1 in of RIo <br />\ (deloyed byA,l <br />\ <br />\ <br />\ <br />\ <br />" <br /> <br />"i <br /> <br />20. <br /> <br />Qp <br /> <br /> <br />1 <br />J <br />~ <br />~ <br /> <br />-I <br /> <br />Figure II-3.--Linearity and superposition concepts. <br /> <br />16 <br /> <br />1 <br />