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<br />3-18 <br /> <br />3.6.1 RUNOFF (Fig. 3-3) <br /> <br />The RUNOFF statement causes a runoff hydrograph to be developed for a <br />subwatershed. The input data is drainage area, CN and time of concen- <br />tration. Determination of the CN is described in Chapters 7t 8, and <br />9, NEH-4. Techniques in NEH-4, Chapter lS may be used for estimation <br />of time of concentration. <br /> <br />(e <br /> <br />3.6.2 RESVOR (Fig. 3-4) <br /> <br />The RESVOR statement causes an inflow hydrographto be routed through <br />a structure such as a reservoir, starting with the outflow discharge <br />rate at the elevation corresponding to the beginning of the storm. The <br />"Surf. Elev. at T = 0, Ft." is the water-surface elevation at the <br />structure at the beginning of the storm (See page A-S, record 170). <br />The routing continues until the outflow rate returns to zero or until <br />the 300 ordinate limit for a hydro graph is reached. If "Surf. Elev. <br />at T = 0, Ft." is left blank, routing begins at the first elevation on <br />the structure data table (page A-4). There are three ways to start <br />routingsl, I ; Normally the starting elevation will be the lowest crest of <br />the principal spillway, with outflow discharge equal to zero. The <br />storage associated with the starting elevation can be equal to or <br />greater than zero. 'l'wo--alternate' ways ,to start, routingsare: <br /> <br />C. <br /> <br />(1) Belo~ the principal spillway crest with zero discharge. The <br />second data card on the structure data table must have a discharge <br />greater than zero and must increase in storage. Therefore, a small <br />discharge may have to be shown, even though it is not the case. <br /> <br />'.; <br />(2) Above the principal spillway crest where discharge is greater <br />,',i;; '-""#~f- .',,-'''', ('('-/~" /" /,"(1 if /-j' <br /> <br />than zero. Routing starts atl'zero,..dischargebut will,immediately <br />increase-to the ,discharge,.shown .forthe starting elevation and routing <br />continues until the outflow discharge returns to zero or where it ends <br />because of 300 point storage limitation. The volume of the outflow <br />hydrograph will include the volume between the starting elevation and <br />the elevation at zero discharge or when it ends because of the 300 <br />point storage limitation. <br /> <br />~ <br /> <br />>---- <br />