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<br />3-14 <br /> <br />by the user. Cross sections can also be a means of denoting reference <br />locations in the system. This is illustrated on page C-2, where 001 <br />and 002 represent rating sections while 004 merely denotes a reference <br />location or an expedient for designating a location. The use of <br />reference locations can aid greatly in describing the Standard Control <br />for the watershed. <br /> <br />~ <br /> <br />. <br /> <br />The sample schematic drawing on page C-2 shows that a hydrograph is to be <br />developed for the area of structure 1 with a drainage area of 1.20 square <br />miles, a runoff curve number of 75, and a time of concentration of 0.33 <br />hours. This hydrograph is to be routed through structure 1 and then <br />through reach 1 with a reach length of 5400 feet, an end area coefficient, <br />x, of 0.4; and an exponent, m, of 1.33. Each reach is referred to by the <br />number of the cross-section at the downstream end of the reach on the <br />schematic. Another runoff hydrograph is to be developed for the inter- <br />vening area (0.46 mi2) between structure 1 and cross section 1 and added <br />t9 the reach routed hydrograph at the downstream end of reach 1. This <br />combined hydrograph is to be reach routed through reach 2. <br /> <br />Another runoff hydrograph is to be developed upstream of structure 2 <br />(D.A.=0.44 mi2), routed through structure 2, and then through reach 3. <br />A runoff hydrograph for the intervening area (D.A.=0.31 mi2) is to be <br />developed and combined with the hydrograph routed through reach 3. <br />The hydrographs, at sections 2 and 3 are then to be combined at location <br />number 4, shown on the schematic drawing as a dashed line. The hydrograph <br />at location 4 is to be routed through reach 5. Since a section rating <br />table (elevation-discharge-endarea data) will be provided for reach 5, <br />no values are given for x and m. <br /> <br />~ <br /> <br />A diversion structure is located at the downstream end of reach 5 that <br />'will divert part of the hydrograph out of the watershed. The remaining <br />portion of the hydrograph is to be routed through reach 6 and combined <br />with a runoff hydrograph for the intervening area (D.A.=1.30 mi2). <br /> <br />This schematic drawing would normally be used for all alternatives, <br />even those not including structures land 2 and the diversion structure <br />at section 5. In cases where structures are not to be included in an <br />alternative, they would be shown in the input data as null structures. <br /> <br />~ <br />