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EXHIBIT A <br />Calulation of Runoff Volumes and Peak Flows <br />Reference: Tech. Procedures for Determining Peak Flows in <br />Colorado, includes Tech. Release No. 55. SCS March 1980. <br />RUNOFF <br />Soils: Area Tvoe <br />Manzano 1 acre C <br />Louviera/Travellisa 1 acre D <br />Cover: Bare - 1 acre <br />Sparse grass - 1 acre <br />CN from Table 2.2: <br />Land use: Range land poor 86/C 89/D 1 acre <br />Disturbed 80/C 80/D 1 acre <br />Note: CMLRD determination for soils in this <br />area is 80, which takes into account <br />depressions, conditions in the Western <br />US, etc. <br />Use CN of 80 with Antecedent Moisture Condition <br />II. Effect of AMC is seen from the following: <br />CN <br />AMC II $6 <br />AMC I 63 <br />(ref. SCS NEH supplement) <br />For Colorado, AMC I is often justified as runoff <br />is generally from thunderstorm activity on lands <br />that are "dry enough for plowing and cultivating" <br />(SCS) <br />Precipitation: From Fig. S-7, the 10-yr 24 hr precip. is <br />3.0 inches. <br />Runoff: With CN=80, Rainfall = 3.0 inches, CN 80 table <br />gives a runoff of 1.25 inches. <br />Volume: Runoff x Area <br />1.25 inches x 2.1 acres /12 inches/ft = 0.22 AF <br />PEAK <br />From Figure D-3: for moderate slopes ( site slope is <br />(6450-6420)/400 = 7.5%) and drainage area of <br />2 acres. <br />Runoff cfs/in cfs <br />10-yr,24-hr <br />25-yr,24-hr 1.72 3.3 5.7 <br />Comparison with Figure D-2: <br />Use smallest time of concentration of .1 hour: <br />Peak = 1000 csm/inch <br />For 10-yr,24-hr, runoff 1.25 inches: <br />1.25 in. x 1000csm/inch x 2 ac./640 ac./aq.mi. = 3_9 cfs <br />Considering applicability of methods, this result <br />is the same as from using Figure D-3. <br />SUMMARY <br />Peak Volume <br />10-yr, 24-hr .1 cfs 0. AF <br />25-yr, 24-hr 5.7 cfs n/a <br />