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• COMMENT 3 <br />For the southeast pond (004) my calculations again show a slight deviation from <br />Peabody's. Please evaluate and correct if necessary. The IOyr-24 hr storm will most <br />likely be passed without using the emergency spillway. Peabody should do a flood routing <br />to verify this. Sediment yield calculotions may also need revising. <br />RESPONSE: <br />This slight deviation is for the same reason presented for pond 003 (Comment 2), i.e., the <br />capacity of the pond from 'the principal spillway, 11.835 ac-ft, is the initial sediment <br />storage capacity of the pond. This is valid because the pond has the capacity to treat the <br />10-yr, 24-hr flow event without discharging through the emergency spillway using the <br />pond capcity between the principal spillway and the emergency spillway. <br />Verification that the 10 yr, 24 hr storm event will be passed through the principal <br />spillway without using the emergency spillway is provided in the following flood routing <br />procedure, the Puls method. The Puls method, as described in Applied Hydrology and <br />Sedimentology for Disturbed Areas (Barfield et al, 1981), is a procedure for graphically <br />solving the equation <br />• (S2+~Qt)-(SI OIOt)=12+Ilet <br />z z z <br />where <br />SI and S2 =Storage at times tl and t2, respectively <br />01 and 02 =Outflow rates at times t I and t2, respectively <br />11 and 12 =Inflow rates at times t1 and t2, respectively <br />~t =time interval over which there is a change in storage, S2 - Sl. <br />Using figures I, 2, and 3, and Tables 2, 3, and 4 according to the procedure detailed by <br />Barfield et al (1981), an outflow hydrograph for Pond dE004 (last column of Table 4) is <br />generated. As is clear from Table 4, at time 13.25 hrs into the 10 yr, 24 hr event, <br />outflow at Pond //004 peaks at 8.0 cfs, with a maximum stage height of 1.2 ft. At time <br />14.375 hrs., the stage height has begun to recede. Because the principal spillway at Pond <br />004 is capable of discharging approximately 33 cfs before using ih emergency spillway, it <br />is clearly evident that the 10 yr, 24 hr event with an outflow peak of 8.0 cfs will not <br />• overflow through the emergency spillway, and that, in fact, the pond has the capacity to <br />treat a much large drainage area Than it does at present. <br />3 <br />