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<br />10 percent. Differences between computed and observed flows at most gage <br />locations on the mainstem and tributaries of the Susquehanna River system, <br />were less than lO percent. The Agnes event was of such a magnitude (esti- <br />mated to be a 300 to 400-year return period at Harrisburg) that many of the <br />discharge gages did not function properly or were destroyed. For many of <br />the gages that did function correctly the observed stages were at or beyond <br />I <br />the upper limit of the historical rating curve. During the time (August- <br />October 1972) when this project was being undertaken, it was not uncommon <br />to have the estimates of river discharges be updated as the flood was <br />studied in more detail. <br />Every possible effort was made within the time constraints of this <br />project to reproduce the observed flows. Because of the differences <br />between the computed and observed flows and because of the uncertainty <br />in the observed flows themselves. a more valid analysis of the effects <br />of the levee overtopping can be accomplished by a comparison of the two <br />computed flows. The differences between computed flows were shown in <br />table 2. The largest increase in flow would have occurred at Sunbury if <br />the levee had not been overtopped. This increase would have been about <br />71,000 cfs. <br />The potentially large increase in flow at Sunbury was due to both <br />the larger peak at Wilkes-Barre (about 27,000 cfs) and the coincident <br />timing with the peak flow coming from the West Branch of the Susquehanna <br />River. The peak flow at Wilkes-Barre, without the levee overtopping, <br />occurred about 20 hours earlier than the peak flow with the levee being <br />overtopped. The difference between the two hydrographs was 77,000 cfs <br />at the time of the earlier peak flow at Wilkes-Barre. The occurrence of <br />the peak at this earlier time would have made it coincide with the peak flo~' <br />from the West Brsnch when they met at Sunbury. The difference of <br />77,000 cfs would reduce to about 7l,OOO cfs when routed to Sunbury. <br />The potential increase in flow was not as large at Danville because <br />Danville is above the confluence with the West Branch and the coincident <br />timing could only have been with the local flow. The increase in flow <br /> <br />6 <br />