Figure 15. 



MALLARD DAYS OF USE ON POOL 24 



MISSISSIPPI RIVER 



MALLARD DAYS OF USE ON POOL 25 



MISSISSIPPI RIVER 



59 



I ' I i I ' I ' I ' I ' I ' I ' I ' 



1 61 ' 63 ' 65 ' 67 ' 69 ' 71 ' 73 ' 75 ' 77 



1958 60 62 W 66 63 70 72 74 76 



YEARS 



159 



