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Show 1009 is , if , in order to explain the level , you have to know what stage the river was at , how does one accept that figure as anything definite to base operations on ? There are permanent bench marks on the banks along the river , although they would not appear on page 1 , because the Coast Survey level party did not overtake them until they were some distance up the river . There is a bench mark near mile 28 , on Page 2 , which is permanently fixed and marked to designate its elevation above sea level as determined by a level line running along the river . This point is fixed by a bronze tablet set in the ledge , and from this bench mark the other matters which appear on the map can be accurately calculated . Of course , the profile represents the level of water ( at -at at ) the time of his survey and if the survey were made when the water were higher or lower there would be a different figure on the profile , but anyone going upon ( the -the the ) land to investigate , would take the permanent bench mark and use the bench marks to determine the elevation of the water and use it in connection with the gage readings , or any other known factors , or combination of factors regarding the conditions of ( the -the the ) river at that time . ( R . 3973-3974 . ) If one , should go down there and see the bench mark , or . have all these other figures , you could adjust these profiles in these maps to the situation . The same ( thing -thing thing ) could be done while sitting here in Washington ; it could be done in connection with the gage readings |