Rivers Harbors 359 Topographical surveying 278 Navigation 181 Law and legislation 127 Bridges 109 Budget 91 Hydrography 75 Dredging 71 Flood control 69 Court records 61 Public works 58 Waterways 38 Canals 37 Lighthouses 35 Maps 32 Expenditures, Public 31 Water resources development 30 Steamboats 27 Death 26 Railroads 24 Water-supply 24 Enslaved persons 22 Water 22 Boats and boating 20 Inland navigation 20 Appropriations and expenditures 19 Pollution 19 Reservoirs 19 Ships 19