Bridges 740 Navigation 187 Flood control 174 History 168 Dredging 134 Topographical surveying 96 Law and legislation 92 Indians of North America 83 Description and travel 76 Reservoirs 74 Waterways 62 Embankments 60 Budget 50 Public works 50 Floods 48 Rivers 47 Canals 46 Expenditures, Public 42 Travel 39 Discovery and exploration 36 Public lands 36 Discoveries in geography 35 Hydrography 33 Land tenure 33 Railroads 33 Disaster relief 30 Roads 30 HISTORY 29 Water resources development 29 Harbors 28