We often have the dichotomy: 'too little water or too much'. In either case, streamflow measurement is crucial. Climate change could have a significant affect on water resources and flood management. Streamflow measurement is necessary for the measurement of flood flows which can cause widespread distress and loss of life in many places. "Streamflow Measurement" deals with all the main methods for measuring the flow in rivers and open channels necessary for the practice of efficient water management. Water is now a major issue in a world of some six and a half billion people where more than one quarter does not have safe drinking water. Only a fraction of the surface water of the Earth is available to us, in fact less than one percent. Whilst this amount of water available is not changing, any future change due to global warming will be made apparent in river measurement.This third edition brings together existing methods of measurement to the state of the art since the last edition and in accordance with international standards (ISO and CEN). A new chapter on the Acoustic Doppler Current Profiler (ADCP) is included in line with new research and development. The chapter on uncertainties has been redrafted in accordance with the recent International Standard on uncertainties in measurement (GUM) and to reflect the growing importance of this topic. The chapters on the Stage-Fall-Discharge method and Hydrometric Data Processing have also been updated in accordance with current practice and a new section on flood flows has been added. The book satisfies the current requirements of the International Organization for Standardization and the European Union's Water Directive.