ABSTRACT
The preparation phase of data analysis involves compilation, preliminary organization, and hypothesis formulation. All available physiographic, climatic, and hydrologic data should be compiled. While a criterion variable, such as annual maximum discharge, is often of primary interest, other hydrologic data can be studied to decide whether a change in the criterion variable occurred. The analysis of daily flows, flow volumes, and low flow magnitudes may be useful for detecting watershed change. Physiographic data, such as land use or channel changes, are useful for assigning responsibility to changes and developing a method that can be used to adjust the flood record. Climatic data, such as rainfall volumes, reflect the extent to which the change in the annual flood series is climate related. If physiographic or climatic data do not suggest a significant watershed change, it may not be necessary to apply trend tests to the flood data. The variation in the annual flood series may simply be a function of random climatic variability, and this hypothesis can be evaluated by applying univariate trend tests to the sequence of data.
