Sample designs for watershed assessment

摘要

This article describes two probability sampling approaches to sampling water resources. In the first approach, eligible sample units (e.g., stream segments, water bodies, drainage basins) are enumerated using GIS (Geographic Information Systems) or paper maps to create a list frame. A probability sample is then selected from this frame. In the second approach, a two-stage sample is selected. In the first stage, area sampling units are selected from the geographic universe using a probability design, such as stratified sampling, Water resources contained in each area sampling unit are enumerated and labeled using field visits or aerial photographs. In a second stage, the water resource or related sampling units (e.g., stream segments, water bodies, measurement points) are selected in each of the segments. Examples of both approaches are presented and their relative strengths and weaknesses are discussed.