Sample Designs for Watershed

This article describes two probability sampling approaches to sampling water resources. In the rst approach, a complete enumeration of eligible sample units (e.g. stream segments, water bodies, drainage basins) is performed using GIS or paper maps to create a list frame. A probability random sample is then selected from this frame. In the second approach, a two-stage sample is selected. In the rst stage, area segments are selected using a probability design, such as stratiied sampling. Water resources contained in each segment are enumerated and labeled using eld 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.