Citation:

Ator, S. W., A R. Olsen, A M. Pitchford, AND J. M. Denver. DESIGN AND APPLICATION OF A STRATIFIED UNEQUAL-PROBABILITY STREAM SURVEY IN THE MID-ATLANTIC COASTAL PLAIN. JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION. American Water Resources Association, Middleburg, VA, 39(4):873-885, (2003).

Description:

A stratified random sample with unequal probability selection within strata was used to design a multipurpose survey of headwater watersheds in the Mid-Atlantic Coastal Plain. Objectives for data from the survey include unbiased estimates of regional headwater watershed conditions as well as adequate coverage of unusual but important environmental settings to support analysis of the factors affecting those conditions. A sample of 175 first-order non-tidal headwater watersheds was randomly selected for synoptic sampling of water quality, benthic ecology, and riparian ecology at the outflow of the watershed during the late winter and spring of 2000. Twenty-five watersheds were chosen within each of seven hydrogeologic subregions (strata) that were delineated from physiography and surficial geology. In each subregion, unequal selection probabilities were used to provide an approximately even distribution of watersheds along a gradient of forested to developed (agricultural or urban) land in the contributing watershed. Alternate watersheds were selected as part of the process. Stream sampling sites in selected watersheds were located in the field on the basis of accessibility; alternate watersheds were included in random groups of five in each subregion when field reconnaissance demonstrated that primary watersheds were not accessible or usable for other reasons. Despite the rejection and replacement of a considerable number of primary watersheds during reconnaissance (up to 40 percent in one subregion), the desired land-use distribution was maintained within each hydrogeologic subregion without sacrificing the probabilistic design.

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