Skip to Main Content
U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Home > Search > Publication Information

  1. Share via EmailShare on FacebookShare on LinkedInShare on Twitter
    Dislike this pubLike this pub
    Author(s): Robert B. Thomas; Jack Lewis
    Date: 1993
    Source: Water Resources Research 29(4): 1247-1256.
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (268 KB)


    Time-stratified sampling of sediment for estimating suspended load is introduced and compared to selection at list time (SALT) sampling. Both methods provide unbiased estimates of load and variance. The magnitude of the variance of the two methods is compared using five storm populations of suspended sediment flux derived from turbidity data. Under like conditions, the SALT coefficient of variation was 1.4-7.7 times that of time-stratified sampling. Time-stratified sampling performs well if the range of sediment flux in each stratum is small. This requirement can be met by using small sample sizes in many short strata. Theoretically, SALT sampling has the potential for smaller sampling variance; however, it is difficult to select an auxiliary variable that predicts flux well under diverse flow conditions. An ""optimum"" auxiliary variable formed from the largest storm performed about as well as time-stratified sampling for the larger storms. Time-stratified sampling ensures that specimens are collected in all storms, facilitating load estimation for individual storms. In contrast, SALT can better allocate sampling resources over different size storms, enabling efficient estimation of the total load for longer periods. Because time-stratified sampling is less sensitive to the way measurements are allocated to different parts of the population, it is preferred for estimating storm loads of multiple constituents from the same sample

    Publication Notes

    • You may send email to to request a hard copy of this publication.
    • (Please specify exactly which publication you are requesting and your mailing address.)
    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Thomas, Robert B.; Lewis, Jack. 1993. A comparison of selection at list time and time-stratified sampling for estimating suspended sediment loads. Water Resources Research 29(4): 1247-1256.


    PSW4351, Caspar Creek, time-stratified sampling, suspended sediment, SALT, measuremen

    Related Search

    XML: View XML
Show More
Show Fewer
Jump to Top of Page