Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Lost in space, the sequel: spatial sampling issues with 1‐D PHABSIM
10.1002/rra.1258.abs
The Physical Habitat Simulation System (PHABSIM) is a popular method for evaluating the habitat value of a stream in terms of a statistic, weighted usable area (WUA). Usually, PHABSIM is used with one‐dimensional (1‐D) hydraulic models, and curves of WUA over discharge are calculated at transects and combined to produce a composite curve. Curves of WUA over discharge are often presented as evidence in proceedings to determine instream flow requirements, so the reliability of these curves is important. Representing a reach of stream with transects introduces ordinary statistical questions: is the sample of transects unbiased, and is it large enough to produce usefully precise estimates? Unfortunately, these questions are seldom considered in PHABSIM studies, even though most PHABSIM studies characterize streams with fewer than 15 transects. Moreover, transect locations usually are selected deliberately, so estimates of WUA will usually be biased. This paper extends an earlier analysis of the uncertainty in composite WUA curves with a much larger set of transect curves, with more analysis of uncertainty in the shape of the WUA curves, and with a different method for simulating errors in estimates of WUA at the transects. The results show that even with larger than usual numbers of transect curves, the precision of composite WUA curves is likely to be poor, especially if there are errors in the transect WUA curves. I also offer suggestions regarding sampling, and for estimating the number of transects that might be needed to achieve a given level of precision in WUA estimates. Copyright © 2009 John Wiley & Sons, Ltd.
Lost in space, the sequel: spatial sampling issues with 1‐D PHABSIM
10.1002/rra.1258.abs
The Physical Habitat Simulation System (PHABSIM) is a popular method for evaluating the habitat value of a stream in terms of a statistic, weighted usable area (WUA). Usually, PHABSIM is used with one‐dimensional (1‐D) hydraulic models, and curves of WUA over discharge are calculated at transects and combined to produce a composite curve. Curves of WUA over discharge are often presented as evidence in proceedings to determine instream flow requirements, so the reliability of these curves is important. Representing a reach of stream with transects introduces ordinary statistical questions: is the sample of transects unbiased, and is it large enough to produce usefully precise estimates? Unfortunately, these questions are seldom considered in PHABSIM studies, even though most PHABSIM studies characterize streams with fewer than 15 transects. Moreover, transect locations usually are selected deliberately, so estimates of WUA will usually be biased. This paper extends an earlier analysis of the uncertainty in composite WUA curves with a much larger set of transect curves, with more analysis of uncertainty in the shape of the WUA curves, and with a different method for simulating errors in estimates of WUA at the transects. The results show that even with larger than usual numbers of transect curves, the precision of composite WUA curves is likely to be poor, especially if there are errors in the transect WUA curves. I also offer suggestions regarding sampling, and for estimating the number of transects that might be needed to achieve a given level of precision in WUA estimates. Copyright © 2009 John Wiley & Sons, Ltd.
Lost in space, the sequel: spatial sampling issues with 1‐D PHABSIM
Williams, John G. (Autor:in)
River Research and Applications ; 26 ; 341-352
01.03.2010
12 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
Comparison of spawning habitat predictions of PHABSIM and River2D models
| Online Contents | 2009
Comparison of spawning habitat predictions of PHABSIM and River2D models
| Online Contents | 2009
Perspectives on Two-Dimensional River Habitat Models: the PHABSIM Experience
| British Library Conference Proceedings | 1996
An Application of PHABSIM in Velhas River, Southeast Brazil
| British Library Conference Proceedings | 2009