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<br />.
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<br />---
<br />
<br />798
<br />
<br />HYDRAULIC ENGINEERING '94
<br />
<br />1_ Vol Dist .-- 95% C, 1.\
<br />
<br /> 100
<br /> 80
<br />8' 60
<br />,,,
<br />II
<br />II
<br />II 40
<br />111
<br />dP
<br /> 20
<br /> 0
<br /> 0
<br />
<br />
<br />--
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<br />/
<br />._.__.:~_..",,/" - .-.,
<br />/~/
<br />/
<br />._--~~.:.-
<br />/'
<br />"",,"
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<br />
<br />
<br />50 100
<br />Grain Size
<br />
<br />150
<br /><mm>
<br />
<br />200
<br />
<br />Sample Distributions (45 stones)
<br />Figure 1.
<br />
<br />I-Vol Dist.-- 95% C.l.l
<br />
<br />"
<br />
<br />
<br /> 100
<br /> 80
<br />8' 60
<br />."
<br />II
<br />II
<br />II 40
<br />111
<br />dP
<br /> 20
<br /> 0
<br /> 0
<br />
<br />50 100
<br />Grain Size
<br />
<br />150
<br /><mml
<br />
<br />200
<br />
<br />;;
<br />
<br />Sample D'stributions (200 stones)
<br />Figure 2. .....
<br />
<br />.
<br />
<br />-,an
<br />
<br />"
<br />
<br />BENEFITS OF NUMBER SAMPLING
<br />
<br />e799
<br />
<br />conclusions
<br />
<br />computer simulations confirm that the accuracy of a
<br />grid sample follows the binomial criteria set forth in
<br />Fripp and oiplas (1993) and that grid samples require
<br />about a third of the material a bulk sample needs to meet
<br />the low accuracy levels described by De Vries (1971). If
<br />these results can be combined with the hybrid sampling
<br />method described in Fripp and Dlplas (1993), which
<br />accounts for the smaller particles that grid by number
<br />cannot sample appropriately, it may be possible to sample
<br />spatial variation in a more efficient way.
<br />
<br />Acknowledament
<br />
<br />The support ot the present study by a NSF grant (CTS-
<br />9257335) is gratefully acknowledged.
<br />
<br />ADD8ndix 1. Referenoes
<br />
<br />De Vries, M. (1970). liOn accuracy of
<br />sampling", J. Hydr. Res., 8(4), 523-533.
<br />
<br />bed-material
<br />
<br />Oiplas, p, and Sutherland, A.J, (1988).
<br />Techniques of Gravel Sized Sediments", J.
<br />ASCE, 114(5), 484-501.
<br />
<br />"Sampling
<br />Hydr. Eng.
<br />
<br />fripp, J.B. and Diplas, P. (1993). IISurface Sampling in
<br />Gravel Streams.., J. Hydr. Eng. ASCE 119(4), 473-490.
<br />
<br />Helfrich, L.A., Weigmann, D.L., Neves, R.J., Bromley,
<br />P.T. (1986). liThe Clinch, Powell, and Holston Rivers of
<br />Virginia and Tennessee: wildlife and Water Quality",
<br />Virginia Cooperative Extension Service Publication 460-
<br />110, Virginia Polytechnic Institute and State University,
<br />Ulacksburg, Va.
<br />
<br />Shirazi, M.A., and seim, W.K., (1981). .'Stream System
<br />Evaluation with Emphasis on Spawning Habitat for
<br />Salmonids", Water Resources Res., 17(3), 592-594.
<br />
<br />Wolcott, J., and Church, M., (1991). "strategies for
<br />Sampling Spatially Heterogeneous Phenomena: The Example
<br />of River Gravels", J. of Sedimentary Petrology, 61 (4) ,
<br />534-543.
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