Water Resources Division (WRD) Policy on Publication of Sediment Size Data Determined by use of the Sedigraph
 

In Reply Refer To:                                January 29, 1993
Mail Stop 415




OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 93.11

Subject:  Water Resources Division (WRD) Policy on Publication of 
          Sediment Size Data Determined by use of the Sedigraph

BACKGROUND

The Water Resources Division has traditionally published only 
sediment fall diameter data which have been determined by the 
visual-accumulation tube, pipet, bottom withdrawal tube, or 
hydrometer.  The Sedigraph is a much faster and cheaper method for 
size analysis and the Sediment Action Committee has recommended 
that it be approved as an alternative method of analysis for fall 
diameter. 

A comparison of pipet and Sedigraph methods has been documented in 
a memorandum from the Branch of Quality Assurance to the Office of 
Surface Water (OSW) dated December 14, 1992.  For sizes in the 
silt-clay range, there is a general tendency for the Sedigraph to 
indicate about 5 to 10 percent more material is finer than a given 
size than indicated by the pipet method.  For a given field site, 
comparison tests indicate that the relationship between sedigraph 
and pipet methods can be established by performing duplicate 
analyses.

POLICY

It is WRD policy that the Sedigraph is an approved method of 
analysis for fall diameter.  Data produced using the sedigraph may 
be included in the WATSTORE System and published in the annual 
report provided the method of analysis is identified.  Each 
District that chooses to use the Sedigraph method should perform 
duplicate sample analyses on at least 10 percent of the samples 
until the relationship between the Sedigraph and pipet results can 
be quantified for the site at which the sediment samples were 
collected.

All future entries to WATSTORE are to include a method code to 
identify the type of analysis.  The existing method code system in 
the QWDATA data structure is currently used by the National Water 
Quality Laboratory to indicate the method of analysis.  Table 1 
gives the method codes that identify the types of analysis used to 
determine sediment size.  The codes D & W are only to be used for 
the sieve analyses, the codes V, S, P, B, & H are only to be used 
for the fall diameter determinations, and the codes C & M are only 
to be used to identify the direct measurement of particle size.

The OSW encourages Sediment Laboratories to offer a silt-clay 
split as an alternative to the complete size analysis of the fine 
material.  The percent clay can be entered as the fall diameter 
less than 0.004 mm with the appropriate method code.

The method codes are not picked up by the tabling programs in 
NWIS-I.  As with all water-quality data, this means that each 
table may display data that have been determined by different 
methods.  Data produced by various methods can be identified by 
sorting the data by the method of analysis code.

Method codes for historical data may be entered at the discretion 
of the individual District.


          Table 1.  Method codes to be used to identify 
          the type of laboratory analysis used for 
          sediment size analysis.

          Method
           CODE   METHOD

            C     Measurement, direct (particle count)
            M     Measurement, direct (optical)
            D     Dry sieve
            W     Wet sieve
            V     V A tube
            S     Sedigraph 
            P     Pipet
            B     B W tube
            H     Hydrometer




                                 Charles W. Boning, Chief
                                 Office of Surface Water

This memorandum does not supersede any previous memorandums.

DISTRIBUTION:  A, B, FO, PO