Seasons Greetings:

     I would like to post the following questions and request for
     information to the group.

     One of the key limitations to the quantification of sediment effects
     on fish and aquatic habitats is the characterization of sediment
     release events (i.e. the concentration and duration of the sediment
     episode).  With respect to in-stream construction operations, the
     elevated sediment loads associated with activities in and about a
     watercourse are highly variable with several peaks of high sediment
     concentrations and then respites of clear water.   As a result, it is
     difficult to describe the event simply as a concentration of sediment
     for a specific duration of time.

     Due to the variable nature of sediment loads associated with in-stream
     construction I have two questions to ask;

     1.  I am aware of turbidity probes which are available which would
     allow for the continuous or quasi-continuous logging of nephlometric
     turbidities.  However, the costs of such probes tend to restrict their
     use ($3,000 Can).  There has been some literature on the design of
     low-cost probes (e.g. Lawler and Brown 1992).  My question is, has
     anyone out there used these designs to construct and use turbidity
     probes and what are their limitations.  Alternately, are there low
     cost alternatives to the probes which are commercially available which
     would allow for the continuous monitoring of high levels of turbidity
     (2000-3000 NTU) at locations through out a watershed.

     2. Once the continuous turbidity information has been collected and
     converted to suspended sediment concentrations (using site-specific
     relationships), what would be the best approach to describing the
     sediment episode (other than a weighted average and duration of
     event)?

     In order to reduce unwanted noise, please send replies to me directly
     and I will post results to the list in the new year.

     Thanks for your interest,  All the best in 1997!


     Paul G. Anderson, M.Sc. P.Biol.
     email - [log in to unmask]

     Golder Associates Ltd.
     1011 Sixth Ave S.W.
     Calgary, Alberta. T2P 0W1