"Proceedings, Federal Interagency Workshop,
"Sediment Technology for the
St. Petersburg, FL, February 17-19,
Pre-proposal on in situ Application of Infrared Nephelometers
By Jack Lewis
Suspended sediment concentrations (SSC) in rivers and
streams commonly vary over short periods (minutes or hours). To estimate
sediment loads accurately requires sampling frequencies that are
impractical to achieve with manual sampling. In tidal rivers or estuaries,
SSC can vary with tides, wind, and runoff, so continuous monitoring is
desirable for interpretive studies of tidal flux. Optical sensors that
allow continuous measurement of turbidity at remote sites are commercially
available but are not part of basic data and interpretive programs of FISP
agencies. With calibration, turbidity probes can provide more detailed
records of SSC and more accurate estimation of suspended sediment fluxes
than traditional methods.
Beneficiaries This technology will make it easier to detect the impacts of
land use activities. Agencies needing detailed suspended sediment
information for management decisions will benefit, as will researchers and
users of basic sediment data and interpretive sediment studies.
Objective We propose to complete the development of this technology to the
point where it can be readily implemented by FISP agencies, and public and
private institutions wishing to gather suspended sediment data. The
primary steps necessary to reach this point are:
- Infrared nephelometers have proven reliable when kept clear of
organisms and debris. A properly designed housing/shield needs to be
developed (from existing prototypes) to exclude debris and organisms, and
to protect the probe from damaging impacts in high energy environments. To
facilitate calibration (as described in step 3 below), a mounting apparatus
for a pumping sampler intake nozzle should be included in the housing
configuration. Further investigation is also needed into mechanical,
chemical, or electromagnetic means of preventing biological colonization of
- The probe/housing should be accessible for inspection and cleaning at
all times. Bed-mounted and overhead support systems have been designed to
facilitate access, and could be further developed as plans or products.
- For estimating SSC, nephelometers require calibration, and, for the
best accuracy, re-calibration is desirable when particle composition or
size distribution changes substantially. A system has been developed and
applied in the field that uses real-time nephelometric turbidity to
automatically control a pumping sampler to obtain calibration data. The
system utilizes a single-board computer, programmed in a high level
language, that requires the user to build an interface circuit for
controlling external devices and to provide a weatherproof enclosure. To
make the system practical for a wider user group, a manufacturer is needed
to build and package these components for off-the-shelf use.
- A comprehensive document (designed after Techniques of Water-Resources
Investigations of the USGS, Book 3) should be prepared to describe how to
apply optical sensors to the measurement of SSC in different types of
environments. This document would serve to transfer this technology from
research programs in FISP agencies to operational programs. A training
class and/or video could also be considered as a supplement.
FISP staff would consult with developers and users of this
technology to engineer and test a debris-shedding housing/shield and
mounting systems; and to provide plans and an implementation document.
Interested FISP agencies could participate in manufacture of mounting
systems from plans, and field testing. Manufacturers would be sought to
produce a housing/shield and to package a data logger and interface
Funding and time table: (Total ~ $100,000, 1-2 years)
- Sensor purchase ($2200)
- Housing design and refinement (2 months, $8000)
- Manufacture prototypes ($2000)
- Flume testing (2 weeks, $3000)
- Field testing (2 weeks, $1500)
- Mounting systems.
- Draw up existing designs (CAD software $500, 2 weeks
- Manufacture of prototypes ($2000 - 5000 each)
- Field testing of prototypes ($1500 each)
- Design refinements and example plans (2 weeks, $2000)
- Data logger/interface production
- Legwork and consultation (3 weeks, $3000)
- Implementation document
- Writing and review process (1 person-year, $50000)
- Production (??)
- Travel/consultation between Calif. and Miss. ($5000)
Jack Lewis, Rand Eads and David Schoellhamer could consult with
FISP staff. Other users of this instrument in FISP agencies could be
included too. Instrument manufacturers may be supportive.
Buchanan, P.A., and Schoellhamer, D.H., 1996, Summary of suspended-solids
concentration data, San Francisco Bay, California, water year 1995: U.S.
Geological Survey Open-File Report 96- 591, 40 p.
Gippel, C. J., 1989, The use of turbidimeters in suspended sediment
research, Hydrobiologia 176/177: 465-480.
Gippel, C. J., 1995, Potential of turbidity monitoring for measuring the
transport of suspended solids in streams, Hydrol. Processes, 9, 83-97.
Levesque, V.A., and Schoellhamer, D.H., 1995, Summary of sediment
resuspension monitoring activities, Old Tampa Bay and Hillsborough Bay,
Florida, 1988-91: U.S. Geological Survey Water Resources Investigations
Report 94-4081, 31 p.
Lewis, J., 1996, Turbidity-controlled suspended sediment sampling for
runoff-event load estimation. Water Resour. Res., 32(7), 2299-2310.
Lewis, J., and R. Eads, 1996, Turbidity-controlled suspended sediment
sampling. Watershed Management Council Newsletter 6(4): 1,4-5.
Schoellhamer, D.H., 1993, Biological interference of optical
backscatterance sensors in Tampa Bay, Florida: Marine Geology, v. 110, p.
Schoellhamer, D.H., 1997, Time Series of Trace Element Concentrations
Calculated from Time Series of Suspended-Solids Concentrations and RMP
Water Samples: 1995 Annual Report of the Regional Monitoring Program for
Trace Substances, p. 53-55.
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