Uses for which the SediMeter was Developed
Background
The SediMeter was invented and patented by Ulf Erlingsson. The challenge was to study the frequency and magnitude of sediment transport in the Baltic Sea, at depths from 5 to 35 m. Since all transport events are associated with wave ripples, the solution was this electronic instrument with a built-in logger. In the research for his doctoral thesis (Erlingsson, 1990), he built two instruments capable of detecting elevation changes as small as 0.1 mm, and had them measure once per hour. The sensor was 15 cm long, and the logger had a 2 kB RAM memory with built-in battery. The modern version is 35 cm long, and can take up to 2 GB of SD-card memory.
After a post-doc period in Copenhagen, researching issues related to the climate change and global warming at the end of the ice age, Dr. Erlingsson worked with geographic information systems (GIS) and with consulting in Sweden and Central America. Projects included mapping of polluted sediments, sediment effects of hydropower development, and natural hazards.
During a number of years Erlingsson was senior expert for the Swedish government, in charge of supervising the sediment spill monitoring during the construction of the Öresund Bridge and Tunnel (spelled Øresund in Danish). This was the largest spill monitoring programme in the world. The Swedish government had limited the spill to 5% of the dredged volume, and the builder had to measure the spill to ±1% (of the dredged volume). The dredging subcontractor set up an enourmous organization for solving this task, the builder supervised the dredger, and the Swedish authorities audited everything based on weekly reports and frequent inspections. While the cost of the monitoring was never revealed by the dredging contractor, there were inofficiel figures floating around. Suffice it to say that there is clearly room for creating a more cost-effective method.
Helcom recommends that monitoring of the sedimentation pattern be mandatory during marine dredging. As an example of criteria, the accumulation of sediment spill on mussel banks around Saltholm in Øresund is limited to 15 kg/m2. The SediMeter provides a cost-effective method of continuously monitoring such spill accumulation.
The Challenge of Sediment Spill
After moving to Miami in 2002 Erlingsson started teaching environmental protection and oceanography at a local university. He soon realized that sediment spill from dredging was a major environmental problem in Florida. To save the beaches through sand replenishment, sand had been dredged offshore. This had harmed both the reefs around the so-called borrow areas, and the nearshore reefs when the fines were washed out by the waves.
Having expert knowledge of spill monitoring, Erlingsson set out to define a new and better method for environmental protection against sediment spill, or siltation (see Siltation Monitoring BMP). The solution builds on experience and knowledge from all levels of the task, from knowledge of physical processes to hands-on experience as a diver, through the design of the measuring instrument, to the experience of auditing spill monitoring data and of geostatistical data processing. The result is a plan for spill monitoring, that defines how the authoritites (or environmental court in Sweden) must phrase the permit in order to make it auditable (and thus enforceable). Furthermore, it is based on the most fundamental premise, namely do no harm to the environment, plus the knowledge that inflexible rules (such as those in the U.S.) either lead to excessive cost, or are impossible to enforce, or both. (Complete document: Monitoring Siltation).
The SediMeter as the Heart of a Cost-Effective Fixed-Sensor Spill Monitoring System
Version two of the SediMeter was developed to provide an optimal hardware and software solution for Erlingsson's spill monitoring strategy. All technical features were designed without compromize to fulfill the mission. The software can post-process recorded data, but also monitor a real-time instrument network with hundreds of sensors. Data handling was designed not just with the user in mind, but also the auditor, who is concerned with data integrity.
We have white papers and powerpoint presentations available that can be used to explain the monitoring strategy and logic to different groups, from environmental engineers to decision-makers.
The new version of the SediMeter developed without sacrificing the existing customer base. In the past the instruments have been used for research, in the field and in the flume. The new version can continue that service, but with improved features overall.
Natural Disaster Mitigation
Cuantitative data is required for expert systems aimed at decreasing the risk for natural disasters. Monitoring of the physical environment is necessary, adn the SediMeter can be used for monitoring erosion and sedimentation. The monitoring should be done in a deliberate way, starting out from a structured definition of hazards and risks.
A theoretical framework for this purpose was developed by Erlingsson (2001). Unfortunately the chapter, Consideraciones sobre desastres naturales, is only available in Spanish. Read especially "Inventario de amenazas naturales" (Inventory of natural hazards), and "Riesgo y vulnerabilidad" (Risk and vulnerability). The definitions are fundamental for being able to create a cuantitative GIS system, into which the field data eventually will fit and be useful, after statistical analysis.
Research and Development
Our R&D core focus is on continued refinement of our unique spill and siltation monitoring system. Our focus is on the bottom line for the client; the optimal overall project cost-benefit is often not the same as lowest purchase price, and sometimes not even the lowest operating cost. For instance, if our system can help the client avoid downtime for a large dredger, the savings quickly offset quite a lot of data collection expense.
Literature
Erlingsson, U., 1990: Geomorphological development of the bottoms off Österlen, southernmost Sweden. UNGI Rapport 76, 136 p. ISBN 91-506-0800-2, ISSN 0375-8109. (The SediMeter was first described in this doctoral thesis, Ch 4, pp. 21-31.)
Erlingsson, U., 1991: A sensor for measuring erosion and deposition. Journal of Sedimentary Petrology, Vol. 61, Nr. 4, pp. 620-623. (A PDF of this the original description of the SediMeter sensor is available upon request)
Erlingsson, U., 1998: Development of Methods for Nearshore Sediment Transport and Sorting Studies as Applied in Southernmost Sweden, Baltic Sea. Journal of Coastal Research, Special Issue No. 26: Preceedings of the International Coastal Symposium ICS98, pp. 107-114.
Jansson, M.B., and Erlingsson, U., 2000: Measurements and Calculations of Sedimentation in a Flushed Reservoir resulting in a sediment budget. Regulated Rivers: Research and Management, Vol. 16, pp 279-306.