Category Archives: History

SediMeter and the Uppsala School of Physical Geography

Eighty-five years ago a student crossed a bridge in Sweden and planted the seed of a new paradigm in Geography. A paradigm that eventually led to the invention of the SediMeter.

The article below originally appeared in the Lindorm Blog.


A hundred years ago Physical Geography concerned itself with the description of landforms and processes, and deductions about how these processes had led to those landscapes. Then in the 1930’s a research student in Uppsala called Filip Hjulström crossed the river called Fyrisån every day on his way to the department. He stopped, took a water sample and measured the water level. He then analyzed the sediment concentration and made a quantitative estimation of soil loss through river runoff. Years later he became the professor of the department, and a series of research students dedicated themselves to the quantification of the geomorphological processes: Åke Sundborg (who would succeed him as professor, studied fluvial processes in the river Klarälven), Anders Rapp (who would become professor in Lund, quantified mass transport in the Swedish mountains), John O Norrman (who succeeded Sundborg, studied coastal processes in the lake Vättern), Valter Axelsson (whose homepage is on a “museum domain”, studied delta deposition), and others.

Filip Hjulström (sitting) and Åke Sundborg in 1957.
Filip Hjulström (sitting) and Åke Sundborg in 1957.

To carry out quantitative geomorphological studies frequently requires inventing new instruments and methods. The department got a world-class Geomorphological Laboratory with flumes and a professionally staffed workshop. Valter Axelsson developed a method for quantification of recently deposited sediments using X-ray and the rectangular Axelsson corer. Bengt Nilsson developed a suspended sediment sampler for vertical integrated suspended sediment sampling, during the International Hydrological Decade. The sampler was widely used especially in remote parts of the world, and it is still available for purchase – even though it will soon turn 50 years!

Valter Axelsson in the Cachí Reservoir, Costa Rica, putting his quantitative X-ray based method of estimating sediment bulk density to good use.
Valter Axelsson in the Cachí Reservoir, Costa Rica, putting his quantitative X-ray based method of estimating sediment bulk density to good use (1989).

I was lucky enough to have Rapp as professor during my undergraduate years in Lund University, and to then come to Uppsala University for my PhD studies. Having access to the Geomorphological Laboratory and the workshop I was able to develop the SediMeter. The purpose of the instrument in my thesis was to determine the onset of bedload transport on nearshore bottoms, and to find out what happens off the “closing depth”. However, already during the initial field trials in 1986 (under the ice of a frozen lake; working near the Arctic Circle does tend to limit the time available for field testing) I found that the instrument had potential applications that went far beyond those initially contemplated.

Bengt Nilsson (left) and Ulf Erlingsson (author) in Örserumsviken, Västervik, Sweden, 1999.
Bengt Nilsson (left) and Ulf Erlingsson (author) in Örserumsviken, Västervik, Sweden, 1999.

Since my career took a different path I didn’t continue using the instrument until I decided in 2007 to develop a new, better version. That second generation was again replaced by a third generation in 2013. Electronics have developed tremendously, but the basic design of the sensor has stayed the same, because it works so well.

We now write 2016 and 30 years has passed since the first field deployment of the SediMeter. It has developed into the world’s arguably best system for monitoring siltation caused by sediment spill and pollution from dredging and other works. It is also used to monitoring sedimentation in reservoirs, harbors, and navigation channels, and in laboratory experiments, as well as for monitoring resuspension and erosion.

The Geomorphological Laboratory is, alas, gone, and the Department of Physical Geography has been merged and reorganized, but a number of instruments and samplers developed in the Uppsala School of Physical Geography live on as commercial products – and the SediMeter is one of them.

The best siltation monitoring system in the world

When Ulf Erlingsson invented the SediMeter™ for his doctoral dissertation in 1985, the goal was to detect incipient sediment motion on the bottom of the sea, so as to compare that with wave and current data to see what combination of processes led to the initiation of sediment transport  for different grainsizes, waves, and currents. The question was how to define sediment transport, but once the SediMeter was invented, it became a non-issue: The instrument is capable of detecting the difference that a single grain of sand makes in front of the sensor, and it is stable enough to give the same value when nothing changes. Thus, the definition became “what the instrument can detect,” and that was pretty much anything that happened to the sediments.

Fast forward to the 1990’s, and now Dr. Erlingsson was hired as an expert in sediment spill monitoring by the Swedish government, during the building of the Öresund bridge and tunnel between Sweden and Denmark, and the dredging of a new navigation channel to the Baltic Sea. Seeing this ambitious project from the front seat, from the regulator’s perspective with full insight into the executor’s monitoring and analysis, he became convinced that it would be more cost-effective, and wise, to use a monitoring system of stationary SediMeters™ in a real-time network, monitoring the sediment accumulation and near-bed turbidity directly, and to connect permit conditions to the sensitivity of each biotope.

When Erlingsson in 2006 got an opportunity to manufacture the SediMeter™ instrument himself, he decided to create “the best siltation monitoring system in the world,” based on his experience from the Öresund project. Since he by then lived in Miami, he designed it with the purpose of monitoring hard bottoms—including coral reefs—when there were dredging operations going on nearby. His new version of the SediMeter™ that came out in 2007 was designed specifically for the requirements identified in the siltation monitoring white-paper.

Since the only transparent anti-fouling paint on the market was banned a few years back, he next had to develop a new method for keeping the sensor clean from biofouling. In 2013 he released the third generation SediMeter™, with exactly the same proven sensor, but with a mechanical cleaner integrated in the instrument from the outset (it is also offered without cleaner). It has no logger house at all, since everything has been made to fit on the half inch wide sensor PCB.

Next Dr. Erlingsson turned his attention to wireless networking. All SediMeters™ made in Miami can be networked using RS485, which allows for mile long cables, but cables cost money. After several semi-custom solutions, in 2015 he developed the SediLink™ radio modem with a built-in small solar panel that can sit on a buoy over a single or a few SediMeters™. This allows for mixed networks with radio links and cables. The radio modem has a socket for a radio that the customer himself can mount, meaning that wherever in the world the client is, there is a license-free radio available.

The SediMeter™, its program and network abilities were developed to fit the role of a siltation monitoring system, which was formulated based on experiences from the most ambitious sedimentation monitoring project in the world. That is why Dr. Erlingsson does not hesitate to say that in his opinion, his design is the best siltation monitoring system in the world.

Dr. Ulf Erlingsson
Dr. Ulf Erlingsson, CEO of Lindorm, Inc.