Doing research on river litter, equipment

The last couple of weeks we have been busy to test the equipment to measure the amount of litter in the Meuse. There are some elements worth mentioning:

The ship de Blauwe Reiger (The Blue Heron) is a 14.95 mtr  long “barkas” build in 1952 in Germany as a service vessel for all kinds of jobs. The skipper (Twan) rescued her from a scrapyard and rebuilt her almost in her original state as a basic recreational vessel. The present owners (Yamila and Hergat) keep Twan using and servicing the boat and go out frequently together just for the pleasure of sailing on the Meuse.

When they heard of our interest in using the Blauwe Reiger for measuring purposes, they immediately agreed to cooperate and they are ever more enthusiastic about the purpose of this whole venture. No other boat owner would allow us to drill holes in the hull or install masts and gear on their ships, but they do… and we cannot be grateful enough for their cooperation!

de Blauwe Reiger , Yamila and Hergat

The catamaran shaped pontoon, carrying the net between the floatation bodies was designed to be towed alongside the boat to prevent measuring in disturbed water from the propellor. As the tests showed, the floatation bodies and the shape they have, just leave the water flowing between them almost undisturbed and the net can cleanly cut through a surface of 1m x 0.5 m  water. After the first test this was not yet perfect, but after modification it worked out beautifully. The net operates at a depth of approx. 10 cm. and catches the materials which are in suspension. As a hypothesis we assume this 10 – 60 cm depth will be representative for the rest of the water column, especially in turbulent conditions, but this has to be proven.

The pontoon can be equipped with a net skimming the surface to catch the materials that really float on the surface like bottles, branches and other products with a low specific surface (surface/volume ratio).

Catnet made by Rene Camps (Camps Constructie)

The rigging needed to tow the net next to the ship (picture)

rigging en catnet

The current speed sensor with the mounting took also some attention. Normally this sensor is used to be mounted in more spacious environments with less chance to get covered with litter or in deeper water. It took some tests to get rid of the vibrations that started to occur in the first runs. We have clear readings now that give us accurate  information of the watervelocity we have when towing the net through the water. It allows us to calculate with great accuracy the volume of water we have sampled.

Current speed sensor (Aquadopp)

Current speed sensor (Aquadopp)

The nets gave us quite some headache. The supplier had send us the nets THREE TIMES !!! and they kept getting lost in the logistic mess of the parcel delivery guys.  Okay, we did the testruns with a improvised net I build in my backyard under the watchfull eye of my dog and we learned what we needed to learn.

The improvised net has a mesh of 24 mm. The real nets will be 18 mm and 1,1 mm. These should give us the information we are looking for.

improvised net, approved by Blister

The basic procedure of the test is as follows:

surface (m2) x velocity (m/s) x duration (s) = volume of sampled water.

Checking the caught litter and categorise it with the OSPAR list, will give us the concentration of litter per cubic meter of river water. This is what we want to know as a first objective.

Further analyses of the data and the samples will give us information on the materials, the sources, and the position in the river where the samples are collected.

Every Wednesday we will be on the Meuse for measuring. Feel free to contact me if you want to join us (call +31 6 53693382 or reply to this blog)