Improved !

Turbidity Wedge, Generation II


The Enviroscopics Visual Clarity Wedge (EVCW) or Secchi Wedge is an inexpensive supplement to the electronic turbidimeter and can be used for estimating and tracking changes in turbidity levels in water courses.

This tool is the culmination of a design process begun with the Triton Turbidity Wedge, which was developed for water quality monitoring for the BC Government on the Vancouver Island Highway Project.  The EVCW has been in use by environmental professionals in the private and public sectors acrosss the globe for the past 15 years.  

Enviroscopics Visual Clarity Wedge 
aka: Turbidity Wedge / Secchi Wedge





Improvements include:

1) Continuous rather than incremental scale.

2) Sliding cursor with "Secchi Disc" type target pattern produces more objectivity in the determination of values.

3) Direct measurement in cm and direct approximations of Nephelometric Turbidity Units (NTU). (Note: This instrament provides approximations of turbidity values only. Different types of suspended sediment have their own unique characteristics regarding light transmission.  To use this tool effectively, it must be callibrated in the field by matching values obtained with measurements from electronic devices and/or measurements of suspended sediment from the same site.)

4) Tougher construction (1/4" Acrylic body)

5) Thumb catch for ease of manipulation.

The Design

Like its pre-cursor, the EVCW is used to measure the distance to extinction of an image by horizontal viewing through a fluid contained within the vessel. The vertically tapered body with opposing viewing window and target plate allows for a range of viewing distanced from 0 to 20 cm. This provides for an approximation of turbidity values from about 50 NTU and up.

 Unlike the former unit, in which the reading scale also served as the reference image, this unit utilizes a visual target design modeled on the pattern used for many years in the "Secchi Disc", used to measure water clarity in large bodies of water.  The diagonally opposed black and white quadrants converging in the centre, provide a visual target which can be moved in and out of the visible range by sliding the card up and down.  After determining the turning point beyond which the image disappears, the reading can be taken on the back. The default reading is distance to image extinction and as it was callibrated in a Formazin Standard Solution, approximate turbidity levels in NTUs, "Nephelometric Turbidity Units" can be read directly from the alternate instrament scale.

The moving target area, while being designed after a well established pattern in use for over 150 years in the Secchi Disc, provides a much more effective visual cue than a static pattern as our visual sense is stimulated by movement. When moving the target back and forth through the medium, we can either see the movement or not. In contrast, looking at a static, repeating pattern, fading gradually out of sight, can be confusing, as our brain is very good at filling in missing information for us.

It has been suggested that the rationale and simplicity of the design give it potential as an industry standard measurement tool.


1) The wedge, being a manual tool contains no batteries or sensitive electronics, prone to break down under rugged field conditions.

2) It can be used as a routine measuring tool or as a back-up to electronic instruments.

3) As well as providing a measurement of turbidity, the tool provides an opportunity for observation of other characteristics of the sample material such as the types of suspended and floating or settling material, colour etc.

4) Hands on contact can help to eliminate a tendency common to electronics of providing unfounded numbers that may be the result of instrument malfunction or reading error.

5) Cost is only a fraction of that of an electronic instrument.

$250 US


More Info and Resources

Channel Suspended Sediment and Fisheries : A concise guide to Impacts.  Page- at- a - glance format, Prepared for Forest Ecosystem Specialists.Charles P. Newcombe Government of British Columbia, (Free Downloadable PDF)   

Channel Sediment Pollution : A Provisional Fisheries Field Guide for Assessment of Risk and Impact. Charles P. Newcombe Government of British Columbia, Jan 1, 1995 - Salmonidae - 59 page.

Channel Suspended Sediment and Fisheries : A Synthesis for Quantitative Assessment of Risk and Impact. Charles P. Newcombe, Jorgen O. T. Jensen, BC Environment. Habitat Protection Branch British Columbia Ministry of Environment, Lands & Parks, Fisheries Branch, Jan 1, 1996 - Fishes - 115 pages


 Pacific Stream Keepers Federation 

The Streamkeepers Program has assembled equipment kits at several locations in the province. These kits contain benthic invertebrate samplers, water quality test kits, and surveying supplies.




Contact Info:

Enviroscopics Services and Products
Nanaimo, BC, Canada
250 741 7983