Methods and Tools the GCBR Applies to Monitor the State of Our Rivers

May 8, 2024 | General News, Gouritz Resilient Rivers

by Nelisiwe Khusi

To collect continuous river health data, assess long-term trends, and raise awareness about the state of rivers and aquatic life within the GCBR region. The GCBR applies the following tools and methods.

The SASS (South African Scoring System) Version 5

The SASS Version 5 is a rapid field-based bioassessment tool for assessing the state of the river system using aquatic macroinvertebrates.  Because most invertebrate species have a very short life cycle and stay in one place during their aquatic life phase, changes in the structure of invertebrate communities are indicative of changes in overall river conditions. This makes them excellent indicators of localised conditions in a river over the short term (WRC, 2018a). Each macroinvertebrate taxon (mostly at family level) is assigned a sensitivity score ranging from 1 to 15 based on its sensitivity or resistance to disturbances. Taxa resistant to habitat disturbances are assigned the lowest scores, while those susceptible are assigned the highest scores.  At the site, macroinvertebrates are sampled considering 3 Biotopes (biological habitat types) : (i) the stone biotope, which constitutes bedrock or any hard surface in or out of current; (ii) vegetation biotope, which constitutes both marginal and aquatic vegetation; and (iii) the gravel, sand, and mud biotope (Dickens and Graham, 2002).  After sampling the three available habitat types, the taxa present are identified, and metrics are determined. The three metrics calculated are (Dickens and Graham, 2002):

  • SASS Score: total of the sensitivity ratings of the sampled taxa at the site
  • Number of taxa
  • Average score per taxon (ASPT): SASS Score divided by the Number of taxa

The SASS Score and ASPT can also be used to determine the ecological condition of the sampled site (A: Natural – B: Good – C: Fair – D: Poor – E/F: Seriously/Critically modified). The ecological categories are based on the interpretation of SASS data using Dallas (2007) SASS data interpretation guidelines. SASS is a cost-effective method as it requires limited sampling equipment, has been thoroughly tested, and is widely used for assessing river health conditions in South Africa. It forms part of the national biomonitoring programme. In addition, SASS has been adopted by a number of Southern African countries, such as Zimbabwe, ‍Zambia, ‍and ‍Mozambique, ‍to ‍assess ‍water ‍quality ‍and ‍ecological ‍health ‍of ‍lotic systems ‍‍(Bere and Nyamupingidza, 2014; Mnisi, 2018; WRC, 2018a)‍‍To ‍learn ‍more ‍about ‍SASS ‍5, ‍follow.


miniSASS is a simplified version of the SASS5 scoring system that any interested community member can apply to monitor the health of a river by recording and scoring the aquatic macroinvertebrates found in a sample of the river water. To find out more about miniSASS follow the link:

In-situ water quality parameters 

In-situ water quality parameters such as Dissolved Oxygen (DO), pH, water temperature, electrical conductivity (EC), and Total Dissolved Solids (TDS). These are measured using a multiparameter water quality meter, providing immediate data about the physico-chemical state of the river and assessing the river’s capacity to support aquatic life.

Water quality analysis using multiparameter
Water quality analysis using multiparameter


Visual transparency of water is measured using the clarity tube, offering insights into the suspended particles’ concentration in the water, which can affect aquatic life and water quality.

River flow

The amount of water flowing in a river, together with the slope of the riverbed, determines the water depth, width, and velocity. The shape and size of the substrate affect turbulence. These factors make up the hydraulic habitat of aquatic organisms. For example, filter-feeding blackflies-, mayflies- or caddisfly-larvae prefer to live in fast currents on rock (cobble, boulder or bedrock). These invertebrates filter the water and remove tiny organic particles for their food. Each has a different feeding adaptation. Their filtering contributes to the capacity of the river to clean itself and thus process wastes (WRC, 2018a).

We use the plank velocity plank to understand river dynamics, sediment transport, and the ecological implications of water flow variations.  The velocity plank is a transparent plastic board with a measuring ruler used to determine a stream’s flow velocity and depth. By standing the board vertically on the streambed, the water depth, and the water level on the upstream and downstream side of the plank can be measured. The difference between these two water levels is used to determine flow velocity. Multiple measurements across the stream’s width can be used to calculate the stream’s depth-averaged flow velocity (metres per second) and discharge (discharge = velocity x depth x width)(WRC, 2018b).

These methods and tools collectively enable continuous data collection, long-term trend assessment, and public awareness about river health within the GCBR region. They offer cost-effective, efficient means to monitor and manage river ecosystems effectively.


Bere, T and Nyamupingidza, BB. 2014. Use of biological monitoring tools beyond their country of origin: a case study of the South African Scoring System Version 5 (SASS5). Hydrobiologia 722 (1): 223-232.

Dallas, HF. 2007. South African Scoring System (SASS) Data Interpretation Guidelines. The Freshwater Consulting Group, Cape Town, South Africa.

Dickens, CW and Graham, PM. 2002. The South African Scoring System (SASS) version 5 rapid bioassessment method for rivers. African Journal of Aquatic Science 27 (1): 1-10.

Mnisi, L. 2018. Development of An Aquatic Toxicity Index For Macroinvertebrates. Unpublished PhD thesis, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.

WRC. 2018a. How to understand Envriomental Water Quality in Water Resources Management [Internet]. Available from: [Accessed: 06 May 2024].

WRC. 2018b. Suite of tools help citizens take control of freshwater management. [Internet]. Pretoria, South Africa. Available from: [Accessed: 06 May 2024].

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