New generation monitoring equipment for Jonkershoek

The new equipment is installed (Pictures: Abri de Buys)

Hourly water level in metres for Bosboukloof weir during September 2011.

- Abri de Buys, Field Technician, SAEON Fynbos Node

August 2011 saw the installation of brand new electronic water level and temperature monitoring equipment at the Jonkershoek weirs.

After many hours of considering options, learning about equipment specifications, testing equipment and getting input from stream monitoring experts, SAEON’s Fynbos Node started a field evaluation period for the new equipment in the middle of August. Valuable advice on equipment selection and generous sharing of expertise by the Department of Water Affairs in Worcester deserve special mention here.

Cost effective “eye” on weir monitoring

The new equipment, purchased with an NRF grant, is capable of recording water level and temperature at set intervals. It can also store these data for long periods and transmit data to a database in the office via SMS. The new equipment will allow daily checking of incoming data, enabling the Node to keep an “eye” on weir monitoring more regularly, while reducing travelling costs to Jonkershoek.

The new equipment is capable of recording water level and temperature at set intervals. It can also store these data for long periods and transmit data to a database in the office via SMS.

Currently the old equipment requires weekly replacement of recording charts, which typically means a round trip of 150 kilometres. The charts from these old recorders also require a time consuming digitising process to obtain data from them that can be statistically analysed. With the new equipment, the digitising process is completely eliminated and replaced by a simple quality check, after which data are in a format ready for analysis. The aim is to eventually replace the old chart recording gauges that have been in service for over 60 years. These are starting to become difficult to maintain due to lack of spare clock parts.

Malfunctioning recorder clocks can sometimes mean significant downtime and loss of data. Once Node staff have done a thorough comparison of the data recorded by old and new equipment running in parallel, we will be able to take the old equipment out of service.

Testing the new rain gauges

The installation of new weir monitoring equipment follows the installation of new tipping bucket rain gauges at Jonkershoek. The new rain gauges have been operating for two months in an experiment where they are paired with the older Nipher Shield gauges. Some differences in recorded amounts between adjacent old and new gauges have been found.

The next step will be to test the calibration of the new gauges in the field to ensure they are accurate within the limits certified by the supplier. Variations exceeding the factory specifications can then be addressed by adjusting the calibration. Data collection over a period of time will illustrate whether there is any systematic bias in data recorded by the different types of gauges. Other factors that may introduce variation in this experiment include local topography or wind.

Eventually the Node staff members want to be certain to what extent we affect the measurements by introducing new measuring tools. By examining and understanding the effects of new equipment on measurements, we reduce the chances of introducing bias in the long-term datasets.