Discharge Monitoring in a Tidally Affected River with the SonTek SL

In 2011 a series of gauging stations were established along the Johor River which measured river water level and velocity to gain a better understanding of the existing river flows. The Johor River is an important source of water for several water treatment plants. However, during high tides and in dry seasons, a saltwater wedge pushes upstream affecting water quality and thus water supply.

Challenge

The measurement objectives and locations along the Johor and Linggiu River represented many challenges. Accurate continuous discharge data was required quickly in locations where tidal influence causing variable backwater effects and reverse flows were present. In addition, the locations were remote with limited access making installation and commissioning work difficult.

“Accurate continuous discharge data was required quickly in locations where tidal influence causing variable back water affects and also reverse flows were present.”

Xylem Solution

Greenspan Singapore Pte Ltd was engaged to undertake the project and chose SonTek Side Looking sensors which combine continuous measurement of level and velocity to continuously derive discharge at the three locations. For velocity index development and cross-section measurement, a SonTek ADCP RiverSurveyor system was used.

Application

Continuous water level, velocity and discharge data were recorded by the sensors for the measurement locations. A velocity index for each site was developed for a range of water levels by undertaking discharge measurement during releases of water from the upstream reservoir.

Customer's Feedback

Faizal Yusoff, the lead Field Hydrographer from Greenspan, noted that the Sontek SL provided a good data record for unattended monitoring. It was also a surprise that the backwater effects from the tide were experienced so far upstream, particularly during low flows which meant direct measurement of velocity was in fact critical as a traditional stage to discharge ratings would have yielded high uncertainties due to the loop rating.