STORMWATER
The typical state of stormwater drainage systems
Stormwater systems need attention Multiple flood events and service delivery protests in recent years have brought stormwater master planning to the forefront. Bio Engineering Solutions resultantly conducted visual condition assessments (VCAs) on several municipalities’ stormwater systems, and the results are alarming. By Danielle Petterson
T
he VCAs found that the general accuracy of the existing stormwater infrastructure asset registers is only 20% to 25%. This is mainly due to missing information such as dimensions of underground pipes as well as invert levels and gradients of stormwater conduits. More concerningly, about 60% to 80% of existing stormwater systems were found to be completely blocked and/or non-functional due to a lack of maintenance.
Stormwater assessments
The Bio Engineering Solutions team, led by director Matt Braune, started the study using aerial photography provided by the municipality as a basis. A team of field inspectors then walked the area to identify all stormwater infrastructure. The locality of all infrastructure was recorded along with photographic
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records. Another team of labourers opened all relevant structures, where they found a high degree of silting and blockages. They unblocked a portion of the infrastructure to take measurements; however, the existing pipe network could not be inspected fully due to severe blockage, which prohibited the use of CCTV. The next phase of the study included the use of a professional surveyor to obtain both ground levels as well as invert levels of all existing stormwater infrastructure. In addition to this, the type of infrastructure, size and hydraulic capacity were also established. Based on the information, a fully integrated and complete asset register was compiled to assist the municipalities with stormwater management. Hydrological as well as hydraulic modelling of the drainage networks was then undertaken, which enabled the compilation of a fully integrated
stormwater master plan (SMP). The master plan was then used to prioritise and highlight problem areas and to establish remedial measures needed to restore the network.
Maintenance challenges
Although each municipality has maintenance departments tasked with cleaning and maintaining stormwater infrastructure, Braune says standard operating procedures are needed to guide this process. “Workers have no guidelines on how to maintain these systems and we often find that they push any surrounding debris into kerb and grid inlets. The surrounding area and the outside of the kerb inlet are now clean, but they have inadvertently blocked the underground pipe drainage system and caused further problems,” he explains. “Local authorities are not maintaining their infrastructure, and maintenance
