Landcom Book 4 Maintenance - WSUD

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Water Sensitive Urban Design 5.1 Performance Monitoring Requirements Surrogate methods can often be equally effective in evaluating the adequacies of the operation, and thus performance, of WSUD elements. Performance monitoring of WSUD elements can be undertaken through detailed water sampling and laboratory analyses for contaminant concentrations or through the use of surrogate performance indicators. With the former, it will be necessary to set up field monitoring sites to undertake the water quality sampling at inlet and outlet of systems. The following points should be considered when setting up a sampling program: •• Auto-sampling with partial or full composite samples is most cost effective •• Monitoring should be accompanied by continuous flow and depth observations •• Design of monitoring set up and sampling intervals is site dependent •• 20 events should be monitored as a minimum to obtain typical performance •• The following key water quality parameters should be analysed in registered laboratories:- –– TSS analysis should be undertaken –– TP (with occasional filter of sample on-site with 0.45um filter to test for Orthophosphate) –– TN (with occasional speciation to organic and inorganic nitrogen An implicit assumption made when water quality improvements are measured by comparing observed water quality at the inlet and outlet of the system, is that these water qualities represent the same ‘parcel’ of water. Occasionally, especially with wetlands and ponds, negative or very low pollutant removal results for a system are observed. These results are common when the volume of an inflow event is less than the permanent pool volume of the wetland or pond. In the case of bioretention systems, accurately accounting for the volumetric balance of inflow, outflow, and soil moisture replenishment, is the main analytical problem that may lead to erroneous performance assessment. Surrogate methods can often be equally effective in evaluating the adequacies of the operation, and thus performance, of WSUD elements. They are often more cost effective and involve the monitoring of the hydrologic and hydraulic performance of these systems. The implicit assumption with surrogate methods is the premise that if the WSUD elements operate in accordance to the design hydrologic and hydraulic characteristics, it follows that these systems can be reasonably expected to deliver the pollutant reduction as determined from laboratory and field experiments. Key hydrologic and hydraulic operation characteristics define the detention time of WSUD elements. Monitoring of the following operation of bioretention systems, wetlands and ponds, can provide important insights on the likely performance of these WSUD elements in pollution reduction: •• Flow pattern (most relevant to wetlands and ponds), to identify the presences of short-circuiting that may inhibit the uniform distribution of inflow to this system •• Duration of inundation (most relevant to wetlands and bioretention systems) to assess the operating detention time of these systems and to highlight potential clogging of soil media (bioretention systems) or the outlet structure (wetlands) that would have a direct impact on its performance in water treatment •• Turbidity of inflow and outflow which are good surrogates for suspended solids, total phosphorus, and metal in urban stormwater 20 Book 4 | MAINTENANCE
Water Sensitive Urban Design WSUD infrastructure requires ongoing inspection and maintenance to ensure they establish and operate in accordance with the design intent. 5.2 Maintenance Requirements WSUD infrastructure requires ongoing inspection and maintenance to ensure they establish and operate in accordance with the design intent. Potential problems associated with WSUD infrastructure as a result of poor maintenance include: •• Decreased aesthetic amenity •• Reduced functional performance •• Public health and safety risks •• Decreased habitat diversity (dominance of exotic weeds) The most time-intensive period of maintenance for a vegetated system is during plant establishment (which typically includes two growing seasons), when supplementary watering, plant replacement and weeding may be required. Generally, WSUD elements are brought online through stages such that the functional elements are protected from elevated pollutant loads generated from a developing catchment. More information regarding staged construction is given in the next section of this booklet. Once WSUD elements are established and operational, on-going inspection, monitoring and maintenance will be required. Maintenance activities fall into one of two categories; predictive maintenance or regular maintenance. 5.2.1 Predictive Maintenance Predictive maintenance is scheduled based on inspections conducted after a significant storm event (defined qualitatively as an event likely to mobilise sediment and coarse material). Predictive inspections are critical to assessing the performance of the treatment system, in particular the hydraulic function and flow distribution of the system. Items that should be considered during the inspection are included over the page. Book 4 | MAINTENANCE 21
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Landcom Book 4 Maintenance - WSUD

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