3.3 Recommendations
The gradual implementation of WSUD, establishes a city that is more resilient and sustainable. However, to ensure the implementation of WSUD in an efficient and sufficient manner, it is important to narrow down some points that, if not being properly addressed, can influence the performance of the interventions. As a first step, it is important to conduct a well-established CBA of the WSUD measures. The cost analysis should include the implementation and maintenance costs, both equally important. In other words, this analysis should decide whether the cost of ‘doing nothing’ surpasses the cost of taking action. If that were to occur, the deployment of WSUD should be considered. The WSUD measures rarely do work separately. Most of the time, several tools are interconnected with one another to ensure the best performance of the system. Therefore, the types of tools selected, should refer to a specific scenario, which combines the measures with one another. For instance, the rainwater falls into a sealed surfaced; through gutters it is conveyed to a water plaza where it is temporarily stored; then through an underground pipe it is discharged to the retention pond where it is treated; the treated water it is reused for non-potable purposes and the excess of it is discharged in the sewage network or in the river. All these chain reactions should be built in a small scale, and also by considering a bigger picture, as at the
end all the chain components (WSUD tools) should function together as an ensemble. The selection of the WSUD tools, and the combination in between them, depends on the climate and local settings of each site. Lastly, it is essential to identify the precipitation targets that the WSUD scenario should respond to. In other worlds, each city has its specific threshold values for normal rain events and heavy rainfall events. The heavy rainfall events are characterized based on the rain intensity and the return period. In most of the cases, a WSUD intervention is undertaken, aiming for a heavy rainfall event with a 20-30 years return period. A rainfall event with a larger return period (70 - 100 years), it is not recommended being taken as a reference, since the climate predictions for such a time span can be not consistent enough. However, proposing a WSUD intervention for a heavy rain event with 20-30 years return period, should be done with a clear vision plan for other possible interventions in the future, that will aim to deal with stormwater from a rainfall event with a bigger return period. In the case of Tirana, the capacity of the existing sewage system can manage rainfall events with an intensity of up to 170 l/sec x ha in 15 minutes (Dervishaj, 2021). The WSUD proposal, in this master thesis, will aim to respond to a heavy rainfall event with a return period 20 years and with an intensity of 250 l/ sec x ha in 20 minutes. 71
