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The alteration of a watershed's hydrologic response due to urban development, population growth, global warming, and sea level rise have increased the frequency and intensity of floods. In order to cope with the new challenges in coastal flood management, many efforts were made after Superstorm Sandy. These efforts call for better understanding of flood hazard, better understanding of the operation of infrastructures in a resilience context, ways to mitigate hazard impacts, rebuilding efforts by adaptive design, and developing a unified scale of resilience for measuring performance. In this paper, attempts have been made to address implementation of these measures. The main purpose of this study is to improve resilience in infrastructures, particularly wastewater-treatment plants (WWTPs), which play a pivotal role in urban lifelines in New York City. To do this, first, a flood inundation map has been generated to evaluate the current response of the study area to a 100-year flood and determine the flood inundation depth at WWTPs. Next, a multicriteria decision-making (MCDM) approach was utilized to quantify the resilience index as a system performance indicator. Afterward, two approaches based on resilience-improving measures have been considered to improve this index. The first approach is to provide redundancies between WWTPs to make a platform for WWTPs' cooperation to move the sewage between them. The second approach is to implement adaptive hazard mitigation practices such as best management practices (BMPs) based on a proposed framework of a key initiative in New York City. In order to prioritize various groups of BMPs, five methods of flood mitigation practices, namely resist, delay, discharge, store, and retreat, have been ranked using experts' opinions in a MCDM framework. Thereafter, resilience improvements based on the two aforementioned approaches have been compared by considering financial resources allocation to each WWTP, and the most efficient alternative solutions have been chosen. The methodology outlined in this paper can be utilized in other urban coastal settings to plan for better flood preparedness.