Increasing the Resilience of Vulnerable Coastal Wastewater Infrastructure in Southeastern Massachusetts to the impacts of Sea Level Rise

Introduction Recently the Federal Emergency Management Agency (FEMA) redefined Base floodplains (more commonly known as 100 year floodplains) in Southeastern Massachusetts. In many coastal communities wastewater infrastructure that was previously considered to be outside the extent of the Base Flood is now shown to be vulnerable to this event. In addition, projections for sea level rise are expected to exacerbate flood risk in future years. One particularly vulnerable area is the low-lying coastal Town of Wareham, Massachusetts. The Town is nestled around Buzzards Bay, which creates several throttling points where catastrophic waves are anticipated to develop from Atlantic Ocean storms. As shown in Table 1, the Town has experienced several near 1% Flood events in the past 100 years. The Town's wastewater infrastructure, which is typically at the lowest elevations, is especially vulnerable to the newly established Base Flood. Background With the significant changes that have been made of late to the FEMA flood elevations, the State of Massachusetts has encouraged its coastal communities to shore up their coastal infrastructure. Through the Massachusetts Office of Coastal Zone Management (CZM), the State has provided funding to communities for projects that support proactive efforts to reduce a vulnerability to coastal flooding with consideration to changing environmental conditions. One proactive effort would be the shoring up of vulnerable, existing coastal wastewater infrastructure. In order to investigate the status of this infrastructure, one first needs to consider what elevation is a safe one for this infrastructure or what is the Design Flood Elevation (DFE). The DFE consists of a number of factors including the base flood elevation, a required minimum freeboard, and other factors the local community deems relevant such as sea level rise. A unique aspect of this project is that CZM requires that communities consider sea level rise when they establish a DFE. Although there are a number of projections for sea level rise, building codes do not yet require this to be considered. CZM requested an allowance be provided to demonstrate consideration for sea level rise. Figure 1 shows one sea level rise projection. Methodology The Town of Wareham (Town) is a coastal community in Southeastern Massachusetts with a year round population of approximately 20,000. The Town operates a wastewater system that serves approximately sixty percent of the Town. The system consists of 92 km (57 miles) of gravity sewer and force mains, 43 pump stations, and a Water Pollution Control Facility (WPCF). The collection system has significant environmental and economic importance to the Town. It serves the most populated portion of the Town as well as the Town's large seasonal summer population and day-trippers. The majority of the Town's pump stations are in vulnerable areas with respect to the Base Flood (especially considering subsequent anticipated wave action). With anticipated sea level rise due to climate change, many of the town's pump stations are in a very precarious position. Twenty nine of the Town's 43 pump stations are located within the Special Flood Hazard Area as shown in Figure 2. Additionally, infrastructure and multiple pump stations outside of flood zones rely on these stations to convey wastewater to the wastewater treatment facility. Figure 3 shows the interdependence of the Towns pump stations and critical infrastructure served by the stations. The evaluation of the twenty nine vulnerable stations included the development of a DFE which considered the base flood elevation, freeboard per the ASCE 24-14 — Flood Resistant Design and Construction reference and an allowance for sea level rise. This elevation was then projected onto each of the pump stations to assess the station's vulnerability (see Figure 4). CZM also required that the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model be considered (see Figure 5). Anticipated impact from the Base Flood ranges from minimal damage to inundation of the station rendering the station inoperable.. With so many pump stations in vulnerable positions, a prioritization methodology needed to be developed. A Risk and Vulnerability Assessment was conducted using the risk and consequence approach outlined in 'Risk Analysis and Management for Critical Asset Protection (RAMCAP) Standard for Risk and Resilience Management for Risk and Resilience Management of Water and Wastewater Systems Using the ASTM-ITI RAMCAP Plus Methodology, 1st Edition (ANSI/AWWA J100- 10(R13))', a document commonly referred to as 'J100'. This document provides a methodology for communities, such as the Town of Wareham, to identify vulnerabilities within their system (as related to coastal flooding and climate change) and the risk associated with these vulnerabilities. Although The Hazards United States (HAZUS) model developed by FEMA to estimate potential losses in disasters was considered for use, the model was not able to converge with the complex coastline in Wareham. As a result, a Benefit Cost Analysis was developed using the FEMA software program BCA 5.1. This software analyzes proposed project costs and benefits, and produces a benefit-cost ratio (BCR). This model considered many factors including the local environment, critical facilities served and interdependency of pump stations. RESULTS Annual flood risks calculated for each station using the BCA methodology are shown in Table 2. Flood risk is the summation of the costs borne by the Town and its citizens. Costs to the Town include replacement of damaged or destroyed equipment and loss of essential services while the station is inoperable (such as hospital, police station, or fire department services). Costs to citizens include impact to natural resources, relocation costs during the period that their house has no sewer service and volunteer costs for clean-up efforts. Infrastructure with a higher annual flood risk typically serves many users, may serve critical infrastructure, and may have many pump stations that rely upon its proper functioning. Infrastructure with a lower annual flood risk typically serves less critical infrastructure and may have no pump stations that rely upon its operation. Conducting a 'Risk and Vulnerability Assessment' allowed the Town to prioritize which of its many competing coastal resilience wastewater infrastructure issues to address first. The Town has now initiated design work on three of its most vulnerable stations (Figure 6) which all serve critical infrastructure (a hospital, police station and fire department). Coastal resilience improvements to the pump stations include: relocating penetrations, installation of structural steel to shore up walls (Figure 7), and the use of carbon fiber to enhance reinforced masonry, raising elevations of generators, reinforcing or replacing walls and relocating portions of the infrastructure. The Town now has a plan and has begun to implement the plan that shall serve as a road map to shore up its most vulnerable wastewater infrastructure to make it more resilient to the impacts of tidal and sea level rise.