Application and Validation of Flood Damage Curves for Wastewater Treatment Facilities (WWTF), Case Examples in Rhode Island

Abstract

The STORMTOOLS Coastal Environmental Risk Index (CERI) has historically been used to assess the damage to residential and commercial structures from coastal flooding, including the effects of sea level rise (SLR) in RI. In the present study, CERI was extended to address the impact of flooding for 100 yr storm, including the effects of SLR, to the newly renovated Warren, RI wastewater treatment facilities (WWTF), located on the tidal Warren River, using FEMA HAZUS damage curves. The analysis shows that the average damage for 100 yr flooding, across all components of the facility, increases with sea level from 16% (0 ft SLR), 23% (2 ft SLR), 26% (3 ft SLR), to 28% (5 ft SLR). The primary settling and chlorination tanks are at most risk and the aeration and reaction tanks at least risk. In an effort to validate the FEMA HAZUS WWTF damage curves, CERI was applied to predict flood damage during the 3 day, March/April 2010 flooding event (500 yr) to the Cranston, Warwick, and West Warwick WWTF located on the Pawtuxet River, RI. The predictions of the damage to each WWTF from this event were compared to observations of the damage made by the plant operators. The percent damage was estimated by comparing the cost of the damage to the assessed value of the facility. Using the FEMA HAZUS damage curves for the observed level of inundation (7 to 8 ft) predicted that the Warwick and West Warwick facility damage ranged from 15 to 45% with an average value of about 30%. The Cranston WWTF damage was very low (<1%) because of the elevation of the facility. The observed damage for the 2010 flood event was approximately 21% for the Warwick facility and 18% for the West Warwick facility, between the FEMA HAZUS lower and average values. Damage to the Cranston facility was consistent between FEMA HAZUS and observed values at <1%.