Shape Our Water - Data Synthesis Task

Seattle Public Utilities - Drainage and Wastewater System Planning

Seattle, WA (2021-2022)

The goal of the ongoing data synthesis task is to integrate all analysis and data collection work done during the “analysis stage” of the planning effort to help better understand our drainage and wastewater system challenges and start to identify opportunities for multi-benefit solutions.

The analysis stage was focused on identifying and prioritizing both existing and future risks and opportunities citywide and provides the foundation for Shape Our Water. This work falls into five Categories: System Capacity; Asset Age and Maintenance; Water Quality and Aquatic Health; Resilience; and Social, Economic, and Regulatory. The Data Synthesis will bring together information from the Analysis Stage through a series of maps and graphics that demonstrate how the drainage and wastewater system and Seattle’s social and environmental conditions are connected or related to each other. The highest and second highest disadvantage tiers of Seattle’s Racial and Social Equity Index are shown on nearly every map in the data synthesis to show the spatial relationship between our system risks, challenges and opportunities and where Seattle’s low-income and communities of color are living.

The maps and graphics will be organized as a story, beginning with critical historical background on Seattle’s physical and social development, followed by the existing conditions of our drainage and wastewater system and its context, and finally, using that information to identify future opportunities to provide multiple benefits with our infrastructure investments.

For example, in the “Existing Conditions” series of maps, the process of mapping DWW’s “Extreme Flooding” challenges revealed a significant relationship between areas that are at risk of flooding in extreme events and the city’s history of development. The radical transformation of Seattle’s land and water since its colonization by white settlers in the late 1800s built vulnerability into the urban landscape when wetlands were filled, rivers channelized, and creeks piped and paved over. The series of citywide maps at right demonstrate that there is a clear relationship between Seattle’s historic hydrology and flood risk, and thus, there is also a relationship between flood risk and areas that were filled in with debris or other landfill materials as the city urbanized.

Furthermore, filled areas are particularly prone to liquefaction in a seismic event, and these maps show that there is significant overlap between liquefaction-prone areas and flood risk. Much of SPU’s infrastructure in areas of liquefaction is at high or critical risk of failure in a seismic event, and if infrastructure were damaged during a seismic event, the impacts of an extreme storm event could be greater.

How can SPU turn challenges like these into opportunities for multi-benefit solutions?

While the final section of the data synthesis is still in the early stages of development, the maps at right offer an example of one such opportunity for a multi-benefit solution. They show sections of Thornton Creek in North Seattle and Longfellow Creek in Southwest Seattle, both of which are vulnerable to flooding in extreme events, and liquefaction in seismic events.

Both riparian corridors also have significant stretches in which these risks overlap with areas considered to have high potential for floodplain reconnection. These locations and others like them would benefit from a citywide program or policy on property acquisition for floodplain reconnection to transition land uses vulnerable to flood and earthquake damage to a more resilient function. Such a program or policy would catalyze a wide range of co-benefits: floodplains are particularly suited for public park space that improves quality of life while also mitigating flood risk, improving water quality, restoring habitat, recharging groundwater, and reducing heat island impacts. Since SPU has partnered with Seattle Parks and Recreation to co-acquire and co-manage creek floodplains in the past, Parks would be a key partner in the development of any citywide program or policy for floodplain reconnection.