Climate Change Vulnerability Analysis for the Milwaukee Metropolitan Sewage District

The Milwaukee Metropolitan Sewage District (District) requested this vulnerability analysis report, which assesses how climate change will impact the District’s existing, as well as proposed, infrastructure and services. The analysis aims to provide the District with the information needed to make strategic planning decisions, such as capital investments. The report documents how climate change may increase flood events and combined sewer overflow volume during larger precipitation events, and increase risk of odor and corrosion within wastewater facilities as well as decreased flow in waterways during periods of warm weather and drought. The analysis also examines the susceptibility of woodpiles and wooden docks at the Jones Island water reclamation facility to degradation resulting from the lower water levels of Lake Michigan brought on by climate change.

The report assesses the two main drivers of climate change that will have the biggest impact on the District: precipitation and temperature change. Based on four different climate scenarios and a baseline scenario (described in detail on page 3-2), average temperature is expected to increase, triggering higher rates of potential evapotranspiration. Precipitation amount is forecasted to remain at current levels, however the distribution of precipitation events is projected to change. Large precipitation events are projected to increase in intensity, while smaller precipitation events are projected to decrease in frequency. For the District, temperature changes may be more important than precipitation changes; since evaporation is expected to outpace rainfall, the District will likely see decreases in flows to watercourses such as streams and rivers, and decreases in water levels in Lake Michigan.

Section 2 provides a broad evaluation of climate change on facilities and operation within the District. The main recommendations include: continual monitoring of climate change indicators, evaluating the effectiveness of green infrastructure as the impacts of climate change shift over time, and implementing “no regrets” actions, which are projects that benefit the District even if the project impacts of climate change do not occur. “No regrets” activities and adaptation actions were identified for the high- and moderate-risk potential impacts and are described in more detail in Table 2-23 and Table 2-24.

The report delves deeper into the scientific assessments in the final sections.  Section 3 details how climate change will impact combined sewer overflows (CSOs), sanitary sewer overflows, metershed flows (subdivisions of sewersheds), and water reclamation operations.  This section determines that the District may see an increase in CSOs, but that the District should continue to monitor peak flows in wastewater and update this assessment going forward. Section 4 provides a detailed analysis of project watercourse impacts for the Menomonee and Kinnickinnic rivers. This analysis projects that increases in peak flows during large rain events could increase risks of flooding given current flood management strategies. They also found that average daily flows will likely decrease, threatening aquatic habitats and water quality. Section 5 provide more in depth analysis of precipitation data and finds that green infrastructure could accommodate any changes in runoff and stormwater management. Section 6 provides an analysis of the wood piles at the Jones Island water reclamation facility and recommends that the district inspect current piles that have been exposed to drying conditions.  

Brown and Caldwell prepared this report on behalf of the Milwaukee Sewage District.

Publication Date: October 2014

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